A mutant of strain 69–1113a of Neurospora crassa, which shows periodic growth upon both complete and minimal media, was named “clock,” and some of the morphological and genetic differences between this mutant and the “patch” and “wild” strains were investigated. In contrast to the uniform growth of “wild,” the “clock” mutant produces a series of bands formed by cymelike aggregations of hyphae which become progressively more dense and finally mark the end (front) of a growth band. A new growth band is formed by a number of hyphae which grow out as in “wild” strains and dichotomize and form new cymes which again become progressively more dense and finally form a new front. It is shown that “clock” continues its rhythmic growth when cultured in continuous darkness. Some “wild” strains were induced to grow periodically on appropriate media. A medium containing equal quantities of sorbose and sucrose caused strain 65–811A (a “wild”) to produce the “patch” type growth. Random isolation, as well as ordered isolation, of ascospores following a cross between “wild” and “clock” show a 1: 1 segregation indicating that “clock” differs from “wild” by a single gene.
Ultrastructural studies of microconidium formation This spores is available in Fungal Genetics Reports:
The investigations described herein were carried out with two standard ('wild') strains and several morphological mutants in order to determine the effect of temperature on the growth rate and, more specificalIy, to study the banding and period of the 'clock' mutants in relation to temperature and growth rate. Strains A description of the strains used is provided below (the roman numeral following most of these descriptions designates the strain's linkage group): 4-121A(TS), 4-137a(TL): standard ('wild') strains of Neuro@ora crassa. Standard strains grow rapidly (approximately 8 cm a day for these strains on complete medium at 25 ° C), produce abtmdant aerial and subsurface growth and nsually some conidia. CLllA: 'clock'. a periodic colonial strain described by Suss~sa~" et al. (1964). The growth bands or 'cycles' are approximately 1.0 cm in length at 25°C on complete medium. (V) CL12a: 'modified clock', a double mutant which has, in addition to the clock allele, another mutant allele called 'mad'. 'Mad' is responsible for the shorter band length of CL12a which is approximately 0.5 cm at 25°C on complete medium. (V) W85a: 'mad', a non-colonial (at temperatures above 15 ° C) nctorphological mutant which has the clock modifier-i allele. (V) El1200: 'osmotic', a strain which is inhibited by high osmotic pressure. (II) P564: 'carpet', a colonial mutant which produces no aerial growth. (II) ¥8743: 'peach', a non-colonial strain which produces quantities of peach colottred conidia. (II) L: 'fluffy', a non-colonial strain in which aerial growth is sparse. (II) 70007: 'colonial-4', a colonial which produces aerial sprays of hyphae, ltsually with much conidiation. (IV) P628: 'fluffyoid'. a non-colonial strain which is aconidial. (IV) R2371: 'shallow', a colonial which grows on the surface of the medium and is very aerobic. (V) B132: 'spray', a semi-colonial strain which produces 'sprays' of aerial hyphae. (V) B106: 'skin', a colonial which does not produce aerial growth or conidia. (VII) These descriptions, strain designations and linkage data are taken from the smnmary of the first 'Neurospora Information Conference' (Publication 950,
Uredospores of Puccinia graminis var. tritici that have been subjected to temperatures below freezing are shown not to differ ultrastructurally from fresh uredospores, although a need for a heat-shock has been induced. Moreover, no ultrastructural differences have been observed between germinating uredospores of both types. Germination results in the formation of large numbers of vesicles and in the change in shape of mitochondria from ellipsoidal and spherical to elongate. A unique aspect of germinating uredospores is found in permanganate-fixed cells wherein electron-transparent patches appear, giving the cytoplasm a "foamy" appearance. The consequences of the suspension of cold-dormant uredospores in liquid medium without a prior heat-shock include irreversible failure to germinate and severe disruption of lipid inclusions and other cytoplasmic elements.
Microconidiating cultures of “peach-fluffy” ( pe, fl; Y8743m, L; FGSC #569) were fixed at various times after the initiation of growth and examined with an electron microscope. Hyphae from which microconidia form are markedly vacuolated and show a much more extensive system of rough endoplasmic reticulum than young vegetative hyphae. A bulge in the hypha presages the start of microconidium formation, followed by the rupture of the outermost wall layers. A thick collar forms around the protruding microconidium due to extensive thickening of the inner wall layer of the parent hypha. At this stage, the cytoplasm of the developing microconidium is still continuous with that of the microsporophore cell from which it arises and is contained by a wall which is derived from the thickened collar. The microconidium is finally isolated from the cytoplasm of the microsporophore by a centripetal extension of the collar. Microconidia differ from macroconidia in having a more extensive endoplasmic reticulum and fewer mitochondria, in addition to being smaller and having a single nucleus.
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