摘要:

The nucleolus organizing region (NOR) in root tip meristems ofAllium cepawas first characterized by electron microscopy during the course of mitosis. The NOR was found to be organized into a cluster of dense bodies in prophase. This structural organization persisted through metaphase and anaphase to early telophase, at which time the cluster of dense bodies began to loosen and intermingle with newly synthesized nucleolar material. In the interphase nucleolus of an actively growing cell, however, the cluster of dense bodies was not detected; instead patches of chromatin-like fibrillar material were found. These fibrillar patches varied in number, size and degree of condensation from cell to cell. Interestingly, clusters of dense bodies essentially the same as those detected in mitosis were also found in poorly developed nucleoli of differentiated cells such as those of the root cap, cortex and stele. The present study suggests that the structural organization of the NOR is closely correlated with nucleolar activity.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797747

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

When exposed to Congo red,Rhodotorula glutinishalts cell proliferation, whereasSaccharomyces cerevisiaecontinues to bud; however, the separation between mother and daughter cells is impeded. Both yeasts develop diverse wall and septum abnormalities due to the accumulation of amorphous materials instead of chitin microfibrils. InSaccbaromyces, the original wall frequently breaks and numerous vesicles, probably of a secretory nature, are visible in the cytoplasm. The microorganisms employed react differently to Congo red exposure due to the different roles that chitin plays in their walls. To explain why Congo red forces chitin synthase to form excessive amounts of N-acetylglucosamine chains with a random distribution, a model is proposed in which multienzyme complexes dissociate into single units since the polymers under synthesis, with the dye attached, can not assemble regularly. Each enzyme subunit continues to form glucan chains while it moves freely and randomly along the plasma membrane.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797748

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

Ten neotropical species of family Cichlidae (Pisces: Perciformes) were analyzed cytogenetically. The results obtained also support the indications that the chromosomal evolution of this group was more conservative than divergent from the numerical point of view. All species showed a chromosome number of 2n= 48, although differences in chromosome morphology were observed. The speciesChaetobranchopsis australeexhibited a karyotype consisting of 48 subtelo-acrocentric chromosomes, which is possibly of a more primitive type in relation to the karyotypes of the remaining species investigated. No chromosome differences were detected between males and females, indicating the absence of morphologically differentiated sex chromosomes.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797749

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

An exhaustive karyometric analysis reaffirms that the Benazzi's G biotype represents a tetraploid or aneutetraploid form ofDugesia benazzti.As previous observations have shown, its characteristics, which combine polyploidy, asynapsis and pseudogamy, are controlled by multifactorial mechanisms that are entirely independent of those determining aneuploidy. We therefore disagree with the claim that the G biotype represents a stabilized interspecific hybrid.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797750

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

Prometaphase preparations have been used to construct a ‘standard’ RBA-banded karyotype of the swamp buffalo(Bubalus bubalisL., 2n= 48) and to compare the banding homologies between buffalo and cattle (Bos taurusL.). A double numbering system, one progressive and one corresponding to the standardized nomenclature of cattle chromosomes, has been used in order to facilitate banding pattern comparisons between the two species. Evolutionary relationships between Asiatic buffalo and European cattle have been also examined on the basis of the RBA and C-banding pattern of the X and Y chromosomes of the two species.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797751

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

Cuttings of2xand4x Ruelliaspecies, their2x, 3x and4xhybrids were irradiated at 2, 4 and 6 Krad of gamma rays (CO60). Radiosensitivity of the above genotypes in relation to ploidy and hybridity was studied using the parameters like sprouting of cuttings, survival, growth reduction, final height, number of branches and pollen fertility. Differences in sensitivity of different species of the same ploidy level were noticed. Tetraploids in general, were radioresistant. Hybridity increases the resistance of diploid hybrid above that of its parents. Polyploid hybrids were intermediate to their parents in radioresistance and the cancellation of the negative and positive effects of the alleles has been suggested as the probable reason for it. ICV (interphase chromosome volume) of all the species and hybrids was determined and the possible correlation of ICV with radiosensitivity is discussed.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797752

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

The constitutive heterochromatin ofProasellus coxalis(2n= 12) fluoresces brightly when stained with chromomycin A3. It is located in a telomeric position on several chromosomes and displays considerable interindividual polymorphism both with regard to the number of sites (1–4) and their size. Silver-staining reveals that there are at least four chromosome pairs bearing nucleolus organizers and these are present at all the stages of mitosis and meiosis. The karyotypes ofProasellus coxalisandAsellus aquations, two species once considered congeneric, are compared.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797753

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

Analyses of the nucleolar organizing region (NOR) of the salivary gland polytene chromosomes ofSciara ocellarisshow that at the end of the 4thinstar, during the time of metamorphosis induction, the NORs undergo a gradual condensation. The cytologically visible nucleolar inactivation is paralleled by the inhibition of the incorporation of (H3)-uridine into the ribosomal RNA. These patterns of nucleolar inactivation could be induced prematurely by an «in vivo» treatment with ecdyster-one.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797754

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

In the present study, 10 neotropical species of family Cichlidae (Pisces, Perciformes) were submitted to analysis of the nucleolar organizing regions (NORs). In 8 of these species, the NORs were located in the first pair in the complement and coincided with the secondary constrictions observed there, whereas inCichlasoma facetumandGeophagus brasiliensisthe NORs were located in another chromosome pair. The possibility that the predominant location of NORs in the 1st pair in the karyotype indicates a more primitive condition of this group of fish is discussed. Variations in NOR size between homologous chromosomes of some species were also observed.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797755

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor

摘要:

The karyotype of the silky anteaterCyclopes didactylus, the smallest of the anteaters is described. A notable difference in karyotypes exists between C.didactylus(2n= 64) and the other species of the family Myrmecophagidae. Both fusion/fission as well as other mechanisms are probably involved in the reduction of the chromosome number of 64 chromosome inCyclopesto 60 and 54 inTamanduaandMyrmecophaga, respectively.

ISSN:0008-7114    

DOI:10.1080/00087114.1985.10797756

出版商:Taylor & Francis    

年代:1985

数据来源: Taylor