Department of Medical Biochemistry and Biophysics, Umeå University, 901 87 Umeå, Sweden.
Department of Environmental Systems Science, ETH Zürich, Universitätstrasse 2, 8092 Zürich, Switzerland.
J Exp Bot. 2021 Oct 26;72(20):7136-7144. doi: 10.1093/jxb/erab316.
Within the plant and Earth sciences, stable isotope analysis is a versatile tool conveying information (inter alia) about plant physiological and paleoclimate variability across scales. Here, we identify a 13C signal (i.e. systematic 13C/12C variation) at tree-ring glucose C-4 and report an experimentally testable theory on its origin. We propose the signal is introduced by glyceraldehyde-3-phosphate dehydrogenases in the cytosol of leaves. It conveys two kinds of (potentially convoluted) information: (i) commitment of glyceraldehyde 3-phosphate to 3-phosphoglycerate versus fructose 1,6-bisphosphate metabolism; and (ii) the contribution of non-phosphorylating versus phosphorylating glyceraldehyde-3-phosphate dehydrogenase to catalysing the glyceraldehyde 3-phosphate to 3-phosphoglycerate forward reaction of glycolysis. The theory is supported by 13C fractionation modelling. Modelling results provide the first evidence in support of the cytosolic oxidation-reduction (COR) cycle, a carbon-neutral mechanism supplying NADPH at the expense of ATP and NADH, which may help to maintain leaf-cytosolic redox balances. In line with expectations related to COR cycling, we found a positive correlation between air vapour pressure deficit and 13C discrimination at glucose C-4. Overall, 13C-4 signal analysis may enable an improved understanding of leaf carbon and energy metabolism.
在植物和地球科学领域，稳定同位素分析是一种多功能工具，可以提供有关植物生理和古气候变异性的信息（inter alia），涵盖多个尺度。在这里，我们在树木年轮葡萄糖 C-4 中发现了一种 13C 信号（即系统的 13C/12C 变化），并报告了一个可通过实验验证的起源理论。我们提出该信号是由细胞质中的甘油醛-3-磷酸脱氢酶引入的。它传递两种（可能复杂的）信息：（i）甘油醛 3-磷酸向 3-磷酸甘油酸的转化与果糖 1,6-二磷酸代谢的关系；（ii）非磷酸化与磷酸化甘油醛-3-磷酸脱氢酶对催化甘油醛 3-磷酸向 3-磷酸甘油酸的糖酵解正向反应的贡献。该理论得到了 13C 分馏模型的支持。模型结果提供了第一个支持细胞质氧化还原（COR）循环的证据，这是一种碳中性机制，以 ATP 和 NADH 的消耗为代价提供 NADPH，这可能有助于维持叶细胞质的氧化还原平衡。与 COR 循环相关的预期一致，我们发现空气蒸气压亏缺与葡萄糖 C-4 处的 13C 歧视之间存在正相关关系。总体而言，13C-4 信号分析可能有助于更好地理解叶片的碳和能量代谢。
