Acclimation of both photosynthesis and respiration to cold are
impaired in plants lacking FUM2
Plants of the wild-type Arabidopsis, accession Col-0 and a mutant in the
same background, fum2.2 , were grown for 8 weeks at a daytime
temperature of 20°C. Plants were then transferred to a growth cabinet
with the same light conditions, but with a temperature of 4°C.
Photosynthetic capacity (Pmax; measured at 20°C in
saturating light and CO2) of these plants was measured
over the following 9 days (Figure 1 a). Prior to transfer to low
temperature, Pmax of Col-0 was slightly higher than that
of fum2.2 . Following one day at low temperature, the capacity for
photosynthesis (Pmax) in Col-0 increased.
Pmax continued to increase over the following days,
rising to a new steady state approximately 50% higher than the starting
value by the sixth day of cold treatment. This indicates that, under our
experimental conditions, dynamic acclimation of photosynthesis occurs in
response to cold and that a new steady-state is reached within 7 days.
In contrast, the Pmax of fum2.2 did not vary over
the course of the experiment, confirming previous evidence that bothfum2.1 and fum2.2 mutants lacking FUM2 are unable to
acclimate their photosynthetic capacity in response to cold (Dysonet al. , 2016).
Measurements of the rate of gas exchange achieved by plants in growth
cabinets, with ambient CO2, light and temperature, were
performed in the last hour of the first day of cold. Transfer to cold
resulted in a small but significant inhibition of both photosynthesis
and respiration at the end of the first day of exposure to cold (ANOVA,
P<0.05; Figure 1 b,c). In Col-0, acclimation of both
parameters had occurred after 7 days, such that in situ rates of
gas exchange recovered and did not differ significantly from those
recorded at 20°C prior to acclimation. In contrast, in fum2.2 , no
recovery occurred in either photosynthesis or respiration. This suggests
that either fumarate accumulation or FUM2 protein, is essential for the
acclimation of both photosynthesis and respiration to cold.