MODIFIED ACTION SPECTRA OF PHOTOGEOTROPIC EQUILIBRIUM IN Phycomyces blakesleeanus MUTANTS WITH DEFECTS IN GENES madA, madB, madC, and madH

Abstract— Action spectra of photogeotropic equilibrium were measured for behavioral mutants of Phycomyces blakesleeanus with defects in the genes madB, madC and madH as well as for a double mutant defective in the genes madA and madC. The action spectra of strains C109 (madB), LI madC and L52 madA madC all lack the broad near‐ultraviolet peak which extends from 347 to 386 nm in the wild type; the peaks at 414 and 491 nm are also missing in these mutants. The double mutant L52 madA madC shows a novel broad peak at 477 nm; the relative quantum effectiveness of L52 at 477 nm is 10 times higher than in LI (madC119). These properties of the double mutant L52 madA madC suggest steric interaction of the madA and the madC gene products in the photoreceptor complex. For the hypertropic mutant L84 madH the action spectrum and absolute sensitivity are similar to those for wild type. These results confirm and extend previous findings that multiple photoreceptors are mediating phototropism in P. blakesleeanus.