Relationship Between AtArgAH1,AtArgAH2 Gene And Salt Tolerance In Arabidopsis Thaliana

Saline-alkali soils severely restrict plant growth,development and biological production,which are also the main factors affecting the ecological environment and agricultural production.Therefore,the study of the molecular response mechanism of plants under salt stress is an important subject in biological research and has important significance.Our previous experiments in the study of the relationship between nitrogen metabolism and plant salt stress showed that at the germination stage,urease deletion mutants and over-expressing glutamine synthetase(AtGSI.1)genes can be increased the plant's tolerance to salt stress and the significant reduction NH4+ content compared to wild-type Arabidopsis thaliana(WT),suggest that nitrogen metabolism(especially urea metabolism)is closely related to plant salt tolerance.Arginase is the key enzyme in the urea metabolism pathway for the hydrolysis of arginine to urea.This study further investigated the relationship between Arabidopsis arginase(AtArgAH1 and AtArgAH2)genes and plant salt tolerance.The specific findings are as follows:First,this study systematically analyzed the expression characteristics of AtArgAHl and AtArgAH2 genes.Through tissue-specific expression analysis,it was found that AtArgAHl had the highest expression level in roots and AtArgAH2 had the highest expression level in fruiting pods at maturity.At the same time,the expression of AtArgAHl and AtArgAH2 was found to be different by abiotic stress treatment.The expression of AtArgAHl and AtArgAH1 in cotyledons and roots was consistent under NaCl salt treatment,but the expression of AtArgAH2 was higher than that of AtArgAH1.AtArgAH1 and AtArgAH2 were up-regulated and down-regulated in cotyledons under different concentrations of NH4CI.Under different concentrations of Urea stress,AtArgAH1 was up-regulated in the cotyledons and down-regulated in roots,while AtArgAH2 was reversed.Under different concentrations of Arginine stress,the expression of AtArgAHl was higher than that of AtArgAH2.In order to understand the function of the arginase gene,the phenotypes of the mutants under different treatment conditions were analyzed.By analyzing the growth and content of WT,argahl and argah2 under different nitrogen treatments,the growth potential of argahl was significantly inhibited compared with that of WT and argah2 when Arginine was the sole nitrogen source,and the content of NH4+ was significantly lower than that of WT and argah2.However,when Urea was the sole nitrogen source,the growth potential of argah2 was significantly inhibited compared with WT and argahl,and the content of NH4+ in the body was significantly lower than that of WT and argahl.The above results suggest that argah1 cannot use exogenous Arginine as the sole nitrogen source and argah2 cannot use the exogenous Urea as the only N source.The activity of arginase was blocked by adding arginase activity inhibitor under salt stress.The seed germination of WT under salt stress could be significantly increased with the increase of inhibitor concentration,and it could significantly reduce WT NH4+ content in vivo.At the same time,under the high salt treatment,argah1 and argah2 had better growth potential than WT,and cotyledon and root urea and NH4+ content were significantly lower than WT.By investigating the arginase action time under salt stress,it was found that two arginase deletion mutants were significantly superior to WT in growth and root length with the prolongation of treatment time before low temperature vernalization for 48h;After 48 hours of vernalization,normal light culture showed that there was no significant difference in growth and root length between WT,argahl and argah2 with the prolonged illumination.Studies on the effects of argahl and argah2 on arginine metabolism-related enzyme(arginine decarboxylase:ADC and nitric oxide synthase:NOS)gene expression found that ADC1,ADC2;and NOS enzyme activities in argah1 and argah2 are not the same in vivo under norma1 conditions.Under salt stress,the expression of ADC1,ADC2,and NOS in argahl and argah2 were significantly increased compared with normal conditions.These results imply that ADC and NOS are also involved in their response under salt stress.The above results indicate that Arabidopsis two arginase genes(AtArgAHl and AtArgAH2)expression have a certain response relationship with salt stress and different forms of nitrogen(Arginine and Urea),and the results of phenotypic analysis of argah1 and argah2 mutants under different treatment conditions also further suggested that nitrogen metabolism(especially urea metabolism)is closely related to the salt tolerance of plants,which will lay a theoretical foundation for further exploring the salt tolerance mechanism of plant seeds at the germination stage.