PHOTOREACTIVATION OF UV-INACTIVATED SPORES OF TRICHODERMA-HARZIANUM

Photoreactivation in the filamentous soil fungus Trichoderma harzianum is of interest because its blue, WA photoreceptors (cryptochromes) ma y share homology with DNA photolyases. Furthermore, this organism anta gonizes, by mycoparasitism, a number of soil-borne pathogens. Photorea ctivation is thus important as one of the factors that may contribute to survival in the held, Exposure of asexually produced spores (conidi a) to UVC inhibits germination. Nongerminating spores either do not sw ell or are inhibited later in germination, swelling but failing to put out a germ tube, Both types of inhibition can be reversed by photorea ctivation with visible and UVA (320-400 nm) light, restoring high germ ination percentages, Conidia of mutants lacking the normal greenish pi gmentation are more sensitive to UVC (200-280 mm) than wild-type conid ia but photoreactivation still occurs, The action spectrum for photore activation indicates that T. harzianum has a DNA photolyase with a pte rin as second chromophore. The most effective wavelengths for photorea ctivation correspond to valleys, rather than peaks, in the action spec trum for photoinduction of sporulation, Furthermore, mutants with defe cts in photoinduction of sporulation (dimY) are not defective in photo reactivation. Induction of sporulation and DNA photorepair, while shar ing parts of the blue/UVA spectrum, are different, by spectroscopic, k inetic and genetic criteria.