Directed Growth of Fungal Hyphae in an Electric Field

Abstract

Abstract The galvanotropic response of the mycelial fungus Neurospora crassa is investigated. The angle distribution function of growing hyphae is described by a generating function which contains two non-trivial terms; one for directional growth and one for bidirectional growth. The following results were obtained, (i) Germ tubes grew towards the anode, (ii) The cellular response was linear for small sized cells and weaker electric fields. The galvanotropic constant, KGROW, which describes the linear response, was small for short germ tubes or hyphae (AGROW -1 = -20 V -cm-1 for I0 = 10 |am) and large for longer cells (AGROW -1 = -1 -7 V ·cm-1 for I0 = 100 μm). The growth coefficient KP of (-18.5 mV) describes the response independent of cell size. The linear response is explained by the field-induced distribution of charged membrane- bound proteins essential for galvanotropism. (iii) For E > E0 = 3.8 V ·cm-1, the linear response is inhibited (inhibition coefficient K1 = 1.11). The inhibition is explained by field-induced changes of the membrane potential, (iv) The galvanotropic response of longer hyphae was bidirectional. The cells grew on average perpendicular to the applied field. The bidirectional response is proportional to Er with a bidirectional growth coefficient K2 of -(0.25 V)-2. The bidirectional growth is explained by the inhibition of the directed growth process. The transition from anode-directed to bidirectional growth was a function of the applied electric field as well as of the tube length (directed growth for E2-l0< 4.4V2·cm-1 and bidirectional growth for E2·l0> 4.4 V2· cm-1).