The Role of the Calcium Gradient in Pollen Tube Growth

小行星9304953 花粉管伸长是将雄配子运送到卵器中的过程，是植物有性生殖的关键。 在这个高度极化的细胞内，整个细胞产生小泡，并通过细胞质流运输到顶端区域。 通过一个尚不清楚的过程，这些囊泡在尖端特异性融合，提供支持单向伸长的新壁材料。 最近的工作表明，生长中的落叶松花粉管中的游离钙有一个明显的梯度，集中在管的最顶端。 进一步观察，这种钙梯度的消散导致停止的增长，并重新启动的增长是伴随着其改造提供的证据表明，梯度是必不可少的尖端生长。 本研究的目的是详细分析钙梯度和尖端延伸之间的关系。 使用指示剂染料，已被显微注射到花粉管中的钙梯度的空间分布将在活细胞中进行检查，并与管伸长的速率直接相关。 然后用各种试剂（包括钙缓冲剂、通道激动剂、拮抗剂、渗透调节剂和生长抑制剂）对细胞进行实验性处理，以仔细探索钙梯度的位置和大小与调节的生长行为以及与细胞质流动的基础细胞结构和模式之间的关系。 钙调素的位置和活性也将在活细胞中使用共聚焦激光扫描显微镜和荧光各向异性进行研究。 最后，钙梯度和肌动蛋白细胞骨架之间的关系将在活的花粉管中使用共聚焦显微镜分析已显微注射荧光肌动蛋白单体的细胞进行检查。 通过将钙梯度与这几个因素相关联，将导致对花粉管伸长机制的新的和更好的理解。 在高等植物中，雄性生殖细胞（配子）由花粉粒携带。 为了使受精作用发生，花粉必须通过产生一个管将雄配子运送到花内的卵器中，雄配子沿着管向卵移动。 花粉管是所有植物细胞中生长最快的。 随着它的生长，它变得比它宽几千倍。 由于其在植物繁殖中的重要性和显著的生长特性，其调控机制一直是植物研究的重要课题。 本项目的目的是了解钙离子在花粉管生长中的作用。 先进的生物物理和结构技术将被用来研究内部钙沿着生长的花粉管的梯度。 结果应确定钙梯度是否在参与花粉管生长的亚细胞结构的组织和运动中起作用。 ***

9304953 Hepler Pollen tube elongation delivers the male gametes to the egg apparatus and is thus essential for sexual reproduction in plants. Within this highly polarized cell, vesicles are produced throughout and transported by cytoplasmic streaming to the apical region. By a process that is not well understood, these vesicles fuse specifically at the tip, providing new wall material that supports unidirectional elongation. Recent work has shown that a growing pollen tube of Llium has a sharply defined gradient in free calcium focused at the extreme apex of the tube. The further observation that dissipation of this calcium gradient leads to cessation of growth, and that reinitiation of growth is accompanied by its reformation provide evidence that the gradient is essential for tip growth. The purpose of this research is to analyze the relationship between the calcium gradient and tip extension in detail. Using indicator dyes that have been microinjected into pollen tubes the spatial profile of the calcium gradient will be examined in living cells and directly correlated with the rate of tube elongation. Cells will then be experimentally treated with a variety of agents including calcium buffers, channel agonists, antagonists, osmotic modulators, and growth inhibitors to allow a careful exploration of the relationship between the position and magnitude of the calcium gradient with the modulated growth behavior, and with the underlying cell structure and patterns of cytoplasmic streaming. The position and activity of calmodulin will also be studied in living cells using confocal laser scanning microscopy and fluorescence anisotropy. Finally, the relationship between the calcium gradient and the actin cytoskeleton will be examined in living pollen tubes using confocal microscopic analysis of cells that have been microinjected with fluorescent actin monomer. By correlating the calcium gradient with these several factors, a new and greater understanding of the mechanism of pollen tube elongation should result. %%% In higher plants, the male reproductive cells (gametes) are carried in pollen grains. For fertilization to take place, the pollen must deliver the male gametes to the egg apparatus within a flower by producing a tube, along which the male gametes move toward the egg. The pollen tube is the fastest growing of all plant cells. As it grows, it becomes several thousand times longer than it is wide. Because of its importance to plant reproduction and its dramatic growth characteristics, the mechanisms regulating pollen tube are important topics of research. The goal of this project is to understand the role of calcium ions in pollen tube growth. Sophisticated biophysical and structural techniques will be used to study the gradient of internal calcium along a growing pollen tube. The results should determine whether the calcium gradient plays a role in the organization and movement of the sub-cellular structures involved in pollen tube growth. ***