Chlorophyll Fluorescence Imaging Analysis

The experimental methods refer to previous descriptions [75 (link)]. The IMAGING-PAM chlorophyll fluorescence imaging system (Heinz Walz, Germany) was selected for the determination of chlorophyll fluorescence parameters, and the leaves were dark-adapted for 30 min before testing. Fo (minimal fluorescence) was induced by measured light, and Fm (maximum fluorescence) was produced by excitation with saturated pulsed light. When the fluorescence was reduced to Fo, fluorescence kinetics were induced using photochemical light (1600 μmol·m⁻²·s⁻¹), and saturating pulses were turned on at 20 s intervals to determine the maximum fluorescence yield, Fm, when all the PS II reaction centers were off, and the actual fluorescence intensity, F, at any given time. The final parameters measured include Fv/Fm (maximum efficiency of PSII photochemistry), Y(II) (actual efficiency of PSII photochemistry), and Fo (initial fluorescence) (Table 4).