Light-controlled phorogenesis and mycelial growth in Phycomyces mutants.

Blue light stimulates the formation of giant sporangiophores (macrophores) and inhibits the formation of dwarf sporangiophores (microphores) in Phycomyces grown under certain conditions. The thresholds for these responses are lower than the threshold for phototropism of the macrophores. Mutants in genes madA and madB, originally isolated because of the defective phototropism of their macrophores, are also defective in photomacrophorogenesis and photomicrophorogenesis. These effects of light on mycelial development are thus mediated by gene products involved in the behavioural responses of the macrophores.Another effect of light, the drastic growth inhibition of Phycomyces in 0.18 mM quinacrine, is seemingly independent of the mad sensory pathway.