Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
School of Physics and Technology, Wuhan University, Wuhan 430072, China.
Int J Mol Sci. 2020 Aug 27;21(17):6184. doi: 10.3390/ijms21176184.
Root hair elongation relies on polarized cell expansion at the growing tip. As a major osmotically active ion, potassium is expected to be continuously assimilated to maintain cell turgor during hair tip growth. However, due to the lack of practicable detection methods, the dynamics and physiological role of K in hair growth are still unclear. In this report, we apply the small-molecule fluorescent K sensor NK3 in root hairs for the first time. By employing NK3, oscillating cytoplasmic K dynamics can be resolved at the tip of growing root hairs, similar to the growth oscillation pattern. Cross-correlation analysis indicates that K oscillation leads the growth oscillations by approximately 1.5 s. Artificially increasing cytoplasmic K level showed no significant influence on hair growth rate, but led to the formation of swelling structures at the tip, an increase of cytosolic Ca level and microfilament depolymerization, implying the involvement of antagonistic regulatory factors (e.g., Ca signaling) in the causality between cytoplasmic K and hair growth. These results suggest that, in each round of oscillating root hair elongation, the oscillatory cell expansion accelerates on the heels of cytosolic K increment, and decelerates with the activation of antagonistic regulators, thus forming a negative feedback loop which ensures the normal growth of root hairs.
根毛的伸长依赖于生长尖端的极化细胞扩展。钾作为一种主要的渗透活性离子，预计在毛尖端生长过程中会不断被吸收以维持细胞膨压。然而，由于缺乏可行的检测方法，钾在毛生长中的动态和生理作用仍不清楚。在本报告中，我们首次将小分子荧光钾传感器 NK3 应用于根毛中。通过使用 NK3，可以解析生长中的根毛尖端的细胞质钾动态，类似于生长的振荡模式。互相关分析表明，钾的振荡先于生长振荡约 1.5 秒。人为增加细胞质钾水平对毛生长速率没有显著影响，但导致尖端形成肿胀结构，细胞质钙离子水平增加和微丝解聚，表明细胞质钾和毛生长之间存在拮抗调节因子（如钙信号）的参与。这些结果表明，在每一轮振荡根毛伸长中，细胞扩展的振荡在细胞质钾增加的推动下加速，而在拮抗调节剂的激活下减速，从而形成一个负反馈环，确保根毛的正常生长。
