The influence of light of different spectral regions on the synthesis of phenolic compounds in gherkin seedlings, in relation to photomorphogenesis. VI. Phenol synthesis and photoperiodism

In the hypocotyl of dark-grown gherkin seedlings a series of maxima in the level of phenylalanine deaminase (PADAse), a key enzyme in phenol synthesis, can be induced by an alternating light-dark treatment. Each PADAse peak corresponds to a temporary increase in the rate of accumulation of hydroxycinnamic acids. The height of a particular enzyme peak is a function of the length of the inducing light period and of the light sensitivity of the plant at the time of irradiation. The light sensitivity is inversely related to the amount of hydroxycinnamic acids that have previously accumulated in consequence of preceding irradiation. Possible implications of these findings on the problem of biological time measurement are discussed.