ELECTRICAL CURRENTS ASSOCIATED WITH ARBUSCULAR MYCORRHIZAL INTERACTIONS

Electrical currents associated with the plant-fungus interaction betwe en roots and an arbuscular mycorrhizal (AM) fungus Gigaspora margarita were measured with a one-dimensional vibrating probe. Uninfected root s of clover (Trifolium repens L. cv. New Zealand White) and carrot (Da ucus carota L. cv. Nantes) had an inwardly directed positive electrica l current at the apical meristematic and elongation zones and an outwa rd flow at the mature non-growing regions. The current profile of endo mycorrhizal colonized roots did not differ markedly in magnitude or pa ttern compared with non-colonized roots of an equivalent stage of deve lopment. A small current was measured circulating around and through s ingle mycorrhizal azygospores of G. margarita. Germ tubes emerged with in 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 cu rrent declined over a period of 6 d. Because hyphal penetration of pla nt roots by AM fungi does not rupture the plant host membrane we propo se that the host current is not the result of wounding but is induced by fungal elicitors at the infection court.