LIGHT-INDUCED CAROTENE SYNTHESIS IN MUTANTS OF PHYCOMYCES WITH ABNORMAL PHOTOTROPISM

Mutants of Phycomyces. abnormal in their phototropic responses (the mad mutants), have been tested for their responses in light-induced carotene synthesis (LICS). The amount of carotene synthesized at any given fluence is significantly lower in the madA, madB and madD mutants than in the wild type. The amount of carotene is not lower in other mad mutants ( madC, madE, madF and madG ). The double mutant mad A madB and the triple mutant mad A madB madC show stronger effects. The wild type strain, as well as those carrying a single mad mutation ( madA and madB ) or those carrying two or three mad mutations ( madA madB. madA madB madC ) show closely similar sensitivity to LICS. This contrasts with phototropism and photoinitiation of sporangiophores which are sensitive to extremely small signals in the wild type and in which the madA mutation decreases the sensitivity by nearly a factor of 10⁴ and madB mutation by a factor of 10⁵. It appears that LICS does not share the signal amplification mechanisms characteristic of the other two responses.