Chromosome-specific desynapsis in the n = 2 race of Haplopappus gracilis (Compositae)

During cytological screening for pollen sterility in a wild population of Haplopappus gracilis (n = 2), several partially sterile plants were found that had good pachytene pairing but varying numbers of univalents. Some plants had chromosome A bivalents or A univalents, while in the same cells chromosome B had only bivalents. In other plants the reverse condition occurred; the B chromosome had B bivalents or B univalents and only A bivalents. This demonstrates a chromosome-specific effect for the desynapsis genes. Hybridization between the two homozygous mutant genotypes produced only normal bivalents; this indicates the two mutants are not alleles and each is recessive. An F2 generation showed independent assortment of the desynaptic mutations. The chromosome A bivalent is the larger of the two and normally has one or two chiasmata; the B bivalent normally has a single chiasma. Chiasmata distribution was tested in the desynaptic mutant A bivalents and showed an acceptable fit to a binomial distribution. This occurs also in heterozygous, asynaptic pairing control gene mutations. Analysis of the NOR bivalent in two hologenomic desynaptic mutations in tomato also showed a good fit to a binomial distribution of chiasmata. This indicates the same methods are applicable to diverse species.     

Desynapsis and spontaneous trisomy in jute (Corchorus olitorius L.)

Summary Cytological studies in desynaptic plants, isolated at the F₆ generation of an intervarietal cross of Corchorus olitorius L., have shown variable numbers of bivalents and univalents in the PMC's at metaphase I, resulting in irregular distribution of chromosomes at anaphase I. The progenies of the desynaptic plants consisted of 9.24 percent of all possible primary trisomies except trisomie 6. The desynaptic condition is controlled by a pair of simple recessive genes.     

Meiotic studies in Acanonicus hahni (Stål) (Coreidae,Heteroptera) I. Behaviour of univalents in desynaptic individuals

Male meiosis was studied in a population of Acanonicus hahni (Stål), and nine of the sixteen individuals analyzed showed desynapsis. The frequency of univalents varied from one to seven percent in eight of them, while in the ninth the percentage of cells with univalents was higher (12%). The univalents auto-orientate at metaphase I in the center of the ring formed by autosomal bivalents and divide equationally at anaphase I; at metaphase II they show touch-and-go pairing, and lie in the center of the ring of autosomes.A desynaptic origin of the univalents is proposed, and the arrangement of the chromosomes in the first and second metaphase plate in the normal and desynaptic individuals is compared and discussed. The meiotic characteristics of these desynaptic individuals are also compared with those described in other insects with holocentric and monocentric chromosomes. It is suggested that any achiasmatic chromosome, whether a univalent, m or sex chromosome, will induce the formation of a ring and with some or all of them lying in its centre.     

Production,morphology, and cytogenetic analysis of Elymus caninus (Agropyron caninum) x Triticum aestivum F1 hybrids and backcross-1 derivatives

Summary Intergeneric hybrids were produced between common wheat, Triticum aestivum (2n=6x=42, AABBDD) and wheatgrass, Etymus caninus (Agropyron caninum) (2n=4x=28, SSHH) — the first successful report of this cross. Reciprocal crosses and genotypes differed for percent seed set, seed development and F₁ hybrid plant production. With E. caninus as the pollen parent, there was no hybrid seed set. In the reciprocal cross, seed set was 23.1–25.4% depending upon wheat genotype used. Hybrid plants were produced only by rescuing embryos 12–13 days post pollination with cv Chinese Spring as the wheat parent. Kinetin in the medium facilitated embryo germination but inhibited root development and seedling growth. The hybrids were vigorous, self sterile, and intermediate between parents. These had expected chromosome number (2n=5x=35, ABDSH), very little chromosome pairing (0.51 II, 0.04 III) and some secondary associations. The hybrids were successfully backcrossed with wheat. Chromosome number in the BC₁ derivatives varied 54–58 with 56 as the modal class. The BC₁ derivatives showed unusually high number of rod bivalents or reduced pairing of wheat homologues. These were sterile and BC₂ seed was produced using wheat pollen.     

Desynapsis inColocasia antiquorum Schott.

