The potential of a halophyte species-Acanthus ilicifolius L.-to phytostabilize zinc (Zn) grown under hydroponics culture conditions was critically evaluated in this study. The propagules after treating with ZnSO4 (4 mM) were analysed for the bioaccumulation pattern, translocation rate of Zn to the shoot, effects of Zn accumulation on organic solutes and the antioxidant defence system. It was found that most of the Zn absorbed by the plant was retained in the root (47%) and only a small portion was transported to stem (12%) and leaves (11%). This is further confirmed by the high BCFroot (bioconcentration factor) value (1.99) and low TFshoot/root (translocation factor) value (0.5), which indicates the increased retention of Zn in the root itself. Moreover, treatment with Zn resulted in an increased accumulation of organic solutes (proline, free amino acids and soluble sugars) and non-enzymatic antioxidants (ascorbate, glutathione and phenol) in the leaf and root tissue. Likewise, the activity of antioxidant enzymes namely superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) recorded an enhanced activity upon exposure to Zn as compared to the control plants. Thus, the increased tolerance for Zn in A. ilicifolius may be attributed to the efficient free radical scavenging mechanisms operating under excess Zn. In addition, being a high accumulator (53.7 mg of Zn) and at the same time a poor translocator of Zn to the aerial parts of the plant, A. ilicifolius can be recommended as a potential candidate for the phytostabilization of Zn in the contaminated wetlands.
Keywords: Bioaccumulation; Phytostabilization; Translocation factor; Wetlands; Zinc.