Pollen tubes rapidly elongate, penetrate, and navigate through multiple female tissues to reach ovules for sperm delivery by utilizing a specialized form of polar growth known as tip growth. This process requires a battery of cellular activities differentially occurring at the apical growing region of the plasma membrane (PM), such as the differential cellular signaling involving calcium (Ca2+), phospholipids, and ROP-type Rho GTPases, fluctuation of ions and pH, exocytosis and endocytosis, and cell wall construction and remodeling. There is an emerging understanding of how at least some of these activities are coordinated and/or interconnected. The apical active ROP modulates exocytosis to the cell apex for PM and cell wall expansion differentially occurring at the tip. The differentiation of the cell wall involves at least the preferential distribution of deformable pectin polymers to the apex and non-deformable pectin polymers to the shank of pollen tubes, facilitating the apical cell expansion driven by high internal turgor pressure. Recent studies have generated inroads into how the ROP GTPase-based intracellular signaling is coordinated spatiotemporally with the external wall mechanics to maintain the tubular cell shape and how the apical cell wall mechanics are regulated to allow rapid tip growth while maintaining the cell wall integrity under the turgor pressure. Evidence suggests that exocytosis and endocytosis play crucial but distinct roles in this spatiotemporal coordination. In this review, we summarize recent advances in the regulation and coordination of the differential pectin distribution and the apical domain of active ROP by exocytosis and endocytosis in pollen tubes.

中文翻译：

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胞吐作用和内吞作用：协调和微调花粉管中的极尖生长域。

花粉管通过利用一种称为尖端生长的特殊极性生长形式，迅速伸长，穿透并穿过多个雌性组织，到达精子递送的胚珠。此过程需要一系列在质膜（PM）顶端生长区发生的细胞活动，例如涉及钙（Ca2 +），磷脂和ROP型Rho GTPases，离子和pH波动，胞吐作用和内吞作用，以及细胞壁的构建和重塑。人们对这些活动中的至少一些活动如何进行协调和/或相互联系有了新的认识。顶端活性ROP调节胞外向PM的胞外分泌，并在尖端不同地发生细胞壁扩张。细胞壁的分化至少涉及可变形果胶聚合物至花粉管的优先分布和不可变形果胶聚合物至花粉管柄的优先分布，从而促进了由高内部膨胀压力驱动的根尖细胞膨胀。最近的研究已经深入研究了如何基于ROP GTPase的细胞内信号传递与外壁机制在时空上协调以维持肾小管细胞的形状，以及如何调节根尖细胞壁机制以允许快速的尖端生长，同时保持细胞壁完整性。膨胀压力。有证据表明，胞吐作用和内吞作用在这种时空协调中起着至关重要的作用。在这篇评论中