Factors affecting synthesis of ascorbic acid in cress seedlings; ascorbic acid synthesis in relation to sugar formation.

In a previous paper (Mapson & Cruickshank, 1947) it was shown that certain salts stimulated the synthesis of ascorbic acid in cress seedlings and increased the pH of the cell sap, whereas other salts had the reverse action. It was concluded from this that the deciding factor was the amount of base made available to the plant after metabolism of the salt. Ray (1934) found that certain sugars increased the production of ascorbic acid when supplied to the excised pea embryo. He calculated his results on the basis of concentration, but, as growth was affected by the various treatments, we have recalculated them as the amount produced by a given number of seedlings. Ofall the substances testedbyhim, hexose sugars alone produced a significant increase in ascorbic acid. Of these fructose was the most effective, followed in descending order by mannose, glucose and galactose. He suggested, therefore, that the hexose sugars served as precursors of ascorbic acid. In view of Ray's (1934) results it seemed desirable to ascertain whether the treatments described in our earlier paper (Mapson & Cruickshank, 1947) had affected the synthesis of ascorbic acid by reason of their effect on the formation of hexose sugars. We therefore followed the formation of hexoses and ascorbic acid in seedlings germinated in the presence of various salts. The salts chosen fell into three groups, viz. those which had been shown (a) to decrease the synthesis, (b) to increase the synthesis, and (c) to have little effect.