Reversibility of the Red – Far-red Reaction by Irradiation at Different Sites

Abstract

SINCE the discovery that red light promotes and far-red light inhibits the germination of lettuce seeds^1,2 this reversible photoreaction has been studied in detail^3,4 and has been found to be identical with that involved in controlling flowering and other biological processes. Because of the widespread occurrence and importance of this reaction, a detailed understanding of its mechanism is of the utmost importance, and attempts to explain it have been made by a number of workers. Most recently, the available knowledge has been summed up by Hendricks in a formula of general terms⁵. The form in which this process is usually stated makes it appear that the same pigment molecules which, for example, have been brought to the far-red absorbing form by red radiation are directly reversed to their former state by the absorption of far-red light.