Tolerance Analysis Of Chloroplast OsCu/Zn-SOD Overexpressing Rice Under NaCl And NaHCO₃ Stress

SODs dismutate O2 into H2O2 and O2.In this study,the role of OsCu/Zn-SOD protein in plant response to saline-alkali stress was investigated.The 636-bp-long cDNA sequence of OsCu/Zn-SOD(AK059841)was cloned from Oryza sativa var.Longjingll via reverse transcription polymerase chain reaction(RT-PCR).The encoded protein comprised of 211 amino acids is highly homologous to Cu/Zn-SOD proteins from tuscacera rice and millet.Quantitative RT-PCR revealed that in rice,the level of OsCu/Zn-SOD gene expression was lowest in roots and was highest in petals and during the S5 leaf stage.Moreover,the expression level of OsCu/Zn-SOD gene expression decreased during the L5 leaf stage to maturity.The possible subcellular location of OsCu/Zn-SOD gene was predicted by TargetP software,and the location of OsCu/Zn-SOD subcell in chloroplast was determined by gene gun mediated transformation test and Arabidopsis transgenic with OsCu/Zn-SOD::GFP gene.The level of OsCu/Zn-SOD gene expression,however,was increased under NaCl stress and NaHCO3 stress.Germination tests under 125,150,and 175 mM NaCl revealed that OsCu/Zn-SOD-overexpressing lines performed better than the non-transgenic(NT)Longjingll lines in terms of germination rate and height.Subjecting seedlings to NaHCO3 and water stress revealed that OsCu/Zn-SOD overexpressing lines performed better than NT in terms of SOD activity,fresh weight,root length,and height.Under simulated saline-sodic stress,OsCu/Zn-SOD-overexpressing lines performed better than NT in terms of survival rate(25.19%>6.67%)and yield traits(average grain weight 20.6>18.15 g).This study showed that OsCu/Zn-SOD gene overexpression increases the detoxification capacity of reactive oxygen species and reduces oxidative damage induced by alkaline salt stress in rice.It is speculated that it may affect the stress resistance of rice by alleviating the secondary oxidative stress caused by saline-alkali stress.