Thylakoid membrane fluidity and its crucial importance in photoinhibition

Abstract

The thylakoid membranes play a crucial role in oxygenic photosynthesis. The physical properties of photosynthetic membranes, in terms of lipid diffusion within the cell, and their relevance to photoinhibition are outlined in this work. Using a one-dimensional variant of Fluorescence Recovery After Photobleaching (FRAP), we measured the diffusion of a lipid-soluble fluorescent marker (BODIPY) in cells of Synechococcus sp. PCC 7942 wild type (Wt) strain and compared it with the transformant desA+ strain. The desA+ transformant contains a copy of the desA gene for D 12 fatty acid desaturase of another cyanobacterium Synechocystis 6803 (Gombos et al., Plant Physiol. 115, 551-559, 1997). As a result, the thylakoid membranes have an increased level of unsaturated fatty acids, which should lead to the production of a more fluid matrix for the photosynthetic apparatus. We find that the diffusion of BODIPY in the desA+ mutant is 6 times faster than in the Wt strain at 30° C. Moreover, the transition between liquid crystalline and gel phase is at around 20° C in wild-type cells, whereas in the mutant cells it occurs at a much lower temperature at around 10° C. These differences can explain the enhance tolerance of the mutant to high light and cold stress (Sippola et al., Eur. J. Biochem. 251, 641-648, 1998).