ELECTRICAL CURRENTS ASSOCIATED WITH ARBUSCULAR MYCORRHIZAL INTERACTIONS

Electrical currents associated with the plant-fungus interaction between roots and an arbuscular mycorrhizal (AM) fungus Gigaspora margarita were measured with a one-dimensional vibrating probe. Uninfected roots of clover (Trifolium repens L. cv. New Zealand White) and carrot (Daucus carota L. cv. Nantes) had an inwardly directed positive electrical current at the apical meristematic and elongation zones and an outward flow at the mature non-growing regions. The current profile of endomycorrhizal colonized roots did not differ markedly in magnitude or pattern compared with non-colonized roots of an equivalent stage of development. A small current was measured circulating around and through single mycorrhizal azygospores of G. margarita. Germ tubes emerged within the zone of outward current and an inward current was found at the hyphal tip. When roots were colonized by the fungus an inward current was induced at the point of hyphal contact with the host root. This current declined over a period of 6 d. Because hyphal penetration of plant roots by AM fungi does not rupture the plant host membrane we propose that the host current is not the result of wounding but is induced by fungal elicitors at the infection court.