Molecular cloning and expression of a vacuolar Na⁺/H⁺ antiporter gene (AgNHX1) in fig (Ficus carica L.) under salt stress

Soil salinity can be a major limiting factor for productivity in agriculture and forestry and in order to fully utilize saline lands productively in plantation forestry for fig production, the genetic modification of tree species for salt tolerance may be required. Na+/H+ antiporters have been suggested to play important roles in salt tolerance in plants. Here, we isolated AgNHX1 a vacuolar Na+/H+ antiporter from a halophytic species Atriplex gmelini and introduced it into fig (Ficus carica L.) cv. Black Mission via Agrobacterium-mediated transformation. Leaf discs explants of fig were co-cultivated for 2 days with Agrobacterium tumefaciens strain LBA 4404 harboring the binary vector pBI121 containing the AgNHX1 gene and the hpt selectable marker gene which encodes hygromycin phosphotransferase. Explants were cultured on MS medium containing 30 mg L−1 hygromycin, 3 % sucrose, 0.2 mg L−1 kinetin and 2.0 mg L−1 2,4-dichlorophenoxyacetic acid solidified with 2.5 g L−1 phytagel in darkness for callus formation. The calli were cultured on MS medium containing 2.0 mg L−1 zeatin riboside in combination with 0.4 mg L−1 indole acetic acid in the light for plant regeneration. Putative regenerated transformant shoots were confirmed by polymerase chain reaction (PCR) and Southern hybridization for the AgNHX1 gene. Reverse transcriptase polymerase chain reaction analysis indicated that the gene was highly expressed in transgenic plants, but the degree of this expression varied among transformants. Overexpression of the AgNHX1 gene conferred high tolerance to salt stress and transgenic fig plants overexpressing AgNHX1 developed normally under salinity conditions compared to those of non-transgenic plants. Salt treated transgenic plants contained high proline and K+ but less Na+ compared to non-transgenic control plants

Phytoremediation of heavy metal-contaminated sites: Eco-environmental concerns, field studies, sustainability issues and future prospects

Environmental contamination due to heavy metals (HMs) is of serious ecotoxicological concern worldwide because of their increasing use at industries. Due to non-biodegradable and persistent nature, HMs cause serious soil/water pollution and severe health hazards in living beings upon exposure. HMs can be genotoxic, carcinogenic, mutagenic, and teratogenic in nature even at low concentration. They may also act as endocrine disruptors and induce developmental as well as neurological disorders and thus, their removal from our natural environment is crucial for the rehabilitation of contaminated sites. To cope with HM pollution, phytoremediation has emerged as a low-cost and eco-sustainable solution to conventional physico-chemical cleanup methods that require high capital investment and labor alter soil properties and disturb soil microflora. Phytoremediation is a green technology wherein plants and associated microbes are used to remediate HM-contaminated sites to safeguard the environment and protect public health. Hence, in view of the above, the present paper aims to examine the feasibility of phytoremediation as a sustainable remediation technology for the management of metals-contaminated sites. Therefore, this paper provides an in-depth review on both the conventional and novel phytoremediation approaches, evaluate their efficacy to remove toxic metals from our natural environment, explore current scientific progresses, field experiences and sustainability issues and revise world over trends in phytoremediation research for its wider recognition and public acceptance as a sustainable remediation technology for the management of contaminated sites in 21st century