Fertility and meiotic chromosome behaviour in autotetraploid pearl millet

Summary Tetraploidy was induced in outbred pearl millet and selection for high and low seed set was started in the C₁ generation. Segregation in the C₃ generation was observed for fertility and also for meiotic features: per cent seed set in selfed earhead, chiasma frequency, chromosome association and chromosome distribution in pollen mother cells were all affected. However, variation in seed set was observed even between samples not differing in meiotic features. It is apparent that factors regulating seed set in autotetraploid pearl millet were genic as well as chromosomal.A high frequency of univalents and trivalents was the main cause of sterility; quadrivalent misdisjunction was not a significant factor. As univalency decreased with increased chiasma formation, the gain was in the form of quadrivalents. However, individuals not differing in chiasma frequency did differ in chromosome association frequencies, indicating that the dependence of chromosome pairing behaviour on chiasmata was subject to genotypic influence.     

Nuclear aberrations and loss of synaptonemal complexes in response to diethylstilbestrol (DES) in Caenorhabditis elegans hermaphrodites

In Caenorhabditis elegans, loss of viability and fertility is observed after treatment with DES. The decrease in life span is associated with senescent morphology of meiotic prophase nuclei, such that nuclei from young and old specimens cannot be differentiated. Aging in oocytes at the pachytene stage of meiotic prophase is manifested by nucleo-cytoplasmic aberrations, increased density of the nucleoplasm and cytoplasm and decrease in numbers of mitochondria. Increasing concentrations of DES are characterized by concomitant decrease in fertility and increased production of abnormal gametes. At DES concentrations higher than 1.25 micrograms/ml, synaptonemal complexes (SC) are absent from the nuclei, thus, effective pairing and segregation of homologous chromosomes is not possible. The absence of SCs may be the result of: a premeiotic colchicine-like effect that influences pairing of chromosomes; changes in the structure of the DNA due to DES binding that results in changes in expression of the DNA; and changes in temporal DNA synthesis in response to DES. Since the SC is essential for regulating pairing and subsequent separation of bivalents, the lack of an SC explains the loss of fertility, due to the production of unbalanced gametes, observed in DES-treated specimens.     

Mutagens induced chromosomal damage in <Emphasis Type="Italic">Lablab purpureus</Emphasis> (L.) Sweet var. <Emphasis Type="Italic">typicus</Emphasis>

Cytological analysis with respect to meiotic behaviour is considered to be the one of the most dependable indices to estimate the potency of mutagens and to elucidate the response of various genotypes to a particular mutagen. Seeds of Lablab purpureus (L.) Sweet var. typicus cv. CO(Gb)14 were subjected to different doses/concentrations of gamma rays and EMS. The effects of different mutagenic treatments on meiosis were studied on treated and control plants. Various types of meiotic aberrations such as stickiness, clumping of chromosomes, laggards, ring chromosomes and precocious movements were observed in the mutagenic treatments. As increase in the concentration, the frequency of cells showing chromosomal aberrations shows a linear increase up to a certain level. However, the EMS treatments proved to be more effective in inducing meiotic aberrations as compared to gamma rays.     

Evaluation of the Effect of Pollen Irradiation on Karyotype Variability in M2 Cotton Plants

The karyotypes of biomorphologically abnormal cotton (Gossypium hirsutum L.) plants obtained in M₂ after pollination with pollen irradiated at dose rates 10, 15, 20, and 25 Gy were studied. Various genomic and chromosomal mutations were detected in 57 M₂ families. The primary monosomics isolated in M₂ were found to be cytologically more stable and more viable, since they had higher meiotic index, pollen fertility, and seed formation. In M₂, a decrease in the number of plants with multiple karyotype aberrations and interchromosomal exchanges with high frequency of multivalent formation was observed. The multivalent configurations had different types and chromosome disjunctions. Their pollen fertility was higher than in translocants found in M₁. Desynapsis often occurred in M₂, including plants with chromosome deficiency or rearrangements. The variation in the number of univalents in various cells was found to result from different expression of synaptic genes. The results indicate stabilization of karyotypes, increase in cytologic stability and viability, and the absence of sterility in aberrant plants.     

