Regulatory Roles in Photosynthesis of Unsaturated Fatty Acids in Membrane Lipids

Abstract

The diversity of lipids in thylakoid membranes and their unique characteristics, in addition to their specific orientation in these membranes, strongly suggest that they play specific and important roles in the thylakoid membrane. In the chloroplasts of plants and algae, as well as in cyanobacterial cells, most of the photosyn-thetic machinery is embedded in thylakoid membranes, which are composed of proteins, lipids and pigments. Alterations in the extent of unsaturation of fatty acids in membrane lipids are expected to affect the physical characteristics of the membranes and, consequently, the activities of the photosynthetic machinery. The availability of entire genome sequences and an understanding of the functions of the individual genes for fatty acid desaturases in cyanobacteria led to the successful site-directed mutagenesis of such genes that reduced the extent of unsaturation of fatty acids in membrane lipids in a step-wise manner and, also, to the genetic transformation of cyanobacterial cells and whole plants that increased the extent of unsaturation of fatty acids in lipids of thylakoid membranes. Characterization of the photosynthetic properties of the transformed cyanobacteria and higher plants revealed that polyunsaturated fatty acids are essential for protection of the photosynthetic machinery against environmental stresses, such as strong light, salt stress, and high and low temperatures. Moreover, the available evidence suggests that the unsaturation of fatty acids enhances the repair of the photosystem II complex that has been damaged by strong light under stress conditions.