Fat metabolism in higher plants XLIX fatty acid biosynthesis by subcellular fractions of higher plants

A method is described for the rapid and comprehensive subcellular fraction‐ation of plant tissue using a combination of differential and discontinuous Ficoll gradient centrifugation. The procedure has been used to study the synthesis of fatty acids from acetate‐1‐ 14 C or malonyl CoA‐1,3‐ 14 C, by fractions of germinating pea and lupin seeds and developing avocado fruit, castor bean and safflower seeds. Particle free supernatants of seeds synthesize fatty acids from 14 C‐malonyl CoA in the presence of added cofactors. Since acetyl CoA carboxylase activity is absent the utilization of 14 C‐acetate by these fractions is minimal. Other particulate fractions show different activities depending on seed types. Active fractions include the low speed particulate of pea and lupin, the pea microsomes, the avocado mesocarp chloroplasts, and the fat fractions of castor bean and safflower. Individual fractions produce characteristic patterns of acids; especially noteworthy is oleic acid biosynthesis by soluble enzymes of castor bean and safflower from 14 C‐malonyl CoA. Some characteristics of the avocado supernatant, pea supernatant, and castor bean fat fraction synthesizing systems are compared. As a result of these studies, generalizations derived from work with mammalian or bacterial systems cannot be applied to higher plants.