Encapsulated ABA treatment fine-tunes hormone signalling and improves salt-stress tolerance in Arabidopsis thaliana

Soil salinity is one of the most widespread environmental stresses affecting plant growth and agricultural productivity. Abscisic acid (ABA) is a key regulator of plant adaptation to salinity; however, the direct application of this phytohormone is constrained by its instability, rapid degradation under field conditions, and the growth-inhibitory effects associated with excessive hormone accumulation. Encapsulation technologies offer an alternative strategy to improve hormone stability and enable controlled delivery in plant systems. In this study, ABA was encapsulated in silica- and chitosan-based matrices and processed by spray drying, a cost-effective and industrially scalable encapsulation technology. The feed suspensions of both encapsulation systems exhibited pseudoplastic behaviour, which facilitated spray-drying processing, and yielded microparticles with homogeneous size distributions. Encapsulation significantly enhanced the thermal stability of ABA and enabled a controlled release profile governed mainly by matrix relaxation mechanisms. The biological performance of the encapsulated formulations was assessed in Arabidopsis thaliana using wild-type plants (Col-0), the ABA-deficient mutant aba2-11, and the ABA-insensitive mutant abi1-2. Encapsulated ABA reduced the pleiotropic effects associated with free ABA application and promoted improved plant growth under salt stress conditions. Fluorescence imaging of the ABA-responsive reporter line 6xABRE_A::erGFP confirmed that encapsulated formulations limited excessive ABA accumulation by enabling gradual hormone uptake. Under salinity stress, plants treated with encapsulated ABA showed reduced oxidative damage and improved hormonal balance compared with plants treated with free ABA. These findings demonstrate that encapsulation improves the stability and biological efficacy of ABA and represents a promising strategy for enhancing plant tolerance to salinity stress.