Heavy metal tolerance in contrasting ecotypes of Alyssum montanum

The response of metallicolous (M) and nonmetallicolous (NM) Alyssum montanum ecotypes to multi-metal stress was investigated under in vitro condition and compared in this study. Shoot cultures were simultaneously treated with 0.7 mM ZnSO4, 3.0 μM Pb(NO3)2 and 16.4 μM CdCl2 for 8 weeks and evaluated for their morphogenetic and ultrastructural reaction, growth tolerance as well as ability to Zn, Pb, and Cd uptake. Moreover, tissue localization and concentrations of antioxidant compounds were determined in order to elucidate the potential role of ROS-scavenging machinery in plant tolerance to metal toxicity. The results clearly demonstrated that M specimens treated with heavy metals showed less phytotoxic symptoms and low level of lipid peroxidation than reference NM one. The enhanced tolerance of M ecotype resulted from heavy metals detoxification in trichomes and intracellular leaf compartments as well as balanced ROS accumulation. The inactivation of ROS in M plants was based on peroxidase-flavonoid system, while in NM plants such relationship was not detected and amounts of antioxidant enzymes or phenolic compounds was comparable to untreated specimens or decreased significantly. Considering the procumbent growth of such hemicryptophyte which reproduce effectively in the presence of heavy metals but is characterized by low biomass production, it is proposed to exploit M ecotype of A. montanum in revegetation schemes of polluted calamine wastes to provide the prompt stabilization of areas prone to erosion.