Cytogenetics of a new type of barley with 16 chromosomes

In the progeny of a trisomic type for chromosome 6, Purple, a 16-chromosome type was obtained, which had a pair of new metacentric chromosome 6 in excess. The new metacentric chromosome 6 was shorter than any of the 14 chromosomes of normal barley complement and showed a heteropycnotic nature at late prophase in somatic mitosis. At metaphase I in the plants with 14+one metacentric chromosome 6 (2n=15) the chromosome configuration was exclusively 7_II+1_I indicating that the extra metacentric chromosome 6 could not associate with the normal chromosome 6. At diakinesis and metaphase I in the new 16-chromosome plants most of the sporocytes showed 8_IIor 7_II+2_I. Neither tetravalents nor trivalents were observed at meiosis. The chromosome behaviour at anaphase I and later stages of meiosis was regular in general, resulted in a fairly high pollen fertility of about 61 per cent. Seed fertility however, was very low. The transmission rate of the new metacentric chromosome 6 through the pollen was extremely low in 16-chromosome plants. Possible origin of new basic number and B-chromosome in diploid level through trisomic condition was suggested (Summary see p. 138).Contribution No. 141 of the Department of Plant Science, University of Manitoba.     

Chromosome organisation in the Australian plague locust,Chortoicetes terminifera

In Chortoicetes terminifera, G-banding, produced by the trypsin treatment of air-dried slides followed by Giemsa staining, leads to light staining gaps at the secondary constrictions on autosomal pair 6 and regions proximal to the centromere on the long arms of pair 4. The variable short arms of two of the three smallest pairs were usually flared and lightly stained after treatment. In contrast to the relatively minor response of the normal chromosome set to G-banding, the large supernumerary chromosomes of C. terminifera show a spectacular series of dark bands alternating with lightly stained gaps. Two G-band variants of the B-chromosome were found in a laboratory stock. These patterns of G-banding are discernable both at mitosis in adults and embryos of both sexes and at all stages of male meiosis. Some regions which are gaps after G-banding appear as dark bands after C-banding. Consequently the supernumerary chromosome is mainly darkly stained with C-banding. In addition the centromeres and some telomeres are C-banded along with narrow interstitial bands and polymorphic heterochromatic blocks. — C-banding was not always successful, the technique often yields a mixture of G- and C-banding. The disparity of banding between the normal complement and the B-chromosome implies that whatever the source of origin of the B it has undergone spectacular changes in organisation since its origin.     

HAPLOIDY IN HAPLOPAPPUS GRACILIS (N = 2)

Analysis of meiosis in a haploid (monoploid) sporophyte of Haplopappus gracilis (n = 2) showed a nonrandom distribution of chromosomes at anaphase I. Chromosomes A and B were associated at various prophase I stages in 34 % of the microsporocytes. Presumably, this association persisted long enough to disrupt random distribution in a portion of those meiocytes showing such an association. Pollen stainability of 26.5 % in the haploid was in agreement with the normal expectation. However, this number resulted from a nonrandom chromosome distribution. The usual method of predicting fertility of haploids, 1/2ⁿ, is not accurate for monoploids with low chromosome numbers, and more functional methods are proposed.     

THE ASSOCIATION OF A SINGLE B-CHROMOSOME WITH MALE STERILITY IN PLANTAGO CORONOPUS

Paliwal , Ripsudan L. (B. R. College, Agra, India.), and Beal B. Hyde . The association of a single B-chromosome with male sterility in Plantago coronopus. Amer. Jour. Bot. 46(6): 460–466. Illus. 1959.—Two species of Plantago showing male sterility have been studied cytogenetically. In P. ovata (n=4) the sterility appears to be cytoplasmic. In P. coronopus (n=5) all male-sterile plants contain a single extra chromosome which is largely heterochromatic, shorter, and not homologous with any of the other chromosomes. No male-fertile plants contain this B-chromosome. Meiosis is regular in the male-sterile lines. The accessory chromosome usually does not divide and moves to one pole at the first division of meiosis and divides regularly in the second division. Degeneration of all microspores occurs before pollen mitosis. Male-sterile plants are apomictic, but whether or not male-fertile plants are also apomictic has not yet been determined.     