Evaluation of the Effect of Pollen Irradiation on Karyotype Variability in M1 Cotton Plants

The effect of pollen irradiation at dose rates of 10, 15, 20, and 25 Gy on variability in cotton plants Gossypium hirsutum L. was studied. The modified plants showed a reduced fertility, mainly caused by chromosomal rearrangements and genomic mutations during meiosis. The genomic mutations involved primary and tertiary monosomics, monotelodisomics, and a haploid plant. The decrease in meiotic index and pollen fertility in the cotton aneuploids was related not only to aberrations in chromosome pairing but also to genetic features of the original plants. It was found that heterozygosity for interchromosomal exchanges found in M₁ plants resulted in the formation of multivalent associations of chromosomes of various forms and types of segregation from translocation complexes. Another result was high variability in pollen fertility. An increase in irradiation dose rate caused an increase in the number of translocants with a high frequency of quadrivalents. The results suggest that the great diversity of forms observed in M₁ after pollination with irradiated pollen is determined, first, by elimination of some chromosomes or their arms or the whole paternal genotype and second, by interchromosomal rearrangements. The high variability in pollen fertility of translocants hampers using this trait as a marker of heterozygosity for exchanges in cotton.     

Meiotic behaviour and pollen fertility in three species of Zephyranthes (Amaryllidaceae)

Studies on meiotic behaviour and pollen fertility have been carried out in Zephyranthes candida, Z. grandiflora and Z. flava. Maximum meiotic abnormalities in chromosome behaviour were observed in Z. candida and Z. grandiflora. There were variations in the number of bivalent formation, multivalents and anaphasic separation. All types of abnormalities were found to be associated with low percentage of pollen fertility. In Z. flava, chromosomal aberrations were low and pollen fertility was high. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromosome damage induced by artificial seed aging in barley

Summary Barley (Hordeum vulgare L. Himalaya) seeds were artificially aged under two storage conditions (32 °C/12% moisture content (m.c.) and 38 °C/18% m.c.) to study the behavior of induced chromosomal aberrations during plant growth. The frequencies of aberrant anaphases at first mitosis in root tips were correlated with loss of germinability. However, after 3 and 5 weeks' growth, aberration frequency declined. In plants grown from artificially aged seeds, the frequency of aberrant anaphases appeared to be stabilized at about 1% after 5 weeks' growth, in spite of the large differences in the frequencies at first mitosis. This suggests that because of their genetic imbalance, cells with chromosomal aberrations induced by seed aging were being excluded during plant growth. Meiotic chromosome configurations at MI were normal (7 II) in all plants studied, although a few precocious separations were found. Meiotic aberrations were found at AI-TI, AII-TII and the tetrad stages in the pollen mother cells of plants grown from the control and artificially aged seeds. However, there were no clear differences among the control and the two aging treatments. It was obvious that some cells with meiotic chromosomal aberrations were lost between the AI-TI and AII-TII stages, and still more between the AII-TII and tetrad stages. The frequency of tetrads with micronuclei in plants produced from artificially aged seeds was the same as in the control. The plants grown from artificially aged seeds showed high pollen fertility (95.2 to 97.0%) and seed fertility (90.1 to 97.2%) which was comparable to the control values (97.4 and 97.9%) respectively, indicating no special effects of seed aging. Anaphase cells of the first mitosis in the next (A₂) generation were analyzed to study the transmission of chromosomal aberrations through mitotic and meiotic cell divisions in the A₁ generation. Aberrant anaphases in the progeny from the artificially aged seeds were not higher than those of the control progeny. This indicates that the chromosomal aberrations induced by seed aging are not transmitted to the next generation.Published with the approval of the Director of the Colorado state Experiment Station as Scientific Series No. 2776     

