A number of tip-growing organisms have been reported to generate transcellular ion currents; these may be implicated in the spatial localization of growth and development, but at present neither the genesis nor the functions of these currents are clearly defined. This program centers on a single organism, the water mold Achlya bisexualis, which seems to lend itself to the requisite examination; we hope to learn just how the flow of electrical current through the hyphae comes about, and what relationship it bears to tip growth, chemotropic orientation and branching. Work completed or in progress shows that positive charges flow into the tip and anterior portions of a growing hypha and leave from the rear. The current is probably carried into the tip by protons. Branching of a hypha is preceded by a new point of current entry, whose locus predicts the site of branching. We propose to test and refine the hypothesis that protons are extruded from the cytoplasm by a proton-translocating ATPase, and return by symport with amino acids. The current pattern, then, may stem from the preferential localization of the symporters at the growing tip. Once the genesis of the current pattern is established, we plan to manipulate the direction and magnitude of the ion current in order to assess its function (if any) in integrated cellular processes. This phase of the program will be guided by the hypothesis that the proton current is one element of the network of causes and effects by which hyphae maintain the polarity of growth and respond to environmental stimuli. Transcellular electrical currents and field are common in higher organisms and may play a role in embryonic development, wound healing and regeneration. The present program claims no immediate bearing on human health, but is intended to provide basic insights on which applications may be based.
| Thiel, R; Schreurs, W J; Harold, F M (1988) Transcellular ion currents during sporangium development in the water mould Achlya bisexualis. J Gen Microbiol 134:1089-97 |
| Schreurs, W J; Harold, F M (1988) Transcellular proton current in Achlya bisexualis hyphae: relationship to polarized growth. Proc Natl Acad Sci U S A 85:1534-8 |
| Takeuchi, Y; Schmid, J; Caldwell, J H et al. (1988) Transcellular ion currents and extension of Neurospora crassa hyphae. J Membr Biol 101:33-41 |
| Harold, F M; Schreurs, W J; Harold, R L et al. (1985) Electrobiology of fungal hyphae. Microbiol Sci 2:363-6 |
