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Plant and Cell Physiology, 2001, Vol. 42, No. 10 1093-1102
© 2001 Oxford University Press

The Mechanism to Suppress Photosynthesis Through End-Product Inhibition in Single-Rooted Soybean Leaves during Acclimation to CO2 Enrichment

Shinichi Sawada, Makoto Kuninaka, Kouki Watanabe, Atsushi Sato, Hitomi Kawamura, Kenichi Komine, Takeshi Sakamoto and Minobu Kasai

Department of Biofunctional Science, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, 036-8561 Japan

Single-rooted soybean leaves were used to investigate the suppression of photosynthesis through end-product inhibition during acclimation to CO2 enrichment. The photosynthetic activity was greater in leaves cultured at a CO2 partial pressure of 70 Pa (high-CO2) than that in the leaves cultured at 35 Pa CO2 (control) during the initial exposure to CO2 enrichment but then decreased rapidly with a large accumulation of starch, to well below the level of the control leaves. The response curve of photosynthesis (A) to the intercellular CO2 concentration (Ci) in the high-CO2 leaves cultured long-term exhibited a significantly low initial gradient. However, on exposure to darkness for 48 h, the initial gradient of the A to Ci curve and rate of photosynthesis were completely restored, and almost all of the accumulated starch was expended. The ribulose bisphosphate carboxylase (RuBPcase) content and activation ratio in the high-CO2 leaves remained high and roughly constant during the experiment, and were unchanged by the exposure, while this enzyme was slightly inactivated or inhibited after long-term exposure to CO2 enrichment. The lower rate of photosynthesis in the high-CO2 leaves could be linearly increased to a rate approaching the control level by increasing the external atmospheric [CO2], which thereby compensated for a reduced CO2 transfer diffusion from the intercellular space to the stroma in chloroplasts. It is consequently concluded that, during the acclimation to CO2 enrichment, the suppression of photosynthesis through end-product inhibition was mainly caused by a lowering of the carboxylation efficiency of RuBPcase due to hindrance of CO2 diffusion from the intercellular space to the stroma in chloroplasts brought about by the large accumulation of starch.


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S. Sawada, M. Sato, A. Kasai, D. Yaochi, Y. Kameya, I. Matsumoto, and M. Kasai
Analysis of the Feed-Forward Effects of Sink Activity on the Photosynthetic Source-Sink Balance in Single-Rooted Sweet Potato Leaves. I. Activation of RuBPcase through the Development of Sinks
Plant Cell Physiol., February 15, 2003; 44(2): 190 - 197.
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