Chromosome numbers,characterization of chromosomal pairing during meiosis,origin and natural propagation in polyploid cytotypes (4x, 5x and 6x) of Agrimonia eupatoria L. (Rosaceae) in northwest Himalayas (India)

Despite the presence of intraspecific polyploidy (2x, 4x, 5x and 6x) in Agrimonia eupatoria, origin of these cytotypes has never been addressed adequately. The aim of the present study was to record the original chromosome counts and characterize chromosomal pairing during meiosis and microsporogenesis in the 5x cytotype, and discussing the hypothesis regarding the possible origin of polyploid cytotypes (4x, 5x and 6x) in the species. The geographical distribution pattern of cytotypes in the Indian Himalayas and elsewhere has also been analyzed. The present meiotic analysis revealed three chromosomes counts, the tetraploid (2n?=?4x?=?56), the pentaploid (2n?=?5x?=?70) and the hexaploid (2n?=?6x?=?84) cytotypes based on x?=?14. Meiotic course was perfectly normal in the 4x and 6x cytotypes resulting into high pollen fertility (94–100 %). Meiotic course in the imbalanced 5x cytotype has been found to be irregular characterized by the presence of high frequency of univalents at diakinesis and metaphase-I. Abnormal meiotic course contributed towards high pollen sterility (74–88 %). Even the apparently fertile/stained pollen grains were of irregular shape and of heterogeneous sizes. Meiotic behaviour of the 5x cytotype is like typical of allopolyploid. Individuals of 5x cytotype did not produce seeds and propagate vegetatively (root suckers) while 4x and 6x cytotypes exploited sexual (seeds) as well as vegetative means for propagation. Chromosomal pairing in pentaploid cytotype is like typical of an allopolyploid and we assume that it might have originated owing to natural inter-cytotype hybridization between 4x and 6x cytotypes in a mixed population. Analysis of geographical distribution pattern of cytotypes shows that Indian Himalayas represent the most cytotype-diverse region for A. eupatoria with the existence of all the four cytotypes (2x, 4x, 5x, 6x). This shows the dynamic nature of the species at chromosomal level in this part of the world.     

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 %).     

Cytological studies of Brassicaceae Burn. (Cruciferae Juss.) from Western Himalayas

Cytological studies have been carried out on 12 species of Brassicaceae Burn. on population basis from different geographical areas of Kashmir and Himachal Pradesh in the Western Himalayas. Variable chromosome reports for Barbaraea intermedia (n = 16), Cardamine loxostemonoides (n = 8), Nasturtium officinale (n = 8), Sisymbrium orientale (n = 14) on world-wide basis have been added to the previous reports of these species. The chromosome numbers in seven species as Barbaraea intermedia (n = 8), B. vulgaris (n = 8), Capsella bursa-pastoris (n = 8), Descuriania Sophia (n = 10), Rorippa islandica (n = 8), Sisymbrium strictum (n = 7) and Thlaspi alpestre (n = 7) have been worked out for the first time from India. The meiotic course in the populations of seven species such as Barbaraea intermedia, Capsella bursa-pastoris, Coronopus didymus, Descuriania sophia, Nasturtium officinale, Sisymbrium orientale and S. strictum varies from normal to abnormal while all the populations of two species Barbaraea vulgaris and Sisymbrium irio show abnormal meiotic course. Meiotic abnormalities are in the form of cytomixis, chromosomal stickiness, unoriented bivalents, inter-bivalent connections, formation of laggards and bridges, all resulting into abnormal microsporogenesis. Heterogenous sized fertile pollen grains and reduced reproductive potentialities have invariably been observed in all the meiotically abnormal populations. However, the meiotic course in all the populations of Cardamine loxostemonoides, Rorippa islandica and Thalspi alpestre is found to be normal with high pollen fertility.     

Cytology of the genus Artemisia (Anthemidae,Asteraceae) in the Western Himalayas

The present study revealed the varied frequency of natural chromosomal abnormalities in 13 populations pertaining to 9 species of the genus Artemisia L. from different localities of Himachal Pradesh (Western Himalaya). Intraspecific chromosome variability has been reported for the first time on worldwide basis in Artemisia vestita (2n = 2x = 36) and from India in A. macrocephala (2n = 2x = 18) and A. scoparia (2n = 2x = 36). Besides, B-chromosomes have been reported here for the first time in A. nilagirica and A. roxburghiana. Most of the populations show anomalous meiotic behaviour resulting in cytomixis, chromosomal stickiness, unoriented bivalents, formation of laggards and bridges which leads to abnormal microsporogenesis, and production of heterogeneous-sized fertile pollen grains along with reduced pollen fertility.     

