Fat metabolism in higher plants: XLIII. Control of fatty acid synthesis in germinating seeds

Abstract

Fatty acid synthesis by germinating pea and safflower seeds has been studied by following acetate incorporation in vivo. The pea synthesizes saturated acids in the C14–28 range. In this plant, increased germination temperature and fluoride addition both reduce elongation of stearic acid. In addition, arsenite blocks elongation at the palmitate level. These blocking effects, which have also been studied with in vitro fatty acid-synthesizing systems, indicate the presence of, at least, three separate enzyme systems in pea which are responsible for (a) de novo synthesis of palmitate, (b) elongation of palmitate to stearate, and (c) further elongation of stearate to the very long-chain fatty acids. Safflower is also sensitive to fluoride or arsenite during germination. In the presence of arsenite, palmitate accumulated with a sharp reduction in synthesis of the very long chain fatty acids and linoleate. Fluoride reduced linoleate formation without affecting the very long chain fatty acids. Thus, arsenite and fluoride effects are not uniform from species to species. Although trichloroacetic acid had no effect on synthesis of fatty acids by either seed, other compounds such as decenylsuccinic acid and carbamate weed killers specifically reduce the formation of the very long chain fatty acids by pea thus suggesting a mode of action for these compounds in wax formation.