Labelling in vivo and in vitro of Molecular Species of Lipids from Chloroplast Envelopes and Thylakoids

Abstract

Lipid mixtures from [spinach] chloroplast envelope and thylakoid membranes were isolated after different labeling times in vivo and in vitro and separated into major components. The isolated compounds were subjected to analyses such as separation of molecular species, determination of radioactivity in fatty acids and water-soluble hydrolysis products and radio GLC of fatty acid mixtures. In the case of monogalactosyl and digalactosyl diacylglycerol, these procedures were also applied to several individual molecular species. To investigate the extent of de novo synthesis, these species were also used for methylation studies and their fatty acids subjected to .alpha.-oxidation. In envelope membranes, diacylglycerols and monogalactosyl diacylglycerols may each be separated into several distinct and nonmixing pools. Molecules made de novo with oligoene fatty acids are very efficient substrates for galactosylation in vivo. The time-dependent changes in patterns of galactolipid molecular species mamay indicate a desaturation of acyl chains operating in close contact to intact lipids. After isolation, envelopes incorporated UDP-[14C]galactose into completely different patterns of galactolipids and molecular species, pointing to changed properties of this membrane system or to a loss of regulatory factors.