Addition of water to dry seeds of Pinus spp. increased the detectable phytochrome immediately and the level reached after 2 h in darkness was retained for at least 20 h at 20° C. The in-vivo difference spectra of phytochrome in Pinus seeds showed absorption maxima at approximately 656 nm and at 710 nm to 715 nm. An isosbestic point was observed at about 680 nm. Shifts towards longer wavebands were obtained especially with tissue containing substantial amounts of chlorophyll and are, therefore, not due to diverse types of phytochrome. Embryo tissue of Ginkgo biloba showed also a maximum in R at 655 nm but the peak in FR occurred at a longer wavelength, 725 nm. This was confirmed by determining action spectra for the phototransformations Pr⇌Pfr.The dark reactions of phytochrome in Pinus differed from those in Ginkgo. Following a short exposure to R light, the total quantity of photoreversible pigment in Pinus seeds remained constant for several hours in darkness at room temperature. Dark reversion of Pfr occurred extremely rapidly and tPfr 50 was only 0.3 h. In Ginkgo embryos total phytochrome in darkness following a brief exposure to R light was not completely stable. Reversion of Pfr was much slower and tPfr 50 was slightly less than 2 h.It is concluded that, at least as regards the spectral qualities, the phytochrome in Gymnospermae differs from that of Angiospermae and is apparently also not identical in Coniferae and Ginkgoinae.
An in vivo phytochrome difference spectrum of dark grown Anemia phyllitidis L. Sw. gametophytes has been measured. The spectral characteristics estimated from the difference spectrum were as follows: red maximum at 662 nanometers, far red maximum at 737 nanometers, isosbestic point at 695 nanometers, and a shoulder from 620 to 630 nanometers.
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.
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