ELECTRIC AND IONIC DIMENSIONS OF APICAL GROWTH IN ACHLYA HYPHAE

Hyphae ofAchlya bisexualis generate endogenous electric currents, which are thought to represent the spatial organization of the chemiosmotic proton circuit. The experiments reported here bear on the relationship between currents and apical extension. The polarity of the current reverses as the colony ages, yet mature hyphae (as well as young ones) extend only at the apex. We also do not find an obligatory connection between inward current and the emergence of antheridial branches inAchlya ambisexualis. Applied electric fields orient hyphal extension, but whether the hyphae grow towards the anode or the cathode depends on the medium. We conclude that the hypothesis that electric currents localize outgrowth and determine polarity is no longer useful, and offer a reassessment of the currents' nature and significance. © 1991 Academic Press, Inc.