Effect of Neutral Salts on Spectral Characteristics of Undegraded Phytochrome Partially Purified from Etiolated Pea Shoots

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Spectral characteristics of partially purified undegraded pea phytochrome were investigated in different ionic conditions. At the red-light-induced photostationary state in low ionic strength buffer phytochrome had reduced absorbance in its far-red peak as reported previously. Elevation of the ionic strength of the buffer reversibly increased the absorbance in the far-red region at the photostationary state. It was found that the effect of increase of ionic strength was strengthened secondarily by chaotropicity of salts. It was confirmed that phytochrome preparations of low ionic strength contained a photosensitive component(s) other than the red-light-absorbing form (P_R) and farred-light-absorbing form (P_<FR>) during photochemical transformation, as well as during the first several min in the dark after phototransformation. At high ionic strength, phytochrome became a two-component system composed of only P_R and P_<FR> at the red-light-induced photostationary state though a significant accumulation of another component(s) occurred during phototransformations. Increasing ionic strength also enhanced A_<723> of phytochrome at the red-light-induced photostationary state. The effect could result from either an increased mole fraction of P_<FR> at the photostationary state induced by red light, or a change in the extinction coefficients of P_<FR>.
日本植物生理学会の論文