title: Induction of Trichoderma sporulation by nanosecond laser pulses: evidence against cryptochrome cycling.
abstract: An important question in the study of photoreceptor action in morphogenesis is whether the chromophore is unidirectionally photobleached, or whether it is recycled, allowing each receptor molecule to be counted more than once. The common soil fungus Trichoderma harzianum grows vegetatively in the dark and sporulates in response to a pulse of blue or UV-A light. Colonies were grown at 26 degrees C, transferred to 3 degrees C, illuminated with non-saturating light, and then put back at 26 degrees C to sporulate. The fluence-response curves for photoinduction in the cold and at 26 degrees C were identical, indicating that there are no enzymatic transduction processes during irradiation. Regions of the perimeter of dark-grown colonies were given single pulses (maximum duration, 30 ns) at 355 nm with a neodymium laser. We obtained a complete fluence-response curve for the laser pulses, which agreed with data for irradiations in the second to minute range. Photoinduction at 3 degrees C, and validity of Bunsen-Roscoe reciprocity from nanoseconds to minutes, support the hypothesis that the inductive event is a simple first-order photobleaching reaction.
authors.affiliation: Department of Biology, Technion-Israel Institute of Technology, Haifa.
authors.forename: B A
authors.initials: BA
authors.lastname: Horwitz
authors.forename: A
authors.initials: A
authors.lastname: Perlman
authors.forename: J
authors.initials: J
authors.lastname: Gressel
mesh_terms: D003080:Cold Temperature; D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D007834:Lasers; D003904:Mitosporic Fungi / Q000502:physiology*; D010777:Photochemistry; D010786:Photoreceptor Cells / Q000378:metabolism; D017956:Photoreceptor Cells, Invertebrate; D010940:Plant Proteins / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D013172:Spores, Fungal; D014242:Trichoderma / Q000502:physiology* / Q000528:radiation effects
chemical_list: D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D010940:Plant Proteins; D043562:Receptors, G-Protein-Coupled; C119828:cry protein, Drosophila