Meiotic analysis of haploid and doubled haploid forms of Nicotiana otophora and N. tabacum

Detailed meiotic studies were conducted on anther-derived haploids of Nicotiana otophora (n = 12) and N. tabacum (n = 24). At midpachytene stages the non-homologous chromosomes apparently remain unpaired. However, since the spreading of chromosomes at this stage was poor, the possible partial pairing, if any, between non-homologues could not be determined with certainty. One to two univalents rarely exhibited partial foldback pairing involving a single arm or the intercalary regions of the same chromosome. — At diakinesis the bivalent-like structures ranged from 0–2 in Otophora and 0–7 per cell in Tabacum haploids. The bivalent-like configurations (mostly rod types with chromatin connections of varying thickness) observed at meta-anaphase I varied from 0 to 1 and 0 to 5 per cell in haploids of Otophora and Tabacum respectively. The various types of secondary associations of univalents at meta-anaphase I were also studied in different haploids. — The probable origin and significance of bivalent-like configurations and secondary associations observed in Nicotiana haploids is briefly discussed. Based on our results, it is concluded that there is very little intra- or intergenomic pairing, if any, in Nicotiana haploids studied. — The meiotic behavior of chromosomes in doubled haploids (N. tabacum) obtained by leaf mid-rib culture, root culture and spontaneous chromosome doubling was remarkably regular with a stable chromosome number of 2n = 48. The meiotic stability of the doubled haploids permits using these materials directly in the breeding program.Contribution from the Department of Agronomy, University of Kentucky. The investigation reported in this paper (72-3-51) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director.     

温度对斯托克通氏烟草雄配子体形成和发育的影响

为探究低温对斯托克通氏烟草(Nicotiana stocktonii)花粉母细胞(PMC)减数分裂及其雄配子体发育过程的影响,采用卡宝品红染色法,研究不同温度条件下该材料雄配子体形成和发育的过程。结果表明:种植于昼温(31±0.5)℃、夜温(11±0.5)℃人工气候箱中的Nicotiana stocktonii花粉母细胞减数分裂过程异常现象较少,出现微核的比率较低,用新鲜成熟的花粉做萌发实验花粉萌发率较高,为(71±3)%; 而种植于昼温(25±0.5)℃、夜温(3±0.5)℃条件下的Nicotiana stocktonii开花后花药大多干瘪,用新鲜成熟花粉做萌发实验花粉萌发率低,为(13.67±3)%,花粉母细胞减数分裂过程出现染色体桥、染色体不同步、染色体断片、落后染色体等现象,存在微核的细胞比率较高。因此,Nicotiana stocktonii花粉母细胞减数分裂与小孢子发育过程易受温度影响,从而影响花粉的可育性。     

Features of the regulation of meiotic restitution in androgenic haploids of wheat-rye substitution lines 2R(2D)1, 2R(2D)3, and 6R(6A) (Triticum aestivum L., cultivar Saratovskaya 29/Secale cereale L., cultivar Onokhoiskaya)

Regulation of meiotic restitution in androgenic haploids generated by cultivation of isolated anthers of three wheat-rye substitution lines 2R(2D)₁, 2R(2D)₃, and 6R(6A) (Triticum aestivum L., cultivar Saratovskaya 29/Secale cereale L., cultivar Onokhoiskaya) was studied. The presence of rye chromosomes and the absence of homeologous wheat chromosomes in the haploid plant genome was shown to cause meiotic restitution, as observed in the case of androgenic haploids 6R(6A), or to inhibit it—in meiosis of haploids 2R(2D)₁ and 2R(2D)₃. In haploids of lines 2R(2D)₁ and 2R(2D)₃, the reductional type of division of univalent chromosomes was observed, leading to preferential formation of tetrads. In haploids of line 6R(6A), the equational type of division of univalents into sister chromatids, resulting in the block of the second division and formation of diads in approximately 50% of cells, was detected. These results confirm data on the effect of the genotype of line 2R(2D)₁ on the induction of reductional type division of univalents and two-phase meiosis, which were earlier obtained in studies of meiosis in polyhaploids 2R(2D)₁ × S. cereale L., cultivar Onokhoiskaya.     

