The influence of chlorophyll on in-vivo difference spectra of phytochrome

A comparison was made between in-vivo phytochrome difference spectra of light- and dark-grown plant material. Spectral differences were found to be caused, at least to a large extent, by screening by chlorophyll and not by differences in phytochrome. Presence of chlorophyll affects the phytochrome in leaves differently from that in stems. In cotyledons the absorption maximum in the R part of the spectrum shifts towards shorter wavelengths, in FR to longer ones. Concomitantly, the R/FR ratio diminishes; this was confirmed in a model experiment. In stem tissue the peak positions remain the same but the isosbestic point shifts towards longer wavelengths and the R/FR ratio increases.In Viola, however, the phytochrome appears to be different from the normal type. In the etiolated hypocotyl, where the difference spectrum of phytochrome is presumably not distorted by chlorophyll, the R and FR maximum was found to be at a shorter wavelength than in hypocotyls from Cornus and turnip or from stem tissue of dark-grown pea.