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\begin{document}

\title{The role of environmental stress in fruit pigmentation}



\author[1]{Richard Espley}%
\author[2]{Laura Jaakola}%
\affil[1]{New Zealand Institute for Plant and Food Research Ltd}%
\affil[2]{UiT Norges arktiske universitet}%


\vspace{-1em}



  
  \date{May 30, 2024}


\begingroup
\let\center\flushleft
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\maketitle
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\selectlanguage{english}
\begin{abstract}
For many fruit crops, the colour of the fruit outwardly defines its
eating quality. Fruit pigments provide reproductive advantage for the
plant as well as providing protection against unfavourable environmental
conditions and pathogens. For consumers these colours are considered
attractive and provide many of the dietary benefits derived from fruits.
In the majority of species, the main pigments are either carotenoids
and/or anthocyanins. They are produced in the fruit as part of the
ripening process, orchestrated by phytohormones and an ensuing
transcriptional cascade, culminating in pigment biosynthesis. Whilst
this is a controlled developmental process, the production of pigments
is also attuned to environmental conditions such as light quantity and
quality, availability of water and ambient temperature. If these factors
intensify to stress levels, fruit tissues respond by increasing (or
ceasing) pigment production. In many cases, if the stress is not severe,
this can have a positive outcome for fruit quality. Here, we focus on
the principal environmental factors (light, temperature and water) that
can influence fruit colour.%
\end{abstract}%



\sloppy


Plant Cell and Environment Invited Review

\textbf{The role of environmental stress in fruit pigmentation}

Richard V. Espley\textsuperscript{1} and Laura
Jaakola\textsuperscript{2,3}

\textsuperscript{1}The New Zealand Institute for Plant and Food Research
Ltd, Auckland 1025, New Zealand

\textsuperscript{2}Department of Arctic and Marine Biology, UiT The
Arctic University of Norway, Troms\selectlanguage{ngerman}ø 9037, Norway

\textsuperscript{3}Norwegian Institute of Bioeconomy Research (NIBIO),
Ås 1431, Norway

\textbf{Abstract}

For many fruit crops, the colour of the fruit outwardly defines its
eating quality. Fruit pigments provide reproductive advantage for the
plant as well as providing protection against unfavourable environmental
conditions and pathogens. For consumers these colours are considered
attractive and provide many of the dietary benefits derived from fruits.
In the majority of species, the main pigments are either carotenoids
and/or anthocyanins. They are produced in the fruit as part of the
ripening process, orchestrated by phytohormones and an ensuing
transcriptional cascade, culminating in pigment biosynthesis. Whilst
this is a controlled developmental process, the production of pigments
is also attuned to environmental conditions such as light quantity and
quality, availability of water and ambient temperature. If these factors
intensify to stress levels, fruit tissues respond by increasing (or
ceasing) pigment production. In many cases, if the stress is not severe,
this can have a positive outcome for fruit quality. Here, we focus on
the principal environmental factors (light, temperature and water) that
can influence fruit colour.

\textbf{Keywords}

Environmental stress, climate, fruit, anthocyanin, carotenoid,
transcription, pigment



\textbf{1 BACKGROUND}

The colour of fruit is generally associated with reproduction,
specifically a means to promote seed dispersal by making the fruit
visually attractive to herbivores/omnivores. Colour, therefore, is a key
component of fruit development and intrinsically related to the ripening
process. Fruit colours are derived from `secondary (or specialised)
metabolite' pathways. In evolutionary terms, these pathways in flowering
plants and the breadth of their products have grown in number and
complexity, in response to environmental and pathogenic stimuli and to
adaptive changes for pollinator attraction. These colour pigments are
largely derived from either the carotenoid and/or flavonoid pathways.

Colour helps to define the attractiveness and quality of fruits and
strongly influences consumer demand. Hence, for many years, improvements
or changes to fruit colour have been a major target of breeding
programmes across a range of crops (Figure 1). Additionally, growers
routinely implement a number of on-orchard management techniques to
enhance fruit colour development (Wang et al., 2020). In this review, we
will consider the impact of environmental stresses on fruit colour.
While the term `stress' usually conjures up negative connotations,
moderate stress can enhance the concentration of numerous
phytochemicals, including those that colour our fruits. The timing,
duration and severity of any stress will determine the plant's response
and consequent impact on colour.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 1}

A range of pigments, including anthocyanins and carotenoids, confer
numerous health benefits to the consumer.

Fruit pigmentation is part of the programmed development that culminates
in ripening. This orchestrated process is largely driven by
phytohormones and mediated via transcription factors (TFs) (Allan \&
Espley 2018; Kumar, Khurana \& Sharma 2013). This process, however, can
be strongly influenced by environmental conditions such as light
intensity and spectral quality as well as temperature. Knowledge of how
the environment affects fruit colour will become increasingly important
under changing climatic conditions globally. Increases in solar
radiation and temperature as well as less predictable rainfall and a
higher incidence of drought are predicted to affect crops
(Challinor\emph{et al.} 2014; Lobell \& Gourdji 2012). Climate change is
expected to require the breeding of new varieties adapted to different
conditions to tackle the potential issues of compromised plant health,
flowering, fruit set and fruit development.

Colours in fruit not only protect the fruit itself, but also have
implications for human health. As such, they have been recognised as an
integral component of a healthy diet (Martin \& Li 2017). In fact,
rather than simply maintain the amounts of these pigmented
phytochemicals, many consider that they should be enhanced to promote
greater potential health benefits (D'Amelia \emph{et al.} 2018;
Poiroux-Gonord \emph{et al.} 2010).

\textbf{2 Fruit pigments and their effects on human health}

One of the key drivers for research into plant pigments is the
association of these compounds with dietary health (Martin \& Li 2017).
Fruits are particularly rich sources of these phytochemicals and so
changes in the composition or concentration are of interest. For
carotenoids, one of the most abundant and important of these pigmented
phytochemicals is \selectlanguage{greek}β-\selectlanguage{english}carotene, which has provitamin A properties and is
converted into retinol (vitamin A) in the body. Other carotenoid sources
of provitamin A include \selectlanguage{greek}α-\selectlanguage{english}carotene and \selectlanguage{greek}β-\selectlanguage{english}cryptoxanthin
(Rodriguez-Concepcion \emph{et al.} 2018). Vitamin A is an essential
part of our diet and deficiency is still a major problem in developing
countries (West \& Darnton-Hill 2008), which prompted the development of
provitamin A-enriched crops (Giuliano 2017). Carotenoids also provide
the macular pigments, xanthophylls including lutein and zeaxanthin,
which have antioxidant and short-wavelength light absorption functions
in the eye (Bernstein \emph{et al.} 2016). These are associated with eye
health, particularly the prevention of age-related macular degeneration
(Carpentier, Knaus \& Suh 2009). Consumption of carotenoids has also
been associated with disease prevention, including a reduced incidence
of cardiovascular disease and some cancers, as well as positive effects
on cognitive function (Leermakers \emph{et al.} 2016; Lindbergh \emph{et
al.} 2018; Mein, Lian \& Wang 2008).

An increasing number of clinical trials have shown evidence for the
health claims associated with anthocyanins. Many of these studies link
anthocyanins to protection against human diseases, including
cardiovascular and age-related degenerative diseases, obesity, metabolic
syndrome and cancer (reviewed by Gon\selectlanguage{ngerman}çalves \emph{et al.} 2021;
Kalt\emph{et al.} 2020; Pojer \emph{et al.} 2013). There was earlier
speculation about the mechanism of action, as these compounds were not
found in human circulatory systems at the site of the action, but it
appears now that bioavailability is greater than originally thought
(Kay\emph{et al.} 2017; Lila \emph{et al.} 2016). If the protection that
pigments provide in fruit is due to their antioxidant activities, is
this also the mechanism the major human health benefits associated with
their dietary consumption? This is less certain, and further research is
required to confirm the modes of action. However, it has recently been
established that one key mechanism for the health effects is via the
extensive impact of an anthocyanin-rich diet on the gut microflora,
which further process the final functional compounds (Espley \emph{et
al.} 2014; Groh \emph{et al.} 2020; Jucá \emph{et al.} 2020;
Liso\emph{et al.} 2018; Ntemiri \emph{et al.} 2020; Ou, Yang \& Liu
2020).

\textbf{3 THE STRESS Response: a brief overview}

When plants are subjected to sufficient environmental stress,
reduction-oxidation (redox) reactions occur (Figure 2). Under normal
conditions, partially reduced or activated forms of oxygen, known as
ROS, are generated, but at a rate that can be managed by the plant's
ROS-scavenging machinery. Under highly stressful conditions, this redox
homeostasis can become unbalanced, and these highly reactive molecules
can cause cellular damage. As cellular ROS concentrations increase, for
example with extreme temperature or drought, damage can afflict DNA,
RNA, membranes and ultimately destroy the cell itself (Mittler 2002). As
oxygen is produced during photosynthesis, the chloroplastic
photosynthetic machinery, particularly in leaves, is the site of much of
the ensuing ROS (Foyer 2018). In green developing fruit, where active
photosynthesis is driving metabolism, this can still apply, but as the
fruit ripens, ROS can be generated in other organelles, particularly
mitochondria (Schertl \& Braun 2014). This rise in respiratory sourced
ROS, may occur when the common chloroplast/chromoplast shift removes the
central mechanisms for coping with ROS: the xanthophyll (and other
carotenoid) cycles embedded within the photosynthetic machinery.

Since these redox reactions are inevitable in an oxygenated world,
plants have had to evolve coping mechanisms. One mechanism is enzymatic,
with enzymes such as superoxide dismutase (SOD), ascorbate peroxidase
(APX), catalase (CAT), glutathione peroxidase, monohydroascorbate
(MDHAR) and dehydroascorbate reductase (DHAR)(Das \& Roychoudhury 2014).
The other major mechanism involves the non-enzymatic antioxidants such
as ascorbic acid (AsA) and numerous polyphenols and terpenes
(Decros\emph{et al.} 2019). AsA is an important scavenger of reactive
oxygen and in a scenario where stress leads to a reduction in
photosynthesis and an increase in photooxidative damage and ROS
production, AsA production may be enhanced. AsA production does not
directly affect the colour of fruit and will not be covered in this
review, but nevertheless it is interesting to consider that the same
signals that mediate changes in the concentration of AsA in fruit, may
also mediate changes in polyphenol and terpene production. The
polyphenols include flavonoids such as catechin, quercetin and
anthocyanins, while terpenes include the pigmented carotenoids lycopene
and \selectlanguage{greek}β-\selectlanguage{english}carotene. It is clear then, that these plant pigments have a role
in fruit beyond facilitating seed dispersal since there is good evidence
for the induction of red pigmentation in vegetative tissues directly in
response to ROS production. Plants have evolved this pigmentation to act
as sunscreens and antioxidants and alleviate stresses from damaging
environmental conditions (Davies \emph{et al} . 2022).

The amount of ROS will also affect the concentrations of plant hormones,
including abscisic acid (ABA), brassinosteroids (BRs), auxin and
gibberellins (GAs). Phytohormones play a major role in ripening, with
ethylene and ABA having key roles in climacteric and non-climacteric
fruits, respectively (Fenn \& Giovannoni 2021). Both ethylene and ABA
play dual roles in the fruit, being not only linked with ripening, but
also with the stress response (Husain \emph{et al.} 2020; Leng, Yuan \&
Guo 2013). Several studies have shown a connection between increased
content of fruit ABA, as a response to stress or at onset of fruit
ripening, and the accumulation of anthocyanins (Jia \emph{et al.} 2011;
Karppinen \emph{et al.} 2018; Wheeler \emph{et al.} 2009; Zifkin\emph{et
al.} 2012). It has been suggested that accumulation of ABA inside the
cell induces downstream signalling involving ROS and calcium as
secondary messengers, resulting in activation of the TFs controlling the
anthocyanin biosynthetic pathway (Vighi \emph{et al.} 2019).
Phytohormones can also interact, sometimes antagonistically such as has
been shown for ABA and ethylene, but sometimes positively through
providing an enhanced response to abiotic stresses (M\selectlanguage{ngerman}üller 2021).

