Heteropteran chromosomes are holokinetic; during mitosis, sister chromatids segregate parallel to each other but, during meiosis, kinetic activity is restricted to one pair of telomeric regions. This meiotic behaviour has been corroborated for all rod bivalents. For ring bivalents, we have previously proposed that one of the two chiasmata releases first, and a telokinetic activity is also achieved. In the present work we analyse the meiotic behaviour of ring bivalents in Pachylis argentinus (Coreidae) and Nezara viridula (Pentatomidae) and we describe for the first time the chromosome complement and male meiosis of the former (2n = 12 + 2m + X0, pre-reduction of the X). Both species possess a large chromosome pair with a secondary constriction which is a nucleolus organizer region as revealed by in-situ hybridization. Here we propose a new mode of segregation for ring bivalents: when the chromosome pair bears a secondary constriction, it is not essential that one of the chiasmata releases first since these regions or repetitive DNA sequences adjacent to them become functional as alternative sites for microtubule attachment and they undertake chromosome segregation to the poles during anaphase I.

No abstract

No abstract

A cytological analysis of eight Argentinean species of Eryngium L. (Saniculoideae, Apiaceae) is carried out. Karyotypes of eight species and original chromosome counts for three of them (indicated with an asterisk) are notified: E. coronatum*Hook.Schlechtd. (2n=6x=48; 26m+ 4m-sm +14sm + 4st). The first three species belong to the Section Foetida, while the remaining five, belong to Panniculata. Both Sections are easily differentiated by morphology; our chromosomal study shows that these sections can also be recognized karyologically. All the species, except E. nudicaule (x=7), present x=8 which is the most common basic chromosome number in the genus and in the subfamily Saniculoideae. The karyotype analysis made on the eight species mainly shows metacentric and submetacentric chromosomes differing in proportion between species; only E. pandanzfolium and E. mesopotamicum show subtelocentric pairs. These two species only differ in the color of their inflorescences; besides, differences in their karyotypes were negligible. These facts agree with the suggestion that they would be varieties of the same species. Two different phenomena seem to have occurred during karyotype evolution in the genus Eryngium: aneuploidy within Section Foetida, and polyploidy within Section Panniculata.

Chromosome in situ hybridization (FISH and GISH) is a powerful tool for determining the chromosomal location of specific sequences and for analysing genome organization and evolution. Tricepiro (2n = 6x = 42) is a synthetic cereal obtained by G. Covas in Argentina (1972), which crosses hexaploid triticale (2n = 6x = 42) and octoploid Trigopiro (2n = 8x = 56). Several years of breeding produced a forage crop with valuable characteristics from Secale, Triticum, and Thinopyrum. The aim of this work is to analyse the real genomic constitution of this important synthetic crop. In situ hybridization using total DNA of Secale, Triticum, and Thinopyrum as a probe (GISH) labelled with biotin and (or) digoxigenin showed that tricepiro is composed of 14 rye chromosomes and 28 wheat chromosomes. Small zones of introgression of Thinopyrum on wheat chromosomes were detected. The FISH using the rye repetitive DNA probe pSc 119.2 labelled with biotin let us characterize the seven pairs of rye chromosomes. Moreover, several wheat chromosomes belonging to A and B genomes were distinguished. Therefore, tricepiro is a synthetic hexaploid (2n = 6x = 42) being AABBRR in its genomic composition, with zones of introgression of Thinopyrum in the A genome of wheat.

No 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.

The meiotic behaviour of 13 spontaneous interspecific F, hybrids of Amaranthus was studied. The hybrids between species with n = 16 chromosomes had 16 bivalents but varied considerably in pollen stainability (0-55%). These results suggest the existence of cryptic structural hybridity. The hybrids involving A. cruentus {n = 17) and species with n = 16 {A. caudatus and A. quitensis) always formed 15II+1III with very low pollen stainability (5-7%). Further observations indicated that Amaranthus species are allotetraploids with basic numbers of .\-= 8 and X = 9 but exhibit x = 16 and x = 11 as secondary basic numbers, as demonstrated by (a) the frequent presence of 811 -I-171 in the meiosis of the hybrid A. spinosus {n = \l)x A. hybridus {n = 16); and the occurrence of secondary associations between bivalents in MI. Genomic formulae are proposed for each species, on the basis of the meiotic behaviour of the hybrids studied.