Factors affecting synthesis of ascorbic acid in cress seedlings. 2. Ascorbic acid synthesis in relation to sugar formation

Abstract

In cress seedlings germinated in the dark, in the presence of various salt solns. a close correlation was generally found between the amt. of ascorbic acid and hexose sugars synthesized. Salts, particularly those of ammonium, which contained an anion not readily utilized, reduced both these constituents. Na and K salts containing an anion readily utilized (e.g., bicarbonate pyruvate, succinate) increased the ascorbic acid but not the hexoses. Solns. of D-glucose, D-galactose and D-fructose alone or combined with various salt solns. increased the hexose sugars. Ascorbic acid was also increased, to an extent detd. by the effect produced on the hexose ascorbic acid relationship by the individual salts. There was no evidence that the hexose supplied behaves differently from that derived from the seed reserves. It is suggested that hexose is converted into ascorbic acid and that the efficiency of the conversion is influenced by the nature of the salt present, possibly through its effect on the pH of the cell sap. Salts which raise the pH increase, and those which lower it decrease, the efficiency of conversion. The rate of mobilization of fat was slower in seedlings grown in ammonium sulfate than in those grown in water, and may partly account for the lowered formation of sugars in the former. In contrast to the other hexose sugars, D-mannose depressed the synthesis of ascorbic acid, but its action could be diminished by supplying in addition D-glucose, D-fructose or D-galactose. The form of growth of the seedlings was modified in the presence of ammonium sulfate or ammonium chloride, but became more nearly normal when such salts were supplied with a Na or K salt containing a utilizable anion.