Exine and tapetum development in Nymphaea capensis (Nymphaeaceae): a comparative study

The developmental events in microspore envelope and cytoplasm and in tapetum from premeiosis until late tetrad stage were studied in Nymphaea capensis. The exceptional feature of microspore development in this species is that post-meiosis cytokinesis is retarded until the late tetrad stage. Thus, the entire development of the exine becomes completed during the tetrad stage. As a consequence of the retarded cytokinesis, the proximal portion of the forming exine lags behind the distal one during the major part of the tetrad period, but eventually the proximal part of the exine overtakes the distal part in development. The significance of this retardation is discussed. This sequence of events differs sharply from corresponding sporoderm development in other Nymphaea species. Another important topic is the microspore surface activities during exine development. The surface coatings-glycocalyx-are very similar in microspores and in tapetum cells, but their functions are completely different; the roots for this difference are discussed. A noteworthy feature of the developing microspores is the presence of gigantic, deeply cup-like mitochondria; this property is also characteristic of the microspore cytoplasm of N colorata and N. mexicana. A functional significance of these organelles and their adaptive role is discussed.     

洋葱花药发育中钙离子分布特征

采用焦锑酸钾沉淀钙离子技术,对洋葱（Alliumcepa）花药发育中Ca^2＋分布进行了研究。在小孢子母细胞时期,小孢子母细胞中的钙沉淀颗粒很少,但绒毡层细胞的内切向壁已出现明显的钙沉淀颗粒。在四分体时期,四分体小孢子的胼胝质壁中出现较多的钙沉淀颗粒;绒毡层细胞内切向壁的钙沉淀颗粒消失,而在外切向壁和径向壁部位的钙沉淀颗粒增加。在小孢子早期,小孢子中也出现了钙沉淀颗粒,而绒毡层细胞内切向壁表面出现了很多絮状物,其上附有细小钙沉淀颗粒。到小孢子晚期,小孢子中出现一些小液泡,细胞质中的钙沉淀颗粒有所下降。此时绒毡层细胞已明显退化,但在绒毡层膜上仍有一些乌氏体和钙沉淀颗粒。在二胞花粉早期,营养细胞中的液泡收缩、消失,细胞质中又出现了较多的钙沉淀颗粒,在质体和其内部的淀粉粒表面上附有较多的钙沉淀颗粒。到二胞花粉晚期,花粉中的钙沉淀颗粒已明显下降,仅在花粉外壁中还有一地钙沉淀颗粒．     

白菜核雄性不育花药超微结构的研究

对白菜核雄性不育两用系的可育与不育花药进行了超微结构的比较观察。结果显示不育花药的造孢细胞核仁靠边分布;包裹小孢子母细胞的胼胝质厚薄不均匀,不完整等早期异常现象。减数分裂后．四分体细胞中常有多个细胞核。从四分体释放出的小孢子外壁的孢粉素物质不均匀沉积,呈不连续的单层异常结构。最后小孢子通过细胞质收缩方式败育。在可育花药中．绒毡层细胞在小孢子发育后期已显示出退化迹象,同时在细胞中开始积累脂类物质。但在同时期的不育花药中．绒毡层细胞没有显示出退化的迹象,也不合成脂类物质。从时间上看,败育花药中小孢子母细胞及小孢子的异常在先,绒毡层细胞的异常在后。本研究揭示了白菜核雄性不育花药的超微结构特征．对我们以前的光学显微镜观察结果予以补充和修正。     

白菜核雄性不育花药超微结构的研究

对白菜核雄性不育两用系的可育与不育花药进行了超微结构的比较观察。结果显示不育花药的造孢细胞核仁靠边分布:包裹小孢子母细胞的胼胝质厚薄不均匀,不完整等早期异常现象。减数分裂后,四分体细胞中常有多个细胞核。从四分体释放出的小孢子外壁的孢粉素物质不均匀沉积．呈不连续的单层异常结构。最后小孢子通过细胞质收缩方式败育。在可育花药中,绒毡层细胞在小孢子发育后期已显示出退化迹象,同时在细胞中开始积累脂类物质。但在同时期的不育花药中, 绒毡层细胞没有显示出退化的迹象,也不合成脂类物质。从时间上看,败育花药中小孢子母细胞及小孢子的异常在先,绒毡层细胞的异常在后。本研究揭示了白菜核雄性不育花药的超微结构特征, 对我们以前的光学显微镜观察结果予以补充和修正。     

