Purpose This work was planned for providing a useful screening tool for the selection of Populus alba clones suitable for phytoremediation techniques. To this aim, we investigated variation in arsenic, cadmium, copper, and zinc tolerance, accumulation and translocation in three poplar clones through an in vitro screening. Poplars have been widely proposed for phytoremediation, as they are adaptable to grow on contaminated areas and able to accumulate metals. The investigation of possible differences among poplar clones in metal tolerance and accumulation deserves to be deeply studied and exploited for the selection of the more suitable tool for phytoremediation purposes. Methods In vitro multiplied microshoots of a commercial and two autochthonous P. alba clones were subcultured on hormone-free WPM medium for 1 month and then transferred for 2 weeks onto media containing different concentrations of the metals investigated. At the end of the treatments, plantlets were sampled, weighed, and mineralised by wet ashing. Metal concentrations were determined by ICP-OES. Results For the metal concentration used in the experiments, our clones of P. alba showed variation in metal tolerance, metal accumulation and content. The fast-growing commercial clone, even if rarely showing the highest plant metal concentration, displayed the highest metal content, suggesting biomass production as the key factor in evaluating the phytoextraction capacity of P. alba clones for the metals studied. Conclusions Data demonstrated that in vitro screening of cuttings represents a valuable way of assessing the ability of different poplar clones to take up, tolerate and survive metal stress.

Soil contamination by heavy metals is among the most serious danger for the environment, and new methods for its containment and removal are claimed, in particular for agricultural soils. Phytoremediation is an emerging, potentially effective technology applicable to restoration of contaminated soils and waters. Besides hyperaccumulator herbaceous plants, several woody species are now considered of interest to this aim. Many woody plants are fast growing, have deep roots, produce abundant biomass, are easy to harvest, and several species revealed some capacity to tolerate and accumulate heavy metals. Biotechnologies are now available for investigating this potential and enlarge the possibilities of exploitation of trees for remediation. The use of in vitro cultures, the role of bacteria and mychorrhizas, the powerful tool of genetic engineering, are some of the aspects focused in this paper that open prospects of global relevance for a better understanding of the processes related to the uptake of heavy metals by woody plants. In recent years significant progress has been made in identifying native plants and developing genetically modified tree plants for the remediation of heavy-metal polluted environment. Despite the intensive research developed in the last years, few field trials demonstrated the feasibility of the approach described, therefore much efforts should be addressed to this goal

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