麦蓝菜的花粉母细胞减数分裂及核型分析

采用压片法,对麦蓝菜的花粉母细胞减数分裂及体细胞核型进行了研究。结果表明,麦蓝菜的绝大多数花粉母细胞减数分裂中染色体的行为正常,在终变期同源染色体配对后可形成15个二价体;在少数花粉母细胞减数分裂中观察到落后染色体、染色体桥等异常行为;其减数分裂为同时型,其花粉粒育性为88.04%。麦蓝菜的染色体数目为2n=2X=30,核型公式为K(2n)=2X=30=22m(2SAT)+8 sm,染色体相对长度组成为2n=16M2+14M1,其核型为"1A"型。     

黄芩的花粉母细胞减数分裂及核型分析

采用压片法,对黄芩花粉母细胞减数分裂及核型进行了研究。结果表明:黄芩的大多数花粉母细胞减数分裂中染色体的行为正常,在终变期同源染色体配对后可形成9个二价体,后期Ⅰ染色体以9∶9的方式向细胞两极分离,其减数分裂为同时型;在少数花粉母细胞减数分裂中观察到落后染色体、染色体桥等异常行为;其花粉粒育性为76.49%。黄芩的染色体数目为2n=2X=18,核型公式为K(2n)=2X=18=16m+2 sm,染色体相对长度组成为2n=1 s+4M1+3M2+1L,其核型为"1A"型。     

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。     

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.     

Microsporogenesis in Brachiaria dictyoneura (Fig. & De Not.) Stapf (Poaceae: Paniceae)

Microsporogenesis was analyzed in five accessions of Brachiaria dictyoneura presenting x = 6 as the basic chromosome number. All accessions were tetraploid (2n = 4x = 24) with chromosome pairing in bi-, tri-, and quadrivalents. The recorded meiotic abnormalities were those typical of polyploids, including precocious chromosome migration to the poles, laggard chromosomes, and micronucleus formation. The frequency of these abnormalities, however, was lower than those reported for other polyploid accessions previously analyzed for other Brachiaria species. Cell fusion and absence of cytokinesis were also recorded in some accessions, leading to restitutional nucleus formation in some cells. Genetically unbalanced microspores, binucleate, and 2n microspores were found among normal meiotic products as results from these abnormalities. The limitation in using these accessions as pollen donor in interspecific crosses with sexual species with x = 7 or x = 9 in breeding programs is discussed.     

Development and cytology of pollen in Dahlstedtia Malme (Leguminosae: Papilionoideae)

Microsporogenesis, chromosome number, meiotic behaviour and meiotic index were investigated in Dahlstedtia pinnata and D . pentaphylla , two legume species occurring largely in Brazil, in order to ascertain whether the pollen could limit fertilization events. Archesporial cells originate primary sporogenous and anther wall precursor cells, the tapetum is uniseriate, uninucleate and glandular. Tetrads are tetrahedric or decussate, and cytokinesis is of the simultaneous type. Mature pollen grains are tricolpate and bicellular. No abnormalities in microsporogenesis were found. In both species the chromosome number is n = 11, a number not reported previously. The base number for Dahlstedtia is also 11, because cytological observations include both species of Dahlstedtia . D. pentaphylla has a higher meiotic index and lower individual variation values, and it is considered meiotically stable. Its pollen grains do not limit fertilization. D. pinnata has a lower meiotic index, and the pollen is one of the factors which limit fertilization. Furthermore, D. pinnata has numerous adventitious shoots, which suggest that vegetative propagation is important in its reproductive process. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 138 , 461–471.     

Cytological studies on meiosis and male gametophyte development in autotetraploid cucumber

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.     

核桃楸的胚胎学研究（Ⅰ）——小孢子发生及雄配子体发育

通过石蜡制片技术对小孢子的发生和雄配子体发育过程进行了系统的研究。结果表明：花药含有4个花粉囊;花粉囊壁包括表皮、纤维层、中层、绒毡层;花药壁发育属基本型,腺质绒毡层,中层和绒毡层在花粉发育过程中逐渐解体,成熟的花粉囊只保留表皮和纤维层。小孢子母细胞减数分裂中,细胞质分裂是同时型。四分体排列方式为四面体型,四分体解体产生单核花粉粒,成熟花粉为2-细胞型。     