In this review, we concentrate on the major environmental stressors that
influence pigment carotenoid and anthocyanin production in fruit crops.
Chlorophyll accumulation and degradation also contribute to fruit
colour, particularly before ripening occurs, but this falls outside the
scope of this review. While betalains are also important plant pigments,
they are most commonly found in leaves, flowers, tubers and only quite
rarely found in fruit, such as in prickly pear (\emph{Opuntia
ficus-indica} ) and dragon fruit/pitaya (\emph{Hylocereus costaricensis}
) (Cheok \emph{et al} . 2022). They too are elevated in response to
various environmental stresses: this has recently been well reviewed
(Davies\emph{et al.} 2018; Li \emph{et al.} 2019) and will not be
covered here.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 2}

The major sources of environmental stress that affect fruit
pigmentation. (a) Examples of sources of environmental stress, (b)
responses to stress as initiated by ROS production, and (c) examples of
the stresses that can increase or decrease concentration of fruit
pigments in apple, grape, tomato and mango.

\textbf{4 THE biosynthesis and transcriptional regulation of Fruit
pigmentS}

\textbf{The biosynthesis of flavonoid pigments}

Anthocyanins are key pigments in fruit, generating red, blue and purple
hues. These compounds usually accumulate in the epidermal or
sub-epidermal tissues of different plant organs, offering protection
against variable environmental stress factors, especially excess of
light. The biosynthesis of anthocyanins occurs in the cytosol via the
phenylpropanoid and flavonoid pathways. The precursors for flavonoids,
including the pigmented anthocyanins, are malonyl-CoA and\emph{p}
-coumaroyl-CoA. From these precursors the first committed enzyme,
chalcone synthase (CHS), forms chalcone, establishing the
C\textsubscript{15} backbone (Figure 3). Chalcone is isomerised by
chalcone isomerase (CHI) to produce chalcone naringenin, which is
hydroxylated by flavanone 3\selectlanguage{greek}β-\selectlanguage{english}hydroxylase (F3H), converting naringenin to
dihydroflavonol. Further hydroxylation is carried out by flavonoid
3'-hydroxylase (F3'H) to form cyanidin, or flavonoid 3'5' -hydroxylase
(F3'5'H) to form delphinidin. Dihydroflavonol is reduced by
dihydroflavonol 4-reductase (\emph{DFR} ) to produce leucoanthocyanidin,
which is converted into the pigmented compound anthocyanidin by
anthocyanidin synthase (ANS), also sometimes referred to as
leucoanthocyanidin dioxygenase (LDOX). Finally, glycosylation is carried
out by uridine diphosphate (UDP)-glycosyl:flavonoid 3-\emph{0}
-glycosyltransferase (UFGT). Further addition of sugars and acyl side
groups may follow. After biosynthesis, anthocyanins are transported to
vacuoles or, rarely, cell walls. The differences in anthocyanin colours
result from various factors, including the number of hydroxyl groups on
the B-ring, the sugars and acyl side groups, the vacuolar pH or the
accumulation of specific metal ions. To date, more than 650 different
anthocyanins have been identified, the most common ones being glucosides
of six aglycons: cyanidin, delphinidin, pelargonidin, petunidin,
peonidin and malvidin (Jaakola 2013; Zhang, Butelli \& Martin 2014).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3}

Simplified overview of the biosynthetic pathway leading to anthocyanin
biosynthesis in fruit. Enzyme abbreviations as follows; PAL,
phenylalanine ammonia lyase; C4H, cinnamate 4-hydroxylase; 4CL,
4-coumarate-CoA ligase; CHS, chalcone synthase; CHI, chalcone isomerase;
F3H, flavanone 3-hydroxylase; F3'H, flavonoid 3' hydroxylase; F3'5'H,
flavonoid 3',5' hydroxylase; FLS, flavonol synthase; OMT,
O-methyltransferase; LAR, leucoanthocyanidin reductase; ANR,
anthocyanidin reductase; DFR, dihydroflavonol 4-reductase; ANS,
anthocyanidin synthase; UFGT, uridine diphosphate
(UDP)-glucose:flavonoid 3-\emph{0} -glucosyltransferase.

\textbf{The biosynthesis of carotenoid pigments}

Carotenoids provide many of the red, orange and yellow pigments in
fruit, as seen in citrus (\emph{Citrus} spp.), tomato (\emph{Solanum
lycopersicon} ), capsicum/pepper (\emph{Capsicum} ~spp.) and papaya
(\emph{Carica papaya} ). Carotenoids are essential for photoprotection
and integral to the photosynthetic machinery and in green tissues are
co-ordinately regulated with chlorophylls (Frank \& Cogdell 1996). The
pathway is located in plastids and derived from the
mevalonate-independent pathway (MEP) pathway, which generates the
C\textsubscript{20} compound geranylgeranyl pyrophosphate (GGPP)
(Cunningham \& Gantt 1998). The condensation of two GGPP molecules
provides the first carotenoids, the colourless phytoene, and is
catalysed by phytoene synthase (PSY) (Figure 4). This is often seen as
the rate-limiting step for carotenoid synthesis, regulating downstream
pathway flux. A two-step desaturation of phytoene, by phytoene
desaturase (PDS), catalyses phytoene into phytofluene and then
zeta-carotene, which is converted to di-cis zeta-carotene by
zeta-carotene isomerase (Z-ISO). Desaturation by zeta-carotene
desaturase (ZDS) and isomerization by carotene isomerase (CRTISO)
produces lycopene and from this the pathway branches, with lycopene beta
cyclases (LCYB) producing alpha-carotene and the nutritional vitamin A
precursor, \selectlanguage{greek}β-\selectlanguage{english}carotene (Moise, Al-Babili \& Wurtzel 2014). The conversion
of alpha-carotene to lutein and beta-carotene to zeaxanthin is through
the action of carotene hydroxylases. Beyond these steps, other
carotenoids such as xanthophylls, including astaxanthin, are generated
and finally, through the actions of nine-\emph{cis} -epoxycarotenoid
dioxygenases (NCEDs) and carotenoid cleavage dioxygenases (CCDs), the
phytohormone abscisic acid (ABA) and a range of apocarotenoids are
produced (Giuliano 2014). Carotenoid accumulation is further influenced
by cell physiology, specifically the number of available carotenoid
storage plastids (Cazzonelli \& Pogson 2010).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

Figure 4

Simplified overview of the carotenoid biosynthetic pathway in fruit.
Enzyme abbreviations as follows; PSY, phytoene synthase; PDS, phytoene
desaturase; Z-ISO, \selectlanguage{greek}ζ-\selectlanguage{english}carotene isomerase; ZDS, \selectlanguage{greek}ζ-\selectlanguage{english}carotene desaturase;
CRTISO, carotenoid isomerase; LCYE, lycopene \selectlanguage{greek}ε-\selectlanguage{english}cyclase; LCYB, lycopene
\selectlanguage{greek}β-\selectlanguage{english}cyclase; BCH, \selectlanguage{greek}β-\selectlanguage{english}carotene hydroxylase; CYP97, cytochrome P450-type
monooxygenase 97; ZEP, zeaxanthin epoxidase; CCS, capsanthin-capsorubin
synthase; NXS, neoxanthin synthase.

\textbf{The transcriptional regulation of plant pigments}

The transcriptional regulation of anthocyanins in fruit has been well
documented: at its core is a TF complex, termed the MYB-bHLH-WD40 (MBW)
complex (Allan, Hellens \& Laing 2008). The MYB component is derived
from the subgroup (SG) 6 class of MYBs (as defined by Stracke et al.
(2001) as opposed to the SG5 MYBs, which control proanthocyanidins) and
has been characterised in many fruit species (Albert \emph{et al.} 2014;
Jaakola 2013). The MYBs are expressed in ripening fruit and activate
either the whole biosynthetic pathway or a subset of genes in the
pathway. Examples of activators include FaMYB10 and FvMYB10 in
strawberry (Lin-Wang \emph{et al.} 2014; Medina-Puche \emph{et
al.}2014), MYB10 in nectarine (\emph{Prunus persica} ) (Ravaglia
\emph{et al.} 2013), VmMYBA in bilberry (\emph{Vaccinium myrtillus} )
(Karppinen\emph{et al.} 2021), PpMYB10.1 in peach (\emph{Prunus persica}
) (Rahim, Busatto \& Trainotti 2014), VcMYBA1 in blueberry
(\emph{Vaccinium}Section \emph{Cyanococcus} ) (Plunkett \emph{et al.}
2018) and MYB114 in pear (\emph{Pyrus bretschneideri} ) (Yao \emph{et
al.} 2017). MYBs can also act as repressors of anthocyanin, such as the
SG4 MYBs, FaMYB1 from strawberry (Aharoni \emph{et al.} 2001) and
MdMYB16 from apple (\emph{Malus domestica} ) (Xu \emph{et al.} 2017), as
recently reviewed by LaFountain \& Yuan (2021). There is increasing
evidence for the interactions of different types of MYBs on anthocyanin
regulation, such as the co-ordinated actions of MYBA1 and MYBPA1.1 in
blueberry (Lafferty\emph{et al.} 2021). Transcriptional regulation of
anthocyanin is not restricted to the MBW complex: other TFs, such as
MADs VmTRD4 in bilberry (Jaakola \emph{et al.} 2010) and PpNAC1 in peach
(Zhou \emph{et al.} 2015) have been shown to have regulatory control.
This TF-mediated control of pigments occurs in response to both
developmental cues, but also environmental stresses.

Carotenoid biosynthesis is stimulated by the presence of ROS
(Pan\emph{et al.} 2009). Stress perceived in the leaves can trigger
responses in the fruit, for example, the incidence of high light in
leaves of citrus leads to increases in carotenoids in the fruit
(Poiroux-Gonord \emph{et al.} 2013). Many TFs have been associated with
carotenoid biosynthesis as part of the fruit ripening cascade, but the
evidence for there being master transcriptional regulators of carotenoid
pigments is less clear cut than for anthocyanins (Stanley \& Yuan 2019).
A number of TFs have recently been shown to control at least parts of
the pathway. In citrus, the AGAMOUS-LIKE MADS TF, CsMADS6, was shown to
activate the promoter of \emph{LCYb1} and drive the expression of
carotenoid pathway genes \emph{PSY} , \emph{PDS} and \emph{CCD1,} while
repressing transcription of LCYE and so increasing the flux towards
\selectlanguage{greek}β-\selectlanguage{english}carotene (Lu \emph{et al.} 2018). Another TF in citrus, CrMYB68,
negatively regulates the expression of beta-carotene hydroxylase (BCH),
controlling the \selectlanguage{greek}α- \selectlanguage{english}and \selectlanguage{greek}β-\selectlanguage{english}branches of carotenoid biosynthesis
(Zhu\emph{et al.} 2017). A MYB from kiwifruit (\emph{Actinidia chinensis
var. deliciosa} ), MYB7, was reported to activate the promoter
of\emph{LCYb} and in heterologous systems elevated expression
of\emph{PSY} , \emph{PDS} and \emph{ZDS} to drive carotenoid
accumulation (Ampomah-Dwamena \emph{et al.} 2019). In papaya, two other
TF classes have been implicated in regulating carotenoids: CpbHLH1 and
CpbHLH2 repress and activate respectively the promoters of CYCB and
LCYB, while the NAC TFs, CpNAC1 and CpNAC2, bind the promoters of PDS
(NAC1) and PDS, ZDS, LYCE and BCH (NAC2) (Fu \emph{et al.} 2016; 2017).
The greatest body of work on the transcriptional control of carotenoids
has been carried out in tomato where the major ripening MADS TFs, Tomato
AGAMOUS-LIKE (TAGL1, homologous to CsMADS6), Ripening Inhibitor (RIN),
FRUITFULL1 (FUL1) and FUL2 exert largely positive effects on the
carotenoid pathway, as reviewed in Stanley \& Yuan (2019).

