The chromosome phenotype in rye changes with growth and development of the plant, such that the largest chromosome volume is attained under conditions of maximum relative growth rate. In addition, a number of environmental factors, viz;-mineral nutrition, growth substances, temperature and root excision, which cause reduced growth, also affect the chromosome phenotype. Slower growth is associated with reduced chromosome volume and a reduced level of total nuclear protein.
Treatment of larvae of Culex pipiens fatigans with chemosterilants viz., apho-late, metepa and hempa, caused various types of chromosomal structural changes in the somatic cells. The action of hempa appeared less drastic than either apholate or metepa. The cytogenetic basis of chemosterilant-induced sterility is discussed in the light of the present findings.
Homologous chromosomes were found to associate in pairs to a varying ex-tent in the root tip cells of Ornithogalum virens (2n=6). In approximately 2 per cent cells, meiosis-like behaviour, viz; bivalent configurations and 'pseudo-chias-mata' were seen. It is proposed that somatic association of homologous chromo-somes may be more prevalent in species with low chromosome number and having vegetative propagation.
The presence of fourth glume, ciliated lodicules, highly irregular meiotic divisions, the nature of inheritance of the character ‘oldness of spikelets’ and functioning of eggs with chromosome numbers other than 2n in crosses with S. spontaneum, distinguish atypical noble canes from S. officinarum 2n=80 forms. Based on the morphological and cytological resemblances of the two of the atypical noble canes to a synthetic interspecific hybrid S. officinarum (2n=80)×S. spontaneum (2n=80), it is suggested that the atypical noble canes are probably of hybrid origin.
Chromosome numbers and karyotypic observations are reported for 22 species of Hesperiidae (Pyrginae and Hesperiinae) found in southwestern North America. Characteristic haploid numbers for certain genera are found: Amblyscirtes (N=29), Chiodes (N=31), Erynnis (N=30 or 31), Heliopetes (N=29 or 30), Panoquina (N=29), and Wallengrenia (N=28, 29, 30). Two genera with widely varying chromo-some numbers are Achalarus (N=16, 29) and Pyrgus (N=28, 32). The pheno-typically unusual Celotes nessus (Edwards) is shown to be cytogenetically distinct from all other Pyrginae with a haploid number of 13-14, the lowest number reported to date for the family Hesperiidae.
Ultrastructural studies of glutaraldehyde-osmium tetroxide fixed root tip cells of Allium sativum revealed that digitonin prevented the formation of microtubules of the mitotic spindle. In telophase, however, a large number of microtubules always formed. These phragmoplast microtubules were functional in the develop-ment of a randomly oriented cell plate. Consequently, the restituted tetraploid nucleus was always associated with a highly branched wall system. A comparative study of treated and untreated cells has indicated that the “mitotic spindle” and the “phragmoplast spindle” are two distinct and functionally independent micro-tubular organelles. Furthermore, it is suggested that the microtubular elements present in these two organelles are not entirely identical in their chemical or archi-tectural makeup.
For the first time the karyotype study is made in the species investigated here. These include one tetraploid taxon also. There are six types of chromosomes in them. All the species studied here excepting C. ferruginea var. β. pilosissima show a pair or two submedian chromosomes with interstitial satellites. On the basis of karyology, C. ferrugiena var. β. pilosissima, C. Wightiana and C. nitens are relatively primitive when compared to C. barkae and C. Grahamiana. The intermediate position is occupied by C. shevaroyensis, C. Leschenaultii and C. orixensis. The inter-relationship among the species is reticulate. The tetraploid C. nitens has closely related genomes. It is possible to say that speciation and evolution in the genus is mostly due to structural changes. The basic number for the genus x=8 is supported by this work.
