Oxalic acid synthesis in shoots of Oxalis pes-caprae. The precursors of glycollic acid and glyoxylic acid

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Abstract
The relative contribution of [2-C14]glucose, [1-C14]ribose, [1,5-Cl4 2]isocitric acid and [1-Cl4]glycollic acid to oxalic acid synthesis in Oxalis has been studied. Shoots were incubated for 1 and 6 hours after the administration of each C14 compound and the products containing radioisotope were extracted and separated by paper chromato-graphy and located by radioautography. The Cl4 content of specific amino acids and of specific organic acids was determined by counting such compounds on paper by a liquid-scintillation technique. The results show that isotope from [1,5-Cl4 2]isocitric acid and from [1-Cl4]giycollic acid was incorporated into oxalic acid more efficiently than from [2-Cl4]glucose or from [1-Cl4]ribose. Contrary to results obtained with photosynthetic tissue, ribose did not contribute significantly to glycollic acid synthesis in white Oxalis shoots. Within 1 hour the percentage incorporation of radioisotope from [1,5-Cl4 2]isocitric acid and from [1-Cl4]glycollic acid into oxalic acid was comparable. After 6 hours the contribution from [1-Cl4]glycollic acid was greater than that from [1,5-Cl4 2]isocitric acid. Glycollic acid also acted as an efficient procursor for the biosynthesis of serine. Oxalic acid synthesis in white Oxalis shoots appears to be associated with the oxidation of glyoxylic acid which may arise from glycollic acid or from the cleavage of isocitric acid.