The environment contamination with different pollutants has become a worldwide problem and the phytoremediation techniques may offer interesting perspectives for counteracting this phenomenon. Many efforts are necessary to improve these techniques aimed to the restoration of contaminated soils and waters, and for this purpose, biotechnologies developed in the last decades are now fully available. Phytoremediation takes advantage of different biological processes involved in the accumulation, complexation, volatilization, and degradation of organic and inorganic pollutants. In recent years, these processes have been studied on a multitude of species and woody plants, in particular, display the most interesting perspectives for their possibility of accumulating high amounts of specific pollutants in their large biomass. in vitro cultures constitute a powerful tool for developing strategies in phytoremediation. Micropropagation and, more in general, cell and tissue culture can be directly exploited in phytoremediation. For research purposes, these techniques offer the advantage of investigating the plant (or plant cells and organs) behaviour under controlled conditions, in comparison with whole plant experiments under field conditions. Under axenic conditions, we can also distinguish the response of plants from those of microorganisms present in the rhizosphere. The attention must be focused also on the rhizosphere and the complex interactions between plants and microbial communities that may play a relevant role in phytoremediation. These subjects have been largely investigated and a huge literature can be found, so our analysis was mainly addressed towards the field of heavy metals contamination and the use of woody plants for remediation. In the second part, the wide subject of genetic engineering is illustrated; the use of genetically modified plants, in fact, is of great usefulness for the understanding of the metabolic processes involved in the mechanisms of pollutants uptake, sequestration and translocation. Special attention is focused on reactive oxygen species, nitric oxide, and phytohormones, which are signaling molecules modulating plant responses to pollutants stress mainly through differentially expressed genes and the antioxidative system activation. In this context, several genes have been functionally characterized and transformed to target plants for enhancing their phytoremediation efficiency. Consequently, whenever possible, and taking into account any possible risk linked to the use of modified organisms, the use of plants overexpressing genes involved in these phenomena is a promising method for improving the efficacy of phytoremediation.
