Eduardo J. Greizerstein

Male meiotic behaviour and nucleolus organizer regions in Camptischium clavipes (Fabr.) (Coreidae, Heteroptera) analyzed by fluorescent banding and in situ hybridization

Abstract — All heteropteran species possess holokinetic chromosomes and a pre-reductional type of meiosis. Autosomal bivalents segregate reductionally at meiosis I while the sex chromosomes do so equationally; the m chromosome pair is achiasmatic and also divides pre-reductionally. Previous reports support the hypothesis that during meiosis both ends of a chromosome are able to show kinetic activity, and that those chromosome ends of the autosomes that were kinetically active during the first meiotic division are inactive in the second one. Camptischium clavipes presents a male karyotype (2n = 21 = 18 + 2m + X0) and a male meiosis that are in agreement with most members of the family Coreidae. Different chromosome banding techniques reveal the presence of small C positive heterochromatin bands at telomeric positions, and a DAPI dull/ CMA bright band at the subtelomeric region of the largest autosomal pair. This band corresponds to the nucleolus organizing region as revealed by in situ hybridization. We used the NOR as a cytological marker and our observations give further support to the hypothesis on the alternate kinetic activity of telomeric regions of autosomes at meiosis I and II in Heteroptera. Besides, the location of the NOR in C. clavipes is compared with previous reports in other heteropteran species.

Ploidy levels and their relationships with the rainfall in several populations of Patagonian species of Berberis L.

Abstract The ploidy levels and pollen staining of 68 populations belonging to 13 species of the genus Berberis L., growing in the Argentinian Patagonia under different environmental conditions, were analyzed as a part of a multidisciplinary study to obtain information about the evolutionary history of the genus. The chromosome number at Berberis bidentata, B. cabrerae, B. chillanensis, B. darwinii, B. empetrifolia, B. ilicifolia, B. linearifolia, B. micro-phylla, B. montana, B. parodii and B. serrato-dentata is 2n = 28, whereas B. buxifolia and B. heterophylla have 2n 56. The relationship between ploidy levels and rainfall showed that, contrarily to the species with 2n = 28, B. buxifolia and B. heterophylla (2n =56) grow in areas where the rainfall range is low. The opening of new habitats for colonization as a result of climatic change provides an ecological opportunity for the polyploids to exploit their inherent advantage.

Cytogenetic studies in four cultivated Amaranthus (Amaranthaceae) species

Abstract In the present study, the chromosomes numbers were confirmed, 2n = 34 for Amaranthus cruentus Linnaeus, 1759, and 2n = 32 for Amaranthus hypochondriacus Linnaeus, 1753, Amaranthus mantegazzianus Passer, 1864, and Amaranthus caudatus Linnaeus, 1753. The distribution and variability of constitutive heterochromatin were detailed using DAPI-CMA3 banding technique. The position of the nucleolus organizer region (NOR) was observed using Ag-NOR banding (active loci) and fluorescent in situ hybridization (rDNA-FISH) in the four Amaranthus species. Variations in the amount of constitutive heterochromatin were detected both within the species and between them, with DAPI-CMA3 stain. One chromosome pair having a NOR was found in each studied accession, with exception of Amaranthus caudatus cv. EEA INTA Anguil. This accession presented four rDNA loci (FISH), being active two of them (Ag- banding).

Cytogenetic studies of Southern South-American Ilex

Abstract The dioecious genus Ilex (Aquifoliaceae) has been poorly studied from a cytogenetic point of view. Chromosome numbers of only ca. 5% of the species have been reported. In the present work the chromosome number of eight taxa from Argentina and Brazil are presented: Ilex taubertiana Loes., I. integerrima (Vell.) Reissek and I. pseudobuxus Reissek present 2n = 40, being this the first report for these species. A diploid number of 40 is also confirmed for I. paraguariensis A. St. - Hil, I. brevicuspis Reissek, I. dumosa Reissek and I. theezans Reissek, and 2n = 80 for I. argentina Lillo. Species with 2n = 40 (n = 20) show a regular meiotic behaviour with 20 bivalents, while I. argentina also shows a regular meiosis with 40 bivalents. Those individuals of I. paraguariensis analyzed in the present paper do not show a heteromorphic bivalent as previously reported and ascribed to sex chromosomes.

