Abstract:Arabidopsis wild type Col-0, glutamine synthetase knockout mutants gs1.1 and gs1.2 were used as experimental materials, pot experiments were conducted to compare the effects of normal culture solution (4 mmol/L NH4+) (CK), the normal culture solution (4 mmol/L NH4+) plus additional 5% sucrose (T1), high NH4+stress (20 mmol/L) (T2), and high NH4+stress plus additional 5% sucrose (T3) on physiological indexes of the three Arabidopsis thaliana lines. By measuring the fresh weight of the aerial part, chlorophyll, free NH4+, soluble sugar, soluble protein, glutamine synthetase (GS), glutamate dehydrogenase (GDH), and mineral element contents, the effects of exogenous sucrose on carbon and nitrogen metabolism in Arabidopsis thaliana under high NH4+stress were preliminarily studied. The results demonstrated that Arabidopsis growth was severely inhibited under high NH4+stress. The fresh weight, the activities of GS and GDH decreased, while the contents of free NH4+, chlorophyll, soluble sugar and soluble protein increased, the contents of N, P, K and Ca in the plant increased, and the contents of Mg and Fe decreased. The inhibitory effects of gs1.1 and gs1.2 mutants under high NH4+were more significant than the wild type. Exogenous addition of 5% sucrose significantly alleviated high NH4+toxicity, with increased soluble sugar and protein contents, and enhanced the activities of GS and GDH. The contents of chlorophyll and free NH4+were reduced. The contents of N, P, K, Ca and Mg in the plant were increased while the content of Fe was reduced. The exogenous sucrose is more significant in alleviation of high NH4+toxicity of gs1.1 and gs1.2 than the wild type.