Cytogenetic investigations were carried out on two populations of Astyanax scabripinnis (Pisces, Characidae, Tetragonopterinae) allopatrically distributed at different altitudes in a stream called Piracuama (Paraíba do Sul Basin, Brazil). Specimens collected at 1800m altitude revealed a diploid number of 2n=50 and a karyotype consisting of 6M+24SM+6ST+14A, with a fundamental number of FN=86. In one of the individuals from this location, we detected the presence of a B-macrochromosome (approximately 8.5% of the haploid complement) similar to those of the first pair in the complement and C positive banding in all extention. The specimens collected from the population located at 780m in the same stream also presented 2n=50, but a karyotype consisting of 4M+10SM+6ST+30A characterized by FN=70. The number of chromosomes bearing nucleolar organizer regions (NORs) also proved to be a differentiation factor at the level of cytogenetic analysis between the specimens of the two populations studied. The distribution of few heterochromatin spots in the chromosomes was a characteristic of both populations. A brief review about the chromosome information currently available about the A. scabripinnis complex is also presented and the possible evolutionary mechanisms involved in the great diversity and speciation of this complex are discussed.
We investigated the change of silicon content in heads and midpieces, of Chinese hamster spermatozoa during the passage through the epididymis. The present result shows that silicon in the spermatozoa tend to reduce during the passage through the epididymis, and silicon in the spermatozoa increased after ejaculation.
Longitudinal differentiation of metaphase chromosomes has been investigated using several techniques. Recently Cuellar et al. (1991) using Fluram induced species dependent C and G-bands in mammaliam chromosomes revealing heterogeneous distribution of chromosomal proteins. Metaphase chromosomes from root tips of three plant species as Vicia faba, Allium cepa and Dasypyrum villosum were tested by Fluram in order to verify if, in plant, is possible to obtain Fluram banding. No banding pattern was observed and all regions of the chromosomes showed a slight and diffuse fluorescence.
Cytological stability of the 6 and 12 week old embryogenic callus initiated from immature inflorescence explant was investigated in five inbred lines of Pennisetum glaucum (L.) R. Br. Three different types of embryogenic cells have been observed. Different types of chromosomal abnormalities in the embryogenic cell populations include hypo-haploidy, aneuploidy and polyploidy. The extent of chromosomal variability depended upon the age of the callus, 2, 4-D concentration and genotype. No specific dose-response relationship was observed between the 2, 4-D concentration and the frequency of abnormalities in the calli. The regenerants were all diploids. The operation of a selection mechanism within the embryogenic callus favouring the development of normal diploid regenerants has been inferred.
Somatic chromosome numbers and 2C DNA values of seven taxa of Leucaena are reported. Leucaena diversifolia subsp. diversifolia, L. d. subsp. stenocarpa, L. lancoelata subsp. lancoelata and L. l. subsp. sousae were diploid. Leucaena confertiflora subsp. adenotheloidea and L. esculenta subspa paniculata were tetraploid. Leucaena esculenta subsp. esculenta, showed diploid and tetraploid froms. Diploid taxa showed intra-individual variation with 2n=52, 54 and 56, the most frequent being 2n=56. Tetraploid taxa showed 2n=104, 108, 110 and 112, the most frequent being 2n=112. In five diploid taxa of Leucaena studied 2C DNA values showed significantl variation only between L. diversifolia subsp. diversifolia (1.81 pg) and L. esculenta subsp. esculenta (1.35 pg). Genome size did not differ among subspecies pairs (L. d. subsp. diversifolia vs L. d. subsp. stenocarpa and L. lanceolata subsp. lanceolata vs L. 1. subsp. sousae). In three tetraploid taxa analyzed, DNA content varied between 2.66 pg (L. esculenta subsp. paniculata) and 3.31 pg (L. confertiflora subsp. adenotheloidea). DNA content of tetraploids was approximately twice that of diploids, suggesting that the polyploid taxa studied have a relatively recent origin. No relation was found between incipient domestication of L. confertiflora subsp. adenotheloidea and ploidy level.
In this paper the karyotype of Plecotus mexicanus, a Mexican endemic species, is described and compared with those of the other species of the genus. It was found that P. mexicanus shares several features with P. townsendii and P. rafinsesqui such as diploid number 2n=32, a fundamental number of 52, acrocentric sex chromosomes and the submetacentric chromosome pair 10; the last is a new distinctive character between the American and European forms of the genus Plecotus.
Drosera dichrosepala was exposed to different doses of Gamma radiation. Fragmented and fused chromosomes were observed as a consequences. Diffused centromeres in every fragment chromosome was detected by centromeric banding (Cd-banding) and was supported by its typical disjunction and totally lack of lagging chromosomes or micronuclei from anaphase to telophase. C-banding revealed that the fragment chromosomes were highly heterochromatic and fragmentation might be occurred at the terminal regions of chromosomes. Fluorescent banding suggested that most of the fragment chromosomes were rich in GC base composition in the species. Alteration of karyotype due to Gamma irradiation also indicated that spontaneous fragmentation or fusion of chromosomes might be a possible factor for promoting the bimodal karyotype in this genus.
