Ca2+ and H+ ion fluxes near the surface of gravitropically stimulated Phycomyces sporangiophore

The single-celled fungus Phycomyces blakesleeanus forms vertically oriented sporangiophores from hyphae, which display a negative gravitropic response. Longitudinal growth and gravitropic bending of these sporangiophores were measured with noninvasive H+ and Ca2+ ion-selective microelectrode measurements. The directions of H+ and Ca2+ fluxes, recorded at different locations of sporangiophores, were opposite when the sporangiophores were kept in vertical position. Ca2+ fluxes were in most experiments positive (efflux), while H+ fluxes were negative (influx). The direction of ion fluxes depended on developmental stage of sporangiophores and changed with gravistimulation.