Phytochrome-mediated detection of changes in reflected light.

Measurements of phytochrome photoequilibria and photoconversion rates in vivo, in seedlings of Cucurbita pepo L. exposed to light in growth chambers, indicate that significant changes in the state of phytochrome can be brought about by changes in the quality and quantity of the light reflected from the walls of the growth chambers. The changes in reflected light, although large, were small in terms of the total radiation (direct light from the lamps plus wall-reflected light) to which the seedlings were exposed. The conditions used were approximate simulations of direct and reflected sunlight conditions in the natural environment. Keeping in mind the limitations imposed by the approximation of the simulations, the results from this study are consistent with the hypothesis that, in the natural environment, a plant might be capable of detecting the presence of nearby plants, before being shaded by them, through the phytochrome-mediated perception of changes in reflected light.