\textbf{Influence of Gene x Environment}

Whilst the general biosynthesis and regulation of colour pathways has
been elucidated, the final colour of the fruit is determined by both
genetic and environmental factors. The genetic background determines the
ability of fruit to produce certain pigments, whilst environmental
factors affect the final composition and amounts of pigments in a ripe
fruit. The fruit skin, which acts as a barrier protecting the internal
tissues of developing fruit, including the photosynthetic machinery, is
where the greatest effects of environmental factors on fruit pigment
production are normally detected. Both controlled and field studies with
cultivated and wild ecotypes have provided a better understanding of
gene x environment (GxE) interaction in fruit pigment production
(Jaakola \& Hohtola 2010). Such studies have identified variation in
anthocyanin content between fruit ecotypes or cultivars growing in
different geographical locations (Fredes \emph{et al.} 2014;
Gonz\selectlanguage{ngerman}ález-de-Peredo \emph{et al.} 2019; Sikuten \emph{et al.} 2021). With
wild \emph{Vaccinium} berries, field studies have often shown high
variation in the anthocyanin composition between growth location and
seasons (Connor \emph{et al.} 2002; Rohloff \emph{et al.} 2015).
However, specific geographical trends also have been observed, such as
higher total anthocyanin contents and a higher proportion of delphinidin
branch anthocyanins towards northern latitudes (Åkerstro\selectlanguage{english}m \emph{et
al.}2010; Latti \emph{et al.} 2010; L\selectlanguage{ngerman}ätti, Riihinen \& Kainulainen 2008)
and at higher altitudes (Zoratti \emph{et al.} 2015). A controlled study
with southern and northern bilberry ecotypes indicated that ecotypes
from higher altitudes produced a higher concentration of anthocyanins
irrespective of day length and temperature conditions (Uleberg \emph{et
al.} 2012). Geographical variation has also been detected in the
carotenoid contents of different fruit species and cultivars
(Dias\emph{et al.} 2021). In some cases, climatic factors have been
found to have greater impacts on carotenoid biosynthesis than cultivar
differences, for instance in papaya (Kimura, Rodriguez-Amaya \& Yokoyama
1991), mango (\emph{Mangifera indica} ) (Mercadante \& Rodriguez-Amaya
1998), and West Indian cherry (\emph{Malpighia glabra} )
(Rodriguez-Amaya 2001). A comprehensive analysis of the carotenoid
content in Portuguese fruit showed variation between the same apple and
orange (\emph{Citrus sinensis} ) cultivars grown in different
geographical regions (Dias, Camões \& Oliveira 2009). High variation in
carotenoid content was detected between wild Seabuckthorn
(\emph{Hippophae rhamnoides} ) populations growing at different
altitudes trans-Himalaya in India (Korekar \emph{et al.} 2014). The
major stressors are considered in the following sections, with the
proviso that GxE can have additional and compounding effects.

\textbf{5 The major environmental stress factors that affect fruit
colour}

\textbf{Light stress}

Light is one of the most important environmental factors affecting the
accumulation of pigments during fruit ripening. Light effects can be
categorised by duration (photoperiod), intensity (quantity), and quality
(wavelength), all of which have been shown to affect pigment production.
Both excess and inadequate light intensities and their fluctuations are
collectively known as light stress. In addition, fluctuations in light
wavelengths, especially excess of UV-light, can also cause light stress.
Stress from non-optimal light conditions can cause alterations in
pigment production (Zoratti \emph{et al} . 2014). Plants convert photons
of light through photosynthetic fixation of carbon dioxide into sugars.
Light quality affects both photosynthetic rate and assimilation.
Exquisite mechanisms have been developed to tolerate light stress,
accumulation of pigments being one of the most important (Yang \emph{et
al.} 2019).

Little or moderate light stress can actually be beneficial for fruit
quality by enhancing pigment concentration. On-tree apple experiments
have shown that light stress induces anthocyanin production: these
anthocyanins may reduce the amount of excess light as well as reducing
the damage from the increased ROS produced to protect chlorophylls and
carotenoids as part of the photooxidative machinery (Merzlyak \&
Chivkunova 2000). On-tree experiments have also shown that full spectra,
including UV light, are essential for anthocyanin production
(Henry\selectlanguage{english}-Kirk\emph{et al.} 2018). Fruit bagging and shading experiments
confirm the importance of direct exposure to light for biosynthesis of
anthocyanins and carotenoids. Light exclusion results in transcriptional
suppression of biosynthetic pathway genes and reduced accumulation of
pigments (Downey, Dokoozlian \& Krstic 2006; Saini \& Keum 2018; Zhu
\emph{et al.} 2021; Zoratti \emph{et al.} 2014). Whereas many fruits,
like apples, have an absolute light requirement for anthocyanin
biosynthesis (An \emph{et al.} 2020a), there are species and cultivars
that show no change in anthocyanin accumulation when in shaded
conditions or any degradation of anthocyanins under high irradiation
(Downey \emph{et al.}2006; Zoratti \emph{et al.} 2014). This indicates
that there are different genetic regulation mechanisms for anthocyanin
biosynthesis in some fruits, which are not fully understood.

Anthocyanins intercept and absorb light energy to avoid photodamage
caused by excess light energy, directly scavenge free radicals and
indirectly remove ROS by interacting with molecules in other signalling
pathways (Li \emph{et al.} 2019). In extreme high light conditions,
anthocyanins play an important role in mitigating photoinhibition and
photodamage. Naturally red-skinned pear species have been shown to
maintain better photosynthetic capacity under high light and high
temperature conditions, while some green-skinned pear cultivars increase
skin anthocyanins in response to high light stress (Thomson, Turpin \&
Goodwin 2018).

In tomato, the accumulation of carotenoids during ripening is
significantly influenced by light. Phytochrome induces degradation of
phytochrome-interacting factor 1 (PIF1), a bHLH-type TF. In mature green
tomato, PIF1 directly binds to the PIF-binding E-box PBE box of the PSY1
promoter of the carotenoid biosynthetic pathway, to repress
carotenogenesis. During ripening, developmentally controlled degradation
of chlorophylls reduces the self-shading effect, allowing
phytochrome-mediated degradation of PIF1, which leads to depression of
PSY1. This accelerates carotenoid biosynthesis and shifts the profile
from xanthophyll, which is typical for leaves, to carotenes, mainly
lycopene and \selectlanguage{greek}β-\selectlanguage{english}carotene (Saini \& Keum 2018). Exposure of tomato to
excessive sunlight has been reported to inhibit the synthesis of
lycopene (Brandt \emph{et al.} 2006; Ili\selectlanguage{polish}ć \selectlanguage{english}\& Fallik 2017). It has been
proposed that ROS and redox status, combined with sugar and carbon
status, integrate the stress response and photosynthetic metabolism, and
so influencing the synthesis of carotenoids (Fanciullino, Bidel \& Urban
2014). In Clementine (\emph{Citrus clementina} ), accumulation of high
amounts of soluble sugars through photosynthesis during the early stages
of fruit development negatively influenced plastid development, which
affected carotenoid accumulation, although later in fruit development,
greater sugar accumulation increased carotenoid production
(Fanciullino\emph{et al.} 2014; Saini \& Keum 2018).

The quality of the light spectrum has been shown to affect fruit
pigments. Treatments with UV-B and UV-C light during ripening or
postharvest resulted in increased anthocyanin concentrations in many
fruit species, including apple, peach, wine grape (\emph{Vitis} spp.),
and blueberry (Chen \emph{et al.} 2021; Henry-Kirk \emph{et al.} 2018;
Zoratti \emph{et al.} 2014). Changes in carotenoid content following
exposure to UV-light have also been reported in tomato (Giuntini\emph{et
al.} 2005) and wine grape berries (\emph{Vitis vinifera} ) (Joubert
\emph{et al.} 2016).

Solar UV-B radiation has extensive photobiological effects on plants:
stress caused by UV-B is known to enhance the production of ROS, leading
to damage of DNA, proteins and the photosynthetic apparatus. In plants,
UV-B light is absorbed by tryptophan amino acid residues in the dimeric
form of UV8 photoreceptor, leading to UVR8 monomerization and formation
of a complex with CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), a known
mediator of diverse light signals in plants interacting with regulators
of both anthocyanin and carotenoid biosynthesis (Stanley \& Yuan 2019;
Zoratti \emph{et al.} 2014). Plant pigments have an important role in
protection of tissues against UV-radiation. For instance, anthocyanins
and flavonols have been shown to accumulate in the epidermal tissues,
such as fruit skin, to shield against excess UV-light (Zoratti \emph{et
al.} 2014). During photosynthesis, carotenoids harvest light energy and
transfer this energy to chlorophylls through singlet-singlet excitation
transfer, a lower energy state transfer. Excessive energy from
chlorophylls is absorbed by carotenoids through triplet-triplet
transfer, which is a higher energy state transfer essential for
photo-protection. Carotenoids with more than eleven conjugated double
bonds have a high capacity for quenching singlet oxygen produced under
light stress (Maoka 2020).

Other light spectrum wavelengths have also been shown to influence the
accumulation of fruit pigments and particularly red and blue wavelengths
affect the biosynthesis of anthocyanins and carotenoids. Red or blue
light treatment has resulted in a detectable increase in anthocyanin
content in several fruit crops, including strawberries, grape, pear,
apple, and cherry (\emph{Prunus avium} ) (Kokalj \emph{et al.} 2019a;
Kokalj \emph{et al.} 2019b; Koyama \emph{et al.} 2012; Miao \emph{et
al.} 2016; Tao \emph{et al.} 2018). Recently, both red and blue light
were shown to increase anthocyanin biosynthesis during bilberry ripening
(Samkumar \emph{et al.} 2021; Samkumar \emph{et al.} 2022).
Interestingly, differences in the perception of red and blue light were
detected between berries ripening whilst remaining attached to the
mother plant, or when detached in Petri dishes. Transcriptomic analysis
revealed differences in red and blue light signalling, leading to
altered anthocyanin content in the ripe, treated berries, with red light
increasing the anthocyanin content 12-fold compared with the control
(Samkumar \emph{et al.} 2021).

Many studies have shown that red light typically increases carotenoid
biosynthesis in fruits, while blue light has less effect, although there
are differences between species, cultivars and ripening stages. Spectral
light quality experiments monitoring carotenoid biosynthesis in
ripening\emph{Capsicum annuum} showed that red radiation was the most
effective in increasing carotenoid accumulation, whereas green and blue
radiation inhibited the formation of capsanthin, the major carotenoid
influencing fruit colour (Lopez, Candela \& Sabater 1986; Pola, Sugaya
\& Photchanachai 2019). Similar results have been shown in
\emph{Citrus}(Gong \emph{et al.} 2021; Ma \emph{et al.} 2012). In
kumquat (\emph{Fortunella crassifolia} ) fruit, a NAC family TF,
FrCNAC22, was shown to mediate red light-induced carotenoid accumulation
(Gong\emph{et al.} 2021). Moreover, PIF1 regulation, following blue
light perception, has been shown to act as a negative regulator of
carotenoid biosynthesis (Gong \emph{et al.} 2021).

\textbf{Temperature stress}

Temperature stresses, both below and above optimal growth temperatures,
have been shown to affect plant pigment accumulation during fruit
ripening. Although there is broad variation in what is the optimal
temperature depending on species, cultivar and ecotype, heat stress can
inhibit pigment biosynthesis in ripening fruits. Studies demonstrate
that this is the case for both carotenoid and anthocyanin pigments
(Gashu \emph{et al.} 2022; Kliewer 1977; Lin-Wang \emph{et al.} 2011;
Tomes 1963). When heat stress is moderate, the changes can be
reversible, whereas severe episodes can cause irreversible changes to
metabolites, resulting in crop failure.

Heat stress has been shown to inhibit anthocyanin biosynthesis in grape
berry skin in controlled studies with temperatures higher than 30\selectlanguage{ngerman}°C
(Ryu\emph{et al.} 2020; Yamane \emph{et al.} 2006). Active inhibition
and degradation of anthocyanin biosynthesis under high temperature
conditions have also been reported in other fruits such as \emph{Malus
profusion} (Rehman \emph{et al.} 2017) as well as in grape
(Mohaved\emph{et al.} 2016). Changes in ABA contents and in ABA/GA ratio
have been associated with changes in anthocyanin concentrations under
different temperature conditions (Ryu \emph{et al.} 2020). Hot
conditions during the growing season can dramatically reduce anthocyanin
production in numerous apple cultivars, with an associated reduction in
the transcription of the biosynthesis genes (Ubi \emph{et al} . 2006)
and the pathway regulating MYB TF, MYB10 (Lin-Wang \emph{et al} . 2011).
This appeared to be repression of anthocyanin activation, rather than an
increase in transcription of known anthocyanin MYB repressors.

Almeida \emph{et al.} (2021) found that ripe tomato fruit had better
plasticity to restore carotenoids following a heat wave compared with
tomatoes that experienced excessive heat during the breaker stage (when
pink colour is just starting to develop). They concluded that
heat-related transcriptional and posttranscriptional mis-regulation
during early carotenogenesis affected the carotenoid composition in the
ripe tomatoes. Moreover, upstream ripening regulators, such as\emph{CNR}
and \emph{NOR} , were also affected by the heat treatments. The results
also suggested that epigenetic mechanisms were mediating heat-induced
transcriptional changes.

It is not only high temperatures that can be problematic for fruit
colour. Low temperature conditions at around 4--10°C can cause stress in
developing fruits because of ROS production and generation of
malondialdehyde (MDA) in the cell, which can lead to severe membrane
lipid peroxidation. Cold stress also promotes the accumulation of
anthocyanin- and carotenoid-regulating phytohormones, ABA, jasmonates
(JA), ethylene (ETH) and salicylic acid (SA) (He \emph{et al.} 2022).
ABA, JA and polyamines have been reported to be associated with
low-temperature stress tolerance in apple fruitlets (Yoshikawa, Honda \&
Kondo 2007).

