The Influence of Light of Different Spectral Regions on the Synthesis of Phenolic Compounds in Gherkin Seedlings in Relation to Photomorphogenesis. I Biosynthesis of Phenolic Compounds

1) Dark-grown gherkin seedlings contain the sugar derivatives of p-coumaric acid and ferulic acid, present in both the cotyledons and hypocotyls, and a number of flavonols, occurring only in the cotyledons. Exposure of these seedlings to light results in an increase in the accumulation of these phenolic compounds after a lag of 1 y2 to 2 hours. 2) The responsivity of this effect to radiation in the blue and far-red wavelength regions is higher than to red light. Both photoresponse I, the “high-energy reaction”, and photoresponse II, the phytochrome reaction, seem to be involved. 3) The distribution pattern of the phenolics in the hypocotyl changes in the course of the irradiation; An initial increase in the concentration of hydroxycinnamic acids is followed by a decrease, particularly in the apical part. The ratio of ferulic acid to p-coumaric acid increases and is always higher in the lower part of the hypocotyl than in the apical part. 4) The accumulation of hydroxycinnamic acids in the hypocotyl in red and far-red light is largely dependent on the presence of the cotyledons. In blue light there is also a considerable synthesis when the cotyledons are excised.