2.1 Plant materials and growth conditions
Plump seeds of winter wheat (Triticum aestivum ) were selected and
cultured on plastic plate with a wet towel. Three days later, after
germinating, seeds were uniformly fixed with special holes in plastic
plates, and then watered daily in a growth chamber at 25ºC. After the
first leaves fully unfolded, the wheat seedlings were cultivated with
Hoagland nutrient solution by hydroponics. When the second leaves
completely expanded, the first group was cultivated with Hoagland
nutrient solution (control), the second group was pretreatment in 1.5 mM
trehalose for 72 h (TRE).
Heat stress: after the pretreatment in 1.5 mM trehalose for 72 h, wheat
seedlings were subjected to heat treatment (40ºC; light intensity: 120
µmol quanta m-2 s-1; humidity: 38%)
for 24 h (day 13 h; night 11 h) in the climate chamber.
Drought stress: wheat seedlings were subjected to drought stress by
immersion in 15% (w/v) polyethylene glycol solutions (PEG-6000). After
the pretreatment in 1.5 mM trehalose for 48 h, wheat seedlings were
cultivated with 15% (w/v) polyethylene glycol solutions.
Drought plus heat stress: after the pretreatment in 1.5 mM trehalose for
48 h, wheat seedlings were cultivated with 15% (w/v) polyethylene
glycol solutions for 24 h. One day later, wheat seedlings of drought
stress pretreatment were subjected to heat treatment (40ºC; light
intensity: 120 µmol quanta
m-2 s-1; humidity: 38%) for 24 h
(day 13 h; night 11 h) in the climate chamber.
Chlorophyll fluorescence and the initial reduction rate of
P700+
The chlorophyll fluorescence and the P700 redox state were measured
using a Dual-PAM-100 fluorometer (Heinz Walz, Effeltrich, Germany). The
maximum photochemical quantum yield of PS II (photochemical efficiency)
was calculated as (Fm -
Fo)/Fm (Genty, Briantais & Baker,
1989). Fo is the minimum chlorophyll fluorescence, and
Fm is the maximum fluorescence of dark-adapted (adapted
30 min in darkness) leaves following a saturation pulse (10000 µmol
quanta m−2 s−1, 300 ms). The
electron transfer rate of the PS II (electron transport rate(II)) was
calculated as 0.5 × PPFD × Y(II) × 0.84, where 0.5 is the proportion of
energy that reaches the PS II, PPFD is the irradiance absorbed by the
leaf, considering 0.84 or 84% light intensity, and Y(II) is the
effective quantum yield of PS II (Baker,2008). Y(II) =
(Fm’ - Fs)/Fm’ (Genty,
Briantais & Baker,1989), where Fm’ is the maximum
fluorescence of light-adapted leaves following a saturation pulse (10000
µmol quanta m−2 s−1, 300 ms) and
Fs is the light-adapted steady-state fluorescence. The
initial reduction rate of P700+ after termination of
far-red light (>705 nm, 5.2 µmol quanta
m−2 s−1, 40 s) was monitored by
absorbance at 810-830 nm in the P700 Measure Mode of a single channel
(Klughammer & Schreiber,1998).
Inhibitors