Lower temperatures have been observed to increase anthocyanin
biosynthesis in many fruits, such as apples, table grapes, black
currants (\emph{Ribes nigrum} ), cloudberries \emph{(Rubus chamaemorus}
), while anthocyanin accumulation is inhibited during heat stress
(Chen\emph{et al.} 2021; Downey \emph{et al.} 2006; Martinussen \emph{et
al.}2010; Wang \emph{et al} . 2018; Woznicki \emph{et al.} 2015). The
subsequent increase in anthocyanin concentration in fruit skin provides
some tolerance to cold stress, for instance in mango
(Sivankalyani\emph{et al.} 2016; Sudheeran \emph{et al.} 2018). This
production of anthocyanin at these lower temperatures is providing an
alternative means to other ROS coping mechanisms which are compromised
by cold. However, for other fruits such as strawberry, temperatures
below 10°C have been shown to inhibit anthocyanin biosynthesis, a
process mediated by MITOGEN-ACTIVATED PROTEIN
KINASE\textsubscript{3}(FvMAPK\textsubscript{3}) (Mao \emph{et al.}
2022).

Whereas high temperature clearly represses transcription of MYB10 in
apple, the opposite is seen with low temperature in crabapple. In this
case, the transcription of the MBW activation complex, including MYB10,
bHLH3/33 and TTG1, is elevated, leading to increased anthocyanin
production (Tian \emph{et al} . 2015). Other TFs are involved in this
response and Fang et al. (2019) showed that the zinc finger TF, MdBBX20,
responds to low temperature via MdbHLH3 interaction, to drive
anthocyanin production in a HY5-dependent manner.

Cold stress has been shown to affect carotenoid contents in fruits as a
response to the production of ROS, in a species-specific manner. For
example, higher lycopene contents have been shown to offer tolerance
against cold stress in grapefruit (\emph{Citrus paradisi} )
(Lado\emph{et al.} 2015), whereas in mango, carotenoid contents
decreased under cold stress (Rosalie \emph{et al} , 2018). In pepper
(\emph{C. annuum} ) fruit, Zhang et al. (2020) showed that
\emph{CaATHB-12} , a member of the HD-ZIP I gene family, is one of the
key regulators of fruit carotenoid content.

Diurnal temperature, with cool nights and warm days, is critical to
optimal fruit colour in some species and a reduction in diurnal
temperature range, as may become more evident with climate change, will
impact anthocyanin in fruit peel, such as in apple (Qu \& Zhou 2016).
Clearly, optimal day and night temperatures help to produce high quality
coloured fruit, while temperatures outside of this range often
positively (cold) or negatively (excess heat) effect the concentration
of colour.

\textbf{Water stress}

Water shortages are already a serious problem for much of the world's
agriculture and horticulture (Lobell \& Gourdji 2012). The predicted
increase in severe climate events due to climate change, including
drought, is likely to present even greater challenges for growers. Of
particular concern is the potential impact on global food supply chains
of reduced yield of major grain crops (Araus \emph{et al.} 2002).
Predicting the outcomes of different water deficiency scenarios and how
these will affect crops is complex (Tramblay \emph{et al.} 2020). For
essential photosynthetic pigments in leaves (carotenoids and
chlorophylls), water deficiency can result in reduced growth and yield
(Jaleel \emph{et al.} 2009) and in some fruits, water deficiency can
reduce both anthocyanin and carotenoid concentrations, reducing fruit
colour (Jiang \emph{et al.} 2020). However, for other fruits, water
deficiency outcomes are not necessarily deleterious. This may seem
counter-intuitive since drought is likely to decrease leaf
photosynthesis and, therefore, the distribution of primary metabolites
to the fruit. These primary metabolites provide the precursors for all
secondary/specialised metabolites and so, logically, may reduce the pool
of substrates for pigmented compounds. However, since both the
carotenoid and phenylpropanoid pathways are partly regulated by
stress-induced ROS production, there are also likely to be positive
effects of water deficiency on fruit pigments. The outcomes can be
species-dependent and, given this tension between pathways, highly
variable owing to the timing of fruit development at which the water
deficiency occurs (cell division, cell expansion or ripening phases),
and the severity and duration of the deficit. In terms of overall fruit
quality, there are possible effects on other major sensory attributes
such as aromas, the sugar/acid balance and texture (Ripoll \emph{et
al.}2014).

In some cropping situations, water deficiency is intentionally used to
improve colour. In red grape, anthocyanin is an important determinant of
wine quality. When water is deficient, grape berry size is reduced,
creating a higher skin:flesh ratio which, when coupled with increased
anthocyanin production, can improve wine quality (Gambetta \emph{et
al.}2020). Increases in grape berry anthocyanin concentrations following
exposure to water deficit have been reported in Cabernet Sauvignon
(Deluc \emph{et al.} 2009), Merlot (Bucchetti \emph{et al.} 2011) and
Tempranillo (Santesteban, Miranda \& Royo 2011). Anthocyanin composition
can also change in a cultivar-specific manner, such as the
drought-induced increase in acylated anthocyanins in Cabernet Sauvignon,
while the same conditions led to a reduction in these compounds in Syrah
(Hochberg \emph{et al.} 2015). Further compositional changes can be
created by a shift towards more tri-hydroxylated anthocyanins (darker
purples and blues) via the up-regulation of flavonoid 3'5' hydroxylases
(Castellarin \emph{et al.} 2007).

Phytohormones are intrinsically linked with drought perception and the
resultant transcriptional cascade (Ullah \emph{et al.} 2018),
particularly ABA (Yamaguchi-Shinozaki \& Shinozaki 2005). For example,
in strawberry fruit, drought conditions increased ABA, which was
correlated with elevated anthocyanin concentration (as well as AsA)
without a reduction in fruit yield (Perin \emph{et al.} 2019). A
previous study in strawberry clearly demonstrated how the presence of
ABA regulated the expression of the anthocyanin-regulating MYB
TF,\emph{FaMYB10,} which, in turn, elevated the anthocyanin biosynthetic
genes and fruit colour (Medina-Puche \emph{et al.} 2013). In apple, an
alternative molecular model of drought-induced anthocyanin production
has been proposed, whereby the ethylene response factor ERF38 partners
with the homologous MYB1 to drive the anthocyanin biosynthetic pathway
genes (An \emph{et al.} 2020c).

For fruit colours derived from carotenoids the picture is less clear cut
than for anthocyanins. In some cases, water deficit has been shown to
reduce fruit carotenoid concentrations (De Pascale \emph{et al.} 2007;
Jiang \emph{et al.} 2020). However, in tomato, there is strong evidence
that concentrations of lycopene (and \selectlanguage{greek}β-\selectlanguage{english}carotene) increase with water
deficiency (Favati \emph{et al.} 2009; Klunklin \& Savage 2017;
Patan\selectlanguage{ngerman}è\emph{et al.} 2021; Zushi \& Matsuzoe 1998).

\textbf{Nutrient stress}

While fruit pigments are highly influenced by temperature, light and
water, it is important to consider that they may also be altered by
other environmental factors. For instance, salinity stress can either
increase or reduce tomato anthocyanins depending on cultivar, while the
pigmented carotenoids are reliably increased by as much as 2--3 fold
across a range of cultivars (Borghesi \emph{et al.} 2011). However,
perhaps the most important consideration is nitrogen (N) status (Wang et
al., 2018). In \emph{Arabidopsis} , restricted N availability has been
shown to shift metabolism towards flavonoid production, including
anthocyanins, with evidence for increased transcription of the
regulating TF (AtPAP1) and the biosynthetic pathway (Lillo, Lea \& Ruoff
2008). If this is also true for fruits, it suggests that horticultural
practices can elevate fruit anthocyanin concentrations, but that in
planning nutrient applications, a balance is required to avoid
detrimental yield effects on the overall crop (Jezek \emph{et al.}2018).
That the effects of N deficiency is not always so clear and in other
crops, such as strawberry, and N application timing needs to be
determined on a crop-by-crop basis (Jezek \emph{et al.} 2018).

At the molecular level, studies in apple show a number of candidate
genes linking N deficiency to an elevation in the anthocyanin pathway.
Low N induces anthocyanin production, partly mediated by the
mitogen-activated protein kinase (MAPK) signalling cascade, as shown for
red-fleshed apples, where a MAPK family gene, \emph{MdMKK9,} regulates
the N status (Sun \emph{et al.} 2022). Under low N conditions the
autophagy nutrient recycling process can be activated, and studies in
apple have demonstrated that the AuTophaGy (ATG) protein, MdATG18a,
improves tolerance to nitrogen deficiency via upregulation of the
anthocyanin pathway (Sun \emph{et al.} 2018). In these cases, the
increases in anthocyanin content are driven by an upregulation of the
anthocyanin-regulating TF, MdMYB1/10. Conversely, the BTB/TAZ protein,
BTB2, which is lowly expressed under low N but highly expressed under
high N, negatively regulates the MYB, suppressing anthocyanin
accumulation (An, Wang \& Hao 2020b). It seems that fruit carotenoid
contents, as shown in tomato, are either decreased or less affected by
low nitrogen supply depending on the timing of the nitrogen supply
reduction (Benard \emph{et al.} 2009; Hernández \emph{et al.} 2020).

\textbf{6 Conclusions and perspectives}

From research reviewed here, it is clear that some environmental
stresses can enhance fruit colour: low temperature, high light (and UV)
and a degree of water deficit can all be beneficial. Against this, the
severity and timing of these stresses are critical in determining
whether outcomes are positive or negative. Some of these stresses can be
controlled horticulturally, such as limiting water supply, but climate
change is outside grower control and thus likely to disrupt our current
growing practices. Consumer desire for ever more healthy fruits is
unlikely to dissipate --- the pigments in fruits provide many of these
health benefits, packaged with one of the strongest motivators for
purchase --- the attractiveness of colourful fruit. Of course, fruit
cultivars, no matter how colourful, will also have to reach other key
consumer expectations, such as texture, storability and flavour. As
climate change creates less predictable temperatures across many
fruit-growing regions, understanding how fruit pigmentation will be
affected will become increasingly important if we are to maintain or
improve fruit colour. For some fruit crops, indoor production may become
a more attractive (and commercial) proposition to avoid crop losses due
to damaging climatic events.

Various options are available to maintain fruit colour in this changing
environment, including agronomic approaches (Poiroux-Gonord \emph{et
al.} 2010). Similarly, postharvest treatments can provide the potential
to preserve and enhance fruit pigments (de Pascual-Teresa \&
Sanchez-Ballesta 2008). In the future, more substantive advances may be
required to augment the incremental changes that can be made by in-field
or postharvest management. In some circumstances, fruit breeding
programmes have reduced the genetic and phenotypic diversity in breeding
populations. To address production challenges associated with severe
climate change, incorporating new genetic diversity is likely to become
essential to maintain or improve fruit crops: the use of crop wild
relatives that are better adapted to environmental stresses should be
considered to introduce beneficial traits. Ideally, this would be in
conjunction with deep bioinformatic resources (high quality genomes,
transcriptomes and metabolomes), and an emphasis on mapping and
molecular markers to help to target `resilience' traits and rapidly
incorporate these in new cultivars that are better adapted to our
changing environment. Breeding varies markedly between species and
varieties, and there will be an increasing need for developing crops
suited to (and tested at) different geographic and environmental
locations. The complexity of GxE interactions on fruit pigmentation is
complex, and more research into this area is required to understand the
plant response and potential breeding strategies for fruit colour
improvement.

`Traditional' genetic engineering has provided many examples of
successfully increasing plant pigments (Martin \& Li 2017).
Sophisticated molecular engineering of fruit can provide platforms for
elevated amounts of specific phytochemicals, including pigments
(Li\emph{et al.} 2018). The new breeding technologies such as CRISPR
provide untapped potential for modifying our fruit crops both to improve
their nutritional benefit (colour) and to tackle changing growing
conditions (Wang, Zhang \& Zhu 2019). It is likely that adoption of new
breeding approaches will be required to maintain and enhance fruit
pigments as we navigate environmental changes to fruit-growing regions
across the globe.

