Red, far-red response & chlorophyll synthesis

One of the earliest observations on the photomorphogenic development of chlorophyll synthesis was made by Withrow et al. (10). In a preliminary report they noted that pretreatment of leaves with up to 10 millijoules (mj/cm2) of red radiant energy followed by a dark period of from 5 to 15 hours, resulted in the elimination of the latent period in subsequent chlorophyll formation, with some indication that the red induction might be reversed by an exposure to far-red. Virgin verified this observation of the involvement of the photomorphogenic induction effect on the development of the chlorophyll synthesizing mechanism (6) and demonstrated the greater effectiveness of red over blue pretreatment (7). Althouggh the induction response has been clearly demonstrated, the far-red reversal phenomenon associated with chlorophyll synthesis has not been previously shown. The data herein presented establish clearly that chlorophyll synthesis is another of the physiological responses referred to as red, far-red reactions, in which stimulation of plastid pigment synthesis by a short red preirradiation may be nullified by a subsequent far-red pretreatment. However, the red, far-red effect on chlorophyll synthesis is not directly associated with the photoconversion of protochlorophyllide (11). It is, rather, a reflection of metabolic and growth changes affecting the rate of synthesis of protochlorophyllide, these growth and metabolic changes having been induced by means of the primary effect of light on the photomorphogenic pigment receptor (4).