Pair Of SAT-chromosomes Research Articles

Australopyrum(Triticeae: Gramineae) in New Zealand

Abstract Australopyrum calcis, a self-compatible, triticoid grass of restricted distribution, is described as new; it comprises two subspecies, ssp. calcis, and ssp. optatum; both are associated with limestone. This is the first species of Australopyrum recognised as endemic to New Zealand, and the first endemic diploid (2n = 14) grass found here. The karyotype is the same as in Australian A. pectinatum, and the SAT-chromosome pair is similar to other genera in the tribe Triticeae. Two Australian species are naturalised here, A. retrofractum since mid-19th century, and A. pectinatum, only recently re-collected.

Physical localization of active and inactive rRNA gene loci in Hordeum marinum spp. gussoneanum (4x) by in situ hybridization

Two populations of the diploid and 10 populations of the tetraploid cytotype of Hordeum marinum ssp. gussoneanum were studied for the presence of chromosomal segments harbouring rDNA. Conventional cytological methods established the presence of only one satellited (SAT) chromosome pair in both cytotypes. This was supported by silver staining revealing two NORs and two standard-sized nucleoli. Two additional micronucleoli were observed in a few interphases of two tetraploid populations indicating the presence of an extra chromosome pair with very low nucleolus-forming activity. In situ hybridization with the wheat rDNA probe pTA71 identified intense signals at the nucleolar constrictions of the SAT chromosomes of both cytotypes and weaker signals in a chromosome pair of the tetraploid cytotype, morphologically similar to the SAT chromosomes but without visible nucleolar constrictions. This confirms the presence of rDNA in two chromosome pairs in the tetraploid cytotype. The morphological similarity between these two pairs and the SAT-chromosome pair of the diploid cytotype as well as an identical position of the signals in all three pairs give additional support to an autoploid origin of the tetraploid cytotype. The rDNA at the nucleolar constrictions consisted of two segments of condensed rDNA of different sizes connected by diffuse rDNA. The rDNA of the chromosome pair without nucleolar constrictions was condensed supporting that this conformation is connected with inactivity. The tripartite structure of the rDNA at the nucleolar constrictions corresponds to similar tripartite structures observed after silver staining and Giemsa C-banding.Key words: in situ hybridization, rDNA location, Hordeum marinum, autoploidy, inactive NORs.

C-banding pattern and polymorphism of Aegilops caudata and chromosomal constitutions of the amphiploid T. aestivum — Ae. caudata and six derived chromosome addition lines

C-banding patterns were analysed in 19 different accessions of Aegilops caudata (= Ae. markgrafii, = Triticum dichasians) (2n = 14, genomically CC) from Turkey, Greece and the USSR, and a generalized C-banded karyotype was established. Chromosome specific C-bands are present in all C-genome chromosomes, allowing the identification of each of the seven chromosome pairs. While only minor variations in the C-banding pattern was observed within the accessions, a large amount of polymorphic variation was found between different accessions. C-banding analysis was carried out to identify Ae. caudata chromosomes in the amphiploid Triticum aestivum cv 'Alcedo' - Ae. caudata and in six derived chromosome addition lines. The results show that the amphiploid carries the complete Ae. Caudate chromosome complement and that the addition lines I, II, III, IV, V and VIII carry the Ae. caudata chromosome pairs B, C, D, F, E and G, respectively. One of the two SAT chromosome pairs (A) is missing from the set. C-banding patterns of the added Ae. caudata chromosomes are identical to those present in the ancestor species, indicating that these chromosomes are not structurally rearranged. The results are discussed with respect to the homoeologous relationships of the Ae. caudata chromosomes.

Karyomorphology of Vitis vinifera, V.rotundifolia and Their Hybrid.

