Abscisic acid (ABA) regulates plant stress adaptation, growth and reproduction. Despite extensive ABA–Ca²⁺ signalling links, imaging ABA-induced increases in Ca²⁺ concentration has been challenging, except in guard cells. Here we visualize ABA-triggered [Ca²⁺] dynamics in diverse organs and cell types of Arabidopsis thaliana using a genetically encoded Ca²⁺ ratiometric sensor with a low-nanomolar Ca²⁺-binding affinity and a large dynamic range. The subcellular-targeted Ca²⁺ ratiometric sensor reveals time-resolved and unique spatiotemporal Ca²⁺ signatures from the initial plasma-membrane nanodomain, to cytosol, to nuclear oscillation. Via receptors and sucrose-non-fermenting1-related protein kinases (SnRK2.2/2.3/2.6), ABA activates low-nanomolar Ca²⁺ transient and Ca²⁺-sensor protein kinase (CPK10/30/32) signalling in the root cap cycle from stem cells to cell detachment. Surprisingly, unlike the prevailing NaCl-stimulated micromolar Ca²⁺ spike, salt stress induces a low-nanomolar Ca²⁺ transient through ABA signalling, repressing key transcription factors that dictate cell fate and enzymes that are crucial to root cap maturation and slough. Our findings uncover ABA–Ca²⁺–CPK signalling that modulates root cap cycle plasticity in adaptation to adverse environments.

脱落酸 （ABA） 调节植物的逆境适应、生长和繁殖。尽管存在广泛的 ABA-Ca²⁺ 信号转导链接，但 ABA 诱导的 Ca²⁺ 浓度增加的成像一直具有挑战性，保卫细胞除外。在这里，我们使用具有低纳摩尔 Ca²⁺ 结合亲和力和大动态范围的基因编码的 Ca²⁺ 比率传感器，可视化拟南芥不同器官和细胞类型中 ABA 触发的 [Ca²⁺] 动力学。亚细胞靶向 Ca²⁺ 比率传感器揭示了从初始质膜纳米结构域到胞质溶胶再到核振荡的时间分辨和独特的时空 Ca²⁺ 特征。通过受体和蔗糖非发酵 1 相关蛋白激酶 （SnRK2.2/2.3/2.6），ABA 激活低纳摩尔 Ca²⁺ 瞬时和 Ca²⁺ 传感器蛋白激酶 （CPK10/30/32） 在从干细胞到细胞分离的根帽循环中发出信号。令人惊讶的是，与普遍的 NaCl 刺激的微摩尔 Ca²⁺ 尖峰不同，盐应激通过 ABA 信号传导诱导低纳摩尔 Ca²⁺ 瞬变，抑制了决定细胞命运的关键转录因子和对根帽成熟和脱落至关重要的酶。我们的研究结果揭示了 ABA-Ca²⁺-CPK 信号传导，可调节根帽循环可塑性以适应恶劣环境。