Salicaceae for phytoremediation: molecular and physiological markers for environmental pollution in fast growing forest trees.

The increasing number of contaminated sites brings several management problems and often leads to a waste of natural resources, such as soils and water, which cannot be utilized. Biological techniques for remediation of polluted soils, bioremediation and phytoremediation, have been studied since many years. They can give acceptable results with a low environmental impact, even if in long term periods. In particular, the use of higher plants in decontamination has been limited by legislation constraints, and also by lack of plant species which can be really effective towards specific contaminants. Poplar is a good candidate for phytoremediation and possesses genetic resources for the identification of genotypes with high tolerance to heavy metals and a good capacity of uptake and accumulation of contaminants. Some recent research works showed a high variability in the uptake capacity and tolerance to Cadmium (Cd) in Salicaceae.This work is focused on genetic basis of Cd tolerance in Populus nigra (P. nigra). Two P. nigra genotypes, belonging to natural Italian populations from contrasting geographical, and environmental origin, were chosen as parents to constitute full sib progenies. Ninety-two F1 individuals were analyzed to construct genetic maps based on the pseudo-testcross strategy. From previous experiments it was observed that the two parental genotypes presented a different tolerance to cadmium stress. Some candidate genes expected to explain these differences were chosen for molecular characterization: metal sequestration (metallothionein 2a), ion transport (vacuolar H+-ATPase), and response to oxidative stress (ascorbate peroxidase 2, glutathione reductase, glutathione S-transferase). The expression of these genes was analysed in plants submitted to Cd stress. They were also used to enrich the genetic maps in candidate genes for Cd tolerance. A Cd stress replicated experiment with controls was carried out on the mapping progeny for QTL analyses. Ecophysiological and chemical parameters measured during the experiment will be used for the genetic dissection of plant response to Cd treatment and correlations among allelic variants and the phenotypic expression of traits will be calculated. Such approach will allow to search for QTLs controlling tolerance and concentration of Cd in plant organs (root, stem, leaf).The perspectives are the identification of key genes (major genes) for phytoremediation in P. nigra and the setup of molecular markers for selection of poplar material suitable for environmental restoration and phytoremediation.