Karyomorphology of V. vinifera cv. Gulabi, V. rotundifolia cv. James and their hybrid, revealed the somatic chromosome numbers as 2n=38, 40 and 39 respectively. In these karyotypes, 13 chromsomes pairs were median and 6 or 7 were sub-median. Total lengths of the complements were 52.78μm in James, 49.30μm in Gulabi and 51.16μm in hybrid. Gulabi had the largest chromosome (1.80μm) and James had the shortest chromosome (0.94μm). Chromosome diameter was inversely proportional to the length. All the karyotypes had only one pair of SAT-chromosomes, SAT-knob being attached to the long-arm of the chromosome. On the whole, karyotypes appeared to be symmetrical, though there are vast variations in morphology and disease resistance, suggesting the inter-chromsomel variations by way of accumulation of genic differences.

Cytological observations inAlbuca, including a survey of polymorphic variation in the Sat-chromosome pair

Chromosome numbers for 14 South African species ofAlbucaL. (Liliaceae) have been determined. Ten of these are first reports, including counts for three new species. Members of all three sections of the genus are represented in this study, and all have a diploid number of 2n = 18. No polyploids or dysploids were encountered in this survey. There is no evidence that the sectional subdivisions ofAlbucacan be readily distinguished on differences in basic chromosome number or karyotype, for all taxa are characterized by a common basic number of x = 9 and by a remarkably uniform, strongly asymmetric and bimodal complement of three long chromosomes and six markedly shorter ones. Special attention is focused on the hitherto largely overlooked variability of the longest chromosome pair which, in a large proportion of the species examined, shows heterozygous variation in the size, morphology and stainability of its satellite and in some cases, also in the short chromosome arm that bears it. This unusually high incidence of polymorphism, and the diversity of form observed in this satellited (Sat-chromosome) pair is discussed in relation to similar patterns reported elsewhere.

Karyological studies of Duchesnea (Rosaceae).

The present investigation on the chromosomes of Duchesnea confirmed previous reports indicating that D. chrysantha f. chrysantha has 2n=14 chromosomes and D. indica has 2n=84 chromosomes. The chromosome number of D. chrysantha f. leucocephala, 2n=14, was also ascertained, together with the meiotic chromosome numbers. The two taxa of D. chrysantha had very similar complements consisting of 5 pairs of metacentrics, one pair of metacentric SAT-chromosomes and one pair of submetacentrics. Duchesnea indica had subtelocentric SAT-chromosomes and many subtelocentric chromosomes in addition to metacentric and submetacentric chromosomes. The genome of D. indica contains a genome set involving subtelocentric chromosomes, which were not detected in D. chrysantha. This finding seems to be of importance in considering the course of evolution in D. indica.

Karyotypes of Fragaria nubicola and F. daltoniana (Rosaceae).

Two species of Fragaria, F. nubicola Lindl. ex Lacaita and F. daltoniana J. Gay were cytologically analyzed. Both were diploid (2n=14) and had similar karyotypes consisting of 4 metacentric pairs, 2 submetacentric pairs, and one subtelocentric pair of SAT-chromosomes. The last pair commonly had the shortest length in complements. Furthermore, one plant of F. daltoniana with a small chromosome was observed and details and origin of the karyotype were also described and discussed.

Inter-specific variation in the karyotypes of the genus Glycine Willd.

Karyotype analysis of six species of genus Glycine indicated chromosome number to be 2n=40 in G. canescens, G. clandestina, G. latifolia, G. max cultivars Monetta and MACS-13 and 2n=80 in G. tabacina and G. tomentella. Tetraploid species (2n=80) had nearly double the length of haploid chromosome complement of diploid species. Chromosomes were median to submedian. Diploid species (2n=40) had one pair of SAT-chromosomes whereas tetraploid species (2n=80) had two pairs of SAT-chromosomes. Karyotypes of all these species were more or less similar, inspite of broad inter-specific variations in the morphological characters, suggesting the species differentiation might have been due to micromutations.

Cytology ofEleutherine Bulbosa: A Reinvestigation with Special Reference to the Nature and Possible Mode of Origin of the Heteromorphic Chromosomes Within the Genome

SUMMARYCytology of Eleutherine bulbosa (Mill.) Urgan (Iridaceae) from the Campus of the University of Kerala is studied. It showed n = 6 and 2n= 12. The somatic complement consists of one pair of very long heterocentric chromosomes, a pair of medium-sized M chromosomes and 4 pairs of very small M chromosomes. The heterocentric long chromosomes and the medium-sized M chromosomes showed slight differences in size between the members of a pair. It is suggested that the heterocentric long pair of chromosomes have evolved as a result of simultaneous multiple breaks and fusions between a pair of A chromosomes and a pair of SAT-chromosomes. The size difference between the two medium-sized M chromosomes is suggested to be result of a small interstitial deficiency.