国产蕺菜的染色体数目变异及核穿壁现象

蕺菜 Houttuynia cordata Thunb.属三白草科蕺菜属,俗称鱼腥草、侧耳根等,主要分 布于 亚洲东部和东南部,我国以长江流域及其以南各省区常见。蕺菜药蔬兼用,为极具开发前景 的植物资源。部分学者曾对蕺菜染色体数目进行过报道,但报道的染色体数目不尽一致（梁汉兴,1991,1995; Hsu,1968; Nilsamranchit et al, 1999）,并且对此 现象未作较为详细而深入的解释。本文对国内部分省区收集的蕺菜种质资源进行染色体数目分析,旨在从细胞学角度探讨蕺菜的遗传多样性,为     

Meiotic mutants of Medicago sativa show altered levels of alpha- and beta-tubulin.

We have analysed the level of accumulation of alpha- and beta-tubulin polypeptides in flowers collected from different meiotic mutants of alfalfa (Medicago sativa L.). The H33 mutant previously identified as a producer of male and female gametes with the somatic chromosome number (2n gametes) as a result of defective spindle orientation or, more rarely, abnormal cytokinesis, showed a higher level of alpha- and beta-tubulin compared to control diploid plants and approximately the same level as control tetraploid plants. A higher level of tubulin was likewise observed in diploid plants displaying abnormalities in spindle orientation and cytokinesis, which had gone through 3-4 cycles of phenotypic recurrent selection to increase 2n gamete production. A similar analysis was performed on another class of Medicago meiotic mutants characterized by production of 4n pollen (jumbo pollen, due to the absence of cytokinesis at the end of meiosis) and 2n eggs. Again, the level of alpha- and beta-tubulin was found to be higher in the mutants than in diploid controls. We conclude that meiotic defects, such as abnormal spindle orientation or cytokinesis leading to the formation of 2n gametes, determine an increased level of tubulin, the main constituent of plant microtubules (MTs).     

Dynamics of microtubular cytoskeleton in higher plant meiosis. X. General scheme of cytoskeletal cycle

An overview of a set of our previous papers titled "Dynamics of microtubular cytoskeleton in higher plant meiosis" is presented, in addition to some data on subcellular mechanisms underlying cytoskeleton reorganization during meiotic division in pollen mother cells. An illustrated scheme of cytoskeleton rearrangements during plant meiosis, both with successive and simultaneous cytokinesis, is given.     

Induction of cytomixis affects microsporogenesis in Sesamum indicum L. (Pedaliaceae)

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.     

Cytomixis in Lolium perenne

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.     

Microsporogenesis in Brachiaria brizantha (Poaceae) as a selection tool for breeding

The genus Brachiaria comprises more than 100 species and is the single most important genus of forage grass in the tropics. Brachiaria brizantha, widely used in Brazilian pastures for beef and dairy production, is native to tropical Africa. As a subsidy to the breeding program underway in Brazil, cytological studies were employed to determine the chromosome number and to evaluate microsporogenesis in 46 accessions of this species available at Embrapa Beef Cattle (Brazil). Thirty-four accessions presented 2n = 36; seven had 2n = 45, and five had 2n = 54 chromosomes. Based on the higher level of chromosome association observed in diakinesis, in tetra-, penta-, and hexavalents, respectively, it was concluded that they are derived from x = 9; consequently, these accessions are tetra- (2n = 4x = 36), penta- (2n = 5x = 45), and hexaploids (2n = 6x = 54). The most common meiotic abnormalities were irregular chromosome segregation due to polyploidy. Chromosome stickiness, abnormal cytokinesis, non-congressed bivalents in metaphase I and chromosomes in metaphase II, and chromosome elimination were recorded at varying frequencies in several accessions. The mean percentage of meiotic abnormalities ranged from 0.36 to 95.76%. All the abnormalities had the potential to affect pollen viability by generating unbalanced gametes. Among the accessions, only the tetraploid ones with less than 40% of abnormalities are suitable as pollen donors in intra- and interspecific crosses. Currently, accessions with a high level of ploidy (5 and 6n) cannot be used as male genitors in crosses because of the lack of sexual female genitors with the same levels of ploidy.     

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.     

The Relation between Cytomixis and Variation of Chromosome Numbers in Pollen Mother ceils of Rye (Secale cereale L.)

