Experimentally induced binding of phytochrome to mitochondrial and microsomal fractions in etiolated pea shoots

A brief irradiation with red light of pea (Pisum sativum L.) shoot segments kept at 0° resulted in very rapid binding of both Pr and Pfr to mitochondrial and microsomal fractions. The effect was not far-red reversible. The amount of phytochrome bound to the mitochondrial fraction was proportional to the percentage of Pfr of the fraction, and the ratio of Pr and Pfr in the bound form was the same as that in 12,000 x g supernatant. After a brief exposure of the segments to red light at 0° and a subsequent dark incubation at 30° in Tris-HCL buffer containing dithiothreitol or EDTA, which bot inhibit Pfr decay, the contents of phytochrome in the mitochondrial and microsomal fractions were significantly enhanced with time. The red-light effect was reversed by far-red light. The increase of the phytochrome content in the particulate fractions continued for at least 2 h, reaching a ca. 3 times higher level in terms of Δ (ΔA) per mg protein.