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1.
We report the occurrence of cytomixis in wild populations of Himalayan poppy (Meconopsis aculeata Royle), which is considered to be an important and threatened medicinal plant growing in the high hills of the Himalayas.
The impact of cytomixis on meiotic behaviour, reduced pollen viability and heterogeneous-sized pollen grains was also studied.
Cytological studies in the seven wild populations from the high hills of Himachal Pradesh revealed that all the Himalayan
populations exist uniformly at the tetraploid level (2n=56) on x=14. The phenomenon of chromatin transfer among the proximate
pollen mother cells (PMCs) in six populations caused various meiotic abnormalities. Chromatin transfer also resulted in the
formation of coenocytes, aneuploid, polyploid and anucleated PMCs. Among individuals that showed chromatin transfer, chromosome
stickiness and interbivalent connections were frequently observed in some PMCs. The phenomenon of cytomixis in the species
seems to be directly under genetic control; it affects the meiotic course considerably and results in reduced pollen viability. 相似文献
2.
Thalictrum foetidum L. (Ranunculaceae), a morphologically variable and widely distributed species of temperate and alpine Himalayas is worked
out cytologically for the first time from India. Earlier studies from outside India were restricted to chromosome counts and
karyotypic analysis. We studied the male meiosis, microsporogenesis and pollen viability in the wild accessions from the cold
deserts of Lahaul-Spiti, Kinnaur and Pangi Valley of Himachal Pradesh. Present cytomorphological surveys in the species record
the existence of two distinct morphotypes involving plant size; colour and size of leaf/leaflet; dentation of leaflet lobes;
and degree of leaf pubescence. All the accessions in the two morphovariants share the same meiotic chromosome number (n = 21) and adds a new intraspecific hexaploid cytotype. The accessions show the phenomenon of cytomixis involving transfer
of chromatin material among proximate pollen mother cells (PMCs) and associated meiotic abnormalities like, out of plate bivalents,
interchromosomal connections, and laggards, bridges and micronuclei at anaphases/telophases. Microsporogenesis results into
abnormal sporads (tetrads with micronuclei, dyads, triads and polyads). The products of such sporads resulted into some pollen
sterility and pollen grains of heterogeneous sizes. The persistent occurrence of phenomenon of cytomixis and associated meiotic
abnormalities and consequently pollen sterility and pollen grains of heterogeneous sizes in the hexaploid cytotype of T. foetidum seems to be under some genetic factors associated with the genome. 相似文献
3.
New Brassica napus inbred lines with different petal colors and with canola quality and increased levels of oleic (∼70%, 10% higher than that of B. napus parent) and linoleic (28%) acids have been developed in the progenies of one B. napus cv. Oro × Orychophragmus violaceus F5 hybrid plant (2n=31). Their genetic constituents were analyzed by using the methods of genomic in situ hybridization (GISH) and amplified fragments length polymorphism (AFLP). No intact chromosomes of O. violaceus origin were detected by GISH in their somatic cells of ovaries and root tips (2n=38) and pollen mother cells (PMCs) with normal chromosome pairing (19 bivalents) and segregation (19:19), though signals of variable sizes and intensities were located mainly at terminal and centromeric parts of some mitotic chromosomes and meiotic bivalents at diakinesis or chromosomes in anaphase I groups and one large patch of chromatin was intensively labeled and separated spatially in some telophase I nuclei and metaphase II PMCs. AFLP analysis revealed that substantial genomic changes have occurred in these lines and O. violaceus–specific bands, deleted bands in ‘Oro’ and novel bands for two parents were detected. The possible mechanisms for these results were discussed. 相似文献
4.
Cytomixis was recorded during microsporogenesis in sesame (Sesamum indicum L.), a member of the family Pedaliaceae. The phenomenon of cytomixis was observed at various stages of meiosis in 0.5% sodium azide (SA) treated populations of Sesamum indicum L. Cytomixis was observed to occur through various methods, i.e. by forming cytoplasmic channels and direct fusion of pollen mother cells (PMCs), the former was more frequent than the latter. The migration of nuclear content involved all the chromatin/chromosomes or part of it from donor to recipient cell/cells. Some completely empty meiocytes were also observed. Stickiness, precocious movement, laggards, unorientation and micronuclei were observed in almost all the sets treated with various doses of SA. Increase in the doses of SA had a positive effect on the percentage of PMCs showing cytomixis and chromosomal abnormalities. The impact of cytomixis on meiotic behaviour, reduced pollen viability and heterogeneous sized pollen grains were observed. 相似文献
5.
