Institut de Biotechnologie des Plantes, Université de Paris sud XI, UMR CNRS 8618, Orsay, France.
Planta. 2010 Apr;231(5):1145-57. doi: 10.1007/s00425-010-1117-x. Epub 2010 Feb 25.
Environmental controls on leaf NAD status remain poorly understood. Here, we analyzed the effects of two key environmental variables, CO(2) and nitrogen, on leaf metabolite profiles, NAD status and the abundance of key transcripts involved in de novo NAD synthesis in wild-type (WT) Nicotiana sylvestris and the CMSII mutant that lacks respiratory complex I. High CO(2) and increased N supply both significantly enhanced NAD(+) and NADH pools in WT leaves. In nitrogen-sufficient conditions, CMSII leaves were enriched in NAD(+) and NADH compared to the WT, but the differences in NADH were smaller at high CO(2) than in air because high CO(2) increased WT NADH/NAD(+). The CMSII-linked increases in NAD(+) and NADH status were abolished by growth with limited nitrogen, which also depleted the nicotine and nicotinic acid pools in the CMSII leaves. Few statistically significant genotype and N-dependent differences were detected in NAD synthesis transcripts, with effects only on aspartate oxidase and NAD synthetase mRNAs. Non-targeted metabolite profiling as well as quantitative amine analysis showed that NAD(+) and NADH contents correlated tightly with leaf amino acid contents across all samples. The results reveal considerable genotype- and condition-dependent plasticity in leaf NAD(+) and NADH contents that is not linked to modified expression of NAD synthesis genes at the transcript level and show that NAD(+) and NADH contents are tightly integrated with nitrogen metabolism. A regulatory two-way feedback circuit between nitrogen and NAD in the regulation of N assimilation is proposed that potentially links the nutritional status to NAD-dependent signaling pathways.
环境对叶片 NAD 状态的控制仍知之甚少。在这里，我们分析了两个关键环境变量，CO2 和氮，对野生型（WT）Nicotiana sylvestris 和缺乏呼吸复合物 I 的 CMSII 突变体叶片代谢物谱、NAD 状态以及新 NAD 合成关键转录物丰度的影响。高 CO2 和增加氮供应都显著增加了 WT 叶片中的 NAD(+)和 NADH 池。在氮充足的条件下，CMSII 叶片中 NAD(+)和 NADH 含量比 WT 更丰富，但在高 CO2 下的差异比在空气中小，因为高 CO2 增加了 WT 的 NADH/NAD(+)。在氮有限的条件下生长，CMSII 叶片中 NAD(+)和 NADH 状态的增加被消除，这也使 CMSII 叶片中的尼古丁和烟酸池枯竭。在 NAD 合成转录物中，只有少数与基因型和氮依赖性相关的统计显著差异，其作用仅在天冬氨酸氧化酶和 NAD 合成酶 mRNA 上。非靶向代谢物谱分析以及定量胺分析表明，NAD(+)和 NADH 含量与所有样品的叶片氨基酸含量密切相关。结果表明，叶片 NAD(+)和 NADH 含量存在相当大的基因型和条件依赖性可塑性，这与转录水平上 NAD 合成基因表达的改变无关，并表明 NAD(+)和 NADH 含量与氮代谢紧密结合。提出了一个氮和 NAD 之间在氮同化调控中的双向反馈回路的调控假说，该假说可能将营养状况与 NAD 依赖性信号通路联系起来。
