Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
Plant Cell Environ. 2013 Jan;36(1):200-12. doi: 10.1111/j.1365-3040.2012.02567.x. Epub 2012 Jul 23.
Photosynthetic carbon gain in plants using the C(3) photosynthetic pathway is substantially inhibited by photorespiration in warm environments, particularly in atmospheres with low CO(2) concentrations. Unlike C(4) plants, C(3) plants are thought to lack any mechanism to compensate for the loss of photosynthetic productivity caused by photorespiration. Here, for the first time, we demonstrate that the C(3) plants rice and wheat employ a specific mechanism to trap and reassimilate photorespired CO(2) . A continuous layer of chloroplasts covering the portion of the mesophyll cell periphery that is exposed to the intercellular air space creates a diffusion barrier for CO(2) exiting the cell. This facilitates the capture and reassimilation of photorespired CO(2) in the chloroplast stroma. In both species, 24-38% of photorespired and respired CO(2) were reassimilated within the cell, thereby boosting photosynthesis by 8-11% at ambient atmospheric CO(2) concentration and 17-33% at a CO(2) concentration of 200 µmol mol(-1) . Widespread use of this mechanism in tropical and subtropical C(3) plants could explain why the diversity of the world's C(3) flora, and dominance of terrestrial net primary productivity, was maintained during the Pleistocene, when atmospheric CO(2) concentrations fell below 200 µmol mol(-1) .
在温暖的环境中，植物的光合作用会受到光呼吸的显著抑制，尤其是在 CO2 浓度较低的大气中。与 C4 植物不同，C3 植物被认为缺乏任何补偿光呼吸导致的光合作用生产力损失的机制。在这里，我们首次证明，C3 植物水稻和小麦采用了一种特殊的机制来捕获和再同化光呼吸释放的 CO2。覆盖暴露于细胞间隙的部分叶肉细胞周边的连续叶绿体层为离开细胞的 CO2 形成扩散屏障。这有助于在叶绿体基质中捕获和再同化光呼吸释放的 CO2。在这两个物种中，24-38%的光呼吸和呼吸释放的 CO2在细胞内被再同化，从而在环境大气 CO2 浓度下提高光合作用 8-11%，在 200 μmol mol(-1)的 CO2 浓度下提高 17-33%。这种机制在热带和亚热带 C3 植物中的广泛应用可以解释为什么在大气 CO2 浓度低于 200 μmol mol(-1)的更新世期间，世界 C3 植物群的多样性和陆地净初级生产力的主导地位得以维持。
