THE UTILIZATION OF CARBON-1 COMPOUNDS BY PLANTS: II. THE FORMATION AND METABOLISM OF FORMATE BY HIGHER PLANT TISSUES

Abstract

Tissue slices of carrot root and sunflower cotyledons readily produce formate-C14when incubated with glyoxylate-1,2-C14and glycine-2-C14solutions. Formate-C14feeding experiments using a wide variety of higher plant tissues have shown that this compound is readily oxidized to carbon dioxide. This oxidation probably involves a formic dehydrogenase system which has been demonstrated to occur in several of the tissues. Large amounts of formate-C14were also incorporated into serine, methionine, and methionine sulfoxide. Degradations of the serine produced from formate-C14showed that the bulk of the C14was present in the 3 position. The incorporation of formate into serine by radish cotyledons was stimulated under anaerobic conditions and by additions of glycine. Synthesis of methionine and methionine sulfoxide from formate-C14was stimulated by additions of homocysteine. The results are interpreted as an indication that formate-C14can be oxidized to carbon dioxide by formic dehydrogenase and can serve as a precursor of carbon-1 units that are to be utilized for the biosynthesis of serine and methionine.