The membrane potential reflects the difference between cytoplasmic and apoplastic electrical potentials and is essential for cellular operation. The application of the phytohormone auxin (3-indoleacetic acid (IAA)) causes instantaneous membrane depolarization in various cell types^1,2,3,4,5,6, making depolarization a hallmark of IAA-induced rapid responses. In root hairs, depolarization requires functional IAA transport and TIR1–AFB signalling⁵, but its physiological importance is not understood. Specifically in roots, auxin triggers rapid growth inhibition^7,8,9 (RGI), a process required for gravitropic bending. RGI is initiated by the TIR1–AFB co-receptors, with the AFB1 paralogue playing a crucial role^10,11. The nature of the underlying rapid signalling is unknown, as well as the molecular machinery executing it. Even though the growth and depolarization responses to auxin show remarkable similarities, the importance of membrane depolarization for root growth inhibition and gravitropism is unclear. Here, by combining the DISBAC₂(3) voltage sensor with microfluidics and vertical-stage microscopy, we show that rapid auxin-induced membrane depolarization tightly correlates with RGI. Rapid depolarization and RGI require the AFB1 auxin co-receptor. Finally, AFB1 is essential for the rapid formation of the membrane depolarization gradient across the gravistimulated root. These results clarify the role of AFB1 as the central receptor for rapid auxin responses.

膜电位反映了细胞质和质外体电位之间的差异，对细胞操作至关重要。植物激素生长素 (3-吲哚乙酸 (IAA)) 的应用导致各种细胞类型^1,2,3,4,5,6的瞬时膜去极化，使去极化成为 IAA 诱导的快速反应的标志。在根毛中，去极化需要功能性 IAA 转运和 TIR1-AFB 信号⁵，但其生理重要性尚不清楚。特别是在根部，生长素会触发快速生长抑制^7,8,9 (RGI)，这是重力弯曲所需的过程。RGI 由 TIR1-AFB 共同受体启动，其中 AFB1 旁系同源物发挥关键作用^10,11. 潜在的快速信号的性质以及执行它的分子机制是未知的。尽管对生长素的生长和去极化反应显示出显着的相似性，但膜去极化对根系生长抑制和向地性的重要性尚不清楚。在这里，通过将 DISBAC ₂ (3) 电压传感器与微流体和垂直显微镜相结合，我们表明快速生长素诱导的膜去极化与 RGI 密切相关。快速去极化和 RGI 需要 AFB1 生长素共受体。最后，AFB1 对于在重力刺激根部快速形成膜去极化梯度至关重要。这些结果阐明了 AFB1 作为快速生长素反应的中心受体的作用。