In current paper, we studied the meiotic chromosome number and details of cytomixis recorded for the first time in Thalictrum cultratum Wall. from the high altitude areas of northwest Himalaya (India). Cytomixis, the phenomenon of inter PMC (pollen mother cell) migration of chromatin material has been reported in many angiosperms and other groups of plants, but there is no published report in Thalictrum cultratum. All the presently studied accessions of the species existed at diploid level (x = 7). The present chromosome count of n = 14 has been reported for the first time from the study area. The cytological stability of any plant is an important consideration in view of its existence in nature. Meiotic disturbances can impose threat to the reproductive potential of plant. Current study reveals the occurrence of inter PMC migration of chromatin material. In present investigation, the phenomenon of cytomixis can be observed between 2 to 9 PMCs. Chromatin migration occurs through narrow and broad cytoplasmic channels or occasionally fused together during metaphase-I and anaphase-I. Cytomixis resulted in the formation of hypo- (n = 2, 2 + 1 small fragment, n = 3 + 3 small fragments, 4, 5 + extra mass of chromatin, 13) and hyperploid (n = 7 + 2 small fragments, 8 + 2 small fragments, 14, 14 + 2 small fragments, 15) PMCs, variable sized pollen grains and pollen sterility (20%). The current study reveals that cytomixis is responsible for formation of PMCs with variable chromosomes (hypoand hyperploid) and pollen grains of heterogeneous sizes and pollen sterility in T. cultratum. This is the first report of cytomixis in the species. 相似文献
6.
Abstract Lindelofia longiflora (Royle ex Benth.) Baill. var. falconeri (Cl.) Brand (Family: Boraginaceae) is investigated cytologically (n= 12) for the first time from the cold deserts of Pangi Valley, Chamba District (Himachal Pradesh) in India. We report the formation of syncytes and 2n pollen grains in the species. During meiosis, the majority of the pollen mother cells (PMCs) exhibited 12 bivalents, equal segregation of chromosomes during anaphases, regular tetrads, and normal‐sized pollen grain formation. Occasionally, two proximate PMCs fused during the early stages of prophase‐I and resulted in the formation of syncytes. The frequency of syncytes in the accession is rather low, at 25 out of 1866 (1.33%). Such syncyte PMCs are detectable during meiosis due to their larger size compared to typical PMCs. The syncytes or polyploid cells showed normal 24 bivalents and depicted perfectly regular meiotic course. But the products of such PMCs yield 2n or larger sized pollen grains that are almost double the size of typical normal or n pollen grains. The origin of syncytes as a consequence of the fusion of meiocytes during the early stages of meiosis‐I could be attributed to low temperature stress conditions prevailing in the Pangi Valley, where temperature during May and June dip to below freezing, the time the plants enters the reproductive/flowering bud stage. It is possible that such apparently fertile 2n pollen grains originating from syncytes might play a role in the origin of intraspecific polyploids in the species. 相似文献
7.
W. -P. Diao S. -Y. Bao B. Jiang L. Cui C. -T. Qian J. -F. Chen 《Biologia Plantarum》2010,54(2):373-376
With improved staining and chromosome preparation techniques, meiosis of pollen mother cells (PMCs) and male gametophyte development
in autotetraploid cucumber (Cucumis sativus L.) was studied to understand the correlation between chromosomes behaviour and fertility. Various chromosome configurations,
e.g. multivalent, quadrivalents, trivalents, bivalents and univalents were observed in most PMCs at metaphase I. Lagging chromosomes
were frequently observed at anaphase in both meiotic divisions. In addition, chromosomes segregations were not synchronous
and equal in some PMCs during anaphase II and telophase II. Dyads, triads, tetrads with micronuclei and polyads were observed
at tetrad stage, and the frequencies of normal tetrad with four microcytes were only 55.4 %. The frequency of abnormal behaviour
in each stage of meiosis was counted, and the average value was 37.2 %. The normal meiotic process could be accomplished to
form the microspore tetrads via simultaneous cytokinesis. Most microspores could develop into fertile gametophytes with 2 cells and 3 germ pores through
the following stages: single-nucleus early stage, single-nucleus late stage and 2-celled stage. The frequency of abnormalities
was low during the process of male gametophyte development. The germination rate of pollen grains was 46.9 %. These results
suggested that abnormal meiosis in PMCs was the reason for low pollen fertility in the autotetraploid cucumber. 相似文献
8.
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 %). 相似文献
9.
Spontaneous intercellular chromatin migration/cytomixis was observed to occur in the pollen mother cells (PMCs) of theChlorophytum comosum for the first time. The migration through cytomictic channels was more pronounced in meiosis-I and very rare in meiosis-II.
