The Inhibition of Photosynthesis after Exposure of Bean Leaves to Various Low Levels of CO_2

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Mature first leaves of Phaseolus vulgaris L. were exposed to low partial pressures of CO_2 (7, 6 and 0 Pa CO_2) for 24 h. After exposure of leaves to 6 Pa CO_2 for 24 h, there was a reduction in the carbon exchange rate (CER) at all partial pressures of CO_2 at which measurements were made. After exposure to 7 Pa CO_2, the CER decreased only at high partial pressures of CO_2. The rates of electron transport from water to methyl viologen, through the whole chain, decreased in parallel with the decrease in CER measured at 90 Pa CO_2. One site of inhibition in leaves exposed for 24 h to 6 Pa CO_2 appeared to be the intersystem electron-transport chain since there were no significant changes in the activities of PSI and PSII, as determined from the level of P-700 and measurement of fluorescence, respectively. Another inhibitory phenomenon appeared to be a negative change in the activation state of Rubisco, while the level of Rubisco was unaffected by the exposure to 6 Pa CO_2. These decreases in photosynthetic activity caused by depletion of CO_2 explains at least in part, the inhibition of photosynthesis that is caused by rain treatment [Ishibashi and Terashima (1995) Plant Cell Environ. 18: 431].
日本植物生理学会の論文