PLANT PHYSIOLOGY , Vol 111, Issue 2 635-640, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
The Loss of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Caused by 24-Hour Rain Treatment Fully Explains the Decrease in the Photosynthetic Rate in Bean Leaves
M. Ishibashi, H. Usuda and I. Terashima
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Hongo, Tokyo, 113 Japan (M.I., I.T.)
Recently, we have found that simulated rainfall causes a chronic inhibition
of leaf photosynthesis in Phaseolus vulgaris (M. Ishibashi and I. Terashima
[1995] Plant Cell Environ 18: 431-438). Mechanisms of this inhibition were
examined in the present study. After the plants were treated with
continuous mist for 24 h and then dried to unwet conditions,
light-saturated photosynthetic rates of the leaves measured at 35 Pa
ambient CO2 decreased to one-half of the control level. The extractable
activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) also
decreased to the same extent. Unexpectedly, this decline was due not to the
lowered activation state but to the decrease in the amount of Rubisco.
Before or after the "rain" treatment, the relationship between the net
photosynthetic rate and the amount of Rubisco was expressed as a unique
linear function with a small intercept (r2 = 0.84). From these it was
inferred that the main cause of the rain-induced decline in photo-synthetic
rate was the loss in amount of Rubisco.