The influence of light of different spectral regions on the synthesis of phenolic compounds in gherkin seedlings in relation to photomorphogenesis. III. Hydroxylation of cinnamic acid

1. Light stimulates the conversion of L-phenylalanine and of trans-cinnamic to p-coumaric acid in hypocotyl segments from dark-grown gherkin seedlings. 2. Inhibition by cycloheximide of the increase in the rate of hydroxylation of cinnamic acid in response to light indicates that de novo synthesis of enzyme, probably cinnamic acid hydroxylase, is involved. 3. The responsivity to light is higher in the apical part than in the basal part but the spectral sensitivity does not alter significantly over the length of the hypocotyl. The photoreceptor directly responsible for the effect of blue light seems to be different from phytochrome. 4. Particularly in red and far-red light an effect of the cotyledons on the hydroxylase activity to be obtained in the hypocotyls becomes apparent. 5. There is a general correlation between the influences of light quality, light intensity and duration of irradiation on the hydroxylase activity and the accumulation of hydroxycinnamic acids in the gherkin hypocotyl. 6. The implications of this photo-inducible reaction for the regulation of lignification and cell elongation are discussed.