Cytomixis is a spontaneous and normal process occurring through the formation of plasma channels between neighbouring pollen mother cells (PMCs). This phenomenon was observed in the PMCs of 2 variaties of Secale cereale which had been collected from Gausu and Shanxi Provinces. The process had led to the formation of up to 6.37% of PMCs with chromosome numbers deviating from the normal haploid number n=7. The abnormal PMCs contained chromosome numbers ranging from 5–9 in metaphase Ⅰ. Abnormal PMCs with decreased and increased chromosome numbers could be the result of cytomixis. The cytological consequences and the evolutionary significance of cytomixis are discussed.     

Chromosome numbers and meiotic analysis in the pre-breeding of <Emphasis Type="BoldItalic">Brachiaria decumbens</Emphasis> (Poaceae)

A total of 44 accessions of Brachiaria decumbens were analysed for chromosome count and meiotic behaviour in order to identify potential progenitors for crosses. Among them, 15 accessions presented 2n = 18; 27 accessions, 2n = 36; and 2 accessions, 2n = 45 chromosomes. Among the diploid accessions, the rate of meiotic abnormalities was low, ranging from 0.82% to 7.93%. In the 27 tetraploid accessions, the rate of meiotic abnormalities ranged from 18.41% to 65.83%. The most common meiotic abnormalities were related to irregular chromosome segregation, but chromosome stickiness and abnormal cytokinesis were observed in low frequency. All abnormalities can compromise pollen viability by generating unbalanced gametes. Based on the chromosome number and meiotic stability, the present study indicates the apomictic tetraploid accessions that can act as male genitor to produce interspecific hybrids with B. ruziziensis or intraspecific hybrids with recently artificially tetraploidized accessions.     

Cytomixis and associated meiotic abnormalities affecting pollen fertility in Clematis orientalis

Present cytological investigations from the cold desert regions of Lahaul-Spiti and Kinnaur (India) record the first ever tetraploid (2n=32) chromosome count and cytomixis in Clematis orientalis L. var. acutifolia Hook. f. et Thoms. The phenomenon of cytomixis (9.33–29.80 %) involving chromatin transfer among 2–3 proximate pollen mother cells (PMCs) during male meiosis occurs through narrow and broad cytoplasmic channels from early prophase to tetrad stage. However, frequency of its occurrence during the later meiotic stages is rather low. Chromatin transfer results into the formation of hypo-, hyperploid and enucleated PMCs. Various meiotic abnormalities associated with cytomixis such as chromatin stickiness, pycnotic chromatin, interbivalent connections, out of plate bivalents, late disjunction of bivalents, and laggards and bridges resulted into some pollen sterility (16.33–49.30 %) and heterogeneous pollen grains size.     

Processes of phragmoplast centrifugal movement in cereal meiosis

A group of new meiotic division abnormalities affecting processes of phragmoplast centrifugal movement in successive cytokinesis in cereal pollen mother cells is described. These phenotypes present new information about motile phragmoplast formation and operation and confirm our model of centrifugal movements as B-ana-phase modification.     

广东万年青的细胞遗传学研究

采用常规压片法和去壁低渗法,以生长于广西凭祥和广东深圳的广东万年青（Aglaonema modestumSchott ex Engl.）为材料,对二者的体细胞染色体、花粉母细胞减数分裂染色体配对行为和花粉发育过程进行了观察。结果表明：（1）野生植株为二倍体2n=40,栽培植株为三倍体2n=60;（2）野生种的小孢子母细胞减数分裂前期I终变期均为二价联会,栽培种偶见三价联会;（3）中期I,野生种为20个二价体排列在赤道板上,未见单价体,栽培种的20个二价体排列于赤道板上,20个单价体随机分布于两极,证实其为三倍体;（4）后期I,野生种二价体分离,出现单染色单体桥和断片,几率为10%,栽培种几率为3%,还存在落后染色体,部分不能进入两极的落后染色体和染色体断片在末期I形成微核;（5）四分体时期,野生种未观察到异常孢子,栽培种出现大量败育的四分体或多分体;（6）小孢子进入正常的发育分化,通过两次有丝分裂形成三细胞型花粉。野生种成熟花粉败育率为2.18%,栽培种为88.29%;（7）野生种正常结实,栽培种果实中未发现种子,为高度不育。