A culture ofColocasia antiquorum Schott. (2n=28) exhibiting desynapsis was detected in the course of cytological screening of a large number of cultivars maintained at the Institute. Intensive studies on the course of meiosis in this material as well as in the normal plants were made commencing from pachytene stage. Meiosis in the normal plants was regular, leading to the production of 95% stainable pollen. On the other hand, meiosis in the desynaptic material was found to be highly irregular resulting in the formation of over 80% sterile pollen. In its meiotic behaviour, the desynapticColocasia conforms to the complete type of desynaptics. The available evidence suggests a spontaneous origin of the desynaptic through gene mutation. The utility of this material in the study of unravelling basic cytogenetical problems is discussed.     

Synthesis and evaluation of Triticum durum — T. monococcum amphiploids

Summary Nine Triticum durum — T. monococcum amphiploids (AABBA^mA^m) were synthesized by chromosome doubling of sterile triploid F₁ hybrids involving nine T. durum (AABB) cultivars and a T. monococcum (A^mA^m) line. The triploid F₁ hybrids had a range of 4–7 bivalents and 7–13 univalents per PMC. The synthetic amphiploids, however, showed a high degree of preferential pairing of chromosomes of the A genomes of diploid and tetraploid wheats. The amphiploids were meiotically stable and fully fertile. Superiority of four amphiploids for tiller number per plant, 100-grain weight, protein content and resistance to Karnal bunt demonstrated that these could either be commercially exploited as such after overcoming certain inherent defects or used to introgress desirable genes into durum and bread wheat cultivars. Methods for improvement of these amphiploids are discussed.     

Development of monosomic alien addition lines and introgression of genes from Oryza australiensis Domin. to cultivated rice O. sativa L.

Oryza australiensis, a diploid wild relative of cultivated rice, is an important source of resistance to brown planthopper (BPH) and bacterial blight (BB). Interspecific hybrids between three breeding lines of O. sativa (2n=24, AA) and four accessions of O. australiensis (2n=24, EE) were obtained through embryo rescue. The crossability ranged from 0.25% to 0.90%. The mean frequency of bivalents at diakinesis/metaphase I in F₁ hybrids (AE) was 2.29 to 4.85 with a range of 0–8 bivalents. F₁ hybrids were completely male sterile. We did not obtain any BC₁ progenies even after pollinating 20,234 spikelets of AE hybrids with O. sativa pollen. We crossed the artificially induced autotetraploid of an elite breeding line (IR31917-45-3-2) with O. australiensis (Acc. 100882) and, following embryo rescue, produced six F₁ hybrid plants (AAE). These triploid hybrids were backcrossed to O. sativa. The chromosome number of 16 BC₁ plants varied from 28 to 31, and all were male sterile. BC₂ plants had 24–28 chromosomes. Eight monosomic alien addition lines (MAALs) having a 2n chromosome complement of O. sativa and one chromosome of O. australiensis were selected from the BC₂ F₂ progenies. The MAALs resembled the primary trisomies of O. sativa in morphology, and on the basis of this morphological similarity the MAALs were designated as MAAL-1, -4, -5, -7, -9, -10, -11, and -12. The identity of the alien chromosome was verified at the pachytene stage of meiosis. The alien chromosomes paired with the homoeologous pairs to form trivalents at a frequency of 13.2% to 24.0% at diakinesis and 7.5% to 18.5% at metaphase I. The female transmission rates of alien chromosomes varied from 4.2% to 37.2%, whereas three of the eight MAALs transmitted the alien chromosome through the male gametes. BC₂ progenies consisting of disomic and aneuploid plants were examined for the presence of O. australiensis traits. Alien introgression was detected for morphological traits, such as long awns, earliness, and Amp-3 and Est-2 allozymes. Of the 600 BC₂ F₄ progenies 4 were resistant to BPH and 1 to race 6 of BB. F₃ segregation data suggest that earliness is a recessive trait and that BPH resistance is monogenic recessive in two of the four lines but controlled by a dominant gene in the other two lines.     

Pollen irradiation and gene transfer in Capsicum

Summary The aim of the experiment was to study the possibility of facilitating the gene transfer and reducing the number of required backcrosses through pollen irradiation and subsequent selection of F₁M₁ plants containing a very high proportion of sterile pollen as male parent for backcrossing. Anthers of a donor line, C-3-1, were irradiated with 1,500 rad -rays and the pollen used for pollination of a recipient genotype W-8 which posseses a number of recessive marker genes. Five F₁M₂ plants containing more than 80% sterile pollen grains and one semi-sterile plant were selected and used for backcross to W-8. The segregation pattern of four characters expressed in the first backcross generation [W–8×(W–8×C–3–1)] was assessed and compared with the non-irradiated control. A changed segregation pattern was observed (in some cases even non-transfer of a paternal allele) as well as a shift towards more plants possessing the investigated maternal alleles. A scheme for backcross procedure in combination with pollen irradiation is discussed.     

