Growth of the morphological, piloboloid mutants ofPhycomyces blakesleeanus

Abstract The sporangiophore of a growth zone-defective mutant, piloboloid (genotype pil ), of Phycomyces gradually ceases longitudinal elongation and radially expands until the growth zone becomes nearly spherical, shortly after the sporangiophore has reached the final developmental stage. The growth of 23 pil mutants, obtained by mutagenesis with N -methyl- N′ -nitro- N -nitrosoguanidine (NTG), 2-methoxy-6-chloro-9-[3-(ethyl-2-chloroethyl)aminopropylamino]acridine-2HCl (ICR-170), or 4-nitroquinoline-1-oxide (NQO), was studied under different conditions. All pil mutants obtained were genetically homokaryotic. Expansion in the growth zone and degree of synchrony of pil sporangiophore length were both greater at low temperature (10°C) and under white light (10 μW/cm 2 ) than at high temperature (20, 25°C) and in the dark. Dwarf sporangiophores of about 1-mm length, which characteristically stop growing immediately after sporangium formation, did not expand radially. The mycelial morphology of pil mutants was almost normal compared with that of the wild type, though growth was some-what slower in the former than the latter.