The karyotype of the hylodine frog Maegaelosia massarti is reported. The species has 2n=28 chromosomes, of which 07 pairs are metacentric, 06 submetacentric and 01 subtelocentric. NOR is located at the secondary constriction on the short arms of the submetacentric third pair. The chromosome number of M. massarti differs from the modal number (2n=26) of hylodine.
A total of 391 accessions from 11 populations of Japanese Artemisia keiskeana were cytologically examined. Twenty-one percent of these accessions carried B chromosomes in addition to the regular diploid complement and 3.5% were triploids. The frequency of plant with B chromosomes ranged from 0% to 59% among 11 populations. B chromosomes were 1/2-1/5 in length as compared with the smallest autosome and were euchromatic in nature. They were ususally mitotically unstable and varied in number from zero to ten both within and between plants. This variation in number of B chromosomes within a plant may be caused by the non-disjunction and unequall segregation during mitotic anaphase. These B chromosomes seemed not to have any phenotypic consequences on plant. Neverthless B chromosomes have been found in 6 examined populations distantly isolated from each other and have occurred in large proportion of the individuals of three populations around the boundary of Okayama and Hiroshima Prefectures. The non-random spatial distribution of plants with or without B chromosome in these natural populations may, at least in part, be due to asexual reproduction. Triploids were found in 2 populations distantly isolated from each other. They are karyotypi-cally auto-triploids. They have occurred spontaneously and are maintained asexually in natual populations.
The chromosome number of Sargassum thunbergii (Mertens ex Roth) Kuntze (Fucales, Phaeophyta) was determined as n=32 at late prophase and early metaphase in the first nuclear divisions in the antheridia. One of the chromosomes was detected as a large element at metaphase in the nuclear divisions leading to the spermatia formation in the antheridia.
Guizotia Cass. is a small genus comprising six species of family Asteraceae and one of the species G. abyssinica is an important oil-seed cultivated in India and east Africa. Baagoe (1974) revised this genus based upon the morphological similarities and she proposed that G. ab-yssinica, G. scabra and G. schimperi are closely related species. Further, she merged G. schimperi under the subspecies ranks as G. scabra. Cytological studies were undertaken to ascertain the taxonomic position of these species and which reveals that karyotype of G. abyssinica and G. schimperi (2n=30) were symmetrical with median chromosomes, whereas, G. scabra (2n=30) showed asymmetrical karyotype with sumbedian and subterminal chromosomes. Further, karyotype of G. schimperi and G. abyssinica were similar and karyomorpholo-gically they are identical. Genome analyses work of Murthy et al. (1993) showed genomes of G. abyssinica and G. schimperi are similar and G. schimperi is thought to be the progenitor of domesticated G. abyssinica. Thus, G. schimperi cannot be considered as subspecies of G. scabra as proposed by Baagoe (1974). We considered that G. schimperi be merged into the subspecies of G. abyssinica.
Embryo sac developmental examination in four cultivated Asian cassava clones: ‘Rayong 3’ (MMex 57×Mven 307), ‘Rayong 60’ (MCol 1684×Rayong 1), ‘Rayong 90’ (CMC 76×V 43, Sarakarn 1993), and ‘CMR 25-105-112’ (27-77-10×Rayong 3, Kawano et al. 1990) was conducted to elucidate the reproductive and conventional breeding barriers (fertilization failure, seed abortion and poor germination) in the genus Manihot. Late pre- and post-pollination embryology revealed absence of functional megaspore mother cell and megagametophytes respectively. Malformed megagametophytes were characterized with reduction in embryo sac volume (8-12.5% of normal), devoid of nucleate cells especially, polar and the antipodal cells, massively vacuolated with no recognizable zygotes or embryos. Regular embryo sacs commenced degeneration 8 days after anthesis in unfertilized ovules of all zero pollinated pistils. Degeneration signal initiated from its thin cell wall and transducted radially inwards and outwards to the central cell and the surrounding nucellus respectively. Both integuments (inner and outer) as well as the nucellus of functional (possessing nucleate cells) and non-functional (deprived of nucleate cells) megagametophytes appeared healthy and developed normally. Physical seed analysis showed that phenotypically normal but functionally deprived ‘pseudo-seed’ (without endosperm and embryo) and ‘true seed’ are produced at a ratio of approximately 1:2. Two distinct but complementary developmental pathways of fertilization failure, seed abortion as well as poor germination in cassava have been identified. They are: 1. Ovules devoid of functional megaspore due to lack of megasporocyte during megasporogenesis and 2. Embryo sacs devoid of nucleate cells due to mitotic inactivity at megagametogenesis resulting in structurally and functionally deprived megagametophyte but morphologically normal ovules. These pathways, either separately or collectively are implicated as largely responsible for the reproductive and conventional breeding barriers in the genus Manihot.
The distribution patterns of microtubules (MTs) in the mitotic cells of Spirogyra were examined by immunofluorescence microscopy. Some of the cortical MTs and MT-fibrils in the cytoplasmic strands at interphase seemed to be organized into MT-belts at prophase. The MT-belts fused side by side, decreased in length and developed into spindle-MTs at metaphase. During polar separation at anaphase, the shape and size of the half-spindles remained almost unchanged. Considerable amounts of polar MTs were seen between the two separating half-spindles. It seems possible that these polar MTs, which could consist of pairs of antiparallel MTs, might push the poles apart by a sliding mechanism.