Chromosomal variations in intergeneric hybrids among the Triticeae occur consistently and at various phases in the formation and the ontogeny of the hybrid. To a certain extent the events are fortuitous but in other situations the variation may pose a serious constraint in alien genetic transfer programs. Stable amphiplopids are a prerequisite for the development of alien chromosome addition lines and the production of disomic alien chromosome additions could be considerably thwarted if stable amphiploids are not available. This constraint forces the adoption of a methodology where the F1 self-sterile hybrid is utilized to generate F1 backcross I (BC1) progeny. The derivatives are generally stable but do possess the potential of yielding alien structural chromosomal modifications. Cytogenetic screening of large amphiploid and BC1 populations has yielded stable, expected normal plants with high seed fertility. Genomic elimination has also been identified in a low frequency. In the applied alien gene transfer however, chromosomal variations have a decided breeding advantage, particularly for the complex polygenically controlled characters. The occurrence of chromosomal variations is a novel means of augmenting those associated with callus culture and induced mutagenesis. This paper reviews our progress as it elucidates the chromosomal variability in various aspects of intergeneric hybrid production, development, and maintenance of the derived genetic stocks.
New hybrids of Thinopyrum elongatum (2n = 2x =14, EE and 2n = 4x = 28, E1E1E2E2) were obtained with Hordeum vulgare (2n = 2x =14, HH), Secale cereale (2n = 2x =14, RR), and Triticum turgidum (2n = 4x = 28, AABB) in a low frequency. The hybrids were somatically stable with 2n = 3x = 21 chromosomes for Th. elongatum/H. vulgare (E1E2H), Th. elongatum/S. cereale (E1E2R) and T. turgidum/ Th. elongatum (ABE). All hybrids had an intermediate phenotype of the parents and where possible to conduct meiotic analyses expressed a predominant univalent formation at MI, a relationship typical of distant hybrids. In Th. elongatum/ H. vulgare F1 meiotic associations of 20.19 univalents suggest an alteration of the anticipated higher pairing possible due to autosyndesis of the E1E22 genomes of tetraploid Th. elongatum. This may presumably be an influence of the H. vulgare genome.
Wheat (Triticum aestivum L.) varieties with the 1BL/1RS chromosome translocation exhibit a major role in agricultural production, partly attributed to their high yield advantage. The evidence as to whether the 1RS segment may have genetically contributed to this yield advantage has not been unequivocally demonstrated due to lack of appropriate testor germplasm. This analysis now appears possible through the testing of a bread wheat (T. aestivum L. cv. Seri 82) and a durum wheat variety (T. turgidum L. cv. Altar 84) in which their homozygous 1BL/1RS and 1B chromosomes have been substituted by 1B and 1BL/1RS chromosomes respectively. Heterozygote (1BL/1RS, 1B) F1 and backcross derivatives were advanced by eight backcrosses respectively to Seri 82 or Altar 84 with an ultimate selfing to obtain homozygous 1B Seri 82 and 1BL/1RS Altar 84 derivatives. Diagnostic procedure for tracking the 1BL/1RS chromosomes in heterozygous and homozygote derivatives utilized Giemsa C-or N-banding differential staining, electrophoretic biochemical assays and FISH.
Spontaneous centric fusions were detected in two natural populations, Raco (RA) and Tafi Viejo (TV), of Dichroplus elongatus from Tucumán Province (Argentina). In TV one male carried centric fusion between autosomes L3 and M4 (3/4 fusion). One male from RA showed two centric fusions, one between the X and M5 (X/5) and the other between autosomes L1 and M4 (1/4) (in homozygous condition). A significant reduction in the number of chiasmata in the fused bivalents or trivalents with respect to standard karyotypes was observed in all cases except the M4 arm of the 1/4 fusion. Significant chiasma redistribution towards more distal positions was observed in the L1 arm of the 1/4 fusion, the L3 arm of the 3/4 fusion and the L5 arm of the X/5 fusion. These results revealed that a) some fusions per se may affect chiasma conditions, b) the intensity of such effect varies among chromosome pairs.
