Pollen tubes elongate within the pistil to transport sperms to the female gametophytes for fertilization. Pollen tubes grow at their tips through a rapid and polarized cell growth process. This tip growth process is supported by an elaborate and dynamic actin cytoskeleton and a highly active membrane trafficking system that together provide the driving force and secretory activities needed for growth. A polarized cytoplasm with an abundance of vesicles and tip-focused Ca(2+) and H(+) concentration gradients are important for the polar cell growth process. Apical membrane-located Rho GTPases regulate Ca(2+) concentration and actin dynamics in the cytoplasm and are crucial for maintaining pollen tube polarity. Pollen tube growth is marked by periods of rapid and slow growth phases. Activities that regulate and support this tip growth process also show oscillatory fluctuations. How these activities correlate with the rapid, polar, and oscillatory pollen tube growth process is discussed.

中文翻译：

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花粉管中极性细胞生长机制的结构和信号网络

花粉管在雌蕊内伸长，将精子运送到雌配子体进行受精。花粉管通过快速极化的细胞生长过程在其尖端生长。这种尖端生长过程由精心制作的动态肌动蛋白细胞骨架和高度活跃的膜运输系统支持，它们共同提供生长所需的驱动力和分泌活动。具有丰富囊泡和尖端聚焦 Ca(2+) 和 H(+) 浓度梯度的极化细胞质对于极地细胞生长过程很重要。位于顶端膜的 Rho GTPases 调节细胞质中的 Ca(2+) 浓度和肌动蛋白动力学，对于维持花粉管极性至关重要。花粉管生长的特点是快速和缓慢的生长阶段。调节和支持这种尖端生长过程的活动也显示出振荡波动。讨论了这些活动如何与快速、极性和振荡的花粉管生长过程相关联。