Engineering Drought-Responsive ABA Signaling: Linking Physiological Stress Cues to Metal-Organic Framework-Mediated...

Drought induces coordinated physiological, biochemical, and molecular responses that extend beyond changes in phytohormone concentrations. Rapid alterations in reactive oxygen species (ROS), apoplastic pH, Ca²⁺ and ionic dynamics, tissue hydration, and cellular redox status provide spatial and temporal information on developing water deficit and regulate stomatal behavior, photosynthesis, water relations, and stress-responsive gene expression. This review explores whether endogenous drought-associated signals can serve as biological triggers for stimulus-responsive metal-organic frameworks (MOFs) designed to regulate abscisic acid (ABA) delivery. We integrate drought-induced changes in redox state, apoplastic pH, ionic composition, and hydration with MOF transformation, host-guest interactions, ABA release, uptake, transport, metabolism, and engagement of the PYR/PYL/RCAR-PP2C-SnRK2 signaling pathway. We propose a framework in which responsive MOFs generate a temporally controlled ABA pulse that follows drought progression, activates protective signaling during water limitation, and attenuates after rewatering to facilitate recovery. Particular emphasis is placed on ROS-Ca²⁺ crosstalk, SnRK2/OST1-dependent guard-cell regulation, hydraulic adjustment, photosynthetic protection, and recovery dynamics. Current studies demonstrate MOF-mediated phytohormone protection, controlled release, and drought-related physiological improvement. Current advances have established the feasibility of MOF-based ABA protection and controlled delivery; however, the integration of drought-responsive carrier activation with receptor-accessible ABA delivery and PYR/PYL/RCAR-PP2C-SnRK2 pathway validation remains an emerging research frontier. We therefore outline a claim-matched validation framework integrating spatial drought-signal analysis, isotope-resolved ABA tracing, carrier localization, phosphorylation-based pathway assays, drought-rewatering experiments, and physiological assessment. This integration of plant stress physiology with responsive nanomaterials provides a conceptual basis for developing more precise ABA delivery strategies for crop resilience under increasingly variable water availability.