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The level of cyclic AMP was studied in two dikaryotic strains of Schizophyllum commune Fr. In the strain 3×4, requiring light for fruiting, the level of cAMP in 72‐h‐old colonies was 12.1 pmol (mg protein)‐1. The level of cAMP increased ca 50% within 2 h of the beginning of exposure to light (UV‐A, 1 h, 8.3 umol m‐2 s_1). During the following 8 h there was a slight decrease in the level of cAMP. In the dark controls the level of cAMP increased ca 13% within 5 h of the light treatment. This slight increase was continued during the next 19 h. In the strain 245 times 252, which forms more fruit bodies than strain 3×4, the increase was ca 110% within 10 h of the light treatment, while in the dark controls the level of cAMP in 82‐h‐old colonies was the same as in 72‐h‐old colonies [10.3 pmol (mg protein)‐1]. During the following 14 h the cAMP content increased sharply (ca 80%) in the dark controls, which might be connected with the ability of strain 245 × 252 to produce fruit bodies in darkness. In dark‐grown colonies of strain 3×4, the level of cAMP was higher in the marginal than in the central zones. The difference disappeared within 2 h of the beginning of exposure to light, since cAMP increased more in the central zone. This difference may be related to the ability of the marginal zone to form fruit bodies in light. [ABSTRACT FROM AUTHOR]

An action spectrum for fruit body formation was determined in the range 280-723 nm for a dikaryon of Schizophyllum commune Fr. Action naxima occurred at 280 and 340-360 nm (main peak), and there were minor peaks at 437 and 467 nm. The quantum effectiveness at 360 nm was ca seven-fold compared to that of 437 nm light. Wavelengths longer than 500 nm were ineffective. Light also induced formation of brown pigment in the area producing fruit bodies. Wavelengths ranging from 260 to 300 nm injured aerial hyphae at the border of the colony. The possibility that a flavin or a pteridine may be the photoreceptor is discussed. [ABSTRACT FROM AUTHOR]