An unidentified substance(s), provisionally named P310, is produced in mycelia ofAlternaria chrysanthemi, Ascochyta pisi, Ophiobolus graminis, Pleospora herbarum, andPyronema omphalodeswhen 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 ofA. pisigrown on media which are able to support sporulation in the absence of light. P310is 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 P310is between 260 and 340ensp;mmu; (310ensp;mmu; maximum) and below 250ensp;mmu;. P310may exist in an oxidized state for when reduced electrolytically, absorption between 260 and 340ensp;mmu; is lost. P310can be detected spectrophotometrically in extracts of colonies exposed to 6 hours of near-ultraviolet radiation, but not after a 1 hour exposure. Conidiospores ofA. pisicontain P310, which may be a "sporulating factor" associated with these spores. The rate of P310production 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 themodus operandiof P310has yet been demonstrated.
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