Unsaturated Fatty Acids in Membrane Lipids Protect the Photosynthetic Machinery against Salt-Induced Damage inSynechococcus

In this study, the tolerance to salt stress of the photosynthetic machinery was examined in relation to the effects of the genetic enhancement of the unsaturation of fatty acids in membrane lipids in wild-type and desA + cells ofSynechococcus sp. PCC 7942. Wild-type cells synthesized saturated and mono-unsaturated fatty acids, whereasdesA + cells, which had been transformed with the desA gene for the Δ12 acyl-lipid desaturase ofSynechocystis sp. PCC 6803, also synthesized di-unsaturated fatty acids. Incubation of wild-type anddesA + cells with 0.5 m NaCl resulted in the rapid loss of the activities of photosystem I, photosystem II, and the Na+/H+ antiport system both in light and in darkness. However,desA + cells were more tolerant to salt stress and osmotic stress than the wild-type cells. The extent of the recovery of the various photosynthetic activities from the effects of 0.5 m NaCl was much greater indesA + cells than in wild-type cells. The photosystem II activity of thylakoid membranes fromdesA + cells was more resistant to 0.5m NaCl than that of membranes from wild-type cells. These results demonstrated that the genetically engineered increase in unsaturation of fatty acids in membrane lipids significantly enhanced the tolerance of the photosynthetic machinery to salt stress. The enhanced tolerance was due both to the increased resistance of the photosynthetic machinery to the salt-induced damage and to the increased ability of desA + cells to repair the photosynthetic and Na+/H+ antiport systems.