摘要:

The properties of constitutive heterochromatin so far described, perhaps with the exception of the possibility of being C-banded, are not all common to all the species examined. The use of staining techniques orin vivotreatments makes it possible to demonstrate the existence of a marked heterogeneity of fractions of heterochromatin sometimes located on the same chromosome or even belonging to the same heterochromatin block. Moreover, the analysis of the DNA sequences located in the heterochromatin demonstrates the existence of a marked molecular heterogeneity. The subject is treated in greater detail with regard to the human karyotype.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796923

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

摘要:

Cell cycle kinetics were determined for roots grown either in tanks of water from 24 to 144 hr or in a moistened mixture of vermiculite and perlite (V/P) from 24 to 96 hr. For roots grown in tanks of water Tc was 23.4 hr (TG1= 6.1 hr, TG2—5.5 hr, T2= 9.6 hr, Tm= 2.3 hr) while roots grown in V/P had a shorter Tcof 17 hr (TG1= 5.6 hr, TG2= 4.0 hr, T, = 5.0 hr, Tm= 2.4 hr). Most of the difference in cycle times was due to a disproportionate increase in the duration of S for water grown roots while the duration of G1and G2showed relatively smaller changes. This difference in TSwas coupled with an increase in L.I. in water grown roots over that seen in V/P grown roots, i.e. 31.0 ± 8.6 cf. 25.9 ± 6.5. Changes in the proportions of fast, slow and non-cycling cells also occurred; i.e. in V/P grown roots there were 83.2% fast, 11.4% slow and 5.4% non-cycling cells, while in tanks of water there were 52.9% fast, 22.7% slow and 24.4% non-cycling cells. The results are evidence of differences both in mean cycle duration and phase duration within the cell cycle for roots grown in different volumes of water. They also show that roots respond to different volumes of water by altering their GF and the proportions of fast, slow and non-cycling cells in their meristems. These changes may be part of a mechanism used by roots to regulate the overall rate of cell proliferation and thus to achieve different TDTvalues under different environmental conditions.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796924

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

摘要:

The occurrence of pollen grains germinated inside the anthers is described in eleven non-cleistogamous plant species systematically unrelated and with various ecological requirements. The germination process is similar to the normal one as it occurs on the stigma; pollen tubes are often covered by tryphine.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796925

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

摘要:

Cytochemical studies were undertaken to analyze the effect of kinetin on quantitative and qualitative changes in histones and endogenous RNA content in differentiating metaxylem cells ofZea maysroots. Microspectrophotometric analysis revealed close association between increase in the DNA: histone ratio and increase in RNA content of differentiating metaxylem cells of both, control and kinetin treated root apices. The kinetin treatment caused a larger increase in RNA content per cell but the increase in the DNA: histone ratio did not differ significantly from the developmentally correlated increase observed in the controls. However, the kinetin induced amplification of RNA is associated with an elevation of the arginine: lysine ratio of the histones. It is suggested that kinetin may bring about removal or acetylation of the lysine rich fraction and that this event is a factor in the elevation of the transcriptional activity of chromatin.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796926

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

摘要:

Pseudodiploid Chinese hamster cells (line CHO) were treatedin vitrofor 2 or 32 h with hexavalent chromium compounds (K2Cr2O7and K2CrO4), at concentrations of 10−5M and 10−6M, in medium containing BUdR, and sister chromatid exchanges (SCEs) in 2nd division metaphases were scored. The frequency of SCEsdoubled in pseudodiploid cells, whereas it only rose by 50% in the pseudotetraploid fraction. Also in cytochalasin B-generated pseudotetraploid cells, 10−6M K2Cr2O7induced less SCEsper chromosome than it did in pseudodiploid cells. These observations suggest that at the concentration of chromium used, the number of active molecules available for interaction with chromosomal sites may be limiting. The ratio of 2nd generation (asymmetrical) to 3rd generation (symmetrical) SCEs, scored in 3rd metaphases, was lowered by continuous K2Cr2O7treatment. This apparent excess of symmetrical SCEsin 3rd metaphases could be explained with the induction of single-strand exchanges by chromium. This possibility was supported by the occurrence of light regions in 1st metaphase chromosomes of chromium-treated cells, as well as both « isolabelling » and « isounlabelling » in 2nd metaphases.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796927

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796928

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

摘要:

A population of fresh water planarians ascribable toDugesia gonocepbala s.l., characterized by individuals with markedly aneuploid chromosome sets was found near Sassari at Scala di Giocca in the Rio Bunnari. The most frequent chromosome number in 100 counts of metaphase plates of regenerative blastemata from the tail end of 7 different specimens proved to be 32, with a rather low frequency of 17%; after 32, the most frequent numbers were found to be 30, 31 and 27. Great numerical variations in the chromosome numbers were found, from a minimum of 16 to a maximum of more than 50. In all the sets with 32 chromosomes studied, 32 was never eutetraploid but always an aneuploid number; furthermore, a varying number of large submetacentric chromosomes was found in all the aneuploid sets examined. The authors point out that gynogenetic planarians with chromosome sets of 2n = 3x = 24 are to be found in the Rio Mascari, near the confluence of the Rio Bunnari, and amphigonic planarians with chromosome sets of 2n = 14; n = 7, characterized by a pair of large submetacentric chromosomes, identical to those in the aneuploid sets, are to be found in the Rio Bunnari. For these reasons the authors believe that the aneuploid population in the Rio Bunnari is in fact a stabilized natural hybrid originated from cross-breeding between individuals with 2n = 3x = 24 chromosomes, functioning as males, and individuals with 2n = 14; n = 7 chromosomes, functioning as females. It is suggested that the hybrid population might have reached its present stabilized condition according to the following succession of events: poly- ploidization of the initial hybrid chromosome set which thus became tetraploid (60 chromosomes); segregational mitoses of the neoblasts with 60 chromosomes resulting in various reductions in the chromosome number of the sets; assertion of the aneuploid sets in which chromosome numbers of 32, 30, 31 and 27 are most frequently found; reproduction by gynogenesis.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796929

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

摘要:

The haploid number 25 has been found in males ofGobius niger jozoandGobius paganellusfrom the Venice Lagon, whereas the diploid number 48 was elsewhere found forG. niger jozofrom the Tirrenian sea. Spermatocyte bivalents at diakinesis seem achiasmatic or bear a low number of chiasmata.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796930

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

摘要:

Nucleolar development and nucleolar organizer (NOR) activity are analyzed during spermatogenesis ofSchistocerca gregariaby silver impregnation. Two NORs located distally in M6and proximally in S9show activity during early prophase of the first meiotic division. A reactivation of the NORs with the appearance of nucleolar masses and a chromosome arrangement in which all centromeres are placed in the nuclear base are observed in spermatids. Different aspects related to the location of NORs and the N-banding patterns based in previous observations are discussed.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796931

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor

摘要:

The karyotypes ofRousettus leschenaulti, Cynopterus spinhx, Eonycteris spelaea, Scotophilus kuhlt, Tadarida plicata, Megaerops ecaudatus, Taphozous theobaldi, Rhinolophus acuminatus, Rhinolophus malayanus, Rhinolophus coelophylus, Hipposideros lekaguliandHipposideros larvatusfrom Thailand are investigated. Karyotypes of 7 latter species are described for the first time. Comparison of karyotypic data of all related species and phylogenetic relationship had been discussed.

ISSN:0008-7114    

DOI:10.1080/00087114.1982.10796932

出版商:Taylor & Francis    

年代:1982

数据来源: Taylor