Photoreception in Neurospora crassa: correlation of reduced light sensitivity with flavin deficiency.

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Abstract
The effect of flavin deficiency on blue light responses in N. crassa was studied through the use of 2 riboflavin mutants (rib-1 and rib-2). The photoresponses assayed were the suppression of circadian conidiation, the phase shifting of the circadian conidiation rhythm and the induction of carotenoid synthesis. Flavin deficiency was induced in the rib-1 mutant by restrictive growth temperatures and in the rib-2 mutant by low levels of supplemental riboflavin. At 26.degree. C, a semirestrictive growth temperature, the rib-1 mutant is .apprx. 1/80th as sensitive to light for the photosuppression of circadian conidiation. Flavin deficiency in the rib-1 and rib-2 strains was effective in reducint the photosensitivity for phase shifting and carotenogenesis to .apprx. 1/16th and 1/4th of normal, respectively. Experiments with permissive temperatures, riboflavin supplementation, and revertants at the rib locus all indicate that the effects on light sensitivity were due solely to the presence of the rib mutations. Evidently, 1 or more flavin photoreceptors are involved in the blue light responses of Neurospora.
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