Detached bean (Phaseolus vulgaris) and strawberry (Fragaria) fruits fed L-gulono-1,4-lactone or L-galactono-1,4-lactone convert this compound, in part, to L-ascorbic acid. When L-galactono-1, 4-lactone is given as a 0.25% solution to detached bean shoots, the ascorbic acid content is tripled in less than 10 hours. L-Gulono-1,4-lactone is only 5 to 10% as effective as its epimer. Experiments with specifically labeled L-gulono-I,A4-lactone and L-galactono-l, 4-lactone prove that conversion is direct. Ascorbic acid is labeled at the same carbon as its precursor.A method is described for preparation of L-galactono-1 , 4-lactone-2-_4C from myo-inositol-2-14C. This method can be extended to the preparation of L-ascorbic acid-2-14C on the basis of results obtained in the present study.During the conversion of an uronic acid ester or lactone to ascorbic acid in higher plants, reduction of carbon-I precedes the oxidative step (6,15
MATERIALS AND METHODSPreparation of L-Galactono-1,4-lactone-2-'4C. myo-Inositol-2-14C is readily converted to D-galacturonic acid-5-'4C in detached ripening strawberries (13). In this study, three ripening strawberries (5 g) were administered myo-inositol-2-14c (2 j,c, 0.5 Aimole in 0.1 ml of water) through freshly severed stems. Label was taken up by the berries in about 2 hr. After 24 hr, berries were ground in 70% ethanol (v/v), and the insoluble residue was washed with fresh portions of solvent until all of the soluble 14C was removed. The residue was hydrolyzed with Pectinol R-10 (Rohm and Haas' commercial pectinase) and D-galacturonic acid (14 mg, containing 21% of the "C supplied) was recovered by procedures already described (13). The labeled D-galacturonic acid was converted to its sodium salt and was reduced to the corresponding L-galactonate with sodium borohydride. Recovery of the free acid was achieved by placing the borohydride reaction mixture (after destroying excess borohydride with formic acid) on a column of Dowex 1 exchange resin (formate form) and then by eluting with a formic acid gradient (13). The free acid was converted to its 1,4-lactone by flash evaporation from glacial acetic acid and finally, by heating the residue to 60 C under reduced pressure. A portion of the lactone was converted to its trimethylsilyl ether, and was found to have the same retention time on SE-30 and OV-1 gas chromatographic columns as an authentic sample of tetrakis-O-trimethylsilyl-L-galactono-1 ,4-lactone (9). The final product had a specific radioactivity of 6 ,uc per mmole.Preparation of L-Gulono-1,4-lactone-1-14C and -6-14C. DGlucuronic acid-6-"4C and-1-"4C, respectively, were converted to sodium salts, were reduced to L-gulonic acids, were purified and lactonized as described above. The labeled D-glucuronic acids used in this preparation had been purified previously (20).Final specific radioactivity of L-gulono-1 ,4-lactone-