[Light-dependent carotenoid synthesis : I. Action spectrum of photoinduction in Fusarium aquaeductuum]

Abstract

As a first step towards the identification of the photoreceptor responsible for the light-dependent carotenoid synthesis, this paper presents an accurate action spectrum of photoinduction in Fusarium aquaeductuum.As a prerequisite for the determination of the spectrum the optimal conditions for the light-dependent synthesis of pigments were studied. Addition of glucose after illumination enhances the amount of pigment produced in the following darkness, indicating that the limiting factor for pigment formation may be a deficiency of carotenoid precursors. The amount of pigments produced depends on the logarithm of the incident light over a 100 fold range. The reciprocity law holds true over a wide range of time and light intensity.Carotenoid synthesis is induced only by light with wavelength shorter than 520 nm. The action spectrum has maxima at 375/380 nm and 450/455 nm, one shoulder at 430/440 nm and a further shoulder (or possibly a third maximum) between 470 and 480 nm.From this action spectrum carotenoids can be ruled out as possible photoreceptors. The spectrum resembles the absorption spectra of certain flavoproteins. It is therefore concluded that a flavoprotein is the acting photoreceptor; data of other investigators with different organisms also support this conclusion. The action spectrum presented also resembles the spectra of phototropism in Phycomyces-sporangiophores and Avena-coleoptiles; therefore, the possibility is discussed that the same photoreceptor might be acting in all cases in which development and movements are mediated by light of short wavelength.