Chlorophyll Fluorescence Kinetics of PSII

Chlorophyll fluorescence kinetics were measured at room temperature on dark-adapted cells. A home-built fluorimeter with a green detecting light was used for measurements on 1-ml aliquots of liquid cultures (56 (link)) before and after the addition of PSII-specific inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU; 10 μM). A fluorescence imaging system (BeamBio, SpeedZen camera) with a blue detecting light was used for measurements of plates as described (57 (link)). The maximum quantum yield of PSII photochemistry (F_v/F_m) was calculated as (F_m-F₀)/F_m, where F₀ is the fluorescence level of dark-adapted cells in the absence of DCMU and F_m is the maximum level of fluorescence in the presence of DCMU or after a saturating light pulse.