Relationship Between Growth and the Electrical Current of Fungal Hyphae

Abstract

The hyphae of filamentous fungi exhibit a highly polarized mode of cell extension and all generate electrical currents around their hyphal tips. Of the 13 fungi that have been examined with the vibrating probe, 12 normally have positive electrical current entering the growing tip. However, the apical current is always outward in Allomyces macrogynus. In those organisms that have inward apical currents, outward currents are found occassionally and transiently in hyphae that extend at normal rates. There is no good correlation between either the extension rate or the length of the growing peripheral cell and the current density. These studies lead one to conclude that the relationship between the generation of an electrical current and the extension of a hypha is superficial and not essential. The association between the flow of protons, which carry most of the current in fungi, and cell extension may be tighter. Comparison of the currents of three water molds A. macrogynus, Blastocladiella emersonii and Achlya bisexualis provides an insight to the probable role of the electrical current. A. macrogynus and B. emersonii both have rhizoids that may take up nutrients by proton-linked transport. The nutrients support growth of the sporangium and hypha, respectively, to which they are joined. In A. bisexualis, proton symport is responsible for nutrient transport into the hyphal tip. There seems to be an excellent correlation between the zones at which proton-coupled nutrient transport occurs and the regions where positive current enters these fungi. Therefore, the current may indicate local nutrient uptake rather than local cell growth.

Harnessing Fungi Signaling in Living Composites

“…Achlya bisexualis [55,105] Neurospora crassa [ 55,105] Basidiobolus ranarum [ 105] Allomyces macrogynus [ 105] Mucor mucedo [ 55] Schizophyllum commune [ 55] Aspergillus nidulans [ 55] Gigaspora margarita [106] Trifolium repens [106] Daucus carota [106] Surface electrodes Used to detect electrical activity directly from the surface of the biological tissue.…”

The electric fungus

“…The evidence for this conclusion stems from observations of (a) non-growing hyphae with normal currents, (b) growing hyphae lacking currents and (c) growing hyphae with outwardly directed electrical currents ( Fig. 2) (McGillivray & Gow, 1987;Schreurs & Harold, 1988;Takeuchi et al, 1988;Youatt, Gow & Gooday, 1988;Gow, 1989a;Cho et al, 1991;De Silva et al, 1992). It must be remembered that electrical currents are the net result of all ionic fluxes and thus it is possible that electrical fluxes are not related to tip growth but that fluxes of individual ions are.…”

Terrestrial rhizophytes and H+ currents circulating over at least a millimetre: an obligate relationship?

“…However, work on other representatives of these higher taxa suggests that it would be extremely unlikely if their mycorrhizal and lichenized relatives lacked circulating electric currents which were carried by H^ (Table 1; Harold, 1986a, 6;Gow, 1989). This generalization extends to the one example (hyphomycete) of a (secondarily) marine fungus examined, at least as far as the primary active transport of H* at the plasmalemma is concerned (Davies, Brownlee & Jennings, 1990), although there are no known examples of marine rhizophytic lichens (Raven et al, 19906) and the mycorrhizal status of marine flowering plants is not clear (Harley & Smith, 1983).…”

“…ADP phosphorylation, or ATP-driven H"^ pumping Elongation and/or differentiation of eukaryotes to solute cotransport (Skulachev, 1981(Skulachev, , 1990; seems to be invariably associated with the occurrence Harold, 1986 a, 6;Gow, 1989) is debatable (Raven, of electric currents carried by ions which circulate 1983, 1984aJunge & McLaughlin, 1987; Irving through the intracellular or intraorgan phase and the et al ., 1990). These doubts as to the quantitative external medium, entering and leaving the organism significance of circulating H"*^ currents in the transacross the plasmalemma (Harold, 1986 a, b).…”