在植物中,谷氨酰胺合成酶-谷氨酸合成酶(GS/GOGAT)循环在氮代谢中起着重要作用,增长,发展,和抗压力。过量的铵(NH4+)限制植物生长,但GS可以帮助缓解NH4+毒性。在这项研究中,在高NH4胁迫下,84K杨树(Populusalba×P.glandulosa)的生物量积累减少,叶片萎黄。在过表达编码谷氨酰胺合成酶(PagGS1;2-OE)的基因的细胞系中,这些症状不太严重,在抑制PagGS1;2表达(PagGS1;2-RNAi)的情况下更严重。与野生型(WT)相比,PagGS1;2-OE品系显示出显着增加的GS和GOGAT活性和较高的游离氨基酸含量,可溶性蛋白质,总氮,和高NH4+胁迫下的叶绿素。相比之下,在高NH4胁迫下,PagGS1;2-RNAi品系的抗氧化能力和NH4同化能力降低。在高NH4胁迫下,PagGS1;2-OE系的根和叶的总碳(C)含量和C/N比(C/N)显着高于WT。过表达PagGS1;2导致各种氨基酸(3-甲基天冬氨酸,谷氨酸,脯氨酸,丝氨酸,和组氨酸);碳水化合物含量降低(果糖,淀粉,半乳糖,葡萄糖1-磷酸,果糖6-磷酸);并增加糖醇的含量(景天庚糖,麦芽糖,甘露醇,半乳糖,山梨糖醇)在高NH4胁迫下的根部。在高NH4+压力下,与氨基酸生物合成相关的基因,蔗糖和淀粉降解,半乳糖代谢,抗氧化系统在PagGS1;2-OE品系的根部显著上调,与野生型相比。因此,PagGS1;2过表达影响高NH4+胁迫下的C代谢和氨基酸代谢途径,这有助于维持C和N代谢的平衡,缓解NH4+毒性症状。通过基因工程修饰GS/GOGAT循环是提高林木对NH4耐受性的有希望的策略。
The glutamine synthetase/glutamic acid synthetase (GS/GOGAT) cycle plays important roles in N metabolism, growth, development, and stress resistance in plants. Excess ammonium (NH4+) restricts growth, but GS can help to alleviate its toxicity. In this study, the 84K model clone of hybrid poplar (Populus alba × P. tremula var. glandulosa), which has reduced biomass accumulation and leaf chlorosis under high-NH4+ stress, showed less severe symptoms in transgenic lines overexpressing GLUTAMINE SYNTHETASE 1;2 (GS1;2-OE), and more severe symptoms in RNAi lines (GS1;2-RNAi). Compared with the wild type, the GS1;2-OE lines had increased GS and GOGAT activities and higher contents of free amino acids, soluble proteins, total N, and chlorophyll under high-NH4+ stress, whilst the antioxidant and NH4+ assimilation capacities of the GS1;2-RNAi lines were decreased. The total C content and C/N ratio in roots and leaves of the overexpression lines were higher under stress, and there were increased contents of various amino acids and sugar alcohols, and reduced contents of carbohydrates in the roots. Under high-NH4+ stress, genes related to amino acid biosynthesis, sucrose and starch degradation, galactose metabolism, and the antioxidant system were significantly up-regulated in the roots of the overexpression lines. Thus, overexpression of GS1;2 affected the carbon and amino acid metabolism pathways under high-NH4+ stress to help maintain the balance between C and N metabolism and alleviate the symptoms of toxicity. Modification of the GS/GOGAT cycle by genetic engineering is therefore a potential strategy for improving the NH4+ tolerance of cultivated trees.