Effect of High Salt Stress on Photosynthetic Electron Transport Activities in the Cyanobacterium, Spirulina Platensis

Environmental stresses like temperature, high light, UV radiation and salt stress are known to affect the efficiency of photosynthesis (Stainer and Cohen –Bazire, 1977; Tandeau de Marsac and Houmard, 1993). Salt stress inhibits fundamental processes such as plant growth and productivity which are often associated with the decreased photosynthesis (Greenway and Munns,1980). A number of studies have been performed to identify the target of salt stress in the photosynthetic electron transport system. Ionic stress due to 0.5 M NaCl inactivated photosynthetic machinery in Synechococcus sp (Allakhverdiev et al., 2000). In Synechocystis sp 0.55 M NaCl decreased the PS II activity and stimulated respiratory electron transport activity (Jeanjean et al., 1993 ). The decrease in PS II activity in Chlamidomaonas reinhardtii has been found to be associated with state 2 transitions (Endo et al., 1995). Biswal et al., (2002) have revealed that salt stress (0.5 M NaCl) caused inhibition in photosynthetic electron transport due to the destabilization of Q A and Q B (the primary and secondary electron acceptors of PS II respectively) in Brassica junica.L. In Triticum aestivum light enhanced the inhibitory effect of salt stress on PS II efficiency (Mishra et al.,1991).