Sensory responses of phycomyces: I. Blue-light control of sporangiophore initiation. II. Classification of mad mutants

• Main Author: Bergman, Kostia
• Format: Others
• Published: 1972
• Online Access: https://thesis.library.caltech.edu/3071/1/Bergman_k_1972.pdf; Bergman, Kostia (1972) Sensory responses of phycomyces: I. Blue-light control of sporangiophore initiation. II. Classification of mad mutants. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/K2PW-6W48. https://resolver.caltech.edu/CaltechETD:etd-08092006-110158 <https://resolver.caltech.edu/CaltechETD:etd-08092006-110158>

Part I. Blue-Light Control of Sporangiophore Initiation: Many fungi produce spores or spore-bearing structures under the control of blue light. Phycomyces sporangiophores are produced continuously along racing tube cultures grown in constant darkness or constant light. However, if a dark-grown culture is exposed to light for a short time on one day a narrow, dense band of sporangiophores is observed the next day at that point of the tube occupied by the mycelial tips during the light pulse. A periodic program with "short days", (e.g. 4-hour light/20-hour dark) leads to periodic bands of sporangiophores spaced at intervals corresponding to one period-length (in this case 24 hours) of mycelial growth. Sporangiophore initiation is inhibited by a light to dark transition and is stimulated by a dark to light transition. A partial action spectrum of the initiation response, covering the critical 480 nm to 540 nm region, strongly suggests that the same photo-receptor-pigment is involved as in the phototropic response and light growth response of sporangiophores. Mutants with altered light control of sporangiophore initiation have been found among those selected for altered phototropism. This joint elimination of these two responses to blue light by a single mutation is evidence for a common early transduction system. The extensive literature on the effects of light on fungal sporulation is reviewed. Part II. Classification of mad Mutants: Mutants of Phycomyces with altered responses of their sporangiophores to light are called mad. Simple quantitative tests have been devised and used to separate the mad mutants into phenotypic classes based on three sensory responses: phototropism of sporangiophores, avoidance of solid objects by sporangiophores (or auto-chemotropism), and light control of sporangiophore initiation. Class 1 mutants have altered phototropism but normal avoidance. Some of these mutants show phototropism only at intensities 10(6) times higher than the wild type threshold, but none are completely non-phototropic. Class 1 is divided into two subclasses. Class 1-1 mutants are also deficient in light control of sporangiophore initiation. Class 1-2 mutants show normal light control of sporangiophore initiation. Class 2 mutants have altered phototropism and altered avoidance but normal light control of sporangiophore initiation. A simple model of the organization of the sensory systems of Phycomyces is proposed.