Wheat univalent orientation at anaphase I in wheat-rye derivatives

The anaphase I behaviour of wheat univalents in plants with the chromosome constitution (0–7)A(0–7)BRR was analyzed using the C-banding technique, which allows to distinguish between wheat and rye chromosomes. The equational division frequencies of univalents observed in the six plants analyzed show a large variation (0.21–0.83). Within each plant syntelic univalents segregate to the poles at random. The frequency distribution of amphitelically dividing univalents does not conform to a random distribution. The lack of fit is attributed to environmental factors which differentially affect the probability of equational division for the univalents in different PMCs. Two other possible causes of the lack of adjustment, namely, each wheat univalent has a different probability of equational division, and wheat univalents do not move independently to the equator to divide equationally, are also discussed. The latter seems improbable in view of the independent behaviour of univalents dividing reductionally. A correlation observed between the behaviour of chromosome 6B and the rest of wheat univalents is attributed to variation between cells due to external causes.     

Genetics of desynaptic mutants in pearl millet

Summary Two desynaptic mutants, one of spontaneous origin and the other induced through colchicine treatment, were obtained in pearl millet. The desynpatic character was a monogenically controlled recessive one. Tests for allelism have indicated that the desynaptic genes of the two sources were allelic. Both complete and medium-strong desynaptic plants followed a monogenic pattern of inheritance and were found to be allelic. Medium-strong desynpatic plants on selfing produced both complete and medium-strong desynaptics in approximately equal numbers. It is suggested that the differential expression of the desynaptic character might be due to the presence of modifying genes.     

Genetic studies of self-fertility in rye (Secale cereale L.). 2. The search for isozyme marker genes linked to self-incompatibility loci

The segregation of several isozyme marker genes has been studied in F₂ inbred families from hybrids between self-sterile and five self-fertile inbred lines (nos. 2, 3, 4, 5, and 8) as well as from interline hybrids. Self-pollination of F₁ hybrids between self-sterile forms and lines 5 and 8 gave an F₂ segregation ratio of 1 heterozygote:1 homozygote for the gene Prx7 (chromosome 1R) against the allele from the line. This is interpreted as a result of tight linkage of the Prx7 gene with the S1 gene in chromosome 1R (recombination at a level of 0–1%). The self-pollination of such hybrids with lines 2,3 and 4 gave normal segregation for the Prx7 gene (1:2:1). This means that these lines carry a self-fertility allele which is not on chromosome 1R. Interline hybrids 5×2, 5×3 and 5×4 had self-fertility alleles for the two S genes and in inbred F₂ progenies gave the expected deviating segregation for the Prx7 gene in a ratio of 2:3:1. The segregation of interline hybrid 5×8 was normal, 1:2:1, as expected. Highly-deviating segregation in an inbred F₂ family of a hybrid with line 5 has also been obtained for another gene from chromosome 1R — Pgi2 (recombination with the S1 locus of 16.7%). By using the same method it has been estimated that line 4 has a self-fertility allele of the S2 locus from chromosome 2R and that the genes -Glu and Est4/11 are linked with it (recombination 16.7% and 17.5–20% respectively). Lines 2 and 3 have a self-fertility allele of the S5 locus from chromosome 5R which is linked with the Est5-7 gene complex (recombination at a level of 28.8–36.0%).     