Chromosome aberration and ploidy equilibrium of Vicia faba in tissue culture

Summary Different phytohormone concentrations induced different fequencies of various chromosome aberrations in calli of Vicia faba. NAA 10 ppm plus KT 2.5 ppm produced more haploids and NAA 30 ppm plus NAA 7.5 ppm produced more tetraploids and breakage. The relationship among the aberrations was analyzed. The hypothesis of ploidy equilibrium was established. The chromosome doubling rate and reduction rate of each treated group were calculated in relation to the observed data and the hypothesis. The frequency of tetraploids and breakage are correlated with each other. The frequency of total aberrations is linearly correlated with that of micronucleus formation. The regression equation is x=31.92+ 10.67 y.     

A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

A cytogenetic analysis in Psophus stridulus (L.) (Orthoptera: Acrididae): B-chromosomes and abnormal spermatid nuclei

The male chromosome complement of Psophus stridulus (L.) (Orthoptera: Acrididae) has been analyzed by using orcein staining, C-banding and silver impregnation. During spermatogenesis only one pair of autosomes (M₉) shows an active nucleolar organizer region located in a C-banded constriction. There are other chromosome pairs with constrictions but these do not show nucleolar activity. The relationship between these constrictions and the C-banding pattern exhibited by this species is analyzed.In a sample of 83 males from five populations, two different supernumerary chromosomes were observed. Four males had a metacentric B-chromosome (B^m) similar in size to the sex chromosome and mitotically stable. Its meiotic behaviour indicates that it is an isochromosome. An additional small B-chromosome (B⁸) was also found in a single follicle of one individual carrying the B^m.A high rate of abnormal spermatids (macrospermatids) was scored in the individuals carrying B's. This proportion is notably higher in the follicle containing both the B^m and the B⁸.     

鱼腥草花粉母细胞减数分裂特征及其育性研究

为深入了解鱼腥草花粉母细胞的减数分裂特征与花粉育性的关系,该研究采用卡宝品红染色法对2个鱼腥草居群花粉母细胞的减数分裂过程进行观察,并采用氯化三苯基四氮唑(TTC)染色法、I2-KI染色法、B-K培养基培养法及荧光显微镜观察法来检测鱼腥草花粉的活力及萌发率。结果发现:(1)鱼腥草减数分裂的进程与花序大小、花药颜色、花药长度均有密切的关系。(2)2个居群的鱼腥草中花粉母细胞减数分裂过程正常占88.2%,有11.8%的花粉母细胞减数分裂异常。(3)减数分裂异常表现在减数分裂过程中出现微核、落后染色体、染色体桥、不均等分离、多分体等现象,并发现在二分体阶段及单核花粉发育过程中存在细胞融合。(4)2个居群的鱼腥草花粉活力均不超过1.5%,花粉几乎不萌发。研究认为,鱼腥草花粉育性低的主要原因是单核花粉的发育过程异常,而非鱼腥草花粉母细胞减数分裂异常所致。     

The centric region of the X chromosome rDNA functions in male meiotic pairing in Drosophila melanogaster

In Drosophila melanogaster males, sex chromosome pairing at meiosis is ensured by so-called pairing site(s) located discretely in the centric heterochromatin. The property of the pairing sites is not well understood. Recently, an hypothesis has been proposed that 240 bp repeats in the nontranscribed spacer region of rDNA function as the pairing sites in male meiosis. However, considerable cytogenetic evidence exists that is contrary to this hypothesis. Hence, the question is whether the chromosomal rDNA clusters, in which a high copy number of 240 bp repeats exists, are involved in the pairing. In order to resolve the problem we X-rayed Drosophila carrying the X chromosome inversion In(1)sc ^V2L sc ^8R and generated free, mini-X chromosomes carrying a substantial amount of rDNA. We defined cytogenetically the size of the mini-chromosomes and studied their meiotic behavior. Our results demonstrate that the heterochromatin at the distal end of the inversion, whose length is approximately 0.4 times that of the fourth chromosome, includes a meiotic pairing site in the male. We discuss the cytological location of the pairing site and the possible role of rDNA in meiotic pairing.     

