Physiological and molecular mechanisms of oxidative stress tolerance in mutant genotypes of rice (Oryza sativa L. cv. Hashemi) under salt stress conditions

Soil salinity is one of the environmental stresses that causes the accumulation of reactive oxygen species (ROS), and oxidative stress, and consequently, reduces crop growth and production. Antioxidative mechanisms are critical to protect cells from the adverse effects of ROS.

Thhis study was conducted in nutrient solution in Rice Research Institute of Iran, Rasht, Iran in 2019. The enzymatic activity and expression of effective genes on antioxidant defense were examined in two selected mutant genotypes (em3hs290 and em3hs84) tolerant to salinity stress, with Hashemi local cultivar, FL478 (tolerant) and IR28 (sensitive) genotypes. Biochemical traits including the activity of antioxidant enzymes, peroxidase, catalase, and ascorbate peroxidase, and the relative expression of genes encoding transcription factors (SNACI, DREB2B, and DREB2A) and genes associated with oxidative stress (OsAOX1C ،POX1، OsGR1، OsAPX2 and OsGPX1) were also measured and detected using real-time PCR technique.

The results showed that enzymatic activity of peroxidase (POX) in control cultivars (cv. Hashemi and IR28 cultivars) and ascorbate peroxidase (APX) in tolerant mutant genotypes and FL478 cultivar increased significantly. The genes expression associated with salinity stress tolerance also indicated that despite the variable behavior of the genes in the studied mutant genotypes, the expression of OSGR1, DREB2B, OsAOX1C and POX1  genes in studied tolerant mutants was more than susceptible cultivar. Transcript abundance of the OsAPX2 gene was significantly higher in salt-tolerant genotypes under short-term salinity stress and correlated with peroxide hydrogen removal and increased activity of ascorbate peroxidase enzyme.

The lack of similarity in the expression pattern of studied genes between the two salt-tolerant mutant genotypes (em4hs290 and em4hs84)  and  cv. Hashemi showed that the mutation could triger the salt-tolerance mechanisms in mutant genotypes, in comparison of cv. Hashemi, through emhancement of antioxidant enzymes activity in response to salt stress. It seemes that the mutant genotypes may have suitable growth in soil salinity conditions.