Kinetics of intracellular redistribution of phytochrome in Avena coleoptiles after its photoconversion to the active, far-red-absorbing form

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Abstract
The kinetics of the intracellular redistribution of phytochrome (sequestering) in Avena sativa L. coleoptiles following a brief, saturating actinic pulse of red (R) light have been determined. Immunocytochemical labelling of phytochrome with monoclonal antibodies showed that at 22°C sequestering can occur within 1–2 s from the onset of R irradiation and is dependent upon the continued presence of the far-red-absorbing form of phytochrome (Pfr). The initial rate, but not the final extent, of sequestering is reduced by lowering the temperature of the tissue to 1°C. Sequestering at 22°C appears to involve two distinct stages: (1) a rapid association of Pfr with putative binding sites initiates the sequestered condition, following which (2) these sites of sequestered phytochrome appear to aggregate. Neither of these two processes was affected by the cytoskeletal inhibitors colchicine or cytochalasin B. Phytochrome sequestering therefore resembles R-light-induced phytochrome pelletability with respect to kinetics, temperature sensitivity, and dependence upon the continued presence of Pfr in the cell.