The dsy10 Mutation of Arabidopsis results in desynapsis and a general breakdown in meiosis

The proper pairing and recombination of chromosomes during prophase is essential for the formation of gametes during meiosis. As part of studies to identify genes required for homologous chromosome pairing and recombination during meiosis in plants, we characterized a number of T-DNA-tagged, male-sterile mutants of Arabidopsis. Preliminary cytological studies on one line, 7219 which is male and female sterile, suggested that the mutation may disrupt meiosis and result in the formation of aberrant microsporocytes and microspores. In this report we present the results of a detailed analysis of meiosis in microsporocytes of sterile plants to elucidate the nature of the 7219 mutation. Analysis indicates that the mutation usually results in a desynaptic phenotype, with ten sister chromatids observed prior to metaphase I in most cells. Based on this, we named the mutation dsy10. The presence of several other meiotic defects suggests that dsy10 may not be a typical desynaptic mutant. Received: 15 December 2000 / Accepted: 19 April 2001     

The effect of deuterium oxide on protein turnover in Lemna minor

Lemna minor fronds transferred to a sterile culture medium containing 50% (v/v) deuterium oxide (²H₂O) rapidly undergo a loss of soluble protein with a corresponding increase in free amino acids. The loss of protein is due to two factors: (i) the inhibition of protein synthesis for 4 h followed by a slower rate of synthesis than normal, (ii) a rapid 9–10 fold increase in protein degradation. In plants grown for longer periods (3–6 days) in 50% ²H₂O medium, protein synthesis is inhibited by 20% and the rate constant of degradation is 2–3 times that measured in fronds growing in normal (H₂O containing) complete medium. The initial loss of protein is not due to the breakdown of any specific protein fraction. Investigation of several enzymes indicates that all proteins are catabolised in response to ²H₂O treatment. The implications of these results with regard to the interpretation of density-labelling experiments are discussed.     

A study of morphology,cytology and sterility in interspecific hybrids and amphidiploids of Nicotiana knightiana X N. umbratica

Summary Interspecific hybrids and amphidiploids of Nicotiana knightiana Goodspeed (n= 12)x N. umbratica Burbidge (n = 23) resembled either parent in some characters and were intermediate in other characters. The F₁ hybrids (2n = 35) showed mostly univalents during meiosis, while the amphidiploids (2n = 70) formed bivalents almost regularly. The former were completely sterile and the latter fully male fertile but predominantly female sterile. This female sterility was due to disintegration of the embryo sacs leading to collapsed ovules. The few fertile ovules, however, showed normal development of embryo sac and embryo. The occurrence of fertile and sterile ovules was believed to be due to segregation of the genes governing sterility.     

Intergeneric hybridization between Brassica napus and Sinapis pubescens,and the cytology and crossability of their progenies

The cytological possibility of gene transfer from Sinapis pubescens to Brassica napus was investigated. Intergeneric hybrids between Brassica napus (2n = 38) and Sinapis pubescens (2n = 18) were produced through ovary culture. The F₁ hybrids were dihaploid and the chromosome configurations were (0–1) _III + (2–11) _II + (5–24) _I . One F₂ plant with 38 chromosomes was obtained from open pollination of the F₁ hybrid. Thirty-one seeds were obtained from the backcross of the F₂ plant with B. napus. Five out of seven plants had 38 chromosomes, and the pollen stainability ranged from 0% to 81.4%. In the B₂ plants obtained from the backcross of B₁ plants with B. napus, 66.7% of the plants examined had 38 chromosomes. S. pubescens may become a gene source for the improvement of B. napus.     

The physiology of spore-negative and spore-positive nodules ofMyrica gale

The physiology of spore-negative and spore-positive root nodules was investigated inMyrica gale L. grown in water culture in a growth chamber. Spore(–) nodules were induced withFrankia cultures and spore(+) nodules with crushed nodules. Gas exchange was measured in a flow-through system.The time course of acetylene reduction following addition of acetylene was essentially the same in both spore(–) and spore(+) nodules with a stable maximum between 2 and 4 minutes followed by a steep decline to a minimum (37% of the maximum) between 9 and 30 minutes depending on the plant. The minimum was followed by a partial recovery. Nodule CO₂ evolution showed a similar pattern but the minimum rate (83% of the maximum) was not nearly as low.Plants nodulated with one spore(–) and one spore(+) strain were compared at 6, 8 and 10 weeks after inoculation. At 6 weeks the spore(–) plants had 52% greater specific nitrogenase activity and 46% more biomass than the spore(+) plants. At 8 and 10 weeks, however, the differences between plants with spore(–) and spore(+) nodules became smaller.Plants nodulated with 4 spore(–) and 5 spore(+) strains were compared at 8 weeks after inoculation. Collectively the spore(–) plants exhibited a 32% greater specific nitrogenase activity, a 15% lower energy cost of nitrogenase activity (CO₂/C₂H₄), and invested 31% less biomass in nodules than the spore(+) plants. The spore(–) plants also produced 16% more biomass indicating that spore(–) strains are generally more desirable than spore(+) strains. However, two spore(+) strains were as effective as the spore(–) strains.     

