L-Ascorbic acid-l-11C and its oxidation product, dehydro-L-ascorbic acid, produced labeled oxalic acid in oxalateaccumulating plants such as spinach seedlings (Spinacia oleracea) and the detached leaves of woodsorrel (Oxalis stricta and 0. oregana), shamrock (Oxalis adenopylla), and begonia (Begonia evansiana). In 0. oregana, conversion occurred equally well in the presence or absenice of light. This relationship between L-ascorbic acid metabolisnm and oxalic acid formation must be given careful consideration in attempts to explain oxalic accumulation in plants.Oxalic acid accumulates in certain species of plants such as spinach, woodsorrel, and begonia (6,10,12,23,24,26 Recently, Wagner and Loewus (27) described the conversion of L-ascorbic acid-1-'4C to labeled oxalic acid in detached vegetative apices of the lemon geranium (Pelargonium crispum). This observation has been extended by the present study to oxalateaccumulating plants. MATERIALS AND METHODSSpinach seedlings (Spinacia oleracea, var. Bloomsdale) were grown under greenhouse conditions in a vermiculite-pearlite mixture. Twelve-day-old seedlings were detached from their roots and placed in vials containing the radioactive solution as described in earlier studies (27)

Labeled tartaric acids from Pelargoniunt crispum apices which had been fed L-ascorbic acid-6-"C and Vitis labrusca and Parthenocissus inserta tissues which had been fed L-ascorbic acid-l-"4C were examined by chemical means to determine chiral configuration. In each instance, label was associated with (+)-tartaric acid.Similar experiments with labeled tartaric acid from P.crispuom which had been labeled with D-glucose-l-"C or -6-'4C led to the same result. No evidence was obtained for formation of labeled meso-tartaric acid in experiments described above.The recent suggestion of H. Ruffner and D. Rast (Z. Pflanzenphysiol. 73: 45-55, 1974) that conversion of L-ascorbic acid to tartaric acid in plants is a nonenzymatic process is re-examined in the light of present findings.All three stereoisomeric forms of tartaric acid have been found in higher plants; (+) TA' in numerous plant families (4) notably the Vitaceae and Geraniaceae (23, 24); (-) TA in Bauhinia reticulata (18) and as esters of caffeic acid in Cichorium intybus L., C. endivia L. and Lactuca sativa L. (6,21,22,30); and meso-TA as an ester of p-coumaric acid in spinach leaves and isolated spinach chloroplasts (16,25) or as an excreted product (5). Only the (+) form has received much attention as regards its metabolic origin. Literature pertinent to biosynthesis of (+) TA is summarized in recent publications (19,(27)(28)(29). These biosynthetic studies employed labeled precursors and, in most instances, recovered TA from solution as its poorly soluble KH salt. In one study (13,14), formation of (+) TA from glycolate-1-"C in Pelargonium zonale L. was accompanied by (-) TA and/or meso TA.This latter observation prompted a careful study of the isomeric form of labeled TA recovered from Pelargonium crispum L. after feeding L-ascorbic acid-6-4C (28) L-AA-6-'4C (28) and from Vitis labrusca berries and Parthenocissus inserta leaves which were labeled with L-AA-1-"4C (29) were used in this study. Samples from P. crispum apices which were labeled for 72 hr with D-glucose-1-"C or -6-"'C by the same procedure used in AA experiments (12) were also studied.Separation of Diastereomeric Forms of TA. Ion exchange chromatography with Dowex 1 (formate) resin and a 0 to 4 M formic acid gradient readily separated meso-TA from the chiral forms. With the two step gradient procedure described earlier (28), meso-TA appeared in the second step of the gradient in the volume eluted between 60 to 110 ml and chiral TA between 100 to 160 ml. Further purification by paper chromatography (28) and GLC (27) was used to identify TA.Resolution of Labeled TA. Samples used for this study had been recovered from plant extracts by ion exchange chromatography using (+) TA as carrier. Chiral TA fractions were combined and adjusted to pH 3.5 with KOH to recover the KH salt of TA. A weighed aliquot containing 0.05 to 0.1 1,Ci was converted to free TA and combined with an equimolar amount of (-) TA to make a racemic mixture. Following further dilution with unlabeled racemic TA, the mixture w...

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