Characteristics of Phytochrome in Glutaraldehyde-Treated Maize Coleoptiles

Abstract

Glutaraldehyde treatment was used to stabilize the in situ distribution of phytochrome at intervals during the course of phytochrome dark reactions. Total cellular phytochrome decreased in maize coleoptiles when they were returned to darkness and incubated after red irradiation. Photoreversibility was lost in both the soluble and particulate fractions, being faster in the particulate fraction. Glutaraldehyde treatment of coleoptiles immediately after irradiation inhibited loss of particulate phytochrome in the dark. When coleoptiles were irradiated with R/FR, i.e, red light (R, 660 nm) followed by far-red light (FR, 737 nm), and then incubated in the dark, the loss of particulate phytochrome was compensated for by an increase of phytochrome in the soluble fraction, resulting in negligible loss of total phytochrome.

The phytochrome dark reactions in subcellular fractions of coleoptiles irradiated in vivo with R and R/FR and extracted in Mg²⁺-containing buffer were similar to those in corresponding subcellular fractions of coleoptiles treated with glutaraldehyde before cell fractionation. If the pattern of phytochrome dark reactions in subcellular fractions of R- and R/FR-irradiated coleoptiles treated with glutaraldehyde before cell fractionation truly reffects the in situ situation, this similarity suggests that the phytochrome distribution in subcellular fractions obtained by extraction in Mg²⁺-containing buffer of coleoptiles irradiated in vivo (without ghtaraldehyde treatment) also represents the intracellular distribution. This conclusion however cannot be extended to the distribution obtained following irradiation of Mg²⁺-containing non-cellular extracts.