Evaluation of meiotic abnormalities and pollen viability in aposporous and sexual tetraploid Paspalum notatum (Poaceae)

We analyzed anaphase I configurations and pollen viability in aposporous and sexual tetraploid (2n?=?4x?=?40) cytotypes of Paspalum notatum. Five natural aposporous accessions and three experimentally obtained sexual individuals were used. In addition, 16 (8 aposporous and 8 sexual) F₁ hybrids, previously classified by their mode of reproduction, were analyzed. Cytogenetic observations revealed normal and abnormal anaphase I configurations in both aposporous and sexual genotypes. Anaphase I abnormalities were mainly laggard chromosomes, chromatin bridges, and micronuclei. On average, 44.36?% of aposporous meiocytes and 29.66?% of sexual ones showed abnormal anaphase I configurations. The total numbers of normal and abnormal anaphase I were highly significantly different between aposporous and sexual strains. The pollen viability test indicated that aposporous individuals had significantly more non-viable pollen than sexual ones; a positive correlation (r?=?0.71; r ²?=?0.50) between the variables was detected. Analysis of aposporous and sexual hybrids confirmed differences in the numbers of normal and abnormal anaphase I patterns in the aposporous and sexual parents. However, similar proportions of viable pollen were produced by both groups of hybrids. In this case, the variables were not correlated (r?=?0.23; r ²?=?0.05). Data from this study indicated that aposporous strains had a genetic rearrangement affecting meiosis that was absent in the experimentally obtained sexual individuals and that it was transmitted to the progeny. The possible association between meiotic abnormalities and the inheritance of apospory is discussed.     

Impact of cytomixis on meiosis, pollen viability and pollen size in wild populations of Himalayan poppy (Meconopsis aculeata Royle)

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.     

Cytogeography and phenomenon of cytomixis in Silene vulgaris from cold regions of Northwest Himalayas (India)

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.     

Chromosome number and secondary chromosomal associations in wild populations of Geranium pratense L. from the cold deserts of Lahaul-Spiti (India)

In this work we studied the meiotic chromosome number and details of secondary chromosomal associations recorded for the first time in Geranium pratense L. from the alpine environments in the cold deserts of Lahaul-Spiti (India). All the presently studied individuals of the species existed at 4x level (x = 14). The present chromosome count of n = 28 in the species adds a new cytotype to the already existing diploid chromosome count of 2n = 28 from the Eastern Himalayas and outside of India. Out of the six accessions scored presently four showed normal meiotic course. However, two accessions investigated from Mud, 3800 m and Koksar, 3140 m depicted abnormal meiotic course due to the presence of multivalents and univalents, and secondary associations of bivalents/chromosomes. The secondary chromosomal associations in the species existed among bivalents/chromosomes were noticed in the PMCs at prophase-I (diakinesis) and persisted till the separation of sister chromatids at M-II. The variation in the number of bivalents/chromosomes involved in the secondary associations at M-I (2–8) and A-I/M-II (2–12) has also been recorded. The occurrence of such secondary associations of bivalents/chromosomes in G. pratense which existed at 4x level indicated the secondary polyploid nature of the species.     

Pollen anomaly - a clue to natural hybridity in Argemone (Papaveraceae)

Studies in the pollen morphology of Argemone mexicana (a diploid species, 2n=28), A. ochroleuca (a tetraploid, 2n=56), the wild populations of which growing side by side, and of a triploid (2n=42) observed in the population of A. ochroleuca, have been carried out using light and scanning electron microscope. Pollen grains in both the species are 3 (-4)-zonocolpate with reticulate exine surface, and are distinguishable only on the basis of pollen size, the tetraploid species having larger pollen grains. In the triploid plant, a large number of grains deviates from the normal 3-zonocolpate condition showing a number of apertural types, such as 1-aperturate-operculate, 2-colpate, 3-syncolpate, 4-zonocolpate and spiraperturate. Besides, planaperturate 3-colpate-trilobed grains also occur. The triploid is also characterised by 'minigrains' (size 13-19 μm), a feature not observed in A. mexicana and A. ochroleuca. Since these species are reported to be genetically close, the occurrence of the triploids (forming nearly 5% of the population of A. ochroleuca) indicates the possibility of a natural hybridization between A. ochroleuca and A. mexicana, which is well pronounced on its anomalous pollen features serving as marker for such a hybrid occurring in nature.     

Detailed cytomorphological investigations through male meiosis of polypetalous plants from the Kashmir Himalaya

Cytomorphological studies were made on 322 populations of 150 species/153 taxa belonging to 79 genera and 23 families of flowering plants. Out of these, 14 species were cytologically worked out for the first time on a worldwide basis along with B-chromosomes (0–1B) recorded for the first time in Agrimonia eupatoria. Similarly, 29 species were reported with varied chromosomal reports on a worldwide basis. The chromosome numbers ranged from 2n = 10 to 2n = 96 and posed high amount of intraspecific genetic diversity when seen in relation to other reports for the worked out species in light of previous chromosomal databases on India and world basis. The different levels of ploidy in these species/taxa vary from 2x to 12x with the overall polyploidy being 27.45 % and predominant in members belonging to the genera Ranunculus and Epilobium as well as families Ranunculaceae and Rosaceae. In the taxa showing anomalous meiotic behavior, cytomixis is found to be quite common and associated with various meiotic abnormalities in the meiocytes, which ultimately leads to pollen sterility and formation of variable sized pollen grains.     

