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Further Studies on Oxalic Acid Biosynthesis in Oxalate-accumulating Plants ¹

Department of Agricultural Chemistry and Graduate Program in Biochemistry and Biophysics, Washington State University, Pullman, Washington 99164

L-Ascorbic acid functions as a precursor of oxalic acid in several oxalate-accumulating plants. The present study extends this observation to include Rumex crispus L. (curly dock), Amaranthus retroflexus L. (red root pigweed), Chenopodium album L. (lamb's-quarters), Beta vulgaris L. (sugar beet), Halogeton glomeratus M. Bieb. (halogeton), and Rheum rhabarbarum L. (rhubarb). Several species with low oxalate content are also examined.

When L-[1-¹⁴C]ascorbic acid is supplied to young seedlings of R. crispus or H. glomeratus, a major portion of the ¹⁴C is released over a 24-hour period as ¹⁴CO₂ and only a small portion is recovered as [¹⁴C]oxalate, unlike cuttings from 2- or 4-month-old plants which retain a large part of the ¹⁴C as [¹⁴C]oxalic acid and release very little ¹⁴CO₂. Support for an intermediate role of oxalate in the release of ¹⁴CO₂ from L-[1-¹⁴C]ascorbic acid is seen in the rapid release of ¹⁴CO₂ by R. crispus and H. glomeratus seedlings labeled with [¹⁴C]oxalic acid.

The common origin of oxalic acid carbon in the C1 and C2 fragment from L-ascorbic acid is demonstrated by comparison of ¹⁴C content of oxalic acid in several oxalate-accumulators after cuttings or seedlings are supplied equal amounts of L-[1-¹⁴C]- or L-[UL-¹⁴C]ascorbic acid. Theoretically, L-[1-¹⁴C]ascorbic acid will produce labeled oxalic acid containing three times as much ¹⁴C as L-[UL-¹⁴C]ascorbic acid when equal amounts of label are provided. Experimentally, a ratio of 2.7 ± 0.5 is obtained in duplicate experiments with six different species.

³ To whom inquiries and requests for reprints should be addressed.

¹ This research was supported by Grant No. GM-22427 from the National Institute of General Medical Sciences, National Institutes of Health, United States Public Health Service. Scientific Paper No. 4930, Project 0266, College of Agriculture Research Center, Washington State University, Pullman, Washington 99164. Taken from a thesis submitted by R. Nuss in partial fulfillment of requirements for the M.S. Degree, Washington State University, Pullman.

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