\textbf{Acknowledgements}

We apologise to those authors whose work was unable to be included in
this review owing to space limitations. Research in the laboratory of
R.V.E. is supported by The New Zealand Government Ministry of Business,
Innovation and Employment's Endeavour Fund, contract C11X1704 `Filling
the Void' and for L.J. by NordPlant (NordForsk grant no. 84597). We
thank our Plant \& Food Research colleagues Kevin Davies for helpful
advice on the manuscript and Elysia Arnold and Ben Lawrence for
illustrations.

\textbf{ORCiD}

Richard V. Espley https://orcid.org/0000-0002-1732-3688

Laura Jaakola https://orcid.org/0000-0001-9379-0862

\textbf{References}

Aharoni A., De Vos C.R., Wein M., Sun Z., Greco R., Kroon A., \ldots{},
O'Connell A.P. (2001) The strawberry FaMYB1 transcription factor
suppresses anthocyanin and flavonol accumulation in transgenic
tobacco.\emph{The Plant Journal} \textbf{28,} 319-332.

Åkerstro\selectlanguage{english}m A., Jaakola L., B\selectlanguage{ngerman}ång U. \& Jaderlund A. (2010) Effects of
latitude-related factors and geographical origin on anthocyanidin
concentrations in fruits of Vaccinium myrtillus
L.(bilberries).\emph{Journal of Agricultural and Food Chemistry}
\textbf{58,}11939-11945.

Albert N.W., Davies K.M., Lewis D.H., Zhang H., Montefiori M.,
Brendolise C., \ldots{}, Schwinn K.E. (2014) A conserved network of
transcriptional activators and repressors regulates anthocyanin
pigmentation in eudicots. \emph{The Plant Cell} \textbf{26,} 962-980.

Allan A.C. \& Espley R.V. (2018) MYBs drive novel consumer traits in
fruits and vegetables. \emph{Trends in plant science}
\textbf{23,}693-705.

Allan A.C., Hellens R.P. \& Laing W.A. (2008) MYB transcription factors
that colour our fruit. \emph{Trends in Plant Science}
\textbf{13,}99-102.

Almeida J., Perez\selectlanguage{english}-Fons L. \& Fraser P.D. (2021) A transcriptomic,
metabolomic and cellular approach to the physiological adaptation of
tomato fruit to high temperature. \emph{Plant, Cell \&
Environment}\textbf{44,} 2211-2229.

Ampomah-Dwamena C., Thrimawithana A.H., Dejnoprat S., Lewis D., Espley
R.V. \& Allan A.C. (2019) A kiwifruit (Actinidia deliciosa) R2R3-MYB
transcription factor modulates chlorophyll and carotenoid
accumulation.\emph{New phytologist} \textbf{221,} 309-325.

An J.-P., Liu Y.-J., Zhang X.-W., Bi S.-Q., Wang X.-F., You C.-X. \& Hao
Y.-J. (2020a) Dynamic regulation of anthocyanin biosynthesis at
different light intensities by the BT2-TCP46-MYB1 module in
apple.\emph{Journal of Experimental Botany} \textbf{71,} 3094-3109.

An J.P., Wang X.F. \& Hao Y.J. (2020b) BTB/TAZ protein MdBT2 integrates
multiple hormonal and environmental signals to regulate anthocyanin
biosynthesis in apple. \emph{Journal of Integrative Plant
Biology}\textbf{62,} 1643-1646.

An J.P., Zhang X.W., Bi S.Q., You C.X., Wang X.F. \& Hao Y.J. (2020c)
The ERF transcription factor MdERF38 promotes drought stress\selectlanguage{english}-induced
anthocyanin biosynthesis in apple. \emph{The Plant Journal}\textbf{101,}
573-589.

Araus J., Slafer G., Reynolds M. \& Royo C. (2002) Plant breeding and
drought in C3 cereals: what should we breed for? \emph{Annals of
botany}\textbf{89,} 925-940.

Benard C., Gautier H., Bourgaud F., Grasselly D., Navez B., Caris-Veyrat
C., \ldots{}, Genard M. (2009) Effects of low nitrogen supply on tomato
(Solanum lycopersicum) fruit yield and quality with special emphasis on
sugars, acids, ascorbate, carotenoids, and phenolic
compounds.\emph{Journal of Agricultural and Food Chemistry}
\textbf{57,}4112-4123.

Bernstein P.S., Li B., Vachali P.P., Gorusupudi A., Shyam R., Henriksen
B.S. \& Nolan J.M. (2016) Lutein, zeaxanthin, and meso-zeaxanthin: The
basic and clinical science underlying carotenoid-based nutritional
interventions against ocular disease. \emph{Progress in Retinal and Eye
Research} \textbf{50,} 34-66.

Borghesi E., Gonzalez-Miret M.L., Escudero-Gilete M.L., Malorgio F.,
Heredia F.J. \& Melendez-Martinez A.J. (2011) Effects of salinity stress
on carotenoids, anthocyanins, and color of diverse tomato
genotypes.\emph{Journal of Agricultural and Food Chemistry}
\textbf{59,}11676-11682.

Brandt S., Pek Z., Barna E., Lugasi A. \& Helyes L. (2006) Lycopene
content and colour of ripening tomatoes as affected by environmental
conditions. \emph{Journal of the Science of Food and
Agriculture}\textbf{86,} 568-572.

Bucchetti B., Matthews M.A., Falginella L., Peterlunger E. \&
Castellarin S.D. (2011) Effect of water deficit on Merlot grape tannins
and anthocyanins across four seasons. \emph{Scientia
Horticulturae}\textbf{128,} 297-305.

Carpentier S., Knaus M. \& Suh M. (2009) Associations between lutein,
zeaxanthin, and age-related macular degeneration: an
overview.\emph{Critical Reviews in Food Science and Nutrition}
\textbf{49,}313-326.

Castellarin S.D., Matthews M.A., Di Gaspero G. \& Gambetta G.A. (2007)
Water deficits accelerate ripening and induce changes in gene expression
regulating flavonoid biosynthesis in grape berries.
\emph{Planta}\textbf{227,} 101-112.

Cazzonelli C.I. \& Pogson B.J. (2010) Source to sink: regulation of
carotenoid biosynthesis in plants. \emph{Trends in Plant
Science}\textbf{15,} 266-274.

Challinor A.J., Watson J., Lobell D.B., Howden S.M., Smith D.R. \&
Chhetri N. (2014) A meta-analysis of crop yield under climate change and
adaptation. \emph{Nature Climate Change} \textbf{4,} 287-291.

Chen Z., Yu L., Liu W., Zhang J., Wang N. \& Chen X. (2021) Research
progress of fruit color development in apple (Malus domestica
Borkh.).\emph{Plant Physiology and Biochemistry} \textbf{162,} 267-279.

Cheok A., Xu Y., Zhang Z., Caton P.W., Rodriguez-Mateos A. (2022)
Betalain-rich dragon fruit (pitaya) consumption improves vascular
function in men and women: a double-blind, randomized controlled
crossover trial. \emph{American Journal of Clinical Nutrition}
.\textbf{115,} 1418-1431.

Connor A.M., Luby J.J., Tong C.B., Finn C.E. \& Hancock J.F. (2002)
Genotypic and environmental variation in antioxidant activity, total
phenolic content, and anthocyanin content among blueberry
cultivars.\emph{Journal of the American Society for Horticultural
Science}\textbf{127,} 89-97.

Cunningham F.X. \& Gantt E. (1998) GENES AND ENZYMES OF CAROTENOID
BIOSYNTHESIS IN PLANTS. \emph{Annu Rev Plant Physiol Plant Mol
Biol}\textbf{49,} 557-583.

D'Amelia V., Aversano R., Chiaiese P. \& Carputo D. (2018) The
antioxidant properties of plant flavonoids: their exploitation by
molecular plant breeding. \emph{Phytochemistry Reviews}
\textbf{17,}611-625.

Das K. \& Roychoudhury A. (2014) Reactive oxygen species (ROS) and
response of antioxidants as ROS-scavengers during environmental stress
in plants. \emph{Frontiers in Environmental Science} \textbf{2} .

Davies K.M., Albert N.W., Zhou Y. \& Schwinn K.E. (2018) Functions of
flavonoid and betalain pigments in abiotic stress tolerance in
plants.\emph{Annual Plant Reviews online} \textbf{,} 21-62.

De Pascale S., Martino A., Raimondi G. \& Maggio A. (2007) Comparative
analysis of water and salt stress-induced modifications of quality
parameters in cherry tomatoes. \emph{The Journal of Horticultural
Science and Biotechnology} \textbf{82,} 283-289.

de Pascual-Teresa S. \& Sanchez-Ballesta M.T. (2008) Anthocyanins: from
plant to health. \emph{Phytochemistry Reviews} \textbf{7,} 281-299.

Decros G., Baldet P., Beauvoit B., Stevens R., Flandin A., Colombie S.,
\ldots{}, Petriacq P. (2019) Get the balance right: ROS homeostasis and
redox signalling in fruit. \emph{Frontiers in Plant Science} \textbf{,}
1091.

Deluc L.G., Quilici D.R., Decendit A., Grimplet J., Wheatley M.D.,
Schlauch K.A., \ldots{}, Cramer G.R. (2009) Water deficit alters
differentially metabolic pathways affecting important flavor and quality
traits in grape berries of Cabernet Sauvignon and Chardonnay. \emph{BMC
Genomics} \textbf{10,} 1-33.

Dias M.G., Borge G.I.A., Kljak K., Mandi\selectlanguage{polish}ć \selectlanguage{english}A.I., Mapelli-Brahm P.,
Olmedilla-Alonso B., \ldots{}, Sereikait\selectlanguage{polish}ė \selectlanguage{english}J. (2021) European database of
carotenoid levels in foods. Factors affecting carotenoid
content.\emph{Foods} \textbf{10,} 912.

Dias M.G., Cam\selectlanguage{ngerman}ões M.F.G. \& Oliveira L. (2009) Carotenoids in
traditional Portuguese fruits and vegetables. \emph{Food
Chemistry}\textbf{113,} 808-815.

Downey M.O., Dokoozlian N.K. \& Krstic M.P. (2006) Cultural practice and
environmental impacts on the flavonoid composition of grapes and wine: a
review of recent research. \emph{American Journal of Enology and
Viticulture} \textbf{57,} 257-268.

Espley R.V., Butts C.A., Laing W.A., Martell S., Smith H., McGhie T.K.,
\ldots{}, Bovy A. (2014) Dietary flavonoids from modified apple reduce
inflammation markers and modulate gut microbiota in mice. \emph{The
Journal of Nutrition} \textbf{144,} 146-154.

Fanciullino A.-L., Bidel L. \& Urban L. (2014) Carotenoid responses to
environmental stimuli: integrating redox and carbon controls into a
fruit model. \emph{Plant, Cell \& Environment} \textbf{37,} 273-289.

Fang H., Dong Y., Yue X., Hu J., Jiang S., Xu H., \ldots{}, Zhang Z.
(2019) The B\selectlanguage{english}-box zinc finger protein MdBBX20 integrates anthocyanin
accumulation in response to ultraviolet radiation and low
temperature.\emph{Plant, Cell \& Environment} \textbf{42,} 2090-2104.

Favati F., Lovelli S., Galgano F., Miccolis V., Di Tommaso T. \& Candido
V. (2009) Processing tomato quality as affected by irrigation
scheduling. \emph{Scientia Horticulturae} \textbf{122,} 562-571.

Fenn M.A. \& Giovannoni J.J. (2021) Phytohormones in fruit development
and maturation. \emph{The Plant Journal} \textbf{105,} 446-458.

Foyer C.H. (2018) Reactive oxygen species, oxidative signaling and the
regulation of photosynthesis. \emph{Environmental and Experimental
Botany} \textbf{154,} 134-142.

Frank H.A. \& Cogdell R.J. (1996) Carotenoids in
photosynthesis.\emph{Photochemistry and Photobiology} \textbf{63,}
257-264.

Fredes C., Yousef G.G., Robert P., Grace M.H., Lila M.A., Gomez M.,
\ldots{}, Montenegro G. (2014) Anthocyanin profiling of wild maqui
berries (Aristotelia chilensis {[}Mol.{]} Stuntz) from different
geographical regions in Chile. \emph{Journal of the Science of Food and
Agriculture}\textbf{94,} 2639-2648.

Fu C.-c., Han Y.-c., Fan Z.-q., Chen J.-y., Chen W.-x., Lu W.-j. \&
Kuang J.-f. (2016) The papaya transcription factor CpNAC1 modulates
carotenoid biosynthesis through activating phytoene desaturase genes
CpPDS2/4 during fruit ripening. \emph{Journal of Agricultural and Food
Chemistry} \textbf{64,} 5454-5463.