莴苣花药发育过程中钙的分布特征

减数分裂前,莴苣花药中的钙颗粒很少。减数分裂后,花药绒毡层细胞中的钙颗粒明显增加。同时在花药药室基质中也出现许多细小的钙颗粒。刚从四分体中释放出的小孢子内钙颗粒很少。伴随着花粉外壁物质在小孢子表面的沉积,钙颗粒开始积累在花粉壁部位。随后。小孢子中开始出现钙颗粒。当小孢子开始形成液泡后,钙颗粒向其中聚集,伴随着小液泡融合成大液泡。体积较大的钙颗粒主要集中在液泡中,而细胞质基质中的钙颗粒很少。随着二胞花粉中的大液泡消失,花粉细胞质中的钙颗粒变得很少。在以后的发育中,只有花粉壁中积累较多的钙颗粒。在莴苣花药发育过程中,钙与绒毡层细胞的退化和小孢子液泡形成以及二胞花粉中大液泡的消失有关。而花粉外壁表面积累丰富的钙与以后花粉的萌发有关。     

莴苣花药发育过程中钙的分布特征

减数分裂前,莴苣花药中的钙颗粒很少。减数分裂后,花药绒毡层细胞中的钙颗粒明显增加, 同时在花药药室基质中也出现许多细小的钙颗粒。刚从四分体中释放出的小孢子内钙颗粒很少,伴随着花粉外壁物质在小孢子表面的沉积,钙颗粒开始积累在花粉壁部位。随后,小孢子中开始出现钙颗粒。当小孢子开始形成液泡后,钙颗粒向其中聚集,伴随着小液泡融合成大液泡,体积较大的钙颗粒主要集中在液泡中,而细胞质基质中的钙颗粒很少。随着二胞花粉中的大液泡消失,花粉细胞质中的钙颗粒变得很少。在以后的发育中,只有花粉壁中积累较多的钙颗粒。在莴苣花药发育过程中,钙与绒毡层细胞的退化和小孢子液泡形成以及二胞花粉中大波泡的消失有关。而花粉外壁表面积累丰富的钙与以后花粉的萌发有关。     

水稻雄性不育系珍汕97A小孢子发育过程中的微管骨架

水稻（Oryza sativaL.)雄性不育系珍汕97A,保持系珍汕97B和恢复系测64三系小孢子发生过程的研究表明;恢复系测64小孢子母细胞细胞质浓,有明显的微管荧光围绕着细胞核。小孢子母细胞经两次减数分裂形成四分体。四分体和小孢子的微管从细胞核表面向胞质周缘延伸,形成放射性排列格局,花粉发育正常。细胞质中有少量点状微管荧光,保持系珍汕97B小孢子发生过程的细胞形态和微管结构与恢复系测64相似。但细胞质中的点状微管荧光多一些。雄性不育系珍汕97A小孢子发生早期,小孢子母细胞内出现液泡,核中染色质凝集,微管荧光很弱,没有清晰的微管丝结构。细胞质中有许多点状微管荧光等不正常现象。小孢子母细胞经过减数分裂形成的四分体也没有清晰的丝状微管结构。随后,所有的小孢子迅速败育,雄性不育系珍汕97A在小孢子母细胞发生的很早时期,微管结构就明显不正常。     

Absence of microspore polarity, symmetric divisions and pollen cell fate in Brachiaria decumbens (Gramineae).

Meiotic division and male gametophyte development were analyzed in one tetraploid (2n = 4x = 36) accession of Brachiaria decumbens cv. Basilisk that showed some pollen sterility. Meiotic process was typical of polyploids in that it consisted of multiple chromosome associations. Precocious chromosome migration to the poles, laggards, and micronucleus formation were abundant in both meiosis I and II and resulted in tetrads with micronuclei. After callose dissolution, microspores were released into the anther locule and had the semblance of being normal. Although each microspore initiated its differentiation by pollen mitosis, in 43.24% of the microspores, nuclear polarization was not observed and the typical hemispherical cell plate was not detected. Division was symmetric and microspores lacked differentiation between the vegetative and the generative cell. Both nuclei were of equal size, presented equal chromatin condensation, and had a spherical shape. After the first pollen mitosis and cytokinesis, each cell underwent a new symmetric mitosis without nuclear polarization. At the end of the second pollen mitosis, four equal nuclei were observed in each pollen grain. After the second cytokinesis, the cells gave rise to four equal-sized pollen grains with a similar tetrad configuration that initially remained together. Sterile pollen grains resulted from abnormal pollen mitosis. This anomaly may be explained by a mutation, probably affecting microtubule cytoskeleton formation. The importance of this male-sterile mutation for Brachiaria breeding programs is discussed.     

Embryological Studies in Glycyrrhiza uralensis Fisch.

