Abstract Ensuring global food security is a worldwide major concern considering the predicted climate change scenarios for the main agricultural regions of the world. Stomatal conductance (gs) and mesophyll conductance (gm) are major drivers limiting photosynthesis (A). Both conductances frequently impose about two-thirds of the total photosynthetic limitation under optimum conditions. However, under abiotic stress, like drought or salinity, the diffusional limitations can reach more than 85 % of the total. Thus, knowledge about both conductances is essential to improve water use efficiency (WUE) through targeted crop breeding programs and to promote sustainable, resource-efficient, and environmental-friendly agriculture strategies. Intriguingly, knowledge obtained from both conductances from decades of research differs importantly by their focus. Whilst the role of both mechanics and metabolism of guard cells on the regulation of stomatal movements remains much less understood, the signaling pathways that regulates stomatal movements are well-documented. The opposite is true for gm, in which the biochemical regulation and signaling pathways remain mostly still unexplored. Even more surprising is the lack of information about the putative molecular mechanisms that should drive the known coupled behavior of both conductances in response to the environment. Here, we discussed the main mechanisms driving the responses of each of the conductances, but highlighting a special focus into the possible common determinants that could link their coupled behavior. Further integrative multidisciplinary studies joining molecular biology and ecophysiology are required in order to improve our understanding of both conductances, the major actors limiting photosynthesis and WUE in a changing environment.

中文翻译：

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光合作用游戏处于“相互作用”中：二氧化碳在叶子中扩散的机制

摘要 考虑到世界主要农业地区的预测气候变化情景，确保全球粮食安全是一个世界性的主要问题。气孔导度 (gs) 和叶肉导度 (gm) 是限制光合作用 (A) 的主要驱动因素。在最佳条件下，两种电导率通常会施加大约三分之二的总光合限制。然而，在干旱或盐度等非生物胁迫下，扩散限制可达到总量的 85% 以上。因此，了解这两种电导对于通过有针对性的作物育种计划提高用水效率 (WUE) 以及促进可持续、资源高效和环境友好的农业战略至关重要。有趣的是，从几十年的研究中从两种电导中获得的知识在其侧重点上存在重大差异。虽然保卫细胞的力学和代谢在调节气孔运动方面的作用仍然知之甚少，但调节气孔运动的信号通路已得到充分证明。转基因的情况正好相反，其中的生化调控和信号通路大部分仍未被探索。更令人惊讶的是，缺乏关于应该驱动两种电导响应环境的已知耦合行为的假定分子机制的信息。在这里，我们讨论了驱动每个电导响应的主要机制，但特别关注可能将它们的耦合行为联系起来的可能的共同决定因素。