Study of photosystem 2 heterogeneity in the sulfur-deficient green alga Chlamydomonas reinhardtii

A set of chlorophyll fluorescence methods, including PEA (Plant Efficiency Analyser), PAM (Pulse Amplitude Modulated fluorometer), and picosecond fluorometer, was employed to study PS 2 heterogeneity in sulfur deprived green algae Chlamydomonas reinhardtii. The regression method and JIP test were applied to analyze chlorophyll fluorescence kinetics. The fractions of PS 2 characterized by the energetic disconnection, smaller antenna size, elevated constant rate of primary photochemistry, and inability to maintain ΔpH-dependent energy dissipation increased essentially already after 12 h of incubation in sulfur depleted medium. The amount of PS 2 centers with reduced Q_A (closed state), Q_B-non-reducing centers with impaired water splitting function, and centers coupled to the plastoquinone pool with the slow cycle rate increased dramatically after 24 h period of deprivation. The mechanisms of PS 2 inactivation under sulfur deprivation are discussed.