Effects of sulfur limitation on photosystem II functioning in Chlamydomonas reinhardtii as probed by chlorophyll a fluorescence

Chlorophyll fluorescence methods were applied to probe in vivo photosystem II (PSII) function in Chlamydomonas reinhardtii grown in sulfur‐depleted media under aerobic conditions. The rates of oxygen evolution and dark reduction decreased during a 24‐h incubation in sulfur‐deficient medium, while the respiration rate increased. The analysis of chlorophyll fluorescence induction curves suggests that electron transport was perturbed on both the acceptor and donor sides of PSII. Light‐induced violaxanthin de‐epoxidation and non‐photochemical fluorescence quenching were suppressed, owing to dark accumulation of zeaxanthin. Also sulfur‐deprived cells showed elevated concentrations of violaxanthin and lutein. Sulfur deprivation stimulated a pronounced (three‐ to four‐fold) increase in chlorophyll a fluorescence intensity (parameters Fo and Fm), probably due to greater light absorption by carotenoids and changes in the excitation energy transfer and deactivation in PSII of C. reinhardtii.