Wang Feng, Gao Jingwen, Tian Zhongwei, Liu Yang, Abid Muhammad, Jiang Dong, Cao Weixing, Dai Tingbo
Key Laboratory of Crop Physiology, Ecology and Production Management, Nanjing Agricultural University, Nanjing, Jiangsu Province, 210095, PR China.
Key Laboratory of Crop Physiology, Ecology and Production Management, Nanjing Agricultural University, Nanjing, Jiangsu Province, 210095, PR China.
Plant Physiol Biochem. 2016 Nov;108:447-455. doi: 10.1016/j.plaphy.2016.08.011. Epub 2016 Aug 12.
Because soil acidification accompanies ammonium (NH) stress, the tolerance of higher plants to ammonium is associated with their adaptation to root medium acidification. However, the underlying mechanisms of this adaptation have not been fully elucidated. The objective of this study was thus to elucidate the effect of rhizosphere pH on NH tolerance in different winter wheat cultivars (Triticum aestivum L.). Hydroponic experiments were carried out on two wheat cultivars: AK58 (an NH-sensitive cultivar) and XM25 (an NH-tolerant cultivar). Four pH levels resembling acidified (4.0, 5.0, 6.0 and 7.0) were tested and 5 mM NH nitrogen (AN) was used as a stress treatment, with 5 mM nitrate nitrogen used as a control. The addition of AN led to a severe reduction in biomass and an increase in free NH, amino acids, and the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in the shoots and roots of the two wheat cultivars. Further decreases in growth medium pH led to further increases in free NH, but decreases in total amino acids and the activities of GS and NADH-dependent glutamate synthase (NADH-GDH). However, there was less of an increase in free NH and less of a reduction in the activities of GS and NADH-GDH in the cultivar XM25 compared with AK58. In addition, total soluble sugar content and the root-to-shoot soluble sugar ratio were also decreased by AN treatment, except in the shoots of XM25. Decreasing pH resulted in lower root-to-shoot soluble sugar ratios with greater reductions in the AK58 cultivar. These results indicate that wheat growth was inhibited significantly by the addition of NH combined with low pH. Low medium pH reduced the capacity for nitrogen assimilation and interrupted carbohydrate transport between the shoot and root. The NH-tolerant cultivar XM25 was better adapted to low rhizosphere pH due to its increased capacity for assimilating NH efficiently and thereby avoiding toxic levels of intracellular NH at low medium pH.
由于土壤酸化伴随着铵（NH）胁迫，高等植物对铵的耐受性与其对根系介质酸化的适应性相关。然而，这种适应的潜在机制尚未完全阐明。因此，本研究的目的是阐明根际pH对不同冬小麦品种（Triticum aestivum L.）铵耐受性的影响。对两个小麦品种进行了水培实验：AK58（铵敏感品种）和XM25（铵耐受品种）。测试了四种类似于酸化的pH水平（4.0、5.0、6.0和7.0），并使用5 mM铵态氮（AN）作为胁迫处理，以5 mM硝态氮作为对照。添加AN导致两个小麦品种地上部和根部的生物量严重降低，游离NH、氨基酸以及谷氨酰胺合成酶（GS）和谷氨酸脱氢酶（GDH）的活性增加。生长介质pH的进一步降低导致游离NH进一步增加，但总氨基酸以及GS和NADH依赖型谷氨酸合酶（NADH-GDH）的活性降低。然而，与AK58相比，XM25品种中游离NH的增加较少，GS和NADH-GDH的活性降低也较少。此外，AN处理还降低了总可溶性糖含量和根冠可溶性糖比，但XM25地上部除外。降低pH导致根冠可溶性糖比降低，AK58品种的降低幅度更大。这些结果表明，添加NH并结合低pH显著抑制了小麦生长。低介质pH降低了氮同化能力，并中断了地上部和根部之间的碳水化合物运输。铵耐受品种XM25由于其有效同化NH的能力增强，从而在低介质pH下避免细胞内NH达到有毒水平，因此对低根际pH具有更好的适应性。