The process was associated with erratic meiosis, which was characterized by defects in chromosome organization and segregation.
Cytomixis was more intense in the month of April than in July and consequently the frequency of meiotic irregularities was
much more pronounced during the month of April. As a consequence of abnormal meiosis, fertility was drastically reduced resulting
in meager seed efficiency of 17% only. Recombination system also does not guarantee the release of sufficient variability.
We view the phenomenon of cytomixis as genetically controlled mechanism involving meiotic genes and operating through signal
transduction pathway triggered by the environmental stimuli. The evolutionary significance and tenable hypothesis in the backdrop
of existing literature is also proposed. 相似文献
10.
《Saudi Journal of Biological Sciences》2022,29(9):103390
Cytomixis is a common phenomenon observed in meiotic cells such as anther which is influenced by various factors. Use of pesticides is a common practice in agriculture. However, it is not known whether pesticides can induce cytomixis in plant cells and induce genetic variation. To understand this, the present study was planned to assess the cytomixis and syncytes behaviors in PMCs of Pisum sativum L. Seeds of P. sativum (Family: Fabaceae) were treated with different concentrations of commonly used pesticides methomyl (ME), imbraclaobrid (IM) and clethodim (CL). Seeds were treated with various concentrations (0.1, 0.2, 0.3, 0.4 and 0.5% of ME, IM and CL prepared in water) for 1 and 3 h. Effect of pesticides on pollen fertility, frequency of cytomixis, and kind of cytomixis cells was assessed. In the cytomixis cells, the cytomictic channel (CC) and direct fusion (DF), and various stages of meiosis (PI, MI, AI and TI) with cytomixis cells were observed. In addition, frequency of syncytes cell and their various stages of meiosis I (PI, MI, AI and TI) in pollen mother cells (PMCs) was assessed. During the microsporogenesis in P. sativum, the occurrence of cytomixis and syncytes at various stages of meiosis I were seen. The formation of cytoplasmic channels and direct fusing of pollen mother cells (PMCs) were both seen to cause cytomixis, with the former being more common than the latter. The percentage of PMCs with cytomixis and syncytes cells increased with increase in the concentration of pesticides. The result of the present investigation indicates that commonly used pesticides ME, IM, and CL have a significant effect on pollen fertility, frequency of cytomixis, and kind of cytomixis cells, the cytomictic channel (CC) and direct fusion (DF), in addition, frequency of syncytes cell and their various stages of meiosis I (PI, MI, AI and TI) in pollen mother cells (PMCs) on P. sativum. 相似文献
11.
Puneet Kumar Pawan Kumar Rana Himshikha Vijay Kumar Singhal Raghbir Chand Gupta 《Plant Systematics and Evolution》2014,300(5):831-842
Silene vulgaris is an important ethnobotanical species, but so far no thorough meiotic analysis has been performed, despite its wide occurrence in temperate and alpine Himalayas, this prompted us to undertake present study. We investigated original meiotic chromosome number and effect of cytomixis on meiotic course, microsporogenesis and pollen grain size and fertility. The paper also summarizes the previously published chromosome counts in the species and cytogeography of 2x and 4x cytotypes in the Indian Himalayas and elsewhere. Meiocytes preparations were made through standard squashed technique in 1 % acetocarmine. Two ploidy levels have been determined during the cytomorphological surveys, diploid (2n = 2x = 24) and tetraploid (2n = 4x = 48). Most of the presently scored populations were found to be diploid (2n = 2x = 24). Morphologically 2x and 4x individuals were indistinguishable from each other. Meiosis was perfectly normal in 4x cytotype. However, some of the 2x plants showed the phenomenon of cytomixis and associated meiotic abnormalities. Consequent to cytomixis, hypo-, hyperploid and enucleated pollen mother cells (PMCs) were resulted. Such PMCs combined with other meiotic abnormalities yielded sterile and variable sized pollen grains. On the basis of overall information, it is clear that 2x cytotype is the most widely distributed cytotype in the Indian Himalayas as well as elsewhere. On the other hand, the 4x cytotype seems to be less frequently present in the Indian Himalayas and outside of India. 相似文献
12.
