The metabolism of [14C]glycine by plant tissues

Abstract

The metabolism of glycine in storage tissues of carrot and the endosperm of 5-day-old castor-bean seedlings was studied with micromolar amounts of [C14 2]glycine. The main products after 6 hours of [C14 2]glycine metabolism in both tissues were serine, glyoxylate, and carbon dioxide. Additions of malonate and iodoacetate to the carrot tissues greatly reduced the amounts of C14 entering the fractions isolated. Both inhibitors decreased the amounts of C14 detected in serine, and malonate increased the percentage of the label in glyoxylate. Degradations of [C14]serine produced from [C14 2glycine feeding indicated that, besides contributing to the C-1 and C- 2 positions of serine, labelling of the C-3 position had occurred. Degradations of [C14 2]glycine remaining in the tissues after the experimental periods indicated that considerable breakdown and resynthesis of glycine had occurred. The results are interpreted as being consistent with a conversion of glycine into glyoxylate, possibly via a transamination reaction. Glyoxylate, possibly by oxidative decarboxylation, contributes to the C-3 position of serine. Changes in the intramolecular distribution of C14 in glycine might indicate breakdown and resynthesis of glycine in the carrot tissues by a pathway established for animal tissues.