Showing papers in "Plant and Cell Physiology in 1974"

Long chain fatty acid synthesis in developing castor bean seeds I. The operation of the path from acetate to long chain fatty acids in a subcellular particulate system

Abstract: The path of LFA synthesis from acetate in developing castor bean seeds was associated with subcellular 10,000; particles. Further fractionation of these particles by a stepwise density gradient method showed the high possibility that the site of LFA synthesis is the proplastid. A study on cofactor requirements when [l-C]acetate predominantly incorporated into LFAa indicated that synthesis would be achieved by acetyl-CoA carboxylation, malonyl-ACP condensation. ATP, GoA, HCOjand Mg-H" or Mn++ were essential for synthesis from acetate by the 10,000 g particulate system. Results of inhibitor experiment suggested that the supply of ATP to the LFA synthesizing system is brought about by mitochondrial oxidative phosphorylation, when acetate is the sole precursor for U A synthesis in this system. The NADPH generating system was contained in the patides, although the addition of NADP+ and G-6-P increased synthesis. NADH markedly stimulated LFA synthesis from acetate. The primary role of NADH seems to be as a direct reductant in both steps involving the reduction and oxidative desaturation of fatty acid chains; particularly, in the former step, although NADH partially contributes to the supply of ATP as a respiratory substrate. It is unlikely that NADH works as a hydrogen donor to NADP+. LFA synthesis by the castor bean particulate system was not stimulated by light, thus differing from that by leaf chloroplasts.