Heavy metals (HM) are a unique class of toxicants since they cannot be broken down to non-toxic forms. Concentration of these heavy metals has increased drastically, posing problems to health and environment, since the onset of the industrial revolution. Once the heavy metals contaminate the ecosystem, they remain a potential threat for many years. Some technologies have long been in use to remove, destroy and sequester these hazardous elements. Even though effective techniques for cleaning the contaminated soils and waters are usually expensive, labour intensive, and often disturbing. Phytoremediation, a fast-emerging new technology for removal of toxic heavy metals, is cost-effective, non-intrusive and aesthetically pleasing. It exploits the ability of selected plants to remediate pollutants from contaminated sites. Plants have inter-linked physiological and molecular mechanisms of tolerance to heavy metals. High tolerance to HM toxicity is based on a reduced metal uptake or increased internal sequestration, which is manifested by interaction between a genotype and its environment. The growing interest in molecular genetics has increased our understanding of mechanisms of HM tolerance in plants and many transgenic plants have displayed increased HM tolerance. Improvement of plants by genetic engineering, i.e., by modifying characteristics like metal uptake, transport and accumulation and plant's tolerance to metals, opens up new possibilities of phytoremediation. This paper presents an overview of the molecular and physiological mechanisms involved in the phytoremediation process, and discusses strategies for engineering plants genetically for this purpose.

Background: There is a growing demand for remedies from natural sources to substitute synthetic therapeutic drugs and minimize their side effects and toxicity. The present study aims to evaluate the defensive ability of an ethanolic extract of Rosmarinus officinalis L. in carbon tetrachloride (CCl 4)-induced nephrotoxicity in male albino rats. Materials and methods: Thirty-six rats were divided into 6 groups (n = 6). Group I (control) received distilled water for 30 days orally. Nephrotoxicity was induced by CCl 4 (11% v/v with olive oil, i.p) 2 ml/kg body weight (b.wt.) in group II once a week for 30 days. Groups III and IV received the only herb in two doses 100 and 250 mg/kg of b.wt. respectively. Groups V and VI received an ethanolic extract of Rosmarinus officinalis (EERO, 100 and 250 mg/kg of b. wt.) along with 2 ml/kg b.wt. CCl 4 weekly for 30 days. Results: CCl 4 treatment induced highly significant (P < 0.001) elevation in kidney biomarkers, i.e., blood urea nitrogen and creatinine, kidney biochemicals, i.e., LPO and XOD, and decrease the levels of superoxide dismutase, catalase, glutathione peroxidase, and glutathione in tissue. However, EERO significantly (P < 0.001) restored the altered levels of these biomarkers in a dose-dependent manner. Furthermore, EERO also prevents histological alteration caused due to the toxicity of CCl 4. Conclusion: Our findings strongly support that ethanolic extract of Rosmarinus officinalis acts as a potent scavenger of free radicals to prevent the toxic effect of CCl 4 and hence validate its ethnomedicinal use.

The hydroponically grown plants of Ocimum basilicum L. were exposed to varying levels of K2Cr2O7 (0, 5, 10, 25 µM). The plants were tested for various morphological and biochemical parameters on 3 rd and 5 th day after treatment. Chromium (Cr) resulted in reduction of plant length and biomass. The deleterious effects of the hexavalent chromium on O. basilicum were further confirmed by the reductions in chlorophyll a and b contents, soluble protein and while as the free amino acid and proline contents were increased. The study concludes that chromium causes stress in the Ocimum basilicum plants and thus alters various morphological and biochemical parameters.

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