In unserer Arbeit über die Ultrastruktur der Zellen der Langerhansschen Inseln gelangten wir zu folgenden Schlulßfolgerungen: 1. Die A-, B- and D-Zellen rind in den Inseln des Kopfes, Körpers and der Kauda des Pankreas. Ihr zytologischer Grundaufbau wurde von einer Reihe von Autoren beschrieben and unsere Beobachtung unterscheidet sich lediglich durch den Befund faseriger Strukturen in den B-Granula. 2. Im Processus uncinatus des Hundepankreas sind in den Langerhansschen Inseln and extrainsulär Zellen mit großen hellen Granula. Wir bezeichneten sie als G-Zellen. Selten kommen sie auch extrainsulär in der Pankreaskauda vor. Sie Bind den Gastrin produzierenden Zellen des Gastrointestinaltraktes sehr ähnlich. Neben diesen Zellen sind in den Inseln des Processus uncinatus B- and D-Zellen. A-Zellen fehlen hier. 3. In unserem Material fanden wir keine von Munger et al. (1965) beschrie-bene F-Zellen.
The trisomic plant isolated from gamma-irradiated barley material was pheno-typically different from the normal diploid. The leaves of the trisome were narrow, margins rolled and light green in colour. Ear heads were also short, narrow and irregular. Ovule sterility (42.88 per cent) was relatively higher than pollen sterility (23.47 per cent). Cytological examination at metaphase I revealed 6II+1III, 7II, +1I and 6II+3I. The trivalents were chains of 3 and V, Y, frying pan and Q shaped indicating it to be a primary trisomic. The trisome was crossed with a set of translocation homozygotes and the cytology of the F1 hybrids was studied. This revealed that it was a trisomic for chromosome 3. However, the present trisomic looked different from the pale trisomic for chromosome 3 described by Tsuchiya in 2-rowed barley. Trisomics occurred more frequently in the progeny of smaller seeds of tri-somic plants. Transmission rate of the extra chromosome through ovule was high while it was nil through pollen.
1. The present paper deals with the studies of life-history based upon the cytological features on a fresh-water species of Cladophora viz. C. uberrima Lam-bert, collected from Ranchi in the month of July 1970. 2. Stages of mitosis as well as of meiosis follow a normal course. 3. A count of 12 mitotic and 6 meiotic chromosomes has been determined for this species. The meiotic chromosomal count (n=6) determined in this species is the first record from India. 4. The chromosomes show median and sub-median centromeres like most higher plants. The number of chiasmata in the bivalents ranges from two to four. 5. Meiosis precedes quadriflagellate zoospore formation. Formation of gametes has not been observed, however, it is suspected that they are formed preceding mitotic divisions. Thus, the present alga possesses isomorphic alternation of generations, as other species of Cladophora reported by Schüssnig (1930), Foÿn (1929 and 1934) and Sinha (1963 and 1965). 6. Geitler (1936) holds that the basic chromosome number in Order Clado-phorales is 6 and this number has actually been determined in the present species of Cladophora, lending support to Geitler's (1936) view. 7. Iron-alum acetocarmine method has been used through out the course of this investigation. The authors are grateful to the authorities of University Grants' Commission, New Delhi for financing the scheme.
The interphase nuclei of only a few tissues of males of Tachycines asynamorus exhibit one particularly condensed and large chromocenter, those of females two, on the contrary. This distribution of the sex chromatin indicates 1) failure of a dosage compensation such as in mammalian X's, and 2) the occurrence of a tissue-specific, functional heterochromatization of the one male X and of both female X's in several tissues.
Cytogenetic analysis of the native African pig revealed the presence of auto-somal mosaicism (38/37) in bone marrow tissue. The population of cells with 37 chromosomes show unbalanced karyotype, lacking on large autosomal acrocentric chromosome. The significance of this finding in relation to the karyotype of the European domestic pig (Sus scrofa) and intraspecies hybrids is discussed.
Spores of Osmunda japonica and Pteris vittata were grown on or in the auxin-and sugar-containing media. After about 20 days, the number and length of the rhizoids from a single spore were investigated. The following results were obtained. 1. Under dim green light, spores of Osmunda cultured on a modified Moore's medium containing glucose (1%) or sucrose (1%) were stimulated to form the primary rhizoid on each sopre. 2. Various sugars at 1% under the mineral deficiency increase the number of rhizoids from Pteris spore cells, especially the submerged condition. In higher concentrations (15 or 20%) of sucrose, rhizoid formation from spore cell was greatly inhibited. It develops into apolar, swollen globe. Terminal rhizoid and twin protonemata were sometimes observed with sucrose at the same concentrations.