SHUGOSHINs and PATRONUS protect meiotic centromere cohesion in Arabidopsis thaliana

In meiosis, chromosome cohesion is maintained by the cohesin complex, which is released in a two‐step manner. At meiosis I, the meiosis‐specific cohesin subunit Rec8 is cleaved by the protease Separase along chromosome arms, allowing homologous chromosome segregation. Next, in meiosis II, cleavage of the remaining centromere cohesin results in separation of the sister chromatids. In eukaryotes, protection of centromeric cohesion in meiosis I is mediated by SHUGOSHINs (SGOs). The Arabidopsis genome contains two SGO homologs. Here we demonstrate that Atsgo1 mutants show a premature loss of cohesion of sister chromatid centromeres at anaphase I and that AtSGO2 partially rescues this loss of cohesion. In addition to SGOs, we characterize PATRONUS which is specifically required for the maintenance of cohesion of sister chromatid centromeres in meiosis II. In contrast to the Atsgo1 Atsgo2 double mutant, patronus T‐DNA insertion mutants only display loss of sister chromatid cohesion after meiosis I, and additionally show disorganized spindles, resulting in defects in chromosome segregation in meiosis. This leads to reduced fertility and aneuploid offspring. Furthermore, we detect aneuploidy in sporophytic tissue, indicating a role for PATRONUS in chromosome segregation in somatic cells. Thus, ploidy stability is preserved in Arabidopsis by PATRONUS during both meiosis and mitosis.     

Chromosome pairing in haploids of Brassica campestris

Summary The maximum chromosome pairing observed in haploids of Brassica campestris was two bivalents plus one trivalent but differences were observed in the chromosome pairing frequencies of the four haploids studied. This pairing supports the theorem that the species is hexasomic for one chromosome, tetrasomic for two and disomic for three others but it is emphasized that some of the observed pairing might be explained by a phenomenon other than homology.     

B-chromosome behaviour in Phaulacridium vittatum

Nine individuals of Phaulacridium vittatum in a single population sample of 1250 males collected at Crookwell, N. S.W. contained a single supernumerary chromosome. One further individual had two B-chromosomes. The supernumerary in question was larger than any of the standard set and was distinguishable from them at all stages of mitosis and meiosis. Like the X-univalent the B-chromosome was heteropycnotic at the onset of meiosis but differed from it in size, structure and behaviour. During first prophase single supernumeraries were frequently associated with the X in a non-homologous fashion as a consequence of their precocity. All such associations lapsed before first metaphase and the X and the B moved at random with respect to one another at first anaphase. In the one individual with two supernumeraries the two B-chromosomes showed regular pairing and segregated in a conventional manner. In all these respects the Crookwell supernumerary differed markedly from a morphologically identical B-chromosome present in a population of the same species from Hobart, Tasmania studied by Jackson and Cheung in 1967. Whether these differences in the behaviour of the B-chromosome in the two populations determines the higher frequency of the supernumerary in Hobart (11.3%) as compared with Crookwell (0.8%) remains to be resolved.     

The B-chromosome system of Allium schoenoprasum

Nine morphologically distinct euchromatic B-chromosomes have been identified in Allium schoenoprasum from the River Wye, South Wales. The most common type (89%) is telocentric (B^t–1) and it is likely that the non-standard Bs are derivatives of B^t–1 by deletion, centric shift and/or centric misdivision. New B-types have also been produced from standard Bs in controlled crosses. In general, the Bs are mitotically extremely stable, although occasional plants, particularly those carrying non-standard Bs, are conspicuously variable in their B-constitution between root-tip cells. In addition, B-chromosome number is enhanced in some anthers of about one third of plants. Behaviour of B-chromosomes during meiosis is described. Although there is little bivalent formation, less than 5% of the Bs are lost during meiosis in anthers. There is, however, no evidence of B-chromosome accumulation in the offspring of controlled crosses, usually a slight loss, and Bs have deleterious effects on aspects of vigour and fertility. Thus, no satisfactory explanation for populations with up to 65% B-containing individuals has yet been found.     

THE CYTOGENETICS OF XANTHISMA TEXANUM DC. (ASTERACEAE) AND ITS B-CHROMOSOMES

The karyotype of A-set and B-chromosomes of Xanthisma texanum DC. are described in detail and measurements are given. The distribution of B-chromosomes in stem tissue is described and the loss of B-chromosomes from primary roots confirmed. The number of B-chromosomes in pollen mother cells was constant within single inflorescence buds and in all buds throughout the flowering period. The behavior of one and two B-chromosomes during meiosis is described in detail. During meiosis, B₁'s divided in 71% of the cases during anaphase II and in 29% of the cases during anaphase I. First anaphase division resulted in some lagging and elimination of B-chromatids during second division. During anaphase I, B₁₁'s divided into chromosomes and in anaphase II these divided into chromatids in 95% of the cases. In the other 5 % non-disjunction of the B-chromosomes or chromatids and A-set chromosome abnormalities occurred. Post meiotic preferential distribution during pollen mitosis resulting in a doubling of the number of B-chromosomes passed to progeny via pollen occurred, but no doubling occurred in the female line. Crosses involving plants with two B-chromosomes each yielded fewer plants with three B-chromosomes than expected. Polyploidy is extremely rare in the species. The evolutionary significance of B-chromosome behavior is discussed in relation to its origin and survival.     

