A greenhouse pot experiment was conducted to investigate the eVects of the colonization of arbuscular mycorrhizal fungus (AMF) Glomus mosseae on the growth and metal uptake of three leguminous plants (Sesbania rostrata, Sesbania cannabina, Medicago sativa) grown in multi-metal contaminated soil. AMF colonization increased the growth of the legumes, indicating that AMF colonization increased the plant's resistance to heavy metals. It also signiWcantly stimulated the formation of root nodules and increased the N and P uptake of all of the tested leguminous plants, which might be one of the tolerance mechanisms conferred by AMF. Compared with the control, colonization by G. mosseae decreased the concentration of metals, such as Cu, in the shoots of the three legumes, indicating that the decreased heavy metals uptake and growth dilution were induced by AMF treatment, thereby reducing the heavy metal toxicity to the plants. The root/shoot ratios of Cu in the three legumes and Zn in M. sativa were signiWcantly increased (P < 0.05) with AMF colonization, indicating that heavy metals were immobilized by the mycorrhiza and the heavy metal translocations to the shoot were decreased.
a b s t r a c tThere is evidence that colonisation by mycorrhizal fungi can protect host plants from toxic concentrations of heavy metals. The mechanism by which protection is provided by the fungus for any particular metal is poorly understood. Rice (Oryza sativa L.) plants were inoculated with Glomus mosseae and grown for 4 weeks to ensure strong colonisation. The plants were then exposed to low to toxic concentrations of copper (Cu) and the uptake and distribution were examined. The effect of mycorrhizal colonisation on the cell wall composition and Cu binding capacity of roots was also investigated. Mycorrhizal plants showed moderate reductions in Cu concentrations in roots but large reductions in shoots. In roots, mycorrhizal plants accumulated more Cu in cell walls but much less in the symplasm compared to nonmycorrhizal plants. The differences in cell wall binding of Cu could be partly explained by changes in the composition of the cell wall. The mechanistic basis for the reduced Cu accumulation and the potential beneficial consequences of mycorrhizal associations on plant growth in Cu toxic soil are discussed.
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