Phytochrome Pelletability Induced by Irradiation in Vivo: TEST FOR IN VITRO BINDING OF ADDED [S]PHYTOCHROME.

Undegraded, highly purified [(35)S]phytochrome was immunoaffinity-purified either from dark control oat (cv. Garry) shoots or from etiolated oat shoots that were previously irradiated first with red and then with far-red light so that, if proper extraction conditions had been utilized, about 60% of the total phytochrome would have been pelletable. When [(35)S]phytochrome was added to extraction buffer immediately prior to homogenization of etiolated oat shoots, pelletability assays indicated that there was no preferential binding of [(35)S]phytochrome regardless of (a) whether it was purified from dark control or irradiated shoots, (b) whether it was added as phytochrome-red-absorbing form or phytochrome-far-red-absorbing form, or (c) whether it was added to dark control or red-irradiated shoots. Similarly, binding of [(35)S]phytochrome to resuspended pellets obtained from crude oat extracts was not specific for the source of [(35)S]phytochrome, for its form, or for the irradiation treatment given to intact shoots used to prepare the resuspended pellets. No evidence was obtained to support the hypothesis that phytochrome binds with specificity to particulate material in vitro under conditions used to assay for light-enhanced, in vivo-induced phytochrome pelletability.