Cytogeography of Cenchrus ciliaris (Poaceae) in Tunisia

Belonging to the genus Cenchrus with 16–22 species, Cenchrus ciliaris L. (syn. Pennisetum ciliare (L.) Link, buffelgrass) is a perennial, common in warmer regions of both hemispheres, growing as a C4 grass in a wide range of habitats. In the present study we determined chromosome number and nuclear DNA content (2C DNA) for 28 natural populations collected from northern to southern Tunisia. Three ploidy levels were found: one tetraploid population (2n?=?4x?=?36), three pentaploid (2n?=?5x?=?45), and 24 hexaploid populations (2n?=?6x?=?54). The hexaploid chromosome number has already been reported for Tunisian populations of C. ciliaris but tetraploid and pentaploid (2n?=?45) are new for this area. The tetraploid population was found in the semi-arid north; pentaploids were mostly on the northern side of the arid region, while the hexaploids were located mainly in the arid southern Tunisian and Saharan region. 2C DNA values, assessed using flow cytometry, correlated with chromosome counts. Nuclear DNA content ranged from 2C?=?3.03 to 4.61 pg, revealing three ploidy levels corresponding to 4x, 5x, 6x, and mean 2C DNA amounts were of 3.03, 3.7 and 4.48 pg, respectively. Each cytotype produced viable pollen. Flow cytometric seed screening neither proved nor disproved apomixis. The most frequent hexaploid populations seem best adapted to arid conditions in southern Tunisia. The monoploid value, 1Cx, was constant. The existence of pentaploid cytotype suggests hybridization ability between tetraploids and hexaploids. It appears that polyploidization is the major evolutionary mechanism in the speciation of C. ciliaris.     

Meiotic behavior and pollen viability of tetraploid Arachis glabrata and A. nitida species (Section Rhizomatosae, Leguminosae): implications concerning their polyploid nature and seed set production

The meiotic behavior and pollen viability of the tetraploids (2n?=?4x?=?40) Arachis glabrata and A. nitida were analyzed aiming to provide insights into the nature of these polyploids and into the mechanism that determines the low seed production of these species. Meiotic analysis revealed 21 different chromosome configurations at diakinesis-metaphase I in A. glabrata (from 20 II to 4 II?+?8 IV) and 7 in A. nitida (from 20 II to 2 I?+?12 II?+?2 III?+?2 IV). The multivalent associations (up to 8 IV) observed in some A. glabrata metaphases suggest that this species may have an autopolyploid origin. However, the fact that the mean number of bivalents varied among accessions indicates different degrees of diploidization among them. In contrast, the multivalents (up to 2 III?+?2 IV) observed in very low frequency in A. nitida indicate that this species may be either a largely diploidized autopolyploid or a segmental allopolyploid. A great diversity, although in low frequency, of meiotic abnormalities (abnormal chromosome orientation and segregation, chromosome bridges, irregular spindles, micronuclei, aneuploid nuclei, restitution nuclei, microcytes, monads, dyads, triads, and hexads) was detected in both species. The meiotic indexes were over 95%, and pollen viabilities ranged from 83.20 to 95.99%. These results suggest that chromosome behavior during meiosis would not severely affect pollen viability. Thus, the irregular chromosome behavior caused by the autopolyploid or segmental allopolyploid nature of these species may not be related to their low seed set production.     

石竹花粉母细胞减数分裂的观察

采用常规压片法对石竹(Dianthus chinensis L.)花粉母细胞减数分裂进行了细胞学观察。结果表明,减数分裂过程中存在二价体提前分离、赤道板外染色体、落后染色体、染色体不均等分离等异常现象,各时期的畸形率都低于3%,石竹的减数分裂过程基本正常,石竹染色体数目2n=2x=30。     

