Pathways for the metabolism of glyoxylate and acetate in germinating fatty seeds.

Abstract

Cotyledons of germinating sunflower, pumpkin, linseed, and watermelon seeds and the endosperm of germinating castor bean seeds have been examined for their ability to utilize glyoxylate-C14and acetate-C14for the biosynthesis of amino acids. All of the tissues examined readily utilized these acids when supplied in micromolar amounts to tissue slices. The chief products of this utilization included the organic acids of the glyoxylate and tricarboxylic acid cycles and a number of amino acids and amides. The results are interpreted as indicating that, in sunflower, watermelon, linseed, and pumpkin seeds, malate formed in the malate synthetase reaction is metabolized by the partial reactions of the tricarboxylic acid cycle. α-Ketoglutarate produced by these reactions is extensively utilized in the biosynthesis of glutamate, γ-aminobutyrate, and glutamine. In agreement with data already published, castor bean endosperm utilized acetate for the biosynthesis of sugars. This tissue also utilized glyoxylate for the formation of glycine, serine, glycollate, and malate. It is concluded that, with the exception of castor bean endosperm, acetyl CoA arising as a result of fatty acid oxidation might be utilized for amino acid biosynthesis via the partial reactions of the glyoxylate and tricarboxylic acid cycles.