Ultraviolet-Absorbing Substances Associated With Light-Induced Sporulation in Fungi

An unidentified substance(s), provisionally named P 310 , is produced in mycelia of Alternaria chrysanthemi, Ascochyta pisi, Ophiobolus graminis, Pleospora herbarum, and Pyronema omphalodes when sporulation has been induced with near-ultraviolet radiation. This same substance is absent in non-sporulating colonies grown in darkness. It is, however, present in unexposed colonies of A. pisi grown on media which are able to support sporulation in the absence of light. P 310 is extractable with cold absolute ethanol, is water-soluble, passes through a dialysis membrane, is retained on a cation exchange resin, and appears to be composed of at least four possibly related substances. Maximum absorption of P 310 is between 260 and 340 mμ (310 mμ maximum) and below 250 mμ. P 310 may exist in an oxidized state for when reduced electrolytically, absorption between 260 and 340 mμ is lost. P 310 can be detected spectrophotometrically in extracts of colonies exposed to 6 hours of near-ultraviolet radiation, but not after a 1 hour exposure. Conidiospores of A. pisi contain P 310 , which may be a "sporulating factor" associated with these spores. The rate of P 310 production in irradiated colonies appears to be related to length of exposure, yet this substance can be produced in darkness for a limited period following stimulation of colonies by near-ultraviolet radiation. Neither the identity nor the modus operandi of P 310 has yet been demonstrated.