Plants mainly acquire N from the soil in the form of nitrate (NO3 -) or ammonium (NH4 +). Ammonium-based nutrition is gaining interest because it helps to avoid the environmental pollution associated with nitrate fertilization. However, in general, plants prefer NO3 - and indeed, when growing only with NH4 + they can encounter so-called ammonium stress. Since Brachypodium distachyon is a useful model species for the study of monocot physiology and genetics, we chose it to characterize performance under ammonium nutrition. Brachypodium distachyon Bd21 plants were grown hydroponically in 1 or 2.5 mM NO3 - or NH4 +. Nitrogen and carbon metabolism associated with NH4 + assimilation was evaluated in terms of tissue contents of NO3 -, NH4 +, K, Mg, Ca, amino acids and organic acids together with tricarboxylic acid (TCA) cycle and NH4 +-assimilating enzyme activities and RNA transcript levels. The roots behaved as a physiological barrier preventing NH4 + translocation to aerial parts, as indicated by a sizeable accumulation of NH4 +, Asn and Gln in the roots. A continuing high NH4 + assimilation rate was made possible by a tuning of the TCA cycle and its associated anaplerotic pathways to match 2-oxoglutarate and oxaloacetate demand for Gln and Asn synthesis. These results show B. distachyon to be a highly suitable tool for the study of the physiological, molecular and genetic basis of ammonium nutrition in cereals.

中文翻译：

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提供碳骨架以维持根中的酰胺合成，突显了短芽孢杆菌适合研究谷物中的铵态氮胁迫。

植物主要从土壤中以硝酸盐（NO3-）或铵盐（NH4 +）的形式获取氮。铵基营养日益受到关注，因为它有助于避免与硝酸盐施肥有关的环境污染。但是，总的来说，植物更喜欢NO3-实际上，当仅用NH4 +种植时，它们会遇到所谓的铵胁迫。由于短枝曲霉是研究单子叶植物生理和遗传学的有用模式物种，因此我们选择它来表征铵营养条件下的性能。短枝曲霉Bd21植物在1或2.5 mM NO3--或NH4 +中水培生长。根据组织中NO3-，NH4 +，K，Mg，Ca，N的含量评估与NH4 +同化相关的氮和碳代谢 氨基酸和有机酸以及三羧酸（TCA）循环和NH4 +同化酶活性以及RNA转录水平。根部表现为生理屏障，可阻止NH4 +易位到地上部分，这是由NH4 +，Asn和Gln在根部大量积累所表明的。通过调整TCA循环及其相关的过失途径，可以实现持续较高的NH4 +同化率，以匹配Gln和Asn合成的2-氧戊二酸和草酰乙酸的需求。这些结果表明，B。distachyon是研究谷物中铵态营养的生理，分子和遗传基础的高度合适的工具。根中有Asn和Gln。通过调整TCA循环及其相关的过失途径，可以实现持续较高的NH4 +同化率，以匹配Gln和Asn合成的2-氧戊二酸和草酰乙酸的需求。这些结果表明，B。distachyon是研究谷物中铵态营养的生理，分子和遗传基础的高度合适的工具。根中有Asn和Gln。通过调整TCA循环及其相关的过失途径，可以实现持续较高的NH4 +同化率，以匹配Gln和Asn合成的2-氧戊二酸和草酰乙酸的需求。这些结果表明，B。distachyon是研究谷物中铵态营养的生理，分子和遗传基础的高度合适的工具。