Inhibitory Effect of Carbohydrate on Flowering in Lemna perpusilla: III. Effects of Respiratory Intermediates, Amino Acids, and CO(2). Glucose 6-Phosphate Dehydrogenase Activity.

A study was done on the effects of various factors on carbohydrate inhibition of flowering and on in vitro activity of glucose 6-phosphate dehydrogenase in Lemna perpusilla 6746 grown on dilute Hutner's medium in short days. Autoclaving decreased the flower inhibitory effect of sucrose but increased the effects of glucose and fructose. Sucrose inhibition was mimicked by CO(2) and was partially reversed by agitation of the cultures. Inhibition by sucrose was also partially reversed by ATP and intermediates of the tricarboxylic acid cycle, the glycolytic pathway, or the pentose phosphate pathway. Tartaric acid was inactive. Glycine, l-alanine, l-aspartate, l-asparagine, l-serine, l-glutamate, and l-glutamine were active, whereas l-cysteine, l-arginine, l-lysine, l-leucine, l-isoleucine, l-proline, l-tyrosine, l-tryptophane, and l-phenylalanine were not. Incubation of cultures on distilled water during a single inductive long night prevented flowering. This inhibition was partially reversed by l-alanine and glucose 6-phosphate. There was a correlation between carbohydrate inhibition of flowering and enhancement of glucose 6-phosphate dehydrogenase. Possible mechanisms for the carbohydrate inhibition of flowering are discussed.