Modified Light-Induced Absorbance Changes indimY Photoresponse Mutants ofTrichodermal Received forpublication November 14,1985andinrevised formMarch3,1986

Abrief pulse ofblue light induces thecommonsoil fungus Trichoderma harziaaum tosporulate. Photoresponse mutants with higher light requirements thanthewild typeareavailable, including oneclass, dimY, with modified absorption spectra. We found blue-light-induced absorbance changes intheblue region ofthespectrum, inwild-type anddimYmutant strains. Thelight-minus-dark difference spectra ofthewild typeandof several other strains indicate photoreduction offlavins andcytochromes, asreported forother fungi andplants. Thedifference spectra instrains with normal photoinduced sporulation have aprominent peakat440nm. After actinic irradiation, this 440nanometer difference peakdecays rapidly inthedark. IntwodimYphotoresponse mutants, thedifference spectra weremodified; inoneofthese, IS44, the440nanometer peak wasundetectable indifference spectra. Detailed study ofthedark-decay kinetics inLS44andthecorresponding control indicated that the440 nanometer difference peakescaped detection in1S44because itdecays faster than inthecontrol. Theaction spectrum ofthe440nmdifference peakisquite different fromthat ofphotoinduced sporulation. Thelightinduced absorbance changes arethusunlikely tobeidentical tothe primary photochemical reaction triggering sporulation. Nevertheless, these results constitute genetic evidence thatphysiologically relevant pigments participate inthese light-induced absorbance changes inTrichoderma.