Evidence for the Occurrence of Feedback Inhibition of Photosynthesis in Rice

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The response of photosynthesis in the flag leaf of rice (Oryza sativa) to elevated CO_2 or reduced O_2 was investigated relative to other environmental factors using steady-state gas exchange techniques. We found under moderate conditions of temperature and photosynthetic flux density (PFD) (26℃ and 700 μmol quanta m^<-2> s^<-1> similar to growth conditions) photosynthesis in the flag leaf of rice during heading and grain filling saturated at near ambient levels of CO_2, with a concomitant loss of O_2 sensitivity, when a high stomatal conductance was maintained by high humidity (low vapor pressure deficit). Under 18℃ there was near complete loss of O_2 sensitivity of photosynthesis at normal ambient levels of CO_2. This is in contrast to the large enhancement of photosynthesis by supra-atmospheric levels of CO_2 and sub-atmospheric levels of O_2 by suppression of photorespiration when there is no limitation on utilizing the initial product of CO_2 assimilation (triose-P) as predicted from Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) kinetic properties. Thus, loss of sensitivity to CO_2 and O_2 has been previously explained as a limitation on utilization of triose-P to synthesize carbohydrates. Under high PFD at 25℃, the rate of photosynthesis in rice declined over a period of hours around midday, while the intercellular levels of CO_2 remained constant suggesting a limitation on utilization of photosynthate. Short-term fluctuations in climatic factors including temperature, light and humidity could result in a feedback limitation on photosynthesis in rice which may be exacerbated by rising CO_2.
日本植物生理学会の論文

Evidence for the Occurrence of Feedback Inhibition of Photosynthesis in Rice

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