Effect of light on growth and carotenogenesis of the tall conidiophores of Aspergillus giganteus

Abstract

Growth and carotene formation of conidiophores of Aspergillus giganteus Wehmer are enhanced by light. The optimum glucose concentration for maximum conidiophore production in light is 5%; glucose concentration has no influence on the carotene content of the conidiophores over the range 1–20%. Dark grown cultures contain low concentrations of β -carotene and a yellow, methanol-soluble pigment which is thought to be an anthraquinone. Metabolic inhibitors of riboflavin activity ( l -lyxoflavin and mepacrine) and carotene production (diphenylamine) do not inhibit photoinduction of conidiophore growth, whilst only diphenylamine inhibits the photoinduction of carotene formation. Photoinduction of conidiophore growth and carotenogenesis is not dependent upon the presence of oxygen during the period of illumination and is only effective when the mycelium is directly irradiated. The photochemical reaction(s) involved in conidiophore extension and carotenogenesis is (are) of the ‘low energy’ type in which light acts as a ‘triggering’ stimulus. Although light is required for continued conidiophore extension, high light intensities inhibit growth and induce sporulation. The carotene content of the conidiophores increases exponentially with the log of duration of daily light dose. The effectiveness of a given period of illumination in inducing conidiophore growth and carotenogenesis is enhanced at high light intensities, but not at low light intensities, when the frequency of illumination is increased. The frequency of illumination at high light intensities has a significant influence on conidiophore orientation.