Untersuchungen über die lichtabhängige Carotinoidsynthese

Abstract

The purpose of these studies was to find which steps in the biosynthetic pathway of carotenoids in Fusarium are under photoregulation. After separation by column chromatography ζ-carotene, neurosporene, γ-carotene, torulene, neurosporaxanthin and lycopene were identified from their absorption spectra in visible light and by co-chromatography tests with carotenoids from other organisms. No other carotenoids were detected. These components were each present in trace amounts (0.5–2 μg/g dry weight) in stricly dark grown cultures. During incubation of the mycelium in buffered glucose solutions in darkness these carotenoids accumulated slowly but linearly with time. After a lag period of 30 min following photoinduction a sequential increase of the carotenoids occurs in the order mentioned above. With the exception of lycopene this sequence follows a decreasing degree of saturation. Addition of cycloheximide at various intervals during the incubation after illumination results in a differential inhibition of the synthesis of the various carotenoids, the pattern of which closely resembles the time sequence of increase of the carotenoids following photoinduction. It is therefore concluded that the synthesis of all these carotenogenic enzymes is photoinduced. Incubation of the mycelium with diphenylamine inhibits carotenoid synthesis; however, after illumination lower concentrations cause an increase in the amount of the more unsaturated components. Incubation with H₂O₂ results in the same time sequence of increase of the carotenoids as after photoinduction, whereas in incubations with mercuribenzoate the pattern is different. Synthesis of sterols (probably ergosterol) is not increased after illumination but is slightly decreased. From these results we conclude that the first step of the biosynthetic pathway on which photoregulation takes place lies between farnesyl-pyrophosphate and the coloured carotenoids.