Biosynthesis of Galactolipids in Plants

Abstract

Abstract Spinach chloroplasts very actively incorporated radioactivity from UDP-galactose-14C into lipids. Among the products formed, monogalactosyl and digalactosyl diglycerides together with a third compound, tentatively identified as the trigalactosyl diglyceride, contained 95% of the total lipid radioactivity. Chloroplasts from young leaves showed higher enzymic activity than those obtained from mature leaves. Dissociation of the enzymes from the acceptors was accomplished by acetone powder preparation of the chloroplasts. It was shown that diolein could serve as an efficient acceptor for the monogalactosyl diglyceride synthesis but not for the digalactosyl diglyceride synthesis. Monogalactosyl diglyceride, naturally found in chloroplasts, was shown to be the acceptor for the second galactosylation. Incubation of radioactive digalactosyl diglyceride with the acetone powder of spinach chloroplasts resulted in the formation of trigalactosyl diglyceride when cold UDP-galactose was used as the substrate. Evidence indicated that two enzymes were involved in galactolipid synthesis in spinach chloroplasts. The enzyme responsible for the synthesis of monogalactosyl diglyceride was more tightly bound to the membranes than the enzyme synthesizing digalactosyl diglyceride. Particles from etiolated pea leaves as well as other nonchlorophyllous tissues were shown to contain active enzymes that synthesize the galactolipids. A light-induced increase in the enzyme activity was observed in pea leaves.