The genus Argemone. I. Cytogenetic relationships between diploid species

Cytogenetic investigations of 5 diploid Argemone species and their hybrids were undertaken. Correlative informations on the morphology, cytology, crossability and interfertility have been secured to understand the mechanism crossability and interfertility have been secured to understand the mechanism of speciation in the genus.All species studied possess 14 bivalents, normal meiosis and perfect pollen and seed fertility.Statistical comparisons regarding two meiotic metrics (frequency of ring bivalents; chiasma frequency) between some of the species revealed significant differences.Crosses were attempted in all species combinations, and hybrids were obtained in several. On the basis of pollen and seed fertility these were classified as fortile (mexicana × subfusiformis; subjusiformis × mexicana f. leiocarpa) and semifertile (mexicana × albiflora; subjusiformis × platyceras; mexicana f. leiocarpa × platyceras) hybrids. F₁'s are intermediate, qualitatively they exhibit heterosis.Meiosis was analysed in all hybrids (pachynema; M-I, A-I) and several metrics e.g. ring bivalent frequency, chiasma frequency were taken as indices of genome affinity.It is suggested that mexicana, mexicana f. leiocarpa and subfusiformis are taxonomically close and display only allelic differentiation: albiflora and platyceras are structurally distinct from each other. Several structural changes e.g. duplications, inversions, translocations etc. were involved in their differentiation.The role of isolation barriers in maintaining species differentiation is discussed.     

Effect of sodium fluoride on radiation sensitivity of barley seeds

Barley seeds soaked in 0.01 M sodium fluoride (NaF) in phosphate buffer (pH7) or in buffer alone for 18 h were dried and equilibrated to 10% moisture, either in air or in nitrogen. Pre-treated and re-dried seeds were irradiated in air or in nitrogen with 0, 13, 20, 26 and 32 kR of γ rays, and were immediately hydrated in oxygen- or nitrogen-bubbled water. Parameters of radiation effect considered were seedling injury, mitotic and meiotic cells with bridge aberrations at anaphase and pollen fertility in M₁, and the frequency of chlorophyll mutations in M₂. NaF at 0.01 M was not mutagenic by itself. Pre-treatment with NaF significantly enhanced the radiation effect, when the irradiation was done in air, in comparison with the buffer soaked seeds. The increased effect due to NaF was additional to the oxygen effect. In nitrogen, NaF pre-treatment increased the mutagenic effect but it was not always significant. Post-soaking of irradiated seeds in 0.01 M NaF for 5 h increased seedling injury in comparison with the irradiated seeds soaked in buffer alone or in 0.01 M NaCl. At least a part of the sensitizing effect of NaF may be due to the inhibition of repair.     

Cytomorphological investigations in Oxyria digyna Hill. from the Kashmir Himalaya,India

In the present paper, detailed cytomorphological investigations in Oxyria digyna Hill. from Kashmir Himalaya—India have been reported for the first time. All the 14 investigated populations of O. digyna are diploid based on x = 7. Out of these in two populations 0–2B chromosomes have been recorded for the first time while 6 populations differed significantly in their meiotic characteristics. Meiotic abnormalities during male meiosis observed include inter PMC chromatin transfer (cytomixis). Non-synchronous disjunction of some bivalents, laggards and bridges at anaphases and telophases. Consequent to these meiotic anomalies, microsporogenesis in meiocytes is abnormal resulting in to dyads, triads and polyads with or without micronuclei. The overall effect is seen in reduced pollen fertility. Unreduced pollen grains were observed in some populations, which differed significantly in their size compared to the normal (reduced) pollen grains. It is observed that a smaller frequency of pollen grains differed morphologically in Aharbal and Yosmarg populations. The remaining eight populations showed regular meiotic course, normal microsporogenesis and high percentage of pollen fertility (95.09–99.09 %).     

Cytogenetic analysis of recombination in males of Drosophila ananassae

Cytogenetic studies of recombination in males of Drosophila ananassae were carried out by examining F₁ males derived from the mating of marker females, b se; bri ru of the BS stock, with males of two wild strains, TNG and L8. The male recombination values in both sections b-se (chromosome 2) and bri-ru (chromosome 3) are high in TNG F₁ but extremely low in L8 F₁ We demonstrate the presence of chiasmata in TNG F₁ males at a frequency capable of accounting for the observed recombination values. A unique series of “iso-site aberrations” was also observed in TNG F₁ males. Because of a parallelism in the distribution pattern between the chiasmata and the isosite aberrations, we propose that recombination in males of D. ananassae is meiotic in origin and that the iso-site aberrations are related to chiasma formation.     

