Overexpression of copper/zinc superoxide dismutase from mangrove Kandelia candel in tobacco enhances salinity tolerance by the reduction of reactive oxygen species in chloroplast

Xiaoshu Jing, Peichen Hou, Yanjun Lu, Shurong Deng, Niya Li, Rui Zhao, Jian Sun, Yang Wang, Yansha Han, Tao Lang, Mingquan Ding, Xin Shen, Shaoliang Chen

Na(+) uptake and transport in Kandelia candel and antioxidative defense were investigated under rising NaCl stress from 100 to 300 mM. Salinized K. candel roots had a net Na(+) efflux with a declined flux rate during an extended NaCl exposure. Na(+) buildup in leaves enhanced H2O2 levels, superoxide dismutase (SOD) activity, and increased transcription of CSD gene encoding a Cu/Zn SOD. Sequence and subcellular localization analyses have revealed that KcCSD is a typical Cu/Zn SOD in chloroplast. The transgenic tobacco experimental system was used as a functional genetics model to test the effect of KcCSD on salinity tolerance. KcCSD-transgenic lines were more Na(+) tolerant than wild-type (WT) tobacco in terms of lipid peroxidation, root growth, and survival rate. In the latter, 100 mM NaCl led to a remarkable reduction in chlorophyll content and a/b ratio, decreased maximal chlorophyll a fluorescence, and photochemical efficiency of photosystem II. NaCl stress in WT resulted from H2O2 burst in chloroplast. Na(+) injury to chloroplast was less pronounced in KcCSD-transgenic plants due to upregulated antioxidant defense. KcCSD-transgenic tobacco enhanced SOD activity by an increment in SOD isoenzymes under 100 mM NaCl stress from 24 h to 7 day. Catalase activity rose in KcCSD overexpressing tobacco plants. KcCSD-transgenic plants better scavenged NaCl-elicited reactive oxygen species (ROS) compared to WT ones. In conclusion, K. candel effectively excluded Na(+) in roots during a short exposure; and increased CSD expression to reduce ROS in chloroplast in a long-term and high saline environment.