Department of Plant Sciences, University of Cambridge, Downing street, Cambridge, UK.
Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
J Exp Bot. 2020 Jan 1;71(1):318-329. doi: 10.1093/jxb/erz442.
Improving photosynthetic efficiency is widely regarded as a major route to achieving much-needed yield gains in crop plants. In plants with C3 photosynthesis, increasing the diffusion conductance for CO2 transfer from substomatal cavity to chloroplast stroma (gm) could help to improve the efficiencies of CO2 assimilation and photosynthetic water use in parallel. The diffusion pathway from substomatal cavity to chloroplast traverses cell wall, plasma membrane, cytosol, chloroplast envelope membranes, and chloroplast stroma. Specific membrane intrinsic proteins of the aquaporin family can facilitate CO2 diffusion across membranes. Some of these aquaporins, such as PIP1;2 in Arabidopsis thaliana, have been suggested to exert control over gm and the magnitude of the CO2 assimilation flux, but the evidence for a direct physiological role of aquaporins in determining gm is limited. Here, we estimated gm with four different methods under a range of light intensities and CO2 concentrations in two previously characterized pip1;2 knock-out lines as well as pip1;3 and pip2;6 knock-out lines, which have not been previously evaluated for a role in gm. This study presents the most in-depth analysis of gm in Arabidopsis aquaporin knock-out mutants to date. Surprisingly, all methods failed to show any significant differences between the pip1;2, pip1;3, or pip2;6 mutants and the Col-0 control.
提高光合作用效率被广泛认为是实现作物产量急需增长的主要途径。在具有 C3 光合作用的植物中，增加从叶肉细胞间隙到叶绿体基质的 CO2 转移的扩散导度（gm），可以帮助平行提高 CO2 同化和光合作用用水的效率。从叶肉细胞间隙到叶绿体的扩散途径穿过细胞壁、质膜、细胞质、叶绿体被膜和叶绿体基质。水通道蛋白家族的特定膜内在蛋白可以促进 CO2 在膜间的扩散。其中一些水通道蛋白，如拟南芥中的 PIP1;2，被认为对 gm 和 CO2 同化通量的大小有控制作用，但水通道蛋白在决定 gm 方面的直接生理作用的证据有限。在这里，我们在两个先前表征的 pip1;2 敲除系以及尚未评估其在 gm 中作用的 pip1;3 和 pip2;6 敲除系中，在一系列光强和 CO2 浓度下，用四种不同的方法来估计 gm。本研究对拟南芥水通道蛋白敲除突变体中的 gm 进行了迄今为止最深入的分析。令人惊讶的是，所有方法都未能显示出 pip1;2、pip1;3 或 pip2;6 突变体与 Col-0 对照之间存在任何显著差异。
