Abstract
Heavy metals are common pollutants of the coastal saline area and Salicornia brachiata an extreme halophyte is frequently exposed to various abiotic stresses including heavy metals. The SbMT-2 gene was cloned and transformed to tobacco for the functional validation. Transgenic tobacco lines (L2, L4, L6 and L13) showed significantly enhanced salt (NaCl), osmotic (PEG) and metals (Zn++, Cu++ and Cd++) tolerance compared to WT plants. Transgenic lines did not show any morphological variation and had enhanced growth parameters viz. shoot length, root length, fresh weight and dry weight. High seed germination percentage, chlorophyll content, relative water content, electrolytic leakage and membrane stability index confirmed that transgenic lines performed better under salt (NaCl), osmotic (PEG) and metals (Zn++, Cu++ and Cd++) stress conditions compared to WT plants. Proline, H2O2 and lipid peroxidation (MDA) analyses suggested the role of SbMT-2 in cellular homeostasis and H2O2 detoxification. Furthermore in vivo localization of H2O2 and O2 −; and elevated expression of key antioxidant enzyme encoding genes, SOD, POD and APX evident the possible role of SbMT-2 in ROS scavenging/detoxification mechanism. Transgenic lines showed accumulation of Cu++ and Cd++ in root while Zn++ in stem under stress condition. Under control (unstressed) condition, Zn++ was accumulated more in root but accumulation of Zn++ in stem under stress condition suggested that SbMT-2 may involve in the selective translocation of Zn++ from root to stem. This observation was further supported by the up-regulation of zinc transporter encoding genes NtZIP1 and NtHMA-A under metal ion stress condition. The study suggested that SbMT-2 modulates ROS scavenging and is a potential candidate to be used for phytoremediation and imparting stress tolerance.
Highlights
Abiotic stresses such as salinity, drought, temperature and heavy metals have significant effect on the agricultural production over the years [1]
T1 Seeds were germinated on hygromycin containing media and selected T1 transgenic lines were confirmed by PCR using gene specific primers (Figure 1b)
Transgenic lines showed higher seed germination percentage, increased root length, shoot length, fresh weight (FW), dry weight (DW) and chlorophyll content under different stress conditions compared to wild type (WT) plants (Figure 3 and 5a) which reveal that SbMT-2 leads to overcome the deleterious effect of salt, drought and metal stresses
Summary
Abiotic stresses such as salinity, drought, temperature and heavy metals have significant effect on the agricultural production over the years [1]. Drought and heavy metals have similar consequences ensuing oxidative stress, disturbances in ionic homeostasis and generation of reactive oxygen species (ROS) [1,4]. Plant MTs belong to Class II and further classified into four types (type 1 to 4) based on the position and allocation of cysteine residues [7]. Overexpression of MTs in various model systems like Arabidopsis, tobacco, yeast and E. coli established its functional role in homeostasis and tolerance to Cu, Zn and Cd [10,11,12,13], high salinity, drought, low temperature, heavy metal ions, abscisic acid (ABA) and ethylene [12,14]. MTs are reported in the inhibition of root elongation [15], fruit ripening, seed development [7] and provide disease resistance against pathogen attack [16]
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