Rubus croceacanthus (2n = 14), R. minusculus (2n = 14), and their F1 hybrids were cytologically studied. Rubus croceacanthus and R. minusculus showed gradient and symmetric karyotypes uniformly formulated as 2n = 14 =10m + 2sm + 2tst. Their F1 hybrids also had the same karyotypic formulae as the parental species. Almost all PMCs of F1 hybrids showed seven bivalents, and univalents were rare. The karyotypic uniformity between the two species, and the preponderant formation of seven bivalents in their F1 hybrids indicates that R.croceacanthus and R. minusculus are closely related species with no perceptible difference in their genomes.
In the present investigation we studied cytotaxonomically three species of grasshoppers of the family Proscopiidae, Tetanorhynchus silvai, Scleratoscopia protopeirae and S. Spinosa. Analysis of the phallic complex and of external morphological traits showed significant differences between species. In particular, comparative analysis of the phallic complex suggested that Scleratoscopia silvai Jago, 1989 should be reassigned to the genus Tetanorhynchus, as first described by Rehn (1957). T. silvai, S. protopeirae and S. spinosa have diploid numbers of 2n =19 X0 in males and 2n = 20 XX in females. The chromosomes of these species are described here for the first time. Although they present the same diploid number, these species differ in chromosome morphology. T. silvai showed a karyotype consisting solely of acrocentric chromosomes, whereas S. protopeirae and S. spinosa have karyotypes formed by two pairs of submetacentric autosomes and seven pairs of acrocentrics. In these two species, chromosome X is submetacentric. The karyotype of Scleratoscopia was considered to be derived due to the probable occurrence of pericentric inversions from an ancestral karyotypes consisting of acrocentrics. Three species analyzed are monomorphic for their karyotypic constituints. C-banding showed that these species have small blocks of constitutive heterochromatin in all chromosomes in the complement, except for pairs 7 and 8 and for chromosome X of T. silvai, which presented larger blocks. Silver nitrate staining in early prophase and in specrmatids showed the occurrence of at least two nucleoli for each species studied. S. protopeirae and S. spinosa represent the first species in the family Proscopiidae, with a karyotype of 2n =19 (_??_) in which biarmed chromosomes occur. The chromosomal differences between T. silvai and the Scleratoscopia species also support the reassignment of S. silvai to the genus Tetanorhynchus.
The life history and cytology of the freshwater alga Chaetomorpha exilissima sp. nov. (Cladophorales, Chlorophyta) has been studied in detail. The adult gametophyte (n =18) and sporophyte (2n = 36), isomorphic plants were free-floating with multinucleate cells. Pairs of zoosporangia were produced after one cytokinesis from vegetative cells and thus differed morphologically from the latter. In all previously described species the zoosporangia are identical to the vegetative cells. Liberation of zoospores occurs by two opposite pores in the zoosporangium. The progress of the mitosis has been followed in sporophytic plants. The present are the first complete observations of the mitosis in the genus Chaetomorpha. During the process six stages could be distinguished : prophase, metaphase, early anaphase, late anaphase, early telophase and late telophase. The nuclear envelope remained intact during all the stages of the mitosis. The gametic chromosome dotation showed median (m) and submedian (sm) centromeres. Ch. exilissima with a proportion, sm. : m =1 : 2, could be interpreted as an aneuploid n =18 = 4x-6 via reduction of the sm dotation. Considering the formation of zoosporangia by cytokinesis of the vegetative cell, the liberation of zoospores by two opposite pores in the zoosporangium and the isolation of the place in which the species has been found with absence of Chaetomorpha populations in the nearby marine environments, we hypothesize this populations is representative of a new exclusive freshwater species. The most resembling but nonetheless clearly different species is the exclusive freshwater C. herbipolensis.
Cytomixis is described as an spontaneous phenomenon in L. odoratus. Cytoplasmic channels were seen at all stages of microsporogenesis connecting from few to several meiocytes. Chromatin migration between cells was observed mainly at early prophase, metaphase II and telophase II with decreasing frequencies as meiosis advanced. Cytological analysis revealed other abnormalities in very low frequencies such as alteration of bivalents disjuction, laggards and bridges. Degenerating gametes as well as nonreduced gametes and microgametes were observed, although their frequencies varied depending on anthers and floral buds. Significance of cytomixis in pollen viability and seed set is discussed.