Fu C.-c., Han Y.-c., Kuang J.-f., Chen J.-y. \& Lu W.-j. (2017) Papaya
CpEIN3a and CpNAC2 co-operatively regulate carotenoid
biosynthesis-related genes CpPDS2/4, CpLCY-e and CpCHY-b during fruit
ripening. \emph{Plant and Cell Physiology} \textbf{58,} 2155-2165.

Gambetta G.A., Herrera J.C., Dayer S., Feng Q., Hochberg U. \&
Castellarin S.D. (2020) The physiology of drought stress in grapevine:
towards an integrative definition of drought tolerance. \emph{Journal of
Experimental Botany} \textbf{71,} 4658-4676.

Gashu K., Song C., Dubey A.K., Acuna T., Sagi M., Agam N., \ldots{},
Fait A. (2022) The effect of topo-climate variation on the secondary
metabolism of berries in white grapevine varieties (Vitis
vinifera).\emph{Frontiers in Plant Science} \textbf{,} 487.

Giuliano G. (2014) Plant carotenoids: genomics meets multi-gene
engineering. \emph{Current Opinion in Plant Biology}
\textbf{19,}111-117.

Giuliano G. (2017) Provitamin A biofortification of crop plants: a gold
rush with many miners. \emph{Current Opinion in
Biotechnology}\textbf{44,} 169-180.

Giuntini D., Graziani G., Lercari B., Fogliano V., Soldatini G.F. \&
Ranieri A. (2005) Changes in carotenoid and ascorbic acid contents in
fruits of different tomato genotypes related to the depletion of UV-B
radiation. \emph{Journal of Agricultural and Food Chemistry}\textbf{53,}
3174-3181.

Goncalves A.C., Nunes A.R., Falcao A., Alves G. \& Silva L.R. (2021)
Dietary effects of anthocyanins in human health: A comprehensive
review.\emph{Pharmaceuticals} \textbf{14,} 690.

Gong J., Zeng Y., Meng Q., Guan Y., Li C., Yang H., \ldots{}, Chen C.
(2021) Red light-induced kumquat fruit coloration is attributable to
increased carotenoid metabolism regulated by FcrNAC22. \emph{Journal of
Experimental Botany} \textbf{72,} 6274-6290.

Gonzalez-de-Peredo A.V., Vazquez-Espinosa M., Espada-Bellido E.,
Ferreiro-Gonzalez M., Amores-Arrocha A., Palma M., \ldots{},
Jimenez-Cantizano A. (2019) Discrimination of myrtle ecotypes from
different geographic areas according to their morphological
characteristics and anthocyanins composition. \emph{Plants}
\textbf{8,}328.

Groh I.A.M., Riva A., Braun D., Sutherland H.G., Williams O., Bakuradze
T., \ldots{}, Griffiths L.R. (2020) Long-term consumption of
anthocyanin-rich fruit juice: Impact on gut microbiota and antioxidant
markers in lymphocytes of healthy males. \emph{Antioxidants}
\textbf{10,} 27.

He J., Yao L., Pecoraro L., Liu C., Wang J., Huang L. \& Gao W. (2022)
Cold stress regulates accumulation of flavonoids and terpenoids in
plants by phytohormone, transcription process, functional enzyme, and
epigenetics. \emph{Critical Reviews in Biotechnology} \textbf{,} 1-18.

Henry\selectlanguage{english}-Kirk R.A., Plunkett B., Hall M., McGhie T., Allan A.C., Wargent
J.J. \& Espley R.V. (2018) Solar UV light regulates flavonoid metabolism
in apple (Malus x domestica). \emph{Plant, Cell \&
Environment}\textbf{41,} 675-688.

Hernandez V., Hellin P., Fenoll J. \& Flores P. (2020) Impact of
nitrogen supply limitation on tomato fruit composition. \emph{Scientia
Horticulturae} \textbf{264,} 109173.

Hochberg U., Degu A., Cramer G.R., Rachmilevitch S. \& Fait A. (2015)
Cultivar specific metabolic changes in grapevines berry skins in
relation to deficit irrigation and hydraulic behavior. \emph{Plant
Physiology and Biochemistry} \textbf{88,} 42-52.

Husain T., Fatima A., Suhel M., Singh S., Sharma A., Prasad S.M. \&
Singh V.P. (2020) A brief appraisal of ethylene signaling under abiotic
stress in plants. \emph{Plant Signaling \& Behavior}
\textbf{15,}1782051.

Ili\selectlanguage{polish}ć \selectlanguage{english}Z.S. \& Fallik E. (2017) Light quality manipulation improves
vegetable quality at harvest and postharvest: A
review.\emph{Environmental and experimental botany} \textbf{139,} 79-90.

Jaakola L. (2013) New insights into the regulation of anthocyanin
biosynthesis in fruits. \emph{Trends in Plant Science} \textbf{18
9,}477-483.

Jaakola L. \& Hohtola A. (2010) Effect of latitude on flavonoid
biosynthesis in plants. \emph{Plant, Cell \& Environment}
\textbf{33,}1239-1247.

Jaakola L., Poole M., Jones M.O., K\selectlanguage{ngerman}ämäräinen-Karppinen T., Koskimäki
J.J., Hohtola A., \ldots{}, Seymour G.B. (2010) A SQUAMOSA MADS Box Gene
Involved in the Regulation of Anthocyanin Accumulation in Bilberry
Fruits ~ ~\emph{Plant Physiology} \textbf{153,} 1619-1629.

Jaleel C.A., Manivannan P., Wahid A., Farooq M., Al-Juburi H.J.,
Somasundaram R. \& Panneerselvam R. (2009) Drought stress in plants: a
review on morphological characteristics and pigments
composition.\emph{International Journal of Agricultural Biology}
\textbf{11,}100-105.

Jezek M., Zo\selectlanguage{english}rb C., Merkt N. \& Geilfus C.-M. (2018) Anthocyanin
management in fruits by fertilization. \emph{Journal of Agricultural and
Food Chemistry} \textbf{66,} 753-764.

Jia H.-F., Chai Y.-M., Li C.-L., Lu D., Luo J.-J., Qin L. \& Shen Y.-Y.
(2011) Abscisic acid plays an important role in the regulation of
strawberry fruit ripening. \emph{Plant Physiology} \textbf{157,}188-199.

Jiang W., Li N., Zhang D., Meinhardt L., Cao B., Li Y. \& Song L. (2020)
Elevated temperature and drought stress significantly affect fruit
quality and activity of anthocyanin-related enzymes in jujube (Ziziphus
jujuba Mill. cv.`Lingwuchangzao'). \emph{PLoS One} \textbf{15,}e0241491.

Joubert C., Young P.R., Ey\selectlanguage{ngerman}éghé-Bickong H.A. \& Vivier M.A. (2016)
Field-grown grapevine berries use carotenoids and the associated
xanthophyll cycles to acclimate to UV exposure differentially in high
and low light (shade) conditions. \emph{Frontiers in Plant
Science}\textbf{7,} 786.

Jucá M.M., Cysne Filho F.M.S., de Almeida J.C., Mesquita D.d.S., Barriga
J.R.d.M., Dias K.C.F., \ldots{}, Ribeiro J.E. (2020) Flavonoids:
biological activities and therapeutic potential. \emph{Natural Product
Research}\textbf{34,} 692-705.

Kalt W., Cassidy A., Howard L.R., Krikorian R., Stull A.J., Tremblay F.
\& Zamora-Ros R. (2020) Recent research on the health benefits of
blueberries and their anthocyanins. \emph{Advances in
Nutrition}\textbf{11,} 224-236.

Karppinen K., Lafferty D.J., Albert N.W., Mikkola N., McGhie T., Allan
A.C., \ldots{}, Jaakola L. (2021) MYBA and MYBPA transcription factors
co-regulate anthocyanin biosynthesis in blue-coloured berries. \emph{New
phytologist} \textbf{232,} 1350-1367.

Karppinen K., Tegelberg P., Häggman H. \& Jaakola L. (2018) Abscisic
acid regulates anthocyanin biosynthesis and gene expression associated
with cell wall modification in ripening bilberry (Vaccinium myrtillus
L.) fruits. \emph{Frontiers in Plant Science} \textbf{9,} 1259.

Kay C.D., Pereira-Caro G., Ludwig I.A., Clifford M.N. \& Crozier A.
(2017) Anthocyanins and flavanones are more bioavailable than previously
perceived: A review of recent evidence. \emph{Annual Review of Food
Science and Technology} \textbf{8,} 155-180.

Kimura M., Rodriguez-Amaya D. \& Yokoyama S. (1991) Cultivar differences
and geographic effects on the carotenoid composition and vitamin A value
of papaya. \emph{Lebensmittel-Wissenschaft+ Technologie}
\textbf{24,}415-418.

Kliewer W.M. (1977) Influence of temperature, solar radiation and
nitrogen on coloration and composition of Emperor grapes. \emph{American
Journal of Enology and Viticulture} \textbf{28,} 96-103.

Klunklin W. \& Savage G. (2017) Effect on quality characteristics of
tomatoes grown under well-watered and drought stress
conditions.\emph{Foods} \textbf{6,} 56.

Kokalj D., Zlati\selectlanguage{polish}ć \selectlanguage{english}E., Cigi\selectlanguage{polish}ć \selectlanguage{english}B., Kobav M.B. \& Vidrih R. (2019a)
Postharvest flavonol and anthocyanin accumulation in three apple
cultivars in response to blue-light-emitting diode light. \emph{Scientia
Horticulturae} \textbf{257,} 108711.

Kokalj D., Zlati\selectlanguage{polish}ć \selectlanguage{english}E., Cigi\selectlanguage{polish}ć \selectlanguage{english}B. \& Vidrih R. (2019b) Postharvest
light-emitting diode irradiation of sweet cherries (Prunus avium L.)
promotes accumulation of anthocyanins. \emph{Postharvest Biology and
Technology} \textbf{148,} 192-199.

Korekar G., Dolkar P., Singh H., Srivastava R.B. \& Stobdan T. (2014)
Variability and the genotypic effect on antioxidant activity, total
phenolics, carotenoids and ascorbic acid content in seventeen natural
population of Seabuckthorn (Hippophae rhamnoides L.) from
trans-Himalaya. \emph{LWT-Food Science and Technology}
\textbf{55,}157-162.

Koyama K., Ikeda H., Poudel P.R. \& Goto-Yamamoto N. (2012) Light
quality affects flavonoid biosynthesis in young berries of Cabernet
Sauvignon grape. \emph{Phytochemistry} \textbf{78,} 54-64.

Kumar R., Khurana A. \& Sharma A.K. (2013) Role of plant hormones and
their interplay in development and ripening of fleshy
fruits.\emph{Journal of Experimental Botany} \textbf{65,} 4561-4575.

Lado J., Rodrigo M.J., Cronje P. \& Zacar\selectlanguage{ngerman}ías L. (2015) Involvement of
lycopene in the induction of tolerance to chilling injury in
grapefruit.\emph{Postharvest Biology and Technology} \textbf{100,}
176-186.

Lafferty D.J., Espley R.V., Deng C.H., Günther C.S., Plunkett B., Turner
J.L., \ldots{}, Albert N.W. (2021) Hierarchical regulation of MYBPA1 by
anthocyanin-and proanthocyanidin-related MYB proteins is conserved in
Vaccinium species. \emph{Journal of Experimental Botany} .

LaFountain A.M. \& Yuan Y.W. (2021) Repressors of anthocyanin
biosynthesis. \emph{New phytologist} \textbf{231,} 933-949.

Latti A.K., Jaakola L., Riihinen K.R. \& Kainulainen P.S. (2010)
Anthocyanin and flavonol variation in bog bilberries (Vaccinium
uliginosum L.) in Finland. \emph{Journal of Agricultural and Food
Chemistry} \textbf{58,} 427-433.

Lätti A.K., Riihinen K.R. \& Kainulainen P.S. (2008) Analysis of
anthocyanin variation in wild populations of bilberry (Vaccinium
myrtillus L.) in Finland. \emph{Journal of Agricultural and Food
Chemistry} \textbf{56,} 190-196.

Leermakers E.T., Darweesh S.K., Baena C.P., Moreira E.M., Melo van Lent
D., Tielemans M.J., \ldots{}, Franco O.H. (2016) The effects of lutein
on cardiometabolic health across the life course: a systematic review
and meta-analysis1,2. \emph{The American Journal of Clinical
Nutrition}\textbf{103,} 481-494.

