Effect of Salt Stress on PSII Efficiency of Dunaliella bardawil under Light and Dark Conditions

In this study, the effect of salt stress on PSII of Dunaliella bardawil as a photosynthesis species model was invesigated to determines more effects of this stress and appropriate solutions to salt stress. In this study, OJIP-test method was used for analyzing of chlorophyll a fluorescence under stress. Different concentrations of NaCl, 1 to 2 M and 1 to 3 M, were applied at light and dark conditions. The results showed in both light and dark regimes, the rate of Fv/Fo, ΦPo, ψo, ΦEo, ΦRo and PIABS were reduced by salt stress of 1 to 3 M NaCl at primary hours after salt stress while Φ Do was increased. After first hours, the efficiency of PSII did not increased in dark regime unlike the samples in light condition. According to the results, salt stress led to reduction of water-splitting complex activity and the function of other electron acceptor in PSII. The rate of electron transport to pheophytin, QA, QB and the other electron acceptors is also reduced. Hence it could be finalized that water-splitting complex is the first site damaged by salt stress. On the other hand, studying on salt stress under light and dark regimes showed that light accompanied by the other mechanisms such as photosynthesis and chlorophyll production increase the efficiency of algae system and recover to the condition before stress.