Arbuscular Mycorrhizal fungi restore normal growth and alter polyamine content and gene expression in AL35 poplar clone grown on highly heavy metal contaminated soil

Heavy metal (HM) pollution is a major worldwide environmental concern. Phytoremediation has become a promising remediation technique that include the use of selected plant species to remove or to stabilize a range of pollutants. Plant tolerance to HM stress is improved by arbuscular mycorrhizal (AM) fungi. Thus, suitable plant fungus combinations may contribute to the success of phytoremediation of HM polluted soil. Metallothioneins (MTs) and polyamines (PAs) are implicated in the response and tolerance to HM stress in several plant species, but whether the response is modulated by AM fungi remains to be clarified. Populus alba AL35 plants were grown in pots containing either soil collected from a HM polluted or unpolluted soil; they were pre-inoculated or not with Glomus mosseae or G. intraradices. At the first and the second growth season, the expression of MT and PA biosynthetic genes was analysed in leaves using quantitative RT-PCR, and free and conjugated foliar PA concentrations were detected. Results indicate that on polluted soil, AM fungi restored plant biomass despite higher Cu and Zn accumulation in plant organs. P. alba mycorrhizal plants exhibit increased capacity for stabilization of soil HMs, and improved stress tolerance through the transcriptional up-regulation of stress-related genes and the protective role of PAs.