“Bouquet arrest”, monopolar chromosomes segregation, and correction of the abnormal spindle

According to our data, the arrest of univalents in bouquet arrangement is a widespread meiotic feature in cereal haploids and allohaploids (wide hybrids F₁). We have analyzed 83 different genotypes of cereal haploids and allohaploids with visualization of the cytoskeleton and found a bouquet arrest in 45 of them (in 30% to 100% pollen mother cells (PMCs)). The meiotic plant cell division in 26 various genotypes with a zygotene bouquet arrest was analyzed in detail. In three of them in PMCs, a very specific monopolar conic-shaped figure at early prometaphase is formed. This monopolar figure consists of mono-oriented univalents and their kinetochore fibers converging in pointed pole. Such figures are never observed at wild-type prometaphase or in asynaptic meiosis in the variants without a bouquet arrest. Later at prometaphase, the bipolar central spindle fibers join in this monopolar figure, and a bipolar spindle with all univalents connected to one pole is formed. As a result of monopolar chromosome segregation at anaphase and normal cytokinesis at telophase, a dyad with one member carrying a restitution nucleus and the other enucleated is formed. However, such phenotype has only three genotypes among 26 analyzed with a bouquet arrest. In the remaining 23 haploids and allohaploids, the course of prometaphase was altered after the conic monopolar figure formation. In these variants, the completely formed conic monopolar figure was disintegrated into a chaotic network of spindle fibers and univalents acquired a random orientation. This arrangement looks like a mid-prometaphase in the wild-type meiosis. At late prometaphase, a bipolar spindle is formed with the univalents distributed more or less equally between two poles, similar to the phenotypes without a bouquet arrest. The product of cell division is a dyad with aneuploid members. Thus, the spindle abnormality—monopolar chromosome orientation—is corrected. In some cells the correction of the prometaphase monopolus occurs by means of its splitting into two half-spindles and their rotation along the future division axis.     

CYTOTAXONOMIC STUDIES IN CHRYSOTHAMNUS (ASTEREAE,COMPOSITAE)

The basic chromosome number for Chrysothamnus is x = 9 as determined by 234 original counts representing all species. Polyploidy is frequent only in C. viscidiflorus where diploids, tetraploids, and hexaploids are found. Pollen size in the genus is basically correlated with style length rather than ploidy level. Most aspects of meiosis appear normal except for the tendency for nucleolar fragmentation. To reduce chromosome clumping during meiosis, an ice-water pretreatment was utilized. Karyotypes in Chrysothamnus reflect similar trends of specialization noted in chromosome structure for other Compositae. The taxa are predominantly self-fertilized; however, one instance of interspecific hybridization is noted. Taxonomic significance of the chromosome numbers, karyotypes, and breeding system in Chrysothamnus is discussed.     

B-Chromosomen beiChironomus

In the population “Herrenmühle” ofChironomus plumosus 11% of the individuals contain one supernumerary chromosome. This B-chromosome is present both in germ-line and somatic cells. — InChironomus melanotus 6% of the larvae of the population “Falkau” carry supernumerary chromosomes. These B-chromosomes cannot be found in all nuclei of testis and soma, their number varies between cells within the individual. In both species the B-chromosomes represent centromeric fragments of chromosome IV as can be shown by their structure and pairing behaviour. — The polytene B-chromosome ofCh. plumosus exhibits a banding pattern in the salivary gland nuclei. Furthermore it is able to form an additional nucleolus in the nuclei of the malpighian tubules. InCh. melanotus band structures can be seen only in the B-chromosome of malpighian tubules. The larvae ofCh. melanotus, carrying B-chromosomes, show heterochromatic bodies in the salivary gland nuclei, varying in number and size in the nuclei of the same gland. These bodies are interpreted to be polytenic B-chromosomes divided into subunits.

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