Experimental research into guard cell metabolism has revealed the roles of the accumulation of various metabolites in guard cell function, but a comprehensive understanding of their metabolism over the diel cycle is still incomplete due to the limitations of current experimental methods. In this study we constructed a four‐phase flux balance model of guard cell metabolism to investigate the changes in guard cell metabolism over the diel cycle, including the day and night and stomatal opening and closing. Our model predicted metabolic flexibility in guard cells of C₃ plants, showing that multiple metabolic processes can contribute to the synthesis and metabolism of malate and sucrose as osmolytes during stomatal opening and closing. Our model showed the possibility of guard cells adapting to varying light availability and sucrose uptake from the apoplast during the day by operating in a mixotrophic mode with a switch between sucrose synthesis via the Calvin–Benson cycle and sucrose degradation via the oxidative pentose phosphate pathway. During stomatal opening, our model predicted an alternative flux mode of the Calvin–Benson cycle with all dephosphorylating steps diverted to diphosphate–fructose‐6‐phosphate 1‐phosphotransferase to produce inorganic pyrophosphate, which is used to pump protons across the tonoplast for the accumulation of osmolytes. An analysis of the energetics of the use of different osmolytes in guard cells showed that malate and Cl⁻ are similarly efficient as the counterion of K⁺ during stomatal opening.

中文翻译：

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多相通量平衡模型揭示了C3植物保卫细胞中央碳代谢的灵活性

对保卫细胞代谢的实验研究已经揭示了各种代谢物的积累在保卫细胞功能中的作用，但是由于当前实验方法的局限性，对它们在狄尔循环中的代谢的全面了解仍然不完整。在这项研究中，我们构建了保卫细胞代谢的四阶段通量平衡模型，以研究保卫细胞代谢在整个昼夜周期中的变化，包括昼夜和气孔的打开和关闭。我们的模型预测了C ₃保卫细胞的代谢灵活性植物，表明在气孔打开和关闭过程中，多种代谢过程可以作为渗透压促进苹果酸和蔗糖的合成和代谢。我们的模型显示了保卫细胞有可能通过以混合营养模式运行，并在通过Calvin-Benson循环的蔗糖合成与通过氧化戊糖磷酸途径的蔗糖降解之间进行切换，来适应白天不同的光利用率和从质外体摄取的蔗糖。在气孔开放期间，我们的模型预测了Calvin-Benson循环的替代通量模式，所有去磷酸化步骤均转移至二磷酸-果糖-6-磷酸1-磷酸转移酶以产生无机焦磷酸，该焦磷酸用于将质子泵送到质膜上进行积累渗透压。⁻在气孔开放期间的效率与K ⁺的抗衡离子相似。