A Diel Flux Balance Model Captures Interactions between Light and Dark Metabolism during Day-Night Cycles in C3 and Crassulacean Acid Metabolism Leaves
A Diel Flux Balance Model Captures Interactions between Light and Dark Metabolism during Day-Night Cycles in C3 and Crassulacean Acid Metabolism Leaves
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DOI：
10.1104/pp.113.234468
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发表时间：
2014-06-01
期刊：
影响因子：
7.4
通讯作者：
Sweetlove, Lee J.
中科院分区：
文献类型：
--
作者：
Cheung, C. Y. Maurice;Poolman, Mark G.;Sweetlove, Lee J.
虽然叶片必须适应显着不同的代谢通量模式在光明和黑暗中，叶片代谢模型的基础上通量平衡分析（FBA）到目前为止，已被限制在考虑网络连续光照下。一个FBA框架，解决了两个阶段的昼夜循环作为一个单一的优化问题，因此，提供了一个更有代表性的叶片代谢模型。为了支持夜间从叶子中持续输出糖和氨基酸，并满足过夜细胞维持成本的要求，迫使模型在白天留出碳和氮的储存。只有最小的限制，该模型成功地捕捉了许多已知的功能的C-3叶代谢，包括最近发现的柠檬酸合成和积累的作用，在夜间作为前体提供碳骨架的氨基酸合成在白天。昼夜FBA模型可以应用于其他时间的分离，如发生在景天科酸代谢（CAM）光合作用，允许CAM的能量学的系统级分析。昼夜模型预测，有没有整体的能量优势CAM，尽管通过CO2浓度抑制光呼吸的潜力。此外，通过抑制光呼吸而节省的酶机械成本可能会被CAM循环的更高通量需求所抵消。它的结论是，精力充沛或氮的使用考虑是不太可能的CAM光合作用的进化驱动程序。
Although leaves have to accommodate markedly different metabolic flux patterns in the light and the dark, models of leaf metabolism based on flux-balance analysis (FBA) have so far been confined to consideration of the network under continuous light. An FBA framework is presented that solves the two phases of the diel cycle as a single optimization problem and, thus, provides a more representative model of leaf metabolism. The requirement to support continued export of sugar and amino acids from the leaf during the night and to meet overnight cellular maintenance costs forces the model to set aside stores of both carbon and nitrogen during the day. With only minimal constraints, the model successfully captures many of the known features of C-3 leaf metabolism, including the recently discovered role of citrate synthesis and accumulation in the night as a precursor for the provision of carbon skeletons for amino acid synthesis during the day. The diel FBA model can be applied to other temporal separations, such as that which occurs in Crassulacean acid metabolism (CAM) photosynthesis, allowing a system-level analysis of the energetics of CAM. The diel model predicts that there is no overall energetic advantage to CAM, despite the potential for suppression of photorespiration through CO2 concentration. Moreover, any savings in enzyme machinery costs through suppression of photorespiration are likely to be offset by the higher flux demand of the CAM cycle. It is concluded that energetic or nitrogen use considerations are unlikely to be evolutionary drivers for CAM photosynthesis.