Diphasic Negative Phototropism of Sporangiophores of the Piloboloid Mutant of Phycomyces blakesleeanus

Abstract

Ootaki, T., and Tsuru, T. 1993. Diphasic negative phototropism of sporangiophores of the piloboloid mutant of Phycomyces blakesleeanus. Experimental Mycology 17, 103-108. The sporangiophore (spph) of a piloboloid mutant of Phycomyces, the extension zone of which expands radially at the final developmental stage (stage IVb) as elongation comes to an end, bends away from light when its diameter exceeds about 210 μm. As spph diameter increases, negative phototropism becomes more marked, with the bending angle showing an asymptotic approach to -40° as the diameter approaches 360 μm. With still larger spphs there is a further rapid increase in bending angle to about -90°. This diphasic pattern of negative bending with the largest spph supports the hypothesis that the optical properties of the nearly transparent extension zone of the spphs are involved in determining the maximal bending angle as well as determining the phototropic direction in this fungus.