A Phytochrome-mediated Sequence of Reactions Regulating Cell Division in Developing Callus Cultures

Abstract

Radiation at the red end of the visible spectrum is active in reducing the extent of the first synchronous division in explants removed from Jerusalem artichoke tubers and cultured in a liquid medium containing 2,4-D. The inhibitory effect of short red light exposures may be overcome by subsequent irradiation with far red light. However, prolonged exposures to red light may only partially be reversed by far red light. The addition of coconut milk to the medium completely overcomes the effect of short light exposures but cannot prevent the effect of prolonged light treatments. These results are consistent with a hypothesis which postulates that a phytochrome-mediated reaction initiates a chain of events which results in the depletion of an essential metabolite, also present in coconut milk, below a critical level required for cell division. There is evidence to suggest that the essential metabolite is L-phenylalanine.