Evidences for Different Acyl Lipid Domains in Spinach and Oat Thylakoid Membranes Supporting Various Photosynthetic Functions

Abstract

One approach to studying the role of acyl lipids in thylakoid membranes has been to incubate intact thylakoids with lipolytic enzymes and then to determine the relationships between the changes occuring in their lipid content and composition and, simultaneously, in their photochemical activities^1–3. whilst phospholipases hydrolyze specifically the two phospholipids (PG and PC) encountered in the thylakoid membrane, lipolytic acyl hydrolases deacylate not only glycolipids (MGDG, DGDG, SQDG) but also phospholipids. The non-specificity of the enzymes used does not allow an unequivocal assessement of function to each of these lipids⁴. Moreover, in most studies, hydrolysis of acyl lipids have been carried out under conditions allowing the attack of all acyl lipids, i.e. of lipids which are localized indistinctly in both monolayers of the membrane. However, it is now well established that all acyl lipids of the thylakoid membrane present a transversal asymmetric distribution^1,3–8, suggesting that different acyl lipid domains may sustain different functions^1,3. Thus, it would be of great interest to establish relationships between the hydrolysis of specific acyl lipids in the outer membrane monolayer only and the resulting changes occurring in various electron flow activities.