Physiological and proteomic responses of different willow clones (Salix fragilis x alba) exposed to dredged sediment contaminated by heavy metals.

High biomass producing species are considered as tools for remediation of contaminated soils. Willows (Salix spp.) are prominent study subjects in this regard. In this study, different willow clones (Salix fragilis x alba) were planted on heavy-metal polluted dredging sludge. A first objective was assessment of the biomass production for these clones. Using a Gupta statistic, four clones were identified as high biomass producers (HBP). For comparison, a group of four clones with lowest biomass production were selected (LBP). A second objective was to compare metal uptake as well as the physiological and proteomic responses of these two groups. All these complementary data's allow us to have a better picture of the health of the clones that would be used in phytoremediation programs. Cd, Zn, and Ni total uptake was higher in the HBPs but Pb total uptake was higher in LBPs. Our proteomic and physiological results showed that the LBPs were able to maintain cellular activity as much as the HBPs although the oxidative stress response was more pronounced in the LBPs. This could be due to the high Pb content found in this group although a combined effect of the other metals cannot be excluded.

A multiple-level study of metal tolerance in Salix fragilis and Salix aurita clones.

The response of two willow clones (Salix fragilis (Sf) and Salix aurita (Sa)) to the presence of metals (Zn, Cu, Cd, Ni) was studied. Rooted cuttings were planted in control and contaminated soil. After 100days, different parameters (biomass, chlorophyll fluorescence (Fv/Fm), pigment and sugar concentrations, electrolyte leakage and proteome-level changes) were analyzed. The growth of Sa was not influenced by metals whereas Sf produced significantly less biomass when exposed to the pollutants. Furthermore, although Sa did not show a growth reduction in the presence of metals, the overall view of the physiological results among others the changes in the accumulation of sugars and pigments indicated that metals had a more severe impact on this clone. The response at the proteome level confirmed these observations. The growth reduction and the proteomic changes in Sf indicate that this clone adjusts its metabolism to maintain cellular homeostasis. Sa on the contrary maintains growth but the physiological and proteomics data suggests that this can only be done at the cost of cellular deregulation. Therefore high biomass is not linked with a good tolerance strategy. In a long-term study the survival of Sa might be compromised making it a poorer candidate for phytoremediation efforts. BIOLOGICAL SIGNIFICANCE: In the last centuries human activity has resulted in the dispersal of heavy metals with potential phytotoxic effects over large areas. The increased knowledge of the responses of Salix-species, a group of trees with potential as biomass producer but also as phytoremediation agent, when growing on metal-polluted substrate provided by this study has the potential to help in the improved selection of clones with more or less potential for these aims. Contrary to most studies the trees in the current study were exposed to a mixture of metals, thereby facing a closer resemblance to the situation on soils polluted by human activity. Whereas many papers focused on the two main phenotypic characteristics (biomass and accumulation), fewer papers studied proteomic and physiological parameters which allow to have a global view of the tolerance of probable willow candidates for phytoremediation purposes. Our data demonstrates that higher biomass production in presence of metals is not necessarily linked with higher tolerance whereas growth reduction might indicate longer long-term tolerance. In the long term and in the purpose of a future use in phytoremediation, the survival of this high producer clone could be compromised.

Potential of kenaf (Hibiscus cannabinus L.) and corn (Zea mays L.) for phytoremediation of dredging sludge contaminated by trace metals.

The potential of kenaf (Hibiscus cannabinus L.) and corn (Zea mays L.) for accumulation of cadmium and zinc was investigated. Plants have been grown in lysimetres containing dredging sludge, a substratum naturally rich in trace metals. Biomass production was determined. Sludge and water percolating from lysimeters were analyzed by atomic absorption spectrometry. No visible symptoms of toxicity were observed during the three- month culture. Kenaf and corn tolerate trace metals content in sludge. Results showed that Zn and Cd were found in corn and kenaf shoots at different levels, 2.49 mg/kg of Cd and 82.5 mg/kg of Zn in kenaf shoots and 2.1 mg/kg of Cd and 10.19 mg/kg in corn shoots. Quantities of extracted trace metals showed that decontamination of Zn and Cd polluted substrates is possible by corn and kenaf crops. Tolerance and bioaccumulation factors indicated that both species could be used in phytoremediation.