Department of Crop Sciences, Section for Plant Nutrition and Crop Physiology, Faculty of Agriculture, University of Goettingen, Carl-Sprengel-Weg 1, 37075 Goettingen, Germany.
Department of Crop Sciences, Section for Quality of Plants Products, Faculty of Agriculture, University of Goettingen, Carl-Sprengel-Weg 1, 37075 Goettingen, Germany.
Plant Sci. 2020 Mar;292:110383. doi: 10.1016/j.plantsci.2019.110383. Epub 2019 Dec 19.
Symbiotic nitrogen fixation (SNF) has a high energetic cost for legume plants; legumes thus reduce SNF when soil N is available. The present study aimed to increase our understanding regarding the impacts of the two principal forms of available N in soils (ammonium and nitrate) on SNF. We continuously measured the SNF of Medicago truncatula under controlled conditions. This permitted nodule sampling for comparative transcriptome profiling at points connected to the nodules' reaction following ammonium or nitrate applications. The N component of both ions systemically induced a rhythmic pattern of SNF, while the activity in control plants remained constant. This rhythmic activity reduced the per-day SNF. The nitrate ion had additional local effects; the more pronounced were a strong downregulation of leghaemoglobin, nodule cysteine-rich (NCR) peptides and nodule-enhanced nicotianamine synthase (neNAS). The neNAS has proven to be of importance for nodule functioning. Although other physiological impacts of nitrate on nodules were observed (e.g. nitrosylation of leghaemoglobin), the main effect was a rapid ion-specific and organ-specific change in gene expression levels. Contrastingly, during the first hours after ammonium applications, the transcriptome remained virtually unaffected. Therefore, nitrate-induced genes could be key for increasing the nitrate tolerance of SNF.
共生固氮 (SNF) 对豆科植物来说具有很高的能量成本；因此，当土壤中的氮可用时，豆科植物会减少 SNF。本研究旨在更深入地了解土壤中两种主要形式的可用氮（铵和硝酸盐）对 SNF 的影响。我们在受控条件下连续测量了蒺藜苜蓿的 SNF。这使得可以在与铵或硝酸盐处理后结节反应相关的时间点对结节进行采样，以进行比较转录组分析。两种离子的 N 成分都系统地诱导了 SNF 的节律性模式，而对照植物的活性保持不变。这种节律性活动降低了每日 SNF。硝酸盐离子还有其他局部效应；更为明显的是强烈下调了豆血红蛋白、结瘤富含半胱氨酸 (NCR) 肽和结瘤增强烟酰胺合成酶 (neNAS)。已经证明 neNAS 对结节的功能很重要。尽管观察到硝酸盐对结节的其他生理影响（例如豆血红蛋白的亚硝化），但主要影响是基因表达水平的快速离子特异性和器官特异性变化。相比之下，在铵处理后的最初几个小时内，转录组几乎没有变化。因此，硝酸盐诱导的基因可能是提高 SNF 对硝酸盐耐受性的关键。