The chromosome morphology and meiotic pairing behavior in the pollen mother cells (PMCs) of Metasequoia glyptostroboides were investigated. The results showed that: (1) The chromosome number of the PMCs was 2n=22. (2) The PMCs developed in the successive manner, and the nucleoids in the dynamic development were similar to those of the other gymnosperms. (3) At prophase, most of the chromosomes were unable to be identified distinctively because the chromosomes were long and tangled together. The chromosome segments were paired non-synchronously. At pachytene, the interstitial or terminal regions of some bivalents did not form synapsis and the paired chromosomes showed difference in sizes, indicating that there were structure differences between the homologous chromosomes. (4) At diakinesis, the ring bivalents showed complicated configurations due to the differences in location and number of chiasmata. In addition, there were cross-linked bivalents. (5) At metaphase I, the chromosome configuration of each cell was 8.2II 0 + 1.1II + 1.3II + + 0.8I. Most of the chromosomes were ring bivalents, but some were cross-linked bivalents, rod bivalents, or univalents. (6) 15\% PMCs at anaphase I and 22\% PMCs at anaphase II presented chromosome bridges, chromosome fragments, micronuclei, and lagging chromosomes. Twenty seven percent microspores finally moved into one to three micronuclei. Twenty five percent pollens were abortive. The results indicated that the observed individual of M. glyptostroboideswas probably a parpcentric inversion heterozygote, and there were structural and behavioral differences between the homologous chromosomes. The chromosomal aberration of M. glyptostroboidesmay play an important role in the evolution of this relict species, which is known as a living fossil. Further evidence is needed to test whether the differences between homologous chromosomes were due to hybridization. 相似文献
13.
Studies on meiosis in pollen mother cells (PMCs) of a triploid interspecific hybrid (3x = 39 chromosomes, AAD) between tetraploid Gossypium hirsutum (4n = 2x = 52,AADD) and diploid G. arboreum (2n = 2x = 26,AA) are reported. During meiotic metaphase I, 13 AA bivalents and 13 D univalents are expected in the hybrid. However,
only 28% of the PMCs had this expected configuration. The rest of the PMCs had between 8 and 12 bivalents and between 12 and
17 univalents. Univalents lagged at anaphase I, and at metaphase II one or a group of univalents remained scattered in the
cytoplasm and failed to assemble at a single metaphase plate. Primary bipolar spindles organized around the bivalents and
multivalents. In addition to the primary spindle, several secondary and smaller bipolar spindles organized themselves around
individual univalents and groups of univalents. Almost all (97%) of the PMCs showed secondary spindles. Each spindle functioned
independently and despite their multiple numbers in a cell, meiosis I proceeded normally, with polyad formation. These observations
strongly support the view that in plant meiocytes bilateral kinetochore symmetry is not required for establishing a bipolar
spindle and that single unpaired chromosomes can initiate and stabilize the formation of a functional bipolar spindle. 相似文献
14.
Intercellular chromatin migration (cytomixis) in the pollen mother cells of two tobacco (Nicotiana tabacum L.) lines was analyzed by electron microscopy during the first meiotic prophase. The maximal manifestation of cytomixis was
observed in the pachytene. As a rule, several cells connected with one another by cytomictic channels wherein the nuclei migrated
were observable at this stage. In the majority of cases, nuclei passed from cell to cell concurrently through several closely
located cytomictic channels. Chromatin migrated between cells within the nuclear envelope, and its disintegration was unobservable.
The nucleus, after passing through cytomictic channels into another cell, can be divided into individual micronuclei or, in
the case of a direct contact with another nucleus, can form a nuclear bridge. It has been demonstrated that the chromatin
structure after intracellular migration visually matches the chromatin structure before it passed through the cytomictic channel.
No signs of pyknosis were observable in the chromatin of the micronuclei formed after cytomixis, and the synaptonemal complex
was distinctly seen. The dynamics of changes in the nucleoli during cytomixis was for the first time monitored on an ultrastructural
level. Possible mechanisms determining cytomixis are discussed and the significance of this process in plant development is
considered. 相似文献
15.
Li MT Li ZY Zhang CY Qian W Meng JL 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2005,110(7):1284-1289
The tri-genomic hybrid (ABC, 2n=27) between Brassica carinata (BBCC, 2n=34) and B. rapa (AA, 2n=20) is a unique material for studying genome relationships among Brassica species and a valuable bridge for transferring desirable characteristics from one species to the other within the genus Brassica. The crossability between B. carinata and B. rapa was varied with the cultivar of B. rapa. Hybrid pollen mother cells (PMCs), confirmed by morphological observation and molecular marker assay, could be grouped into 20 classes on the basis of chromosome pairing configurations. More than 30% of the PMCs had nine or more bivalents. Genomic in situ hybridization confirmed that two of the bivalents most likely belonged to the B genome. Nearly one-half of the PMCs had trivalents (0–2) and quadrivalents (0–2), which revealed partial homology among the A, B, and C genomes and suggested that there is a good possibility to transfer genes by means of recombination among the three genomes. The advantages of using the tri-genomic hybrids as bridge material for breeding new types of B. napus are discussed. 相似文献
16.
