4.3. Chlorophyll Fluorescence Measurements

Chlorophyll fluorescence imaging and analysis were performed using a chlorophyll imaging system (FluorCam FC 800-C/1010, PSI), with photosynthetic parameters determined as described previously [43]. Before each measurement, plants were dark-adapted for 20 min. The F_v/F_m ratio was defined as (F_m − F_o)/Fm. The nonphotochemical quenching (NPQ) was calculated as (F_m − F′m)/F′_m, where F_m is the maximum fluorescence value in the dark-adapted state; F′_m is the maximum fluorescence value in any light-adapted state; and F_o is the minimal fluorescence value in the dark-adapted state.