Chlorophyll fluorescence, NPQ kinetic, and state transition measurements

Chlorophyll (Chl) fluorescence of PSII was analyzed at room temperature using a modulated imaging fluorometer (the Imaging PAM M-Series Chlorophyll Fluorescence System, Heinz-Walz Instruments, Effeltrich, Germany) according to our previous methods (Chen et al., 2017b, 2018b). Before the measurements of Chl fluorescence, wheat samples were put in the dark for 1 h. The saturation pulse intensity of 8,000 μmol m⁻² s⁻¹ and the actinic light intensity of 150 μmol m⁻² s⁻¹ are given. The maximum efficiency of PSII photochemistry (Fv/Fm), quantum yield of non-regulated energy dissipation [Y(NO)], non-photochemical quenching coefficient (qN), quantum yield of regulated energy dissipation [Y(NPQ)], effective PS II quantum yield [Y(II)], and coefficient of photochemical quenching (qL and qP) were imaged and calculated as following previous method (Maxwell and Johnson, 2000).

Dual PAM-100 fluorometer (Heinz-Walz Instruments, Effeltrich, Germany) was used to measure NPQ kinetic and state transition in whole plants as the previous method described (Pietrzykowska et al., 2014). Wheat plants were adapted in dark for 1 h prior to measurements. The NPQ kinetics was obtained based on the Fm value measured from an untreated plant. At the end of each state, the level of Fm in State I (Fm′) and State II (Fm″) was recorded using the application of the saturating light pulse.