Campuloclinium macrocephalum DC. is a perennial herb widely distributed in the New World and introduced in South Africa, where it is commonly called “pompom weed”. This species is considered one of the most important weeds of Brazil and one of the problematic invasive plants of South Africa. The meiotic system can be studied to assess the ability of a weed to spread, but only few studies on C. macrocephalum have been realized. In this study, we examined the meiotic behavior and pollen fertility of 14 natural populations of C. macrocephalum from Argentina and Uruguay. Meiotic analysis revealed 2 triploid (2n = 3x = 30), 11 tetraploid (2n = 4x = 40) and 1 mixed population (2n = 2x = 20, 2n = 4x = 40). Both, triploid and tetraploid specimens showed a widely variable meiotic behavior with irregular chromosome pairing showing univalents, bivalents, trivalents (in triploids) and tetravalents (in tetraploids) at diacinesis of first meiotic division. Different abnormalities were observed, such as: laggard chromosomes, chromatin bridges, and out of plate chromosomes at metaphase I. During meiosis I (prophase), some cells showed the phenomenon of cytomixis or chromatin transfer between pollen mother cells. The meiotic indexes suggest that only four populations were normally fertile (over 90 % of fertile pollen), indicating meiotically stable plants. The remaining populations share variable pollen fertility, with triploids ranging from 46.64 to 54.83 % and tetraploids varying from 3.54 to 45.30 %. We suggest that polyploidy seems to be recurrent in C. macrocephalum, promoting partial sterility of pollen grains, generating large numbers of individuals by apomixis promoting invasion of crop fields. This study presents the meiotic behavior of this weed, these could be useful for future studies of biological control in areas with no natural enemies. 相似文献
17.
Polyploidy, which is thought to have played an important role in plant evolution and speciation, is prevalent in Chrysanthemum (x = 9). In fact, polyploid series are known in C. zawadskii (2x, 4x, 6x, 8x, and 10x) and C. indicum (2x, 4x, and 6x), but the mechanism by which polyploidization occurs is unknown. Here we show that in diploid individuals of both C. zawadskii and C. indicum, the fusion between two adjacent pollen mother cells (PMCs) occurs at a frequency of 1.1–1.3% early in the first meiotic
division. While possessing the chromosomes of both PMCs, the fused cell or syncyte undertakes subsequent meiotic division
processes as a single large PMC, producing four 2n pollen grains that are able to germinate. Despite their low frequency, syncyte formation may have played a major role in
the production of infraspecific polyploids in Chrysanthemum. 相似文献
18.
19.
M. K. Omara 《Chromosoma》1976,55(3):267-271
Cytomixis is a spontaneous process occurring through the formation of cytoplasmic bridges between adjacent pollen mother cells. This phenomenon was observed in the pollen mother cells of 3 genotypes of Lolium perenne which had been subjected to directional selection for productivity of green material. — The process has led to the formation of up to 34.8% of PMCs with chromosome numbers deviating from the normal diploid number 2n=14. The abnormal PMCs contained chromosome numbers ranging from 2–56 as observed at first metaphase. — Abnormal PMCs were also observed with approximately the same frequency in Meiosis II. This phenomenon is under genetic control. The evolutionary significance of cytomixis and the cytological consequences are discussed. 相似文献
20.
Intertribal somatic hybrids of Raphanus sativus (2n = 18, RR) and Brassica rapa spp. chinensis (2n = 20, AA) with the dye and medicinal plant Isatis indigotica (2n = 14, I I) were firstly obtained by polyethylene glycol-induced symmetric fusions of mesophyll protoplasts. One mature hybrid
with R. sativus established in field had intermediate morphology but was totally sterile. It had the expected chromosome number (2n = 32, RRI I) and parental chromosomes were distinguished by genomic in situ hybridization (GISH) analysis, and these chromosomes
were paired as 16 bivalents in pollen mother cells (PMCs) at diakinesis and mainly segregated equally as 16:16 at anaphase
I (A I), but the meiotic disturbance in second division was obvious. Five mature hybrids with B. rapa established in field were morphologically intermediate but showed some differences in phenotypic traits and fertility, two
were partially fertile. Cytological and GISH investigations revealed that these hybrids had 2n = 48 with AAIIII complement and their PMCs showed normal pairing of 24 bivalents and mainly equal segregation 24:24, but meiotic
abnormalities of lagging chromosomes and micronuclei appeared frequently during second divisions. AFLP analysis showed that
all of these hybrids had mainly the DNA banding pattern from the addition of two parents plus some alterations. Some hybrids
should be used for the genetic improvement of crops and the dye and medicinal plant. 相似文献