Cytological evaluation of Apiaceae Lindl. from Western Himalayas

The present paper deals with cytological studies on 31 populations covering 17 species belonging to 10 genera of Apiaceae from Western Himalayas. The chromosome numbers in the two species as Chaerophyllum capnoides (n = 11) and Heracleum brunonis (n = 11), along with additional cytotypes for Pimpinella acuminata (n = 9) and Sium latijugum (n = 12) have been reported for the first time on world-wide basis. The genus Pleurospermum, although cytologically worked out earlier from outside India, its species densiflorum (n = 11) makes first representation of the genus from India. Besides, the chromosome number in Chaerophyllum aromaticum (n = 11) have been worked out for the first time from India. The course of meiosis varies from normal to abnormal in different populations of Chaerophyllum villosum, Pimpinella achilleifolia and Sium latijugum while abnormal meiotic course has been observed in all the studied populations of Chaerophyllum acuminatum, C. aromaticum, C. capnoides, Pimpinella acuminata, P. diversifolia, Pleurospermum densiflorum and Vicatia coniifolia. Such taxa are marked with meiotic abnormalities in the form of cytomixis, chromatin stickiness, formation of laggards and bridges resulting into abnormal microsporogenesis. The occurrence of structural heterozygosity has been recorded in the Chaerophyllum acuminatum and C. aromaticum. The effect of these abnormalities is clearly seen on the pollen size and fertility.     

Chromosome number, male meiosis and pollen fertility in selected angiosperms of the cold deserts of Lahaul-Spiti and adjoining areas (Himachal Pradesh, India)

In this study the exact chromosome number, detailed meiotic behavior in pollen mother cells and pollen viability were investigated, which can contribute to a better understanding of the cytological evolution of the species growing in the cold deserts of Lahaul-Spiti (Himachal Pradesh, India). This study is the first such comprehensive attempt to explore the region chromosomally. Chromosome number, meiotic behavior and pollen fertility were analyzed in 301 accessions of 140 species of Polypetalae. Chromosome counts in 14 species are the first ever records, viz., Aquilegia pubiflora (n?=?7), Corydalis govaniana (n?=?8), C. thyrsiflora (n?=?8), Hedysarum astragaloides (n?=?7), H. microcalyx (n?=?7), Oxytropis thomsoni (n?=?8), Rhodiola tibetica (n?=?10), R. wallichianum (n?=?16), Rosularia alpestris (n?=?14), Epilobium chitralense (n?=?18), E. leiospermum (n?=?18), Heracleum brunonis (2n?=?33), H. thomsonii (n?=?11) and Pleurospermum govanianum (n?=?9). New intraspecific diploid or polyploid cytotypes have been recorded in 13 species. The species of these cold deserts are quite active in evolution, depicting heterogeneity in chromosome number involving polyploidy, 51 species (36.43%) and/or aneuploidy (37 species). Various meiotic abnormalities were observed in the majority of the species, causing pollen sterility and pollen grains of variable sizes. We are of the opinion that harsh climatic conditions have caused various meiotic abnormalities in the majority of the plants, which has affected the genetic constitution and viability of male gametes.     

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。     

Meiotic behavior and pollen morphology variation in Centaurium pulchellum (Gentianaceae)

Centaurium pulchellum is an annual herb native to Europe, but introduced in South America, where it is widely used in the preparation of digestive infusions and bitter drinks. In this species, a wide variation in the aperture pattern of pollen grains was reported and has been attributed to environmental factors or irregularities at meiosis. For this reason, cytological and palynological studies have been undertaken on two different populations. The pollen grain analysis showed that some types are more frequent within each population, but the most common forms were the typical 3-colporate and 4-colporate. The cytological analysis revealed that the analyzed populations of C. pulchellum have chromosome number 2n = 36. The presence of tetravalents at meiosis strongly suggests that these populations are autotetraploid based on x = 9. The meiotic behavior showed a significant percentage of irregularities in different phases: off-plate bivalents, precocious segregation, laggard chromosomes, bridges, and cytomixis. However these irregularities are not related to the variation in the aperture pattern of pollen grains. The heteromorphism in the pollen grains observed in C. pulchellum could be a normal condition to which the species is well adapted.     

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.     

Abnormal male meiosis explains pollen sterility in the polyploid medicinal plant Pinellia ternata (Araceae)

Pinellia ternata is an important traditional Chinese medicinal plant. Its different populations in China have various ploidy levels, based on x = 13, as well as extensive aneuploid series. The microsporogenesis process was observed in specimens from three populations from three regions of Hubei Province; they were characterized by normal and abnormal meiotic divisions in pollen mother cells (PMCs) at all stages simultaneously. Meiotic abnormalities including univalents/multivalents, chromosomal laggards/bridges and micronuclei appeared in about 50% of the PMCs, together with abnormal cytokinesis. Chromatin/chromosome transfer between meiocytes occurred only during the first division, at low frequency; this might contribute to these meiotic abnormalities. Although the remaining 50% of the PMCs presented normal cytological behavior, pollen fertility was only about 2%. These results provide cytological explanations for its low seed-set and the general use of asexual reproduction through tubers and bulbils; it also explains the wide variations in chromosome number.     

Phenolics from the seeds of Argemone mexicana

Two new phenolic compounds, 5, 7, 2′, 6′-tetrahydroxyflavone and 5, 7-dihydroxychromone 7- neohesperidoside have been characterized from the seeds of Argemone mexicana.