Oxalic acid synthesis in shoots of Oxalis pes-caprae (L.)

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Abstract
The pathway of oxalic acid synthesis in white shoots of O. pes-caprae was investigated by administering C14-iabelled glucose, glyoxylic acid, glycollic acid, oxalic acid, sodium hydrogen carbonate, glycine and serine. The products that became labelled after injection of these compounds were examined qualitatively by paper chromatography and radio-autography, and quantitatively by column chromatography. Experiments with labelled D-[C6glucose indicated that the C for synthesis of oxalic acid was derived from the sugar pool. The results obtained with sodium hydrogen [C14carbonate indicated that malate was not a direct precursor of oxalate; glycollate was not rapidly labelled from sodium hydrogen carbonate. Although labelled [C2glycine and L-[C3serine both gave rise to some label in oxalic acid, the relatively low incorporation suggests that these are unimportant physiologically in the synthesis of oxalic acid. The results indicate that glycollic acid and glyoxylic acid are immediate precursors of oxalic acid in Oxalic shoots, and are consistent with formation of glyoxylic acid by cleavage of isocitric acid catalyzed by isocitratase.