This paper reports the studies of overall embryology of Glycyrrhiza uralensis Fisch. Development of the anther wall follows the dicotyledonous type. The cytokinesis of the microspore mother cell in meiosis is of simultaneous type. The arrangement of microspores in tetrad is tetrahedral, isobilateral and decussate. Microspores have various types of abortive to development. Mature pollen grain is of the 2-celled type. The ovule is bitegminous, crassinucellate and campylotropous. The megaspore mother cell gives rise to unequal dyad and then linear tetrad. The chalazal megaspore, the second or the third megaspore towards the micropylar end are functional megaspore. The development of the embryo sac conforms to the Polygonum type. Mature embryo sac has various types of variation. The fertilization belongs to the premitotic type of syngamy. The development of most embryoes belongs to the Onagrad type. The development of the endosperm belongs to the nuclear type and the endosperm near the chalazal end develops into haustorium.     

蜡梅小孢子发生和花粉形成的研究

通过对蜡梅小孢子发生和花粉形成的研究,结果表明：蜡梅幼小花药中的多列孢原细胞经造孢细胞发良为小孢子母细胞。减数分裂为同时型。四分体呈四面体型排列,同时观察了小孢子在发育过程中液泡的动态变化。成熟花粉为２－细胞型。花药壁的发育为双子叶型。花药壁由５－６层细胞组成,腺质绒毡层。花粉具有异型性现象。     

THE CYTOLOGY OF POLLEN ABORTION IN C-CYTOPLASMIC MALE-STERILE CORN ANTHERS

Anther development of the C-cytoplasmic male-sterile (cms C) and the normal cytoplasm version (N) in the W182BN corn inbred was studied by light and electron microscopy. Deviation from normal pollen development was first observed in the tapetal cells at the tetrad stage of development. Two types of tapetal abnormalities were observed in plants with C cytoplasm. The first behaved like the N anther until the tetrad stage, when numerous small vacuoles appeared in the tapetal cells. Inner and radial tapetal cell walls broke down normally, but irregular Ubisch body deposition was observed, and exine development was inhibited and delayed. The tapetum and microspores disintegrated at the intermediate microspore stage. The second type of tapetum was highly vacuolated at the early tetrad stage, with dense inner and radial cell walls that remained intact and enlarged when the tetrads aborted. No organellar abnormalities, such as the mitochondrial changes observed in cms T, were observed in C anthers.     

The Formation of Pollen Dimorphism in Paris axialis in Vivo

It is obsreved that the dimorphic populations of pollen are producedin Paris axialis H. Li In vivo. The normal pollen grains and abnormal pollen grainsare 77.1% and 22.9% respectively; more than 70% of abnormal pollen grains conformto the equal nucleus type. The abnormal pollen grains show no delayed development,and thay are stained as dark as the normal ones. During the first mitotic division of microspore, most of the spindles are anticlinal(perpendicular to the intine), the cytokinesis is generally asymmetric, and a completewall is formed. However, a few mitotic spindles of mitotic microspores are periclinal,and the cytokinesis are symmetric. Sometimes a partial wall is observed between twodaughter nuclei, which are produced by the abnormal pollen grains. We believe thatthese phenomena are related to differentiation of the dimorphic pollen.     

An original mutation in soybean (Glycine max (L.) Merrill) involving degeneration of the generative cell and causing male sterility.

A spontaneous mutation causing male sterility has been detected in line BR97-17739 from the soybean breeding program conducted by Embrapa-National Soybean Research Center. Meiotic division and male gametophyte development were analyzed in 10 male-sterile, female-fertile plants. Meiotic process had few irregularities related to chromosome segregation and affected about 2% of tetrads. Despite the high frequency of normal microspores, pollen sterility was total. After callose dissolution, microspores were released into the anther loculle and interphase nucleus was displaced from the center to one side of the cell. Displacement continued throughout normal microspore mitosis (PMI). After telophase, the hemispherical phragmoplast marked the place of cytokinesis. A typical generative cell, adjacent to the plasma membrane, and the vegetative one, containing most of the cytoplasm, were formed. In spite of the well-formed generative cell, pollen mitosis (PMII) failed to occur. The generative cell degenerated and was completely destroyed. The 3:1 segregation for male sterility in this line and its progenies indicate that a single recessive gene controls mutation.     

