Accumulation of Ascorbic Acid in the Cotyledons of Morning Glory (Pharbitis nil) Seedlings during the Induction of Flowering by Low-Temperature Treatment and the Effect of Prior Exposure to High-Intensity Light

摘要

Seedlings ofPharbitis nilstrain‘Violet’were cultured at a low temperature, which induces their flowering even in continuous light, with or without prior exposure to high-intensity light, which enhances the flower-inducing effect of the exposure to low temperature. Analysis by HPLC of extracts of cotyledons showed that the level of an unstable compound increased during these treatments, in addition to the increase in levels of phenylpropanoids reported previously. The compound was identified as ascorbic acid from the spectroscopic data. The change in the concentration of ascorbic acid at low temperature was correlated with the increase in the induction of flowering and the increase in levels of the phenylpropanoids. The rapid increase in level of ascorbic acid after exposure to high-intensity light reflected the promotive effect of high-intensity light on the induction of flowering at low temperature. However, levels of ascorbic acid also increased in seedlings ofP. nilstrain‘Kidachi’that were cultured in high-intensity light, a treatment that does not induce flowering in this strain. Thus, ascorbic acid cannot be associated with the induction of flowering by high-intensity light alone. Ascorbic acid increased the rate of formation of caffeic acid fromp-coumaric acid in vitro, a result that suggests that ascorbic acid might be involved in the increases in levels of phenylpropanoids in the se