Leng P., Yuan B. \& Guo Y. (2013) The role of abscisic acid in fruit
ripening and responses to abiotic stress. \emph{Journal of Experimental
Botany} \textbf{65,} 4577-4588.

Li G., Meng X., Zhu M. \& Li Z. (2019) Research progress of betalain in
response to adverse stresses and evolutionary relationship compared with
anthocyanin. \emph{Molecules} \textbf{24,} 3078.

Li Y., Wang H., Zhang Y. \& Martin C. (2018) Can the world's favorite
fruit, tomato, provide an effective biosynthetic chassis for high-value
metabolites? \emph{Plant Cell Reports} \textbf{37,} 1443-1450.

Lila M.A., Burton-Freeman B., Grace M. \& Kalt W. (2016) Unraveling
anthocyanin bioavailability for human health. \emph{Annual Reviews in
Food Science Technology} \textbf{7,} 17.11-17.19.

Lillo C., Lea U.S. \& Ruoff P. (2008) Nutrient depletion as a key factor
for manipulating gene expression and product formation in different
branches of the flavonoid pathway. \emph{Plant, Cell \&
Environment}\textbf{31,} 587-601.

Lin-Wang K., McGhie T.K., Wang M., Liu Y., Warren B., Storey R.,
\ldots{}, Allan A.C. (2014) Engineering the anthocyanin regulatory
complex of strawberry (Fragaria vesca). \emph{Frontiers in Plant
Science}\textbf{5} .

Lin\selectlanguage{english}-Wang K., Micheletti D., Palmer J., Volz R., Lozano L., Espley R.,
\ldots{}, Troggio M. (2011) High temperature reduces apple fruit colour
via modulation of the anthocyanin regulatory complex. \emph{Plant, Cell
\& Environment} \textbf{34,} 1176-1190.

Lindbergh C.A., Renzi-Hammond L.M., Hammond B.R., Terry D.P., Mewborn
C.M., Puente A.N. \& Miller L.S. (2018) Lutein and zeaxanthin influence
brain function in older adults: a randomized controlled
trial.\emph{Journal of the International Neuropsychological
Society}\textbf{24,} 77-90.

Liso M., De Santis S., Scarano A., Verna G., Dicarlo M., Galleggiante
V., \ldots{}, Vacca M. (2018) A bronze-tomato enriched diet affects the
intestinal microbiome under homeostatic and inflammatory
conditions.\emph{Nutrients} \textbf{10,} 1862.

Lobell D.B. \& Gourdji S.M. (2012) The influence of climate change on
global crop productivity. \emph{Plant Physiology}
\textbf{160,}1686-1697.

Lopez M., Candela M.E. \& Sabater F. (1986) Carotenoids fromCapsicum
annuum fruits: Influence of spectral quality of radiation.\emph{Biologia
Plantarum} \textbf{28,} 100-104.

Lu S., Zhang Y., Zhu K., Yang W., Ye J., Chai L., \ldots{}, Deng X.
(2018) The citrus transcription factor CsMADS6 modulates carotenoid
metabolism by directly regulating carotenogenic genes. \emph{Plant
Physiology}\textbf{176,} 2657-2676.

Ma G., Zhang L., Kato M., Yamawaki K., Kiriiwa Y., Yahata M., \ldots{},
Matsumoto H. (2012) Effect of blue and red LED light irradiation on
\selectlanguage{greek}β-\selectlanguage{english}cryptoxanthin accumulation in the flavedo of citrus
fruits.\emph{Journal of Agricultural and Food Chemistry} \textbf{60,}
197-201.

Mao W., Han Y., Chen Y., Sun M., Feng Q., Li L., \ldots{}, Han Z. (2022)
Low temperature inhibits anthocyanin accumulation in strawberry fruit by
activating FvMAPK3-induced phosphorylation of FvMYB10 and degradation of
Chalcone Synthase 1. \emph{The Plant Cell} \textbf{34,} 1226-1249.

Maoka T. (2020) Carotenoids as natural functional pigments.\emph{Journal
of Natural Medicines} \textbf{74,} 1-16.

Martin C. \& Li J. (2017) Medicine is not health care, food is health
care: plant metabolic engineering, diet and human health. \emph{New
Phytologist} \textbf{216,} 699-719.

Martinussen I., Uleberg E., McDougall G.J., Stewart D. \& Junttila O.
(2010) Development and quality of cloudberry (Rubus chamaemorus L.) as
affected by female parent, male parent and temperature. \emph{Journal of
Berry Research} \textbf{1,} 91-101.

Medina-Puche L., Cumplido-Laso G., Amil-Ruiz F., Hoffmann T., Ring L.,
Rodr\selectlanguage{ngerman}íguez-Franco A., \ldots{}, Blanco-Portales R. (2013) MYB10 plays a
major role in the regulation of flavonoid/phenylpropanoid metabolism
during ripening of Fragaria × ananassa fruits. \emph{Journal of
Experimental Botany} \textbf{65,} 401-417.

Medina-Puche L., Cumplido-Laso G., Amil-Ruiz F., Hoffmann T., Ring L.,
Rodríguez-Franco A., \ldots{}, Blanco-Portales R. (2014) MYB10 plays a
major role in the regulation of flavonoid/phenylpropanoid metabolism
during ripening of Fragaria× ananassa fruits. \emph{Journal of
Experimental Botany} \textbf{65,} 401-417.

Mein J.R., Lian F. \& Wang X.-D. (2008) Biological activity of lycopene
metabolites: implications for cancer prevention. \emph{Nutrition
Reviews} \textbf{66,} 667-683.

Mercadante A.Z. \& Rodriguez-Amaya D.B. (1998) Effects of ripening,
cultivar differences, and processing on the carotenoid composition of
mango. \emph{Journal of Agricultural and Food Chemistry}
\textbf{46,}128-130.

Merzlyak M.N. \& Chivkunova O.B. (2000) Light-stress-induced pigment
changes and evidence for anthocyanin photoprotection in
apples.\emph{Journal of Photochemistry and Photobiology B:
Biology}\textbf{55,} 155-163.

Miao L., Zhang Y., Yang X., Xiao J., Zhang H., Zhang Z., \ldots{}, Jiang
G. (2016) Colored light-quality selective plastic films affect
anthocyanin content, enzyme activities, and the expression of flavonoid
genes in strawberry (Fragaria× ananassa) fruit. \emph{Food
Chemistry}\textbf{207,} 93-100.

Mittler R. (2002) Oxidative stress, antioxidants and stress
tolerance.\emph{Trends in Plant Science} \textbf{7,} 405-410.

Moise A.R., Al-Babili S. \& Wurtzel E.T. (2014) Mechanistic aspects of
carotenoid biosynthesis. \emph{Chemical Reviews} \textbf{114,} 164-193.

Movahed N., Pastore C., Cellini A., Allegro G., Valentini G., Zenoni S.,
\ldots{}, Filippetti I. (2016) The grapevine VviPrx31 peroxidase as a
candidate gene involved in anthocyanin degradation in ripening berries
under high temperature. \emph{Journal of Plant Research}
\textbf{129,}513-526.

Müller M. (2021) Foes or friends: ABA and ethylene interaction under
abiotic stress. \emph{Plants} \textbf{10,} 448.

Ntemiri A., Ghosh T.S., Gheller M.E., Tran T.T., Blum J.E., Pellanda P.,
\ldots{}, Thalacker-Mercer A. (2020) Whole blueberry and isolated
polyphenol-rich fractions modulate specific gut microbes in an in vitro
colon model and in a pilot study in human consumers.
\emph{Nutrients}\textbf{12,} 2800.

Ou J.L.S., Yang D. \& Liu M.H. (2020) Effects of Anthocyanins in
Composite Meals on Cardiometabolic Outcomes---A Systematic Review of
Randomized Controlled Feeding Trials. \emph{Nutrients} \textbf{12,}3781.

Pan Z., Liu Q., Yun Z., Guan R., Zeng W., Xu Q. \& Deng X. (2009)
Comparative proteomics of a lycopene\selectlanguage{english}-accumulating mutant reveals the
important role of oxidative stress on carotenogenesis in sweet orange
(Citrus sinensis {[}L.{]} osbeck). \emph{Proteomics}
\textbf{9,}5455-5470.

Patane C., Siah S., Pellegrino A., Cosentino S.L. \& Siracusa L. (2021)
Fruit yield, polyphenols, and carotenoids in Long Shelf-Life tomatoes in
response to drought stress and rewatering. \emph{Agronomy}
\textbf{11,}1943.

Perin E.C., da Silva Messias R., Borowski J.M., Crizel R.L., Schott
I.B., Carvalho I.R., \ldots{}, Galli V. (2019) ABA-dependent salt and
drought stress improve strawberry fruit quality. \emph{Food
Chemistry}\textbf{271,} 516-526.

Plunkett B.J., Espley R.V., Dare A.P., Warren B.A.W., Grierson E.R.P.,
Cordiner S., \ldots{}, Schwinn K.E. (2018) MYBA From Blueberry
(Vaccinium Section Cyanococcus) Is a Subgroup 6 Type R2R3MYB
Transcription Factor That Activates Anthocyanin Production.
\emph{Frontiers in Plant Science}\textbf{9} .

Poiroux-Gonord F., Bidel L.P., Fanciullino A.-L., Gautier H.,
Lauri-Lopez F. \& Urban L. (2010) Health benefits of vitamins and
secondary metabolites of fruits and vegetables and prospects to increase
their concentrations by agronomic approaches. \emph{Journal of
Agricultural and Food Chemistry} \textbf{58,} 12065-12082.

Poiroux\selectlanguage{english}-Gonord F., Santini J., Fanciullino A.L., Lopez\selectlanguage{english}-Lauri F.,
Giannettini J., Sallanon H., \ldots{}, Urban L. (2013) Metabolism in
orange fruits is driven by photooxidative stress in the
leaves.\emph{Physiologia Plantarum} \textbf{149,} 175-187.

Pojer E., Mattivi F., Johnson D. \& Stockley C.S. (2013) The case for
anthocyanin consumption to promote human health: a
review.\emph{Comprehensive Reviews in Food Science and Food
Safety}\textbf{12,} 483-508.

Pola W., Sugaya S. \& Photchanachai S. (2019) Color development and
phytochemical changes in mature green chili (Capsicum annuum L.) exposed
to red and blue light-emitting diodes. \emph{Journal of Agricultural and
Food Chemistry} \textbf{68,} 59-66.

Qu Z. \& Zhou G. (2016) Possible Impact of Climate Change on the Quality
of Apples from the Major Producing Areas of China.
\emph{Atmosphere}\textbf{7,} 113.

Rahim M., Busatto N. \& Trainotti L. (2014) Regulation of anthocyanin
biosynthesis in peach fruits. \emph{Planta} \textbf{240,} 913-929.

Ravaglia D., Espley R.V., Henry-Kirk R.A., Andreotti C., Ziosi V.,
Hellens R.P., \ldots{}, Allan A.C. (2013) Transcriptional regulation of
flavonoid biosynthesis in nectarine (Prunus persica) by a set of R2R3
MYB transcription factors. \emph{BMC Plant Biology} \textbf{13,} 1-14.

Rehman R.N.U., You Y., Zhang L., Goudia B.D., Khan A.R., Li P. \& Ma F.
(2017) High temperature induced anthocyanin inhibition and active
degradation in Malus profusion. \emph{Frontiers in Plant
Science}\textbf{8,} 1401.

Ripoll J., Urban L., Staudt M., Lopez-Lauri F., Bidel L.P. \& Bertin N.
(2014) Water shortage and quality of fleshy fruits--making the most of
the unavoidable. \emph{Journal of Experimental Botany}
\textbf{65,}4097-4117.

Rodriguez-Amaya D.B. (2001) \emph{A guide to carotenoid analysis in
foods} (vol. 71). ILSI press Washington.

Rodriguez-Concepcion M., Avalos J., Bonet M.L., Boronat A., Gomez-Gomez
L., Hornero-Mendez D., \ldots{}, Zhu C. (2018) A global perspective on
carotenoids: Metabolism, biotechnology, and benefits for nutrition and
health. \emph{Progress in Lipid Research} \textbf{70,} 62-93.

Rohloff J., Uleberg E., Nes A., Krogstad T., Nestby R. \& Martinussen I.
(2015) Nutritional composition of bilberries (Vaccinium myrtillus L.)
from forest fields in Norway--Effects of geographic origin, climate,
fertilization and soil properties. \emph{Journal of Applied Botany and
Food Quality} \textbf{88} , 274 - 287

Rosalie R., Lechaudel M., Dhuique-Mayer C., Dufosse L. \& Joas J. (2018)
Antioxidant and enzymatic responses to oxidative stress induced by cold
temperature storage and ripening in mango (Mangifera indica L. cv.
`Cogshall') in relation to carotenoid content. \emph{Journal of Plant
Physiology} \textbf{224-225,} 75-85.