白菜核雄性不育两用系可育和不育花药ATPase的分布

对白菜核雄性不育两用系可育花药和不育花药的ATPase做了定位分析。可育花药的花粉母细胞核中积累了大量的ATPase反应颗粒,而细胞质中ATPase反应颗粒较少,但在线粒体中特异地聚集了一些大的ATPase反应颗粒。减数分裂后,小孢子细胞质中ATPase反应颗粒明显增加。随着小孢子发育,其细胞质中ATPase反应颗粒逐渐减少,但在线粒体中又特异性地聚集了较多的AT-Pase反应颗粒。当花药发育到二胞花粉时期,花粉和绒毡层细胞中的ATPase反应颗粒已很少了。不育花药的花粉母细胞中呈现较多的ATPase,然而在线粒体中很少。异常四分体小孢子细胞质中虽然有较多的ATPase反应颗粒,但还是通过细胞质收缩和质壁分离方式退化。对可育花药的花粉母细胞线粒体中特异出现的簇状ATPase分布现象进行了分析,讨论了不育花药中花粉母细胞线粒体ATPase的异常与花粉败育的可能关系。     

含笑花药发育的超微结构研究

对含笑花药发育中的超微结构变化进行观察,结果显示:(1)花粉发育中有三次液泡变化过程——第一次是小孢子母细胞在形成时内部出现了液泡,这可能与胼胝质壁的形成有关;第二次是在小孢子母细胞减数分裂之前,细胞内壁纤维素降解区域形成液泡,它的功能可能是消化原有的纤维素细胞壁;第三次是在小孢子液泡化时期,形成的大液泡将细胞核挤到边缘,产生极性。(2)含笑花粉在小孢子早期形成花粉外壁外层,花粉外壁内层在小孢子晚期形成,而花粉内壁是在二胞花粉早期形成;花粉成熟时,表面上沉积了绒毡层细胞的降解物而形成了花粉覆盖物。研究认为,含笑花粉原外壁的形成可能与母细胞胼胝质壁有关,而由绒毡层细胞提供的孢粉素物质按一定结构建成了花粉覆盖物。     

芝麻核雄性不育系ms86-1微粉发生的细胞学观察

芝麻(Sesamum indicum)核雄性不育系ms86-1姊妹交后代表现为可育、部分不育(即微粉)及完全不育(简称不育)3种类型。不同育性类型的花药及花粉粒形态差异明显。Alexander染色实验显示微粉植株花粉粒外壁为蓝绿色, 内部为不均一洋红色, 与可育株及不育株花粉粒的染色特征均不相同。为探明芝麻微粉发生机理, 在电子显微镜下比较观察了可育、微粉、不育类型的小孢子发育过程。结果表明, 可育株小孢子母细胞减数分裂时期代谢旺盛, 胞质中出现大量脂质小球; 四分体时期绒毡层细胞开始降解, 单核小孢子时期开始出现乌氏体, 成熟花粉时期花粉囊腔内及花粉粒周围分布着大量乌氏体, 花粉粒外壁有11–13个棱状凸起, 表面存在大量基粒棒, 形成紧密的覆盖层。不育株小孢子发育异常显现于减数分裂时期, 此时胞质中无脂质小球出现, 细胞壁开始积累胼胝质; 四分体时期绒毡层细胞未见降解; 单核小孢子时期无乌氏体出现; 成熟花粉时期花粉囊腔中未发现正常的乌氏体, 存在大量空瘪的败育小孢子, 外壁积累胼胝质, 缺乏基粒棒。微粉株小孢子在减数分裂时期可见胞质内有大量脂质小球, 四分体时期部分绒毡层发生变形, 单核小孢子时期有部分绒毡层开始降解; 绒毡层细胞降解滞后为少量发育进程迟缓的小孢子提供了营养物质, 部分小孢子发育为正常花粉粒; 这些花粉粒比较饱满, 表面有少量颗粒状突起, 但未能形成覆盖层, 花粉囊腔中及小孢子周围存在少量的乌氏体。小孢子形成的育性类型与绒毡层降解是否正常有关。     

Actin microfilament organization during pollen development ofBrassica napus cv. Topas

Summary The organization of actin microfilaments (MFs) was studied during pollen development ofBrassica napus cv. Topas. Cells were prepared using three techniques and double labelled for fluorescence microscopy with rhodamine-labelled phalloidin for MFs and Hoechst 33258 for DNA. Microfilaments are present at all stages of pollen development with the exception of tricellular pollen just prior to anthesis. Unicellular microspores contain MFs which radiate from the surface of the nuclear envelope into the cytoplasm. During mitosis MFs form a network partially surrounding the mitotic apparatus and extend into the cytoplasm. Both cytoplasmic and phragmoplast-associated MFs are present during cytokinesis. Nuclear associated-, cytoplasmic, and randomly oriented cortical MFs appear in the vegetative cell of the bicellular microspore. Cortical MFs in the vegetative cell organize into parallel MF bundles (MFBs) aligned transverse to the furrows. The MFBs disappear prior to microspore elongation. At anthesis MFs are restricted to the cortical areas subjacent to the furrows of the vegetative cell. The use of cytochalasin D to disrupt MF function resulted in: (1) displacement of the acentric nucleus in the unicellular microspore; (2) displacement of the spindle apparatus in the mitotic cell; (3) symmetrical growth of the bicellular microspore rather than elongation and (4) inhibition of pollen tube germination in the mature pollen grain. This suggests that MFs play an important role in anchoring the nucleus in the unicellular microspore as well as the spindle apparatus during microspore mitosis, in microspore shape determination and in pollen tube germination.Abbreviations MF microfilament - MFB microfilament bundle - rhph rhodamine phalloidin Dedicated to the memory of Professor John G. Torrey     

