Efficient regulation of arsenic translocation to shoot tissue and modulation of phytochelatin levels and antioxidative defense system confers salinity and arsenic tolerance in the Halophyte Suaeda maritima

Abstract

Salinity and heavy metal contaminations of the soil are the major environmental factors deleteriously affecting the agricultural yield. Suaeda maritima (L.) Dumort is a halophytic species that grows proficiently in high saline coastal areas. In the present study, individual effects of various levels of salinity (0, 200 and 600mM NaCl) and arsenic (0, 200 and 400μM As), as well as combined effects of As and salinity (200μM As+200mM NaCl and 400μM As+200mM NaCl) on growth, water status, mineral ion homeostasis, photosynthetic pigments, lipid peroxidation, phytochelatin levels and antioxidative components were investigated in the halophyte S. maritima to get an insight into salinity and arsenic tolerance mechanisms. The seedlings of S. maritima survived under prolonged exposure to high dosage of As (400μM As). The oxidative stress indicators such as H2O2, O2− and MDA remained at a low level in both NaCl and As treated seedlings. The levels of GSSG, GSH, total glutathione and TAST increased in seedlings treated with As alone whereas it declined under combined treatments of As with NaCl. The antioxidative response showed a decreased activity of SOD and increased activity of CAT both in NaCl and As treated seedlings as compared to control. In contrasts, the activities of other antioxidative enzymes such as APX, POX, and GR consistently decreased in NaCl-treated seedlings and increased in As-treated seedlings. The ratios of AsA/DHA and GSH/GSSG (indicators of cellular redox potential) were either elevated or remained unchanged in S. maritima seedlings subjected to salinity and As treatments. Our results suggest that the halophyte, S. maritima can withstand high salinity and As by regulating antioxidative enzymes and maintaining cellular redox level. Moreover, the salinity and arsenic tolerance index (Ti) of S. maritima was at par to the control or more than the control value in all the treatments. The arsenic bio-concentration factor (BCF) and translocation factor (Tf) values of S. maritima were all greater than 1.0 which clearly indicates that this plant has the basic characteristics of As-hyperaccumulator. Taken together, our results suggest that S. maritima plants can be utilized for phytoremediation/phytostabilization of saline soils contaminated with high arsenic.