title: Action spectrum for the induction of hyphal branches of an arbuscular mycorrhizal fungus: exposure sites versus branching sites.
abstract: The first action spectrum for a photo-induced response of an arbuscular mycorrhizal fungus is reported. At low light intensity, the responsive wavelengths for light-induced hyphal branching of the primary germ tube of Gigaspora gigantea were determined to be in the blue to uv-A range. The action spectrum showed the greatest stimulation of branching occurred around 390 nm although a shoulder was observed between 360-370 nm. A second major peak of light-induced branching occurred at 430 nm. The exposure of specific areas of the germ tube to high intensity blue light for a short period led to several interesting observations. By exposing 2 mm segments (0-2, 2-4, 4-6, etc.) or 3 mm segments away from the tip, it was determined that photoinduction of hyphal branches could occur anywhere along the axis of a growing germ tube except in the apical 2 mm. When 3 mm segments were exposed at greater distances from the tip (6-9, 9-12, and up to 33-36 mm), branches frequently formed in areas not directly exposed to light. The branches were usually in clusters which were spaced approximately 3 or 6 mm apart. Since light scattering could be ruled out, these results indicated that the exposure sites and sites of hyphal branching did not necessarily coincide and suggested the probable involvement of a second messenger during this blue light-induced event.
authors.affiliation: USDA Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA. gnagahashi@arserrc.gov
authors.forename: Gerald
authors.initials: G
authors.lastname: Nagahashi
authors.forename: David D
authors.initials: DD
authors.lastname: Douds
mesh_terms: D008027:Light; D038821:Mycorrhizae / Q000254:growth & development* / Q000502:physiology / Q000528:radiation effects*; D031781:Paspalum / Q000382:microbiology; D018462:Photobiology; D020283:Photoreceptors, Microbial / Q000502:physiology / Q000528:radiation effects
chemical_list: D020283:Photoreceptors, Microbial