Numerous stages of apparent cytomixis were observed in one root apex of Allium cepa examined by both light and electron microscopy. The likelihood of this being an artifact due to injury during excision is discussed in relation to report of cytomixis in roots of other species.
Echinochloa crus-galli and E. colonum are widely distributed hexaploid species, and differ from each other in their genomic constitutions. Tetraploid species E. oryzicola is frequently found in paddy fields as a weed mainly in north-east Asia, and is recognized cytologically as a possible tetraploid progenitor of E. crus-galli. Tetraploid strain of E. haploclada used in this study cannot be a tetraploid progenitor of E. colonum, but shows a fair amount of chromosome pairing at nearly the same degree in the F1 hybrids with E. crus-galli, E. colonum and E. oryzicola. This cytological evidence and occurrence of diploid strains of E. pyramidalis and E. haploclada in Kenya and Tanganyika respectively, indicate that tropical East Africa might be one of the presumable centres of origin of the genus.
The chromosome complement of both species of New World flying squirrels, Glaucomys volans and Glaucomys sabrinus, comprise 48 chromosomes, with identical karyotypes. The northern flying squirrel (Gl. sabrinus) distinguishes itself from its southern counterpart (GlL volans) mainly by different geographical distribution and by minor skeletal and coat differences. The discrete morphological differences and the identical karyotypes suggest that the two animals are taxonomically closely related. Autoradiographic studies of somatic chromosomes have revealed the presence of large blocs of autosomal heterochromatin in both species. This heterochromatin was expressed at mitosis by a particular fuzziness of the respective chromosome segments, at interphase as large chromocenters, and at meiosis by heteropycnosis during the first prophase and by diakinetic figures suggesting absence of pairing. The meiotic findings are interpreted as indirect evidence of genetic inactivity of heterochromatin. Autosomal heterochromatin was present in all animals studied (5) and in both species. Two different locations of heterochromatin were found in different animals of the same species (Gl. volans). The two late-labelling patterns appeared mutually exclusive and did not express tissue specificity. This variability of the location of heterochromatin remains unexplained.
Morphological (seedling performance) and cytological (abnormal anaphase) criteria for determining radiosensitivity of Pisum sativum L. were evaluated. The extent of mitotic abnormalities induced by gamma radiation was also considered. The cytological criteria were more nearly accurate and differed significantly from the morphological. Both were negatively correlated with dosage, former being more depressed. Mitotic abnormalities showed dependence of fragment cells and bridges on dosage. Fragments were many and bridges few at low dosages, but fragments declined and bridges increased proportionately at higher dosages.
Observations in the present study have shown a 2.8±0.141 percent incidence of supercontracted metaphases derived from human short-term leucocyte cultures. It is apparent that a type of C-mitosis exists in short-term human leucocyte cul-tures as indicated by the occurrence of C-pairs, by the occurrence of diplo-chromo-somes, and by an indication of the beginning of C-anaphase. Furthermore the occurrence of many scattered supercontracted metaphases can be taken as an indi-cation of C-mitosis. Anaphases derived from both normal and supercontracted metaphases are apparently asynchronous for centromeric separation.
In the multinucleated plasmodium of Physarum polycephalum all nuclei are completely synchronized in mitotic cycle. The duration of a mitotic cycle was 9 hours at 25°C and those of M, G1, S and G2-phase were 0.5 hours, less than 1 minute, 2.5 hours and 6.0 hours, respectively. M-phase was further divided into 15 minutes of prophase, 10 minutes of prometaphase, 5 minutes of metaphase, less than 1 minute of anaphase and 4 minutes of telophase. In the first, incorporation of arginine-3H into total protein of plasmodium was investigated. There were three main peaks: the first one in early S-phase, the second in early G2-phase, and the third in late G2-phase. From the inhibitory effect of cycloheximide on protein syntheses just before and after the start of mitosis, it is considered that protein required for initiation of mitosis is synthesized until before prophase, in the other words, at a phase just before prophase or a little more earlier phase, and another protein that required for shift of mitotic phase from metaphase to anaphase is synthesized probably in prophase and in prometaphase in a certain synthetic rate. Besides, from the inhibitory effect of actinomycin D on mitosis, the RNA required for this mitotic shift is synthesized in premitotic phase about 40 minutes before the start of prophase.