Evolution of Pollen Development in Orchids

;​R o o t E n t y F t fB C o m p o b j b W o r d d o c u m e n t * O b j e c t P O O l t fB fB​F Microsoft Word 6.0文档MSWordDoc。6;Oh +' 0 D h @ D R:\WWUSER\TEMPLATE\NORMAL。点 细胞P: \ \文摘\ 9418015。ASC Una Solomon Una = e / * / j j j j j j M C / T F M j兰科植物褐花粉和柠檬花粉的发育是研究植物自身发生方面的一个有前景的新系统。在没有前期微管带（PBB）的情况下，减数分裂和花粉有丝分裂都发生精确的核分裂和细胞质分裂。此外，小孢子细胞的不同之处在于，核分裂和细胞分裂可能暂时不耦合，导致短暂的共胞期，然后同时四分体分裂成小孢子的四分体。在同步胞质分裂中，膜质体在非姐妹核和姐妹核之间发育，这为膜质体发育和分裂平面的确定提供了额外的信息。在最近的比较研究的基础上，我们提出了一个假设，即在缺乏PPBs的细胞中，直接控制分裂平面的是核基径向微管系统（RMS）的功能，RMS定义了细胞质的结构域。核细胞质结构域模型假设纺锤体排列，因此细胞核的位置，源于分裂极性的建立，而分裂极性又可能受到不同程度的控制。我们建议对花粉发育过程中细胞骨架元件（微管和肌动蛋白）、细胞器和内膜之间的组织和功能相互作用进行比较、发育和实验研究。由于小孢子发生中的细胞动力学装置比组织发生的变化更大，我们将使用比较研究来确定花粉发育事件的共性。兰花的小孢子细胞和花粉都可以用现代免疫细胞化学方法和电子显微镜观察。研究人员最近在蛾兰花粉中发现了生殖极微管系统（GPMS），该系统为药物扰动研究提供了一个有针对性的结构标记，旨在了解花粉中不等一分裂微管的极性建立和组织，这对雄性配子体的发育至关重要。这是由从事细胞骨架参与建立细胞分裂平面和可能引导分裂的细胞质结构域形成的备受尊敬的资深研究人员提出的建议。他们选择的系统，兰花的花粉形成，之所以被选择，是因为潜在的机制经常被主题变化所揭示。兰花家族在减数分裂和有丝分裂的细胞分裂模式以及在花粉形成过程中经历错误减数分裂的复杂杂交种的可用性方面提供了许多多样性。花粉分裂特别有趣，因为决定未来细胞分裂位置的结构，微管的前期带，缺失了。本研究的目标是：1)研究减数分裂和花粉有丝分裂中分裂极性的建立；2)研究与细胞核相关的径向微管系统与分裂过程中参与子细胞壁形成的微管组织的关系；3)确定在减数分裂和花粉有丝分裂过程中，由共扩展微管定义的细胞质结构域是否控制分裂平面。4)将花粉发育数据与兰科多种花粉类型的进化联系起来。关于目标(2)和(3)，这项工作有可能揭示核相关微管在植物微管生长和启动中的重要性。细胞生物学鉴定其为微管组织中心（MTOC）。植物的微管已经被证明对植物细胞的形状和大小有巨大的影响。与质膜相关的皮质阵列有助于确定细胞延伸轴，而与细胞分裂面相关的阵列有助于确定植物组织的形态发生。这些现象是生产有效的、选择性除草剂的基础，这些除草剂利用了植物、动物和真菌细胞骨架组装之间的差异。这里提出的工作将为植物控制细胞骨架组装的独特机制提供额外的见解。此外，通过分析细胞骨架参与植物花粉形成的本质所获得的见解，将从根本上有助于我们对植物生殖的了解。*** ;

; R o o t E n t r y F t fB C o m p O b j b W o r d D o c u m e n t * O b j e c t P o o l t fB t fB F Microsoft Word 6.0 Document MSWordDoc Word.Document.6 ; Oh +' 0 D h @ d R:\WWUSER\TEMPLATE\NORMAL.DOT P:\CELL\ABSTRACT\9418015.ASC Una Solomon Una e = e / * / j j j j j j j M C / T F M j M j j j j ~ j j j j 7 9418015 Brown and Lemmon Pollen development in orchids is a promising new system for studying ontogenetic aspects of plant evolution. Precise nulcear and cytoplasmic divisions occur in both meiosis and pollen mitosis in the absence of a preprophase band of microtubules (PBB). In addition, microsporocytes differ in that karyokinesis and cytokinesis may be temporally uncoupled resulting in a brief coenocytic stage before simultaneous quadripartioning into a tetrad of microspores. In simulatneous cytokinesis, phragmoplasts develop between non-sister as well as siter nuclei providing additonal information on phragmoplast development and the determination of division plane. On the basis of recent comparative studies we have put forth the hypothesis that the direct control of division plane in cells lacking PPBs is a function of nuclear-based radial microtubule systems (RMS) that define domains of cytoplasm. The nuclear cytoplasmic domain model assumes that spindle alignment, and therefore placement of nuclei, stems from establishment of division polarity which, in turn may be subject to various levels of contol. We propose comparative, developmental and experimental studies of the organization and functional interactions among cytoskeletal elements (microtubules and F actin), organelles, and endomembranes in pollen development. Since the cytokinetic apparatus in microsporogenesis is much more variable than histogenesis, we will use comparative studies to identify commonalities that underlie events of pollen development. Both the microsprorocytes and pollen of orchids are amenable to modern methods of immunocytochemstry and electron microscopy. The generative pole microtubule system (GPMS), which we recently discovered in the exineless pollen of moth orchids, provides a targetable structural marker for drug perturbation sutdies aimed at understanding the establishment of polarity and organization of microtubles of the unequal first division in pollen that is critical to development of the male gametophyte. %%% This is a proposal by highly regarded senior investigators working on cytoskeletal involvement in establishing planes of cell division and on the formation of cytoplasmic domains which may orient division. The system they have selected, pollen formation in orchids, is chosen because underlying mechanisms are often revealed by thematic variation. The orchid family offers much variety in mode of meiotic and mitotic cytokinesis and in the availability of complex hybrids which undergo faulty meiosis during pollen formation. Pollen division is particularly interesting because the structure which determines the future site of cell division, the pre prophase band of microtubules, is missing. The goa ls of the proposal are to 1) investigate the establishment of division polarity in meiosis and pollen mitosis, 2) investigate the relationship of the radial microtubule system associated with the cell nucleus to the organization of the microtubules involved in laying down the daughter cell wall during division , 3) establish if cytoplasmic domains defined by co-extensive microtubules control the division plane during meiosis and pollen mitosis, and 4) relate the data on pollen development to the evolution of the diverse pollen types found in the Orchidaceae. With regard to objectives (2) and (3), this work has the potential to reveal the importance of nuclearassociated microtubules in microtubule growth and initiation in plants in general. Its identification as a microtubule organizing center (MTOC)cell biology. The microtubules of plants have been shown to have a dramatic influence on plant cell shape and size. The cortical array associated with the plasma membrane helps determines the axis of cell extension, while the array associated with the cell division plane helps determine the morphogenesis of plant tissues. These phenomena are the bases for the production of potent, selective herbicides which take advantage of the differences between plant, animal, and fungal cytoskeletal assembly. Work proposed here will offer additional insight into those mechanisms unique to plants which control cytoskeletal assembly. In addition, insights gained by this analysis of cytoskeletal involvement inthe nature of pollen formation in plants will contribute fundamentally to our knowledge about plant reproduction. *** ;