Male meiosis and behaviour of sex chromosomes in different populations of Rumex acetosa L. from the Western Himalayas, India

Detailed meiotic analysis in 28 North West Himalayan populations of dioecious plant Rumex acetosa L. was carried out. The species is generally discussed as an important plant having sex chromosomes. Male meiosis in all the studied populations clearly showed the formation of six bivalents and one trivalent during diakinesis and metaphase-I. The sex chromosomes in male plants exhibit a chain of trivalent (Y₁–X–Y₂). In addition, among the presently investigated populations ring-shaped trivalents were also observed for the first time in the species. Varied frequency of abnormal segregation of sex trivalent was also observed leading to XY:Y segregation instead of normal X:Y₁Y₂ segregation. A majority of the populations exhibit normal meiosis. Plants of six populations show meiotic abnormalities like cytomixis, laggards, bridges, chromatin stickiness, etc., leading to reduced pollen fertility. Translocation between an autosome and sex chromosomes was also observed in some of the populations. 0–1B chromosomes were noticed in one population. This is the first ever meiotic analysis of the species from India.     

Chiasmata and variability in Lolium and Festuca populations

There are significant differences in mean pollen mother cell chiasma frequencies between populations within Lolium perenne, L. multiflorum and Festuca pratensis. The differences are genotypically controlled. With low chiasma frequencies the chiasmata are distally located. With increasing chiasma frequency the frequency of chiasmata in interstitial segments increases. Shorter lived populations have higher chiasma frequencies than the more perennial. — The higher the chiasma frequency of a population the lower the phenotypic and genetic variance for characters under polygenic control, such as flowering time, and the less effective also is the response to selection for such characters. These observations are interpreted on the premise that high chiasma frequencies are instrumental in the breaking up of supergene sequences in interstitial chromosome segments.     

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 induction of chromosome-type aberrations in G1 by methyl methanesulfonate and 4-nitroquinoline-N-oxide,and the non-requirement of an S-phase for their production

Human lymphocyte were treated in G₁ with 4-nitroquinoline-N-oxide (4NQO) and methyl methanesulfonate (MMS) and then incubated in the presence or absence of cytosine arabinoside (ara-C). There was an increase in aberration frequency in those cells incubated with ara-C compared with those treated with 4NQO or MMS alone. This increase was restricted to chromosome-type aberrations. When cells were treated in G₂ with 4NQO and then incubated with ara-C until fixation, there was an increase in deletions compared with cells treated with 4NQO alone. No exchange aberrations were observed following any treatment even when deletion frequencies were high, as in the case with 4NQO plus ara-C treatment. These results suggest that ara-C can inhibit the repair of DNA damage induced by 4NQO and MMS that is converted into aberrations. They also show that the terms “S-dependent” and “S-independent” used to describe the modes of action of chemical clastogens are not valid.     

Genetic interactions between wheat and rye genomes in triticale

Summary Six primary triticale lines were produced from two advanced breeding lines of Triticum durum and three inbred genotypes of Secale cereale. The wheat and rye parents and the triticale derivatives were crossed in all possible combinations within each species group. Chiasma and univalent frequency of parents and hybrids were determined. The primary triticale lines had more univalents and less chiasmata per pollen mother cell than the corresponding wheat and rye parents together. The parental wheat F₁ exhibited negative heterosis for chiasma frequency whereas all rye hybrids had much higher chiasma frequencies than their inbred parents. Triticale F₁s generally showed lower chiasma frequencies and more univalents than their parents, but the degree of pairing failure was dependent upon which of the parental species within the triticale, wheat or rye, was in the heterozygous state. F₁s with heterozygous wheat genome only showed the least reduction in chiasma number (presumably caused by gene actions within the wheat genome), while F₁s with heterozygous rye genome showed high reduction in chiasma frequency and an increase in pairing failure (induced by negative interactions between the heterozygous rye and the wheat genome in triticale). A high correlation was found between the frequency of undisturbed pollen mother cells and the frequency of aneuploids in the subsequent generation. A higher number of aneuploids occurred in those populations which were heterozygous for the rye genome.     

