Biosynthesis of vitamin C in germinating legumes

Abstract

Working on sprouted mung (Phaseolus radiatus), we have observed that, contrary to what has been reported for the maturing fruit, there is a rapid and progressive decrease in the proportion of ascorbic acid to dehydro-ascorbic acid with germination, which is paralleled by corresponding increases in ascorbic acid oxidase activity. Germination in absence of light or after short preliminary periods of steeping in the cold (5°C.), which result in 62 and 23 per cent respectively enhanced vitamin C formation during five days, also cause lowering of oxidase activity; these treatments are additive in their effects. Typical of related changes are the increases in glutathione, reducing sugars and amylase activity, phosphates and phosphatase activity, and nicotinic acid. Especially interesting are the increases, in five-day old seedlings germinated in the dark, in glutathione (158 per cent) and total ascorbic acid (45 per cent) on one hand, and the decreases in dehydroascorbic acid (37 per cent) and oxidase activity (25 per cent) on the other. The changes in the reductase activities were not followed; but the results of germination in the dark cannot be explained on the basis of the effect of glutathione on dehydro-ascorbic acid alone, on account of the difference in the total ascorbic acid contents of these seedlings as compared to those sprouted normally.