Abstract
Modulated chlorophyll fluorescence and fluorescence induction kinetics were used to evaluate the PS II photochemistry in Spirulina platensis exposed to osmotic stress (0–0.8 M mannitol). Osmotic stress decreased the efficiency of excitation energy capture by open PS II reaction centres (Fv′/Fm′) and more significantly, decreased photochemical quenching (qP). Osmotic stress also decreased the maximal efficiency of PS II photochemistry (Fv/Fm). There was no significant change in non-photochemical quenching (qN), indicating that the decreased Fv′/Fm′ was not due to an increase in qN. Analyses of the fast fluorescence induction kinetics indicated that osmotic stress caused a significant increase in the proportion of the QB-non-reducing PS II reaction centres. Based on the results in this study, we suggest that a substantial increase in the proportion of the QB-non-reducing PS II reaction centres may be responsible for the decrease in qP and Fv′/Fm′, of which both resulted in the decrease in the quantum yield of PS II electron transport (ΦPSII ).
Published Version
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