Lipid biosynthesis in developing and germinating soybean cotyledons: The formation of palmitate and stearate by chopped tissue and supernatant preparations

Chopped tissue from developing soybean cotyledons incorporated 1-¹⁴C]acetate into palmitate, stearate, oleate, and linoleate, but with germinating cotyledons much less 1-¹⁴C]acetate was incorporated and the principal labeled products were palmitate, stearate, and oleate. When supernatant fractions from developing cotyledons were incubated with 1-¹⁴C]acetate or 2-¹⁴C]malonate the principal labeled products were palmitate and stearate. Supernatant fractions from germinating seed incorporated 2-¹⁴C]malonate into palmitate and also into short chain fatty acids including decanoate, laurate, and myristate. Supernatants from developing cotyledons required acyl carrier protein (ACP), ATP, CoA, and reduced pyridine nucleotides for maximal rates of incorporation of either 1-¹⁴C]acetate or 2-¹⁴C]malonate into palmitate and stearate. The de novo fatty acid synthetase which converts acetyl- and malonyl-ACP's to palmityl ACP was active in supernatant fractions from both young and old developing cotyledons. The elongation system, converting palmityl ACP to stearyl ACP, was more active in supernatants from younger than from older developing cotyledons. In experiments with chopped tissue the elongation system appeared equally active throughout the development process. These results are consistent with the view that the de novo and elongation systems are separate entities and that the elongation system in older cotyledons is less stable to the methods used to prepare supernatant fractions.