Induction of rapid chlorophyll accumulation in dark grown seedlings. II. Photoreversibility

A short pre-irradiation with red light some hours before the start of continuous illumination with white light eliminates the lag phase in chlorophyll-a (Chl-a) accumulation. In seedlings of several cultivate of bean, pea, and maize, grown in complete darkness, this inductive action of red light is hardly reversible by far red. Most cases of low reversal can be explained by the considerable inductive capacity of far red light itself. However, far red reversibility of the effect induced by red increased considerably with increasing duration of the period of dark incubation between pre-irradiation and continuous white light. On the other hand, more or less complete red-far red reversal was observed in plants de-etiolated by a pre-irradiation given some hours prior to the normal inductive treatment. Even relatively short exposures to a green safelight caused a significant degree of de-etiolation with concomitant increase in subsequent red-far red antagonism. It is concluded that the biosynthetic pathway leading to protochlorophyll (Pchl) and Chl-a is not directly under phytochrome control. In excised leaf material the rate of Chl-a accumulation in continuous light proved strongly depressed and completely insensitive to irradiations that were inductive in intact plants.