FUNGAL SLIME AND ITS ROLE IN THE MYCORRHIZAL AMELIORATION OF ZINC TOXICITY TO HIGHER-PLANTS

The degree of sliminess of a range of fungal isolates which form endomycorrhizas with Calluna vulgaris L. was investigated and related to their performance in the presence of potentially toxic concentrations of zinc. Some fungal isolates possess, to a greater or lesser extent, a mass of loosely adherent slime (LAS). The amount of this was proportional to the ability of the fungal mycelium to take up zinc from solution, the zinc tolerance of the fungal isolates, and the amount of growth enhancement exhibited by the associated C. vulgaris plants in the presence of potentially toxic concentrations of zinc. Furthermore the amount of LAS was inversely proportional to the concentration of zinc found in the shoots of the associated C. vulgaris plants. These observations support the hypothesis that LAS plays a central role in removing zinc ions from solution, removal which in turn determines the zinc tolerance of the fungus itself and the degree of amelioration of zinc toxicity to the host plant.