| Summary: In our study, to shed light on the potential relationship with SOS5, ROS and ABA metabolism in Arabidopsis thaliana, lipid peroxidation, prolin and hydrogen peroxide (H2O2) contents were determined. Furthermore, antioxidant enzyme activities such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) were determined with ABA treatment under salt stress. Under salt stress to establish the relationship of SOS5 with genetic regulators which have a role in ABA response, double mutants were obtained. To enlighten the SOS5 relationships with some genes that induced in response to abiotic stresses, expression level of genes were checked. It was found that ABA fully suppressed salt overly sensitive root phenotype of sos5 under salt stress conditions and sos5 seed germination rates were higher compared to the wild type. On the other hand, it was found that under salt stress conditions endogenous H2O2 content increased in mutant plants. With the application of ABA under salt stress while raises in prolin content, APX, CAT and GPX activities were observed, SOD activity and in particular MDA content reduction at mutant roots were recorded. Under salt stress conditions it was found that sos5 root phenotype was enhanced by abi4-1 mutations but suppressed by cpl1-1 and sad1-1. In sos5 mutant that exposed to salt stress, decrease in expression were found in genes. According to the findings, under salt stress SOS5 gene acts synergistic with ABI4 gene and antagonistic with CPL1, SAD1 genes in roots. In conclusion, this suggests that SOS5 gene acts as a positive regulator of ABA and stimulate some tolerance mechanisms.
Key Words: Arabidopsis thaliana; sos5 mutant, ABA signalization, antioxidant system, salt stress, gene expression
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