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