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

doi:10.3389/fpls.2015.00023

Abstract

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.

Highlights

NaCl-exposed plants accumulate a high level of Na+ in roots and leaves regardless of Na+-resistant or -sensitive species (Chen and Polle, 2010; Polle and Chen, 2014)
This study has revealed that K. candel has different physiological mechanisms to adapt to NaCl stress (Figure 12)
As shown in the schematic model, K. candel roots could maintain a high capacity to extrude Na+ via a PM Na+/H+ antiport system driven by H+-ATPase

Summary

Introduction

NaCl-exposed plants accumulate a high level of Na+ in roots and leaves regardless of Na+-resistant or -sensitive species (Chen and Polle, 2010; Polle and Chen, 2014). To avoid excessive buildup of Na+, non-secretor mangrove species (Kandelia candel) can maintain a high capacity to restrict Na+. Its roots and shoots could accumulate large amount of Na+ under a long-term of increasing salinity (Li et al, 2008). This implies that the capacity for Na+ exclusion decreased in salinized roots

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