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

Abstract

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 P700+ 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. Copyright © Physiologia Plantarum 2006.