Nucleolar organizer activity and competition in Tricepiro Don Rene INTA, a synthetic forage crop

Abstract The nucleolar organizer activity and the presence of rDNA zones were studied in Tricepiro Don René INTA, a synthetic forage crop (2n=42,6x, AABBRR with introgression of Thinopyrum in 6A chromosome). The use of pTa71 probe revealed the presence of six rDNA zones but Ag-NOR indicated the presence of only four NORs (nucleolus organizer regions). Differential amphiplasty phenomenon could explain the inactivity of some rDNA zones. Simultaneous use of FISH (pTa71 probe) and DAPI banding analysis indicated that the chromosomes with rDNA zones belong to two rye and to four wheat chromosomes. The maximum number of nucleoli observed in somatic cells and the number of chromosomes with secondary constrictions agreed with the four active NORs detected with the Ag-staining method. The use of the pSc119.2 probe allowed to recognize that chromosomes with secondary constrictions are the wheat chromosomes IB and 6 B. The results obtained using classical and molecular cytogenetics lead us to conclude that this crop has a similar behavior to that observed in hexaploid triticales in relation to the phenomenon of amphiplasty. Furthermore, the complexity of genetic interactions between wheat and rye genomes described in triticales, are not modified by the presence of Thinopyron introgression in Tricepiro Don René INTA.

Variability in the amount of homoeologous pairing among F1 hybrids

Genes involved in the exclusive pairing of homologous chromosomes have been described in several polyploid species but little is known about the activity of these genes in diploids (which have only one dose of each homoeologous genome). Analysis of the meiotic behaviour of species, natural and artificial hybrids and polyploids of Glandularia suggests that, in allopolyploids where homoeologous genomes are in two doses, regulator genes prevent homoeologous pairing. The different meiotic phenotypes in diploid F1 hybrids between Glandularia pulchella and Glandularia incisa strongly suggest that these pairing regulator genes possess an incomplete penetrance when homoeologous genomes are in only one dose. Moreover, the meiotic analysis of natural and artificial F1 hybrids suggests that the genetic constitution of parental species influences the activity of pairing regulator genes and is mainly responsible for variability in the amount of homoeologous pairing observed in diploid hybrids. In Glandularia, the pairing regulator genes originated in South American diploid species. The cytogenetic characteristics of this genus make it a good model to analyse and explore in greater depth the activity of pairing regulator genes at different ploidy levels.

HETEROCROMATINA TELOMÉRICA, SEMILLAS Y CARACTERÍSTICAS MEIÓTICAS EN DOS LÍNEAS DE TRICEPIRO

A hybrid, named tricepiro, was obtained in 1972, by crossing a hexaploid triticale (2n=6x=42) and an octoploid trigopiro (2n=8x=56). The lines achieved include the tricepiro Don Rene INTA, which has shriveled kernels, and FA-L2, which has smooth ones. The relationship between the heterochromatin content of the rye chromosomes, the seed weight, the presence of meiotic abnormalities and the kernel shriveling has been documented previously in other intergeneric hybrids. The purpose of this study was to determine the average percentage of heterochromatin content in the rye chromosomes of the two tricepiro lines mentioned above and to relate this feature to some characteristics of the meiosis and seeds. We confirmed that the two lines have the same total chromosome number (2n=42) and the same number of rye chromosomes (14). We found that both lines have a complete chromosome mating until late diakinesis, but differ in the percentage of cells with univalents outside the equatorial plate in Metaphase I (Don Rene 42.85% and FA-L2 14.00%). In addition, the two lines differed in their meiotic index (Don Rene 66.47% and FA-L2 87.90%) and seed weight (Don Rene 0.029 ± 0.000 g and FA-L2 0.038 ± 0.001 g). The C-banding in rye chromosomes in mitotic metaphase indicated that the average percentage of heterochromatin content did not differ significantly between the two lines. In contrast to our expectations, the meiotic behavior and seed characteristics were not related to the heterochromatin percentage of the rye chromosomes of the tricepiro lines studied.