Phycomyces

Carotene Yellow-orange Phycomyces blakesleeanus (fungus) RP... 

The core of the iron storage protein ferritin consists of a hydrated ferric oxide-phosphate complex. Various models have been proposed which feature Fe111 06 oct., Fe111 O4 tet. or Fe111 O4 tet. Fe111 06 oct. complexing the first listed is preferred by Gray (99) on the basis of the electronic absorption spectrum. The protein very closely related to ferritin which occurs in the mold Phycomyces blakesleeanus contains... 

Fig. 5. Absorption and action spectra in the UV-region. Absorption spectra of (2) auxin178), (4) carotene183), (5) flavin165). Action spectra of (1) the negative phototropism of Phycomyces l, (S) second positive curvature of the avena coleotile38)...

It has been suggested that the photoreceptor might be the 15—15-cis-isomer of j3-carotenoid, which — in contrast to the trans-isomer — shows a UV-peak, as demonstrated in Fig.6 2 and 3,183,194). However, its position exhibits ahypsochromic shift of 30 to 40 nm compared to known action spectra. Moreover, in the only case investigated, that of Phycomyces, no cis-0-carotenoid has been found138). 

Fig. 19. Hypothetical orientation of the SO - SI transition dipoles (blue band) of the bluelight photoreceptor in the Phycomyces sporangiophore as concluded from polarized light experiments96). Horizontally polarized light is about 20% more effective than vertically polarized light, as sketched...

Fig. 22. (A) Comparison of flavin triplet -> triplet absorption spectra (downwards drawn) with bluelight-induced (440 nm) phototropic curvature of aVena coleoptiles as inhibited by strong monochromatic light in the long wave visible region 154). (B) Comparison of the growth response of Phycomyces induced by strong laser light of wavelength longer than 590nm46, with the flavin phosphorescence spectrum los)...

Phycomyces has aroused the interest of biologists for over a century. Yet, in the present mode of approach and definition of its aims, the research with this fungus, as it is being conducted nowadays, is clearly a child of the early period of molecular biology. 

An important basis for the choice of Phycomyces as a model system is its wide range of sensitivity to light which covers about nine decades and which is therefore similar to vertebrate vision. This makes the organism especially suitable for the study of range adjustment, i.e., the phenomenon of adaptation. The potential of Phycomyces as a model system for investigation of differentiation and photo-differentiation has not yet been fully exploited. 

Fig. 3. Phototropism in the wild type NRRL1555 strain and three mutant strains of Phycomyces. After 6 h of illumination with blue light the deviation from the vertical was determined. C47 and 012 are classl mutants C110 is a classII mutant. (From Bergman et al., 1973)...

Fig. 4. Pleiotropism of Phycomyces strains selected as phototropic defective mutants. Mutants madA and madB are defective in all photoresponses, mutants madD, E, F, G only in tropic and growth responses...

The gravity sensor is unknown in Phycomyces. Statoliths have not been detected. Any particle with a density different from that of the average density of the cytoplasm could be a candidate, e.g., mitochondria, lipid droplets, nuclei or crystals. The work of Dennison (1961) has clearly shown that the gravity sensor must be inside the cell because the response is independent of the density of the medium outside the sporangiophore. 

Phycomyces is by no means the only organism that can regulate its own growth with volatile substances. Bonner and Dodd (1962) have reported that Polysphondilium pallidum,Dictyostelium discoideum,D. mucoroides,D. purpureum have the capacity to avoid obstacles. A series of experiments has clearly shown that this orientating effect is due to a gas made by the organism. Attempts to identify this gas have been unsuccessful. 

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