Karyomorphological studies in Chlorophytum Ker-Gawl.

Chromosome morphology of six Chlorophytum species reveal symmetrical karyotypes in C. laxum (2n=16) and asymmetrical in C. glaucum and C. orchidastrum (2n=42). Remaining three species, viz. C. tuberosum, C. attenuatum (2n=16) and C. comosum (2n=28) appear to be intermediate in the karyotype symmetry. In C. attenuatum and C. orchidastrum two pairs of SAT chromosomes with variations in their sequence numbers and arm ratios have been observed, whereas in rest of the species only one SAT pair could be observed. Tentative basic chromosome number for the genus has been suggested to be x=8 and 7, possibly derived as secondary number from x=4. Role of polyploidy in the speciation process, centre of origin and geographical distribution in relation to karyomorphology have been discussed.

Karyotypic analysis of Cajanus, Atylosia, and Rhynchosia species

Somatic chromosomes of two cultivais of Cajanus cajan, eight species of Atylosia (A. albicans, A. cajanifolia, A. lineata, A. platycarpa, A. scarabaeoides, A. serica, A. trinervia and A. volubilis), and of Rhynchosia rothii were analysed. All species had 2n=22. Eight of the 10 species studied had two pairs of satchromosomes while A. scarabaeoides and A. sericea had only one sat-chromosome pair. Based on relative chromosome length (L%), arm ratio (pa-value) and presence or absence of secondary constriction, a karyotype formula for each species was formulated. Based on these parameters the chromosome pairs could also be assigned to groups ranging from 8 to 10 in different species. Except for the asymmetrical karyotype of A. albicans, the other species had rather moderately symmetrical karyotypes.

Identification of the somatic chromosomes of Psathyrostachys fragilis (Poaceae)

The karyotype of the outbreeding P. fragilis (2n = 2x = 14) was investigated by Feulgen staining and by C-, N-, and Ag-banding techniques. The complement consisted of 14 large chromosomes, 8 metacentrics and 6 satellite (SAT) chromosomes, probably among the longest within the Poaceae. Two SAT-chromosome pairs carried small, and one pair carried minute, polymorphic, completely heterochromatic satellites. Each chromosome could be referred to one of the seven chromosome pairs by its C-banding pattern. The patterns comprised from zero to three conspicuous, but not large bands per chromosome resulting in an overall low content of constitutive heterochromatin (<4%). The C-banded karyotype of P. fragilis differed from any previously reported in the Triticeae. Six of seven chromosome pairs were polymorphic either for C-banding patterns or satellite size (or for both). N-banding gave no differential staining of chromosomes. Silver nitrate staining established that the nucleolar organizers had different nucleolus-forming capacities. The presence of the small and minute satellites was more consistently demonstrated after C- and N-banding than after Feulgen staining.Key words: Triticeae, Poaceae, karyotype, C-, N-, and Ag-banding.

Karyotype Analysis inVicia Hirsuta(L.) S. F. Gray andVicia MeyeriBoiss.

SUMMARYResults of a preliminary karyological study of bulgarian populations of Vicia hirsuta and V. meyeri are reported. Diploid chromosome number 2n = 2x=14 was observed in all populations studied. The karyotypes of the two species are characterized by quite similar chromosome types and a high level of symmetry. Along with that, certain differences are evident. The karyotype of V. meyeri consists of slightly longer chromosomes. Most obvious difference is observed in the SAT-chromosome pair morphology; in V. hirsuta it possesses a smaller satellite attached to the short arm; in V. meyeri the satellite is considerably larger than that in V. hirsuta. It is equal in length to the shorter arm, from which it is separated by a secondary constriction.

