Suppression of Quantum Yield of Photosystem II by Hyperosmotic Stress inChlamydomonas reinhardtii

摘要

Addition of ethylene glycol (EG) or NaCl to cells ofChlamydomonas reinhardtiiinduced transient non-photochemical quenching of Chl fluorescence correlated with the inhibition of photosynthetic oxygen evolution. The induction of the quenching and subsequent recovery proceeded not only in the light but also in the dark. The quenching was almost unaffected by the protonophore nigericin, suggesting the involvement of a type of non-photochemical quenching attributable to a state 2 transition. Higher concentrations of EG or NaCl caused a delay of the recovery of the maximum fluorescence yield (Fm′). Dark reduction rate of P700+after the application of a flash light in the presence of DCMU was enhanced by the hyperosmotic shock, suggesting a stimulated reduction of the intersystem electron carriers. It is proposed that the osmotic stress stimulates electron donation from stromal components via the NAD(P)H dehydrogenase, which results in the reduction of the intersystem chain and triggering of a state 2 transition leading to stimulated cyclic PSI activit