Cytological studies on degenerative nuclei at pollen development ofCarex ciliato-marginata

Chromosomes in degenerative and functional nuclei ofCarex ciliato-marginata Nakai were investigated during meiotic and primary pollen nuclear division. The nuclear DNA content of these nuclei was also measured using Feulgen microspectrophotometry. At metaphase of the primary pollen nuclear division, the chromosomes of degenerative nuclei were the same length as those of the functional nucleus, but only half their width. The functional nucleus divided into two, each of which moved to a pole, but the degenerative nuclei did not divide. The nuclear DNA content of the degenerative nucleus was half that of the functional nucleus and equal to that of one of the tetrads of a meiotic division. It is concluded that DNA replication was carried out in only one nucleus of the tetrad and that the other three nuclei were composed of unreplicated chromosomes at metaphase of the primary pollen nuclear division.     

Pollen ultrastructure in anther cultures of Datura innoxia. III. Incomplete microspore division.

During the microspore division in Datura innoxia, the mitotic spindle is oriented in planes both perpendicular (PE) and oblique (OB) to the spore wall against which the nucleus is situated. However, irrespective of polarity, the usual type of hemispherical wall is laid down at cytokinesis and isolates the generative cell from the rest of the pollen grain (type A). In PE spores the vegetative nucleus initially occupies a central position in the pollen grain, whereas in OB spores the vegetative nucleus lies at the periphery of the grain close to the generative cell. In anther cultures initiated just before the microspore division is due to take place, no marked change can be observed in either orientation or symmetry of the mitotic spindle when the spores divide. In some, however, cytokinesis is disrupted and deposition of the hemispherical wall arrested. In the absence of a complete wall, differentiation of the generative cell cannot take place and binucleate pollen grains are formed having 2 vegetative-type nuclei (type B). The 2 nuclei in the B pollens are always situated against the pollen-grain wall, suggesting that the disruption phenomenon is related to the OB spores. The incomplete wall always makes contact with the intine on the intine-side of the spindle. Wall material may be represented merely as short stubs projecting out from the intine into the cytoplasm, in which event the 2 nuclei lie close to each other and are separated by only a narrow zone of cytoplasm. In other grains the wall is partially developed between the nuclei and terminates at varying distances from the tonoplast; in these, the nuclei are separated by a wider zone of cytoplasm. The significance of these binucleate grains in pollen embryogenesis is discussed.     

Postmeiotic cytokinesis and pollen aperture number determination in eudicots: effect of the cleavage wall number

Summary.  In eudicot postmeiotic tetrads, apertures are usually joined in pairs in highly conserved areas. These appear to be located at the last points of contact persisting at the end of cytokinesis between the cytoplasm of the future microspores. In order to investigate the relationship between cytokinesis and aperture formation, aperture distribution within postmeiotic tetrads and the progression of meiosis were studied in Nicotiana tabacum cv. Ambalema. This variety (inbred line) produces about 85% tricolporate pollen and 15% tetracolporate pollen grains. In addition, about 7% of tetrads are composed of four equal-sized microspores and a supernumerary pseudomicrospore of small size and an equal proportion of tetrads exhibit unpaired apertures (these apertures are not joined in pairs within tetrads). Observation of cytokinesis indicates that both unpaired apertures and pseudomicrospores could result from the persistence of late communications between microsporocytes. Observations of tetrads indicate that an increase in the number of elements that are separated during cytokinesis is correlated with an increase in microspore aperture number. All data converge to support the hypothesis that aperture site determination is partly controlled by the number of walls formed to separate the different elements of the tetrad. Received May 22, 2002; accepted October 29, 2002; published online April 2, 2003 RID="*" ID="*" Correspondence and reprints: Laboratoire de Ecologie, Systematique et Evolution, Batiment 362, Université Paris Sud, 91405 Orsay cedex, France.