The behavior of nucleolus organizers in structurally changed karyotypes of barley

Two standard karyotype barley lines and 18 lines with karyotypes reconstructed by means of induced reciprocal translocations have been studied with respect to nucleolus formation. The standard karyotype contains two pairs of satellite chromosomes (pairs 6 and 7). Five of the structurally changed karyotypes contain, as a result of reciprocal translocations between the standard satellite chromosomes, only one satellite chromosome pair, each chromosome with two satellites and two nucleolus organizing regions. Under these circumstances, only two of the four NORs are active in nucleolus formation while the other two — probably the transposed ones — remain inactive; hence the maximum number of primary nucleoli per nucleus is two. — When NORs are translocated to chromosomes with no NOR in the standard karyotyp, the normal pattern of nucleolus formation remains unchanged. The same is true after transposition of segments from other chromosomes to the satellites of the standard SAT-chromosome pairs 6 and 7. The results obtained are discussed with respect to effects of translocations on the activity and behaviour of nucleolus organizing regions.

Karyotype Analysis and Meiotic Studies in Three Varieties of Grape (<i>Vitis vinifera</i> L.)

Three varieties of grape viz., Alamwick, Gros colman and Selection 7 were studied with the intention of determining chromosome number as well as cytological abnormalities. The somatic chromosome number was found to be 38 in all the 3 varieties. The length of chromosomes varied in between 2.163 and 0.786 microns. Chromosomes could be classified as median and submedian. A pair of sat-chromosomes were observed in all the 3 varieties.A maximum of 1.18 chiasma frequency per bivalent was noticed in Selection 7. In all the 3 varieties 3 bivalents were associated with nucleolus. Occurrence of lagging bivalents and binucleolar condition are the only abnormalities noticed in these studies. Meiotic index was cent per cent in all the varieties. Pollen fertility varied from 91.11% to 83.47%. Slight variation was noticed in pollen diameter. Since all the 3 varieties are cytologically stable, it is recommended that all these varieties can be used in breeding programme without any hindrance for grape improvement.

Tetrasomaty in the roots ofCicer arietinum Linn.

Sporadic instances of tetrasomaty in the primary and secondary roots of five varieties ofCicer arietinum Linn. are illustrated. The phenomenon was more common in Varieties I and II. The SAT-chromosomes are reliable guides to estimate the degree of polysomaty, since pre-treatment withp-dichlorobenzene revealed that cell types with 32 chromosomes at metaphase had two pairs of SAT-chromosomes associated with the nucleolus at prophase. Tetrasomatic cells appear to be limited to the dermatogen and periblem. Higher degrees of polysomaty were not observed.

Cytoplasmic male sterility in relation to hybrid wheat breeding

The method of substitution and restoration of nucleus is briefly described. Three species, Aegilops caudata, Ae. ovata and Triticum timopheevi, were used as donors of male sterility cytoplasms. The characteristics of these three cytoplasms are summarized as follows: Caudata-cytoplasm: This cytoplasm has in many respects deleterious effects on the manifestation of alien genomes. Substitution lines having hexaploid wheat genome constitution are mostly male sterile while the female organ is normal. Some lines set frequently germless seeds. Haploid and twin seedlings are of common occurrence in other lines. Pistillody is common in the substitution lines with tetraploid wheat genomes. Ovata-cytoplasm: No pistillody was found in the substitution lines, both with hexaploid and tetraploid wheats. Male sterility is always complete in the substitution lines of hexaploid wheats with the exception of P 168, a variety of common wheat having a pair of satchromosomes of Ae. caudata. This variety restores male fertility completely. No effective restorers were found for the substitution lines of emmer wheat. Delayed heading is common in the 4x substitution lines. Timopheevi-cytoplasm: Substitution lines of 6x wheats are mostly male sterile, while those of 4x wheats are more or less male fertile. Only the genome of T. spelta duhamelianum restores completely pollen fertility. Among the indispensable factors for the success of hybrid wheat, five were discussed. They were (1) hetero sis, (2) selection of male sterile cytoplasms, (3) discovery of restoring genes, (4) production of hybrid seeds and (5) quality.