Untersuchungen über die lichtabhängige Carotinoidsynthese

Summary 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 -carotene, neurosporene, -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 g/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.

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Die Untersuchungen wurden in großzügiger Weise von der Deutschen Forschungsgemeinschaft unterstützt.     

VIRUS-LIKE PARTICLES AND NUCLEAR INCLUSIONS IN THE RED ALGA PORPHYRIDIUM PURPUREUM (BORY) DREW ET ROSS1

Ultrastructural examination of the unicellular red alga Porphyridium purpureum has revealed cytoplasmic and nuclear inclusions termed concentrosomes. These bodies are morphologically distinct from the irregular membranous inclusions previously reported by others as concentric bodies. In thin section, the morphology of concentrosomes varies from a simple set of 3 or 4 (or rarely 5) concentrically arranged, electron-opaque, circular profiles to elongate, sinuous forms and particulate aggregations, the majority clearly within the nucleus but separated front the nucleoplasm by what appears to be the nuclear envelope. Although simple concentrosomes may be observed in either the cytoplasm or the nuclei, the more elaborate forms occur only in nuclei. In addition to the concentrosomes, subspherical to polygonal virus-like particles of approximately 40 nm diameter have been observed in P. purpureum. These particles are characterized by an electron-opaque perimeter that, in approximately equal numbers, surrounds an “empty” or an opaque core. Dense arrays of the virus-like particles appear in the cytoplasm but not in the nuclei. Similarities between certain forms of the concentrosomes and the virus-like particles are suggestive of an ontogenetic relationship. The infrequency with which either the concentrosomes or the virus-like particles are observed has hampered attempts to verify a developmental sequence or to establish unequivocally the infectious nature of the virus-like particles.     

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Theoretical and Applied Genetics -     

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