Cytogenetics of the parthenogenetic grasshopper Warramaba (formerly Moraba) virgo and its bisexual relatives

Hybrids of both sexes were obtained from the reciprocal crosses, carried out in the laboratory, between the species believed to have given rise, by hybridization some thousands of years ago, to the parthenogenetic species W. virgo. All males with a Y-chromosome derived from P196 died before reaching the adult stage, but two males from the reciprocal cross (i.e., with a Y from P169) survived up to the adult stage. Their testes were small but normal in structure and histology. At the first meiotic division almost all the chromosomes were univalents, 0–2 bivalents being formed. Some chiasmata between non-homologous chromosomes were present. Segregation at first anaphase is irregular so that sperms with 3–15 chromosomes are formed. Such hybrids appear to be entirely sterile.     

The role of sister chromatid cohesiveness and structure in meiotic behaviour

Sister chromatid cores, kinetochores and the connecting strand between sister kinetochores were differentially silver stained to analyse the behaviour of these structures during meiosis in normal and two spontaneous desynaptic individuals of Chorthippus jucundus (Orthoptera). In these desynaptic individuals most of the chromosomes appear as univalents and orient equationally in the first meiotic division. Despite this abnormal segregation pattern, the changes in chromosome structure follow the same timing as in normal individuals and seem to be strictly phase dependent. Chromosomes in the first prometaphase have associated sister kinetochores and sister chromatid cores that lie in the chromosome midline; we propose that this promotes the initial monopolar orientation of chromosomes. However, the requirements of tension for stable attachment to the spindle force the autosomal univalents to acquire amphitelic orientation. Sister kinetochores behave in a chromosome orientation-dependent manner and, in the first metaphase, they appear to be interconnected by a strand that can be detected by silver impregnation, as seen in the second metaphase of wild-type individuals. The disappearance of the sister kinetochore-connecting strand, needed for equational chromatid segregation, however, can only take place in the second meiotic division. This connecting strand is ultimately responsible for the inability of chromosomes to segregate sister chromatids in the first anaphase. Received: 25 March 1997; in revised form: 14 July 1997 / Accepted: 22 August 1997     

The Development and a Cytogenetic Study of Monosomics of Gossypium Hirsutum L.

Monosomics of cotton (Gossypium hirsutum L.) were obtained by irradiation of pollen by -rays and by irradiation of seeds by thermal neutrons. Many monosomics were derived directly from irradiation, but a number of monosomics were also recovered in the progeny of plants with translocations and of desynaptic plants. Only 28 primary monosomics showed normal pairing at metaphase-1 of meiosis. The others formec rare trivalents or additional univalents. Partial desynapsis was detected in some monosomics. The pollen fertility levels of monosomics are presented. New morphological characters were detected among the monosome plants of cotton.     

Cytological analysis of tetraploid hybrids between sweet potato and diploid Ipomoea trifida (H. B. K.) Don.

Summary Tetraploid F₁ hybrids between Ipomoea batatas, sweet potato (2n = 6x = ca. 90), and diploid (2n = 2x = 30) I. trifida (H. B. K.) Don. showed various degrees of fertility reduction. The present study aimed to clarify its causes by cytological analysis of meiotic chromosome behavior in the diploid and sweet potato parents and their tetraploid hybrids. The diploid parents showed exclusively 15 bivalents, and the sweet potato parents exhibited almost perfect chromosome pairing along with predominant multivalent formation. Their hybrids (2n = 4x= 57–63) formed 2.6–5.0 quadrivalents per cell, supporting the autotetraploid nature. The meiotic aberratios of the hybrids were characterized by the formation of univalents, micronuclei, and abnormal sporads (monad, dyad, triad, and polyad). The causes underlying these aberrations were attributed in part to the multivalent formation, and in part to a disturbance in the spindle function. Three hybrids showing serious meiotic aberrations were very low in fertility. The utilization of the sweet potato-diploid I. trifida hybrids for sweet potato improvement is described and, further, the role of interploidy hybridization in the study of the sweet potato evolution is discussed.