Effect of pH on Absorption Spectra of Pea 114 and 121 Kilodalton Phytochromes during and after Red-Light Irradiation

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Absorption spectra of pea 114 and 121 kDa phytochromes were measured at pH 6.8, 7.8 and 8.8 using a custom-made transient multichannel spectrum analyzer. The absorption spectra of I 14 kDa phytochrome as P_R and P_<FR> were least affected by medium pH. The absorption spectra at photostationary state under red light, however, were different under the three diffcrent pH conditions, and were different from those obtained 55 s after red-light irradiation, owing to rapid pH-dependent absorbance increase in both red and far-red regions in the dark. In contrast, the absorption spectra of 121 kDa phytochrome were significantly less affected by medium pH. The absorption spectra measured at the photostationary state showed a lower P_<FR> Peak at higher pH. The absorption spectra obtained 55 s after the irradiation were similar under the three pH conditions since the rapid absorbance increase in the far-red region in the dark was small. Possible accumulation of 114 kDa phytochrome population(s) with low absorbance at red-light-induced photostationary state at pH 8.8, and the protective role of the 7 kDa polypeptide at the amino terminus against the pH effect in 121 kDa phytochrome are discussed.
日本植物生理学会の論文