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Heavy metals resulting from mining and industrial activities are pollutants. They can be toxic not only to plants but also to animals and humans through their entry in the food chain through agricultural production. The increasing size of areas polluted by heavy metals makes necessary the use of new strategies to limit the diffusion of this pollution. One of these new strategies is phytoremediation, which consists in using plants to stabilise a polluted soil or to extract metals from such a soil. Phytoremediation could represent an ecologic, alternative and “cheap” option adapted to mild polluted soils. To develop a phytoremediation strategy, one needs plants that are primarily tolerant to metals and, if possible, that are also able to accumulate high concentrations of metals in their tissues. Such plants exist. They are irreplaceable materials to understand the physiological and genetic bases of metal tolerance and hyper accumulation. They unfortunately have reduced biomasses, which limits their potential use for phytoremediation. We need to understand the mechanisms involved in metal tolerance and metal homeostasis and use that information to breed plants that could be used for phytoremediation.
The objective of our group is to unravel mechanisms: (i) that allow plants to sustain their growth and development in toxic metal environments and (ii) that are involved in the control of metal accumulation in plant aerial tissues. In the past four years, we focused our studies on the metal tolerant and hyper accumulating species Thlaspi caerulescens and Arabidopsis halleri.
Thlaspi caerulescens (left) and Arabidopsis halleri (right) are hyperaccumulators of zinc and cadmium and they are tolerant to these metals. In addition, the Ganges ecotype of Thlaspi caerulescens is tolerant to nickel and hyperaccumulates this metal. The species were photographed in their natural habitats: settling sludge from the Saint Laurent le Minier mine (near Ganges) that contain 12% (w/w) zinc, and the zinc contaminated industrial site of Auby (north of France)
The main achievements of the team have been to shed light on two original mechanisms involved as components of metal tolerance and homeostasis in plants. We showed that the metal tolerance of T. caerulescens and A. halleri occurs, at least in part, at the cellular level. Screening yeast cells expressing cDNA libraries from T. caerulescens and A. halleri for metal tolerance revealed that expression of nicotianamine synthase from T. caerulescens and of type I defensins from A. halleri resulted in nickel and zinc tolerances, respectively. Further analyses showed that (i) nicotianamine plays an important role in nickel tolerance and metal transport in metal hyper accumulating plants; (ii) plant type I defensins have a potential and never mentioned specific role in zinc tolerance.
The Atmosphere Comments These ratios are the same through most of the atmospheric height. Total - is almost 99.99%. Where the pollution goes to ??? Typical atmosphere: N2 - 79%, O2 - 21% and MW - 28.85.
Minor Constituents Other constituents of the atmosphere include pollen, bacteria, fungi, particles (smoke, sea spray, dust), oxides of carbon, sulfur and nitrogen, and organic gases.