Ryu S., Han J.H., Cho J.G., Jeong J.H., Lee S.K. \& Lee H.J. (2020) High
temperature at veraison inhibits anthocyanin biosynthesis in berry skins
during ripening in `Kyoho'grapevines. \emph{Plant Physiology and
Biochemistry} \textbf{157,} 219-228.

Saini R.K. \& Keum Y.-S. (2018) Significance of genetic, environmental,
and pre-and postharvest factors affecting carotenoid contents in crops:
a review. \emph{Journal of Agricultural and Food Chemistry}
\textbf{66,}5310-5324.

Samkumar A., Jones D., Karppinen K., Dare A.P., Sipari N., Espley R.V.,
\ldots{}, Jaakola L. (2021) Red and blue light treatments of ripening
bilberry fruits reveal differences in signalling through abscisic
acid\selectlanguage{english}-regulated anthocyanin biosynthesis. \emph{Plant, Cell \&
Environment} \textbf{44,} 3227-3245.

Samkumar A., Karppinen K., McGhie T.K., Espley R.V., Martinussen I. \&
Jaakola L. (2022) Flavonoid biosynthesis is differentially altered in
detached and attached ripening bilberries in response to spectral light
quality. \emph{Frontiers in Plant Science} \textbf{,} 2529.

Santesteban L., Miranda C. \& Royo J. (2011) Regulated deficit
irrigation effects on growth, yield, grape quality and individual
anthocyanin composition in Vitis vinifera L.
cv.`Tempranillo'.\emph{Agricultural Water Management} \textbf{98,}
1171-1179.

Schertl P. \& Braun H.-P. (2014) Respiratory electron transfer pathways
in plant mitochondria. \emph{Frontiers in Plant Science} \textbf{5,}163.

Sikuten I., Stambuk P., Tomaz I., Marchal C., Kontic J.K., Lacombe T.,
\ldots{}, Preiner D. (2021) Discrimination of genetic and geographical
groups of grape varieties (Vitis vinifera L.) based on their
polyphenolic profiles. \emph{Journal of Food Composition and Analysis}
\textbf{102,}104062.

Sivankalyani V., Feygenberg O., Diskin S., Wright B. \& Alkan N. (2016)
Increased anthocyanin and flavonoids in mango fruit peel are associated
with cold and pathogen resistance. \emph{Postharvest Biology and
Technology} \textbf{111,} 132-139.

Stanley L. \& Yuan Y.-W. (2019) Transcriptional regulation of carotenoid
biosynthesis in plants: so many regulators, so little
consensus.\emph{Frontiers in Plant Science} \textbf{,} 1017.

Stracke R., Werber M. \& Weisshaar B. (2001) The R2R3-MYB gene family in
Arabidopsis thaliana. \emph{Current Opinion in Plant Biology}\textbf{4,}
447-456.

Sudheeran P.K., Feygenberg O., Maurer D. \& Alkan N. (2018) Improved
cold tolerance of mango fruit with enhanced anthocyanin and flavonoid
contents. \emph{Molecules} \textbf{23,} 1832.

Sun X., Jia X., Huo L., Che R., Gong X., Wang P. \& Ma F. (2018)
MdATG18a overexpression improves tolerance to nitrogen deficiency and
regulates anthocyanin accumulation through increased autophagy in
transgenic apple. \emph{Plant, Cell \& Environment} \textbf{41,}469-480.

Sun X., Li X., Wang Y., Xu J., Jiang S. \& Zhang Y. (2022)
MdMKK9-Mediated the Regulation of Anthocyanin Synthesis in Red-Fleshed
Apple in Response to Different Nitrogen Signals. \emph{International
Journal of Molecular Sciences} \textbf{23,} 7755.

Tao R., Bai S., Ni J., Yang Q., Zhao Y. \& Teng Y. (2018) The blue light
signal transduction pathway is involved in anthocyanin accumulation in
`Red Zaosu'pear. \emph{Planta} \textbf{248,} 37-48.

Thomson G.E., Turpin S. \& Goodwin I. (2018) A review of preharvest
anthocyanin development in full red and blush cultivars of European
pear. \emph{New Zealand Journal of Crop and Horticultural
Science}\textbf{46,} 81-100.

Tomes M.L. (1963) Temperature inhibition of carotene synthesis in
tomato. \emph{Botanical Gazette} \textbf{124,} 180-185.

Tramblay Y., Koutroulis A., Samaniego L., Vicente-Serrano S.M., Volaire
F., Boone A., \ldots{}, Burak S. (2020) Challenges for drought
assessment in the Mediterranean region under future climate
scenarios.\emph{Earth-Science Reviews} \textbf{210,} 103348.

Ubi B.E., Honda C., Bessho H., Kondo S., Wada M., Kobayashi S. \&
Moriguchi T. (2006) Expression analysis of anthocyanin biosynthetic
genes in apple skin: Effect of UV-B and temperature. \emph{Plant
Science} \textbf{170,} 571-578.

Uleberg E., Rohloff J., Jaakola L., Tro\selectlanguage{english}st K., Junttila O., Ha\selectlanguage{english}ggman H. \&
Martinussen I. (2012) Effects of temperature and photoperiod on yield
and chemical composition of northern and southern clones of bilberry
(Vaccinium myrtillus L.). \emph{Journal of Agricultural and Food
Chemistry} \textbf{60,} 10406-10414.

Ullah A., Manghwar H., Shaban M., Khan A.H., Akbar A., Ali U., \ldots{},
Fahad S. (2018) Phytohormones enhanced drought tolerance in plants: a
coping strategy. \emph{Environmental Science and Pollution
Research}\textbf{25,} 33103-33118.

Vighi I., Crizel R., Perin E., Rombaldi C. \& Galli V. (2019) Crosstalk
during fruit ripening and stress response among abscisic acid,
calcium-dependent protein kinase and phenylpropanoid. \emph{Critical
Reviews in Plant Sciences} \textbf{38,} 99-116.

Wang T., Zhang H. \& Zhu H. (2019) CRISPR technology is revolutionizing
the improvement of tomato and other fruit crops. \emph{Horticulture
Research} \textbf{6} .

Wang N., Qu C.Z., Jiang S.H., Chen Z.J., Xu H.F., Fang H.C., \ldots{},
Chen X.S. (2018) The proanthocyanidin-specific transcription factor
MdMYBPA1 initiates anthocyanin synthesis under low-temperature
conditions in red-fleshed apples. \emph{Plant Journal} \textbf{96,}
39-55.

Wang W., Celton J.-M., Buck-Sorlin G., Balzergue S., Bucher E. \&
Laurens F.o. (2020) Skin Color in Apple Fruit (Malus \selectlanguage{ngerman}× domestica):
Genetic and Epigenetic Insights. \emph{Epigenomes} \textbf{4,} 13.

Wang X.F., An J.P., Liu X., Su L., You C.X. \& Hao Y.J. (2018) The
Nitrate-Responsive Protein MdBT2 Regulates Anthocyanin Biosynthesis by
Interacting with the MdMYB1 Transcription Factor. \emph{Plant
Physiology} \textbf{178,} 890-906.

West K.P. \& Darnton-Hill I. (2008) Vitamin A deficiency.
In\emph{Nutrition and health in developing countries} , pp. 377-433.
Springer.

Wheeler S., Loveys B., Ford C. \& Davies C. (2009) The relationship
between the expression of abscisic acid biosynthesis genes, accumulation
of abscisic acid and the promotion of Vitis vinifera L. berry ripening
by abscisic acid. \emph{Australian Journal of Grape and Wine
Research}\textbf{15,} 195-204.

Woznicki T., Heide O., Sønsteby A., Wold A.-B. \& Remberg S. (2015)
Yield and fruit quality of black currant (Ribes nigrum L.) are favoured
by precipitation and cool summer conditions. \emph{Acta Agriculturae
Scandinavica, Section B---Soil \& Plant Science} \textbf{65,} 702-712.

Xu H., Wang N., Liu J., Qu C., Wang Y., Jiang S., \ldots{}, Chen X.
(2017) The molecular mechanism underlying anthocyanin metabolism in
apple using the MdMYB16 and MdbHLH33 genes. \emph{Plant Molecular
Biology}\textbf{94,} 149-165.

Yamaguchi-Shinozaki K. \& Shinozaki K. (2005) Organization of cis-acting
regulatory elements in osmotic-and cold-stress-responsive
promoters.\emph{Trends in Plant Science} \textbf{10,} 88-94.

Yamane T., Jeong S.T., Goto-Yamamoto N., Koshita Y. \& Kobayashi S.
(2006) Effects of temperature on anthocyanin biosynthesis in grape berry
skins. \emph{American Journal of Enology and Viticulture}
\textbf{57,}54-59.

Yang B., Tang J., Yu Z., Khare T., Srivastav A., Datir S. \& Kumar V.
(2019) Light stress responses and prospects for engineering light stress
tolerance in crop plants. \emph{Journal of Plant Growth
Regulation}\textbf{38,} 1489-1506.

Yao G., Ming M., Allan A.C., Gu C., Li L., Wu X., \ldots{}, Wu J. (2017)
Map-based cloning of the pear gene MYB114 identifies an interaction with
other transcription factors to coordinately regulate fruit anthocyanin
biosynthesis. \emph{The Plant Journal} \textbf{92,} 437-451.

Yoshikawa H., Honda C. \& Kondo S. (2007) Effect of low-temperature
stress on abscisic acid, jasmonates, and polyamines in
apples.\emph{Plant Growth Regulation} \textbf{52,} 199-206.

Zhang R.-X., Zhu W.-C., Cheng G.-X., Yu Y.-N., Li Q.-H., ul Haq S.,
\ldots{}, Gong Z.-H. (2020) A novel gene, CaATHB-12, negatively
regulates fruit carotenoid content under cold stress in Capsicum annuum.
\emph{Food \& Nutrition Research} \textbf{64} .

Zhang Y., Butelli E. \& Martin C. (2014) Engineering anthocyanin
biosynthesis in plants. \emph{Current Opinion in Plant
Biology}\textbf{19,} 81-90.

Zhou H., Lin-Wang K., Wang H., Gu C., Dare A.P., Espley R.V., \ldots{},
Han Y. (2015) Molecular genetics of blood-fleshed peach reveals
activation of anthocyanin biosynthesis by NAC transcription factors.
\emph{The Plant Journal} \textbf{82,} 105-121.

Zhu F., Luo T., Liu C., Wang Y., Yang H., Yang W., \ldots{}, Cheng Y.
(2017) An R2R3-MYB transcription factor represses the transformation of
\selectlanguage{greek}α- \selectlanguage{english}and \selectlanguage{greek}β-\selectlanguage{english}branch carotenoids by negatively regulating expression of
CrBCH2 and CrNCED5 in flavedo of Citrus reticulate. \emph{New
phytologist}\textbf{216,} 178-192.

Zhu M., Fang W., Chen C., Wang L. \& Cao K. (2021) Effects of shading by
bagging on carotenoid accumulation in peach fruit flesh. \emph{Journal
of Plant Growth Regulation} \textbf{40,} 1912-1921.

Zifkin M., Jin A., Ozga J.A., Zaharia L.I., Schernthaner J.P., Gesell
A., \ldots{}, Constabel C.P. (2012) Gene expression and metabolite
profiling of developing highbush blueberry fruit indicates
transcriptional regulation of flavonoid metabolism and activation of
abscisic acid metabolism. \emph{Plant Physiology} \textbf{158,} 200-224.

Zoratti L., Jaakola L., Ha\selectlanguage{english}ggman H. \& Giongo L. (2015) Anthocyanin
profile in berries of wild and cultivated Vaccinium spp. along
altitudinal gradients in the Alps. \emph{Journal of Agricultural and
Food Chemistry} \textbf{63,} 8641-8650.

Zoratti L., Karppinen K., Luengo Escobar A., H\selectlanguage{ngerman}äggman H. \& Jaakola L.
(2014) Light-controlled flavonoid biosynthesis in fruits.\emph{Frontiers
in Plant Science} \textbf{5,} 534.

Zushi K. \& Matsuzoe N. (1998) Effect of soil water deficit on vitamin
C, sugar, organic acid, amino acid and carotene contents of
large-fruited tomatoes. \emph{Journal of the Japanese Society for
Horticultural Science} \textbf{67,} 927-933.

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