Cytology of inbreds and f 1 hybrids of pearl millet

Summary The meiotic behaviour of chromosomes was studied in four inbred lines and their F ₁ hybrids of P. typhoides. The inbred lines showed a decrease in mean chiasma frequency when compared with the population plants, but differed from one another in their mean chiasma frequencies. Together with the decrease in mean chiasma frequency the inbreds showed variation in mean chiasma frequencies. The inbred lines showed a number of meiotic abnormalities such as extra chromosomes, extra fragments, desynapsis, persistent nucleoli and differential condensation of chromosomes. The F ₁ hybrids of these inbreds exhibited heterosis for chiasma frequency. All the F ₁'s had mean chiasma frequencies higher than the means of the respective participating parents. The F ₁'s, however, differed in the degree of heterosis exhibited. In the F ₁ hybrids, the variation in mean chiasma frequency, both between plants and between PMC's within plants, was significantly lower than that of the inbred lines. The effect of environment was studied in the inbred lines and their F ₁ hybrids. The mean chiasma frequencies of the inbred lines were significantly lower, and the variation in mean chiasma frequencies was greater, in the stress season. The mean chiasma frequencies of F ₁'s did not show any significant differences between the two seasons. The F ₁'s exhibited less variation in mean chiasma frequency than the inbred lines, showing that F ₁'s were developmentally more stable. The F ₁'s did not show any meiotic abnormalities in either season.     

C-bands and chiasma distribution inScilla amoena,S. ingridae,andS. mischtschenkoana (Hyacinthaceae)

An effect of C-band pattern and polymorphism on chiasma distribution in pollen meiosis was recently demonstrated inScilla siberica. A further meiotic banding study has been performed in the alliesS. amoena, S. ingridae, andS. mischtschenkoana in order to analyze the effect, if any, of their specific C-band patterns and cytochemically different heterochromatin types on recombination. No clear evidence for a preferential formation of chiasmata adjacent to homozygous intercalary heterochromatin and no consistent reduction of chiasma frequency near strongly heterozygous intercalary heterochromatin blocks, as observed inS. siberica, could be found. Terminal C-band heteromorphism is suspected to cause distal chiasma defaults. The results suggest once more that there is no uniform effect of heterochromatin on crossover distribution.     

The effect of X-irradiation on male meiosis in Schistocerca gregaria (Forskål)

The pattern of response of chiasma frequency to X-irradiation has been studied in germ line cells of male imagines of Schistocerca gregaria. A correlation has been established between the observed changes in chiasma frequency of the L and M type bivalents and the time in the meiotic cycle at which the treatment is given. Two radio-sensitive periods have been identified in meiosis itself. At one (meiotic DNA synthesis) X-irradiation produces a decrease in chiasma frequency while at the other (leptotene-early zygotene) the treatment leads to an increase in chiasma frequency. Small bivalents however do not respond to treatment and form a single chiasma under all conditions.     

Estimation of efficiency of seed irradiation by thermal neutrons for inducing chromosomal aberration in M<Subscript>2</Subscript> of cotton <Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.

Cytogenetic analysis of M₂ plants after irradiation of cotton by thermal neutrons was performed in 56 families. In 40 plants of 27 M₂ families, different abnormalities of chromosome pairing were found. These abnormalities were caused by primary monosomy, chromosomal interchange, and desynapsis. The presence of chromosome aberrations in some cases decreased meiotic index and pollen fertility. Comparison of the results of cytogenetics analysis, performed in M₁ and M₂ after irradiation, showed a nearly twofold decrease in the number of plants with chromosomal aberrations in M₂, as well as narrowing of the spectrum of these aberrations. The latter result is explained by the fact that some mutations are impossible to detect in subsequent generations because of complete or partial sterility of aberrant M₁ plants. It was established that the most efficient radiation doses for inducing chromosomal aberrations in the present study were 15 and 25 Gy, since they affected survival and fertility of altered plant to a lesser extent.