A high-resolution G-banding technique was used for identification of the chromosomes of the house musk shrew (Suncus murinusu) and for characterizing their individual G-banding pattern. In order to outline the main identifying characteristics of the individual chromosomes and to make comparable the previously published karyotypes of races and individuals, we included in our analysis a detailed study of G-banded chromosomes of different degrees of resolution at metaphase, prometaphase and prophase. On the basis of this study we have constructed idiograms of prometaphase chromosomes and have proposed a standard karyotype of Suncus murinus.
Actively growing root tips of Vida fabaexcised to about 5 mm length were exposed to hypoxia and the structures of nucleoli were examined under light microscopy. Hypoxic conditions were attained by boiling distilled water for 10 min and immediately cooling with cold tap water. The excised root tips were placed in this hypoxic water for 1, 2, 4, 8, and 16 hr. Controls were kept in distilled water with continuous aeration for the same times. A structural alterations first discerned at 1st hr under hypoxia was segregation of the nucleolar components. This phenomenon, so called the nucleolar segregation, was prominent until 4th hr. Then, the nucleoli began to erode extremely through dispersion, projection or fragmentation of the nucleolar material after the nucleolar segregation. The nucleolar erosion continued to exposed argyrophilic strands, which consisted of beaded segments. These strands are expected to correspond with the nucleolar organizing secondary-constrictions.
Karyotypic analysis of Echeandia hintonii, E. montealbanensis, E. pubescens and three populations of E. reflexa, showed that all of them were diploid with 2n = 16, n = 8 and X = 8. Each species had a distinctive karyotype. Also, each one of the populations of Echeandia reflexa analyzed presented a distinct karyotype. Cytotype variation was observed in heteromorphic chromosome pairs. Meiotic analysis showed heteromorphic exchanges. Analysis ofMI showed heteromorphic IIs, while AI analysis showed U-type chromatid exchanges and subchromatid aberrations. Lagging chromosomes were recorded in AI of E. pubescens and in cytotypes of E. reflexa. Those cytotypes with a larger proportion of chromosomal aberrations, were also those with greater proportion of unviable pollen and a larger value of TCL (genome size). Based on these results and on previous reports, we can suggest that translocations and chromatid exchange, follow a behavior pattern common to species and cytotypes of Echeandia, and that these chromosome aberations have played a major role in the evolution of the genus, providing with a larger potential for colonization and distribution in new habitats.
In this paper, the study of nuclear DNA content was made in nine populations of six taxa in Vicia sect. Vicilla. 2C DNA nuclear content in this section showed significant differences beween species studied. In three infraspecific tetraploid cytotypes observed, variation was found between the highest 2C DNA amount for V. unijuga (32.45 pg) and the lowest for two populations of V. amoena (18.60 pg and 17.19 pg respectively). Those infratetraploid cytotypes in V. amoena, V. ramuliflora and V. unijuga have less DNA amount per basic genome than the conspecific diploids. It was discussed primarily that evolutionary trend of nuclear DNA amount in sect. Vicilla.
We fractionated heat-stable proteins co-purified with microtubules from tobacco BY-2 cells. One of them, a 70 kDa protein, cross-reacted with antibodies against bovine adrenal MAP4. It was also revealed that common epitopes exist in the amino-terminal projection domain of MAP4, at the end opposite the microtubule-binding domain.
Elevation of intra-cellular organelle DNA levels due to preferential synthesis of organelle DNAs before cell multiplication is generally observed in meristematic cells of higher plants, such as those in apical meristems and cultured cells. We analyzed the physiological significance of this phenomena using cultured tobacco cell BY-2 as a model system for cell multiplication in plants. Cultured tobacco cell BY-2 multiplied approximately 50-fold in a week in normal culture medium. However, when nalidixic acid, which inhibits prokaryotic DNA gyrase, was added to the culture, synthesis of organelle DNA was selectively inhibited and cell multiplication was arrested. This indicates that the synthesis of organelle DNAs is a prerequisite for cell multiplication. To quantitatively clarify the effect of the elevation of organelle DNA levels on the capacity for cell proliferation, cells with various organelle DNA levels were prepared by preculturing cells for various lengths of time in culture medium which contained aphidicolin, a specific inhibitor of eukaryotic DNA polymerase a, and then transferring them to culture medium which contained nalidixic acid. Their growth rates in the absence of further organelle DNA synthesis were monitored. A correlation was observed between intra-cellular organelle DNA levels and the capacity of the cells to proliferate, indicating that intra-cellular organelle DNA levels limited the capacity for cell proliferation.