Photoswelling and light-inactivation of isolated chloroplasts I. Change in lipid content in light-aged chloroplasts

Abstract

The formation of lipid peroxide and changes in the lipid composition of isolated chloroplasts aged in the light or dark, were investigated in more detail. Lipid peroxide formation was observed in the thylakoid membrane as well as in the supernatant from dark-aged chloroplasts. Light was necessary for its formation in both systems. We confirmed that the peroxidation of lipids formed during aging did not induce the inhibition of photochemical activities in chloroplasts. Aged chloroplasts underwent decomposition of their endogeneous monogalactolipid and phosphatidylcholine (lecithin) resulting in free fatty acids and lysophosphatidylcholine (lysolecithin). Decomposition of monogalactolipid occurred in both the light- and dark-aged chloroplasts. The change of lecithin to lysolecithin was stimulated by illumination. This suggests that the peroxidation of lipids occurs as a result of the illumination of free fatty acids released from monogalactolipid and lecithin in the thylakoid membranes, and that the change of lecithin to lysolecithin is related to the inactivation of photochemical activities and to swelling in light-aged chloroplasts.