Phycomyces sporangiophores exposed to continuous unilateral illumination reach an angle determined by the competition between phototropism and geotropism. This photogeotropism angle provides a quantitative assay for phototropic sensitivity as a function of light intensity. Seven unlinked genes have been associated with the sensory transduction chain for phototropism. A complete family of single and double mutant strains are available for a standard set of alleles for these genes. Photogeotropism measurements have been carried out comparatively on these strains as well as wild-type and one triple mutant affected in genes associated with early steps in the sensory pathway. These measurements were recorded over a millionfold range of light intensity. The results reveal a variety of reductions in sensitivity and responsiveness for the double mutants. Some of the double mutants, as well as the triple mutant, are extremely insensitive to light, but at the highest intensities none appear to be totally blind. The results are examined in the framework of two models for photogeotropism.
- blue light
- sensory transduction
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology