The conversion of isopentenyl pyrophosphate to phytoene in Neurospora crassa requires both a soluble and a particulate fraction. Soluble and particulate enzyme factions obtained from light-treated and dark-grown wid type, albino-i, alZbi-2, albino-3, and white collar-I strains were mixed in various combinations, and the activity for conversion of 11-'4Clisopen-tenyl pyrophosphate to phytoene was assayed. From such experiments it can be concluded that (a) albino-3 is defective in the soluble fraction; (b) albino-2 is defective in the particulate fraction; (c) the in vivo lght treatment increases the enzyme actvity in the particulate fraction; (d) this light effect occurs in wild type, albno-I, and albin-3 straiw and (e) enzyme activity is present in the particulate faction obtained from the white collar-i mutant, but the in vivo light treatment does not cause an increase in this activity. To measure directly the level of particulate enzyme activity,

Positive phototropism of perithecial beaks in the fungus Newrospora crassa has been demonstrated. The effect was shown to be mediated by blue Hght. When mutants (white collar-i and white collar-2) which are blocked In the Ught induction of enzymes in the carotenoid biosynthetic pathway were used as the protoperithecial parent in crosses, the resulting perithecial beaks did not show a phototropic response. However, when wild type, albino-i, albino-2, or albino-3 strains were used as the protoperithecial parent, phototropism occurred.The results show that both photoinduced carotenogenesis and phototropism in N. crassa are controlled by the white collar-i and white collar-2 loci. Thus, the sensory transduction pathways for the two photoresponses must have some steps in common. The results further support the proposal that the white collar strains are regulatory mutants blocked in the light induction process, whereas the albino-1, albino-2, and albino-3 strains can carry out light induction but have the albino phenotype because they are each defective for a different enzyme in the carotenoid biosynthetic pathway.Blue light-induced responses both in higher plants and microorganisms have been extensively studied (see reviews 27, 28). In the fungus Neurospora crassa, blue light has been shown to regulate a number of important processes including carotenoid biosynthesis (8, 24), photosuppression and phase shifting of the circadian rhythm of conidiation (5), photoinduction of protoperithecia formation (15), and under certain conditions promotion of conidiation (16). In Neurospora sitophila, positive phototropism of perithecial beaks (also referred to as perithecial necks) has also been demonstrated (1), but it was not determined whether this phototropic effect is a blue light response.Genetic studies have been carried out with N. crassa (9,17,19,20), Phycomyces blakesleeanus (2, 3, 18, 25), and Trichoderma (11) which are aimed at eventually identifying the blue light photoreceptor(s) (designated 'cryptochrome' [6]). In N. crassa, photoinduced carotenoid biosynthesis was investigated using wc and al mutants (9). The wc phenotype is defined as albino mycelia with normal pigmentation in the conidia, while the a) strains have a reduced level of carotenoid pigment in both the mycelia and conidia (21)(22)(23) proposal, it was predicted that the wc mutants may be blocked in other blue light-mediated responses in Neurospora (9). The present study was undertaken to test this hypothesis. Inasmuch as a phototropic response of N. sitophila perithecial beaks has been previously demonstrated (1), it was decided to determine whether such a response occurs in N. crassa.In the present study, phototropism of perithecial beaks in N. crassa was demonstrated. Furthermore, this response was blocked in perithecial beaks derived from crosses in which wc mutants were used as the protoperithecial (maternal) parent. No defect in phototropism was observed when the protoperithecial parent was wild type or al.MATERIALS AND METHODS Strains. Th...

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An action spectrum for light-induced carotenoid biosynthesis in Neurospora crassa was determined in 4 to 20 nm steps from 260 to 800 nm. Four-day, dark-grown mycelial pads of N. crassa were exposed to varying amounts of monochromatic radiant energy and time. After a 48-hour incubation period at 6 C, carotenoid content was assayed spectrophotometrically in vivo. The action spectrum has maxima at 450 and 481 nm in the visible range and at 280 and 370 nm in the ultraviolet. A pigment synthesized by Neurospora whose absorption spectrum resembles the action spectrum is fl-carotene.A model for the regulation of carotenoid biosynthesis in N. crassa is proposed which describes a mechanism by which f8-carotene could act as a photoregulator. This carotenoid is suggested to be both photoreceptor for and regulator of carotenoid biosynthesis.

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