Tissue and canopy-level evidence suggests that elevated carbon dioxide (EC) inhibits shoot nitrate assimilation in plants and thereby affects nitrogen (N) and protein content of the economic produce. It is speculated that species or genotypes relying more on root nitrate assimilation can adapt better under EC due to the improved/steady supply of reductants required for nitrate assimilation. A study was conducted to examine the effect of EC on N assimilation and associated gene expression in wheat seedlings. Wheat genotypes, BT-Schomburgk (BTS) with comparatively high leaf nitrate reductase (NR) activity and Gluyas Early (GE) with high root NR activity were grown in hydroponic culture for 30 days with two different nitrate levels (0.05 mM and 5 mM) in the climate controlled growth chambers maintained at either ambient (400 ± 10 μmol mol −1 ) or EC (700 ± 10 μmol mol −1 ) conditions. Exposure to EC downregulated the activity of enzyme NR and glutamate synthase (GOGAT) in leaf tissues, whereas in roots, activities of both the enzymes were upregulated by exposure to EC. In addition, EC downregulated N assimilation and signalling gene expression under high N availability. Root N assimilation was less affected in comparison with shoot N assimilation; thereby, the proportion of root contribution towards total assimilation was higher. The results suggest that EC could alter and re-programme N assimilation and signalling in wheat seedlings. The genotype and tissue-specific effects of EC on N assimilation also warrants the need for identification of suitable genotypes and revision of fertiliser regime for tapping the beneficial effects of EC conditions.

中文翻译：

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升高的二氧化碳改变氮代谢的组织平衡并下调接受高硝酸盐供应的小麦幼苗的氮同化和信号基因表达

组织和冠层水平的证据表明，二氧化碳 (EC) 升高会抑制植物中硝酸盐的同化作用，从而影响经济产品的氮 (N) 和蛋白质含量。据推测，由于硝酸盐同化所需的还原剂的改善/稳定供应，更多依赖根硝酸盐同化的物种或基因型可以更好地适应 EC。进行了一项研究，以检查 EC 对小麦幼苗中 N 同化和相关基因表达的影响。小麦基因型、具有较高叶片硝酸还原酶 (NR) 活性的 BT-Schomburgk (BTS) 和具有高根 NR 活性的 Gluyas Early (GE) 在两种不同硝酸盐水平 (0. 05 mM 和 5 mM) 在维持在环境 (400 ± 10 μmol mol -1 ) 或 EC (700 ± 10 μmol mol -1 ) 条件下的气候控制生长室中。暴露于 EC 会下调叶组织中酶 NR 和谷氨酸合酶 (GOGAT) 的活性，而在根中，暴露于 EC 会上调这两种酶的活性。此外，EC 在高 N 可用性下下调 N 同化和信号基因表达。根系氮的同化比茎的氮同化影响更小；因此，根对总同化的贡献比例更高。结果表明，EC 可以改变和重新编程小麦幼苗中的 N 同化和信号传导。