Brassinosteroids and Abscisic Acid Interplay in Sodium Salt Responses of Glycophyte Glycine max (L.) Merr. and Halophyte Strombocarpa strombulifera (Lam.) A. Gray

Abstract

Brassinosteroids (BR) and abscisic acid (ABA) play key roles in coordinating plant responses to abiotic stress. This study aimed to comparatively analyze the hormonal and growth responses of the glycophyte Glycine max and the halophyte Strombocarpa strombulifera under different sodium salts to better understand the BR and ABA interplay. Plants were grown hydroponically and subjected to salt treatments (NaCl, Na2SO4 and their iso-osmotic mixture) at varying osmotic potentials. Growth parameters, water content, transpiration, and hormone accumulation (ABA, castasterone and 24-epibrassinolide) were quantified. The effects of exogenous ABA application were also evaluated. In both species, Na₂SO₄ treatments caused the most severe growth inhibition, reduced water content, and elevated ABA and BR levels. In contrast, NaCl induced moderate stress responses, while the iso-osmotic mixture of salts resulted in intermediate growth and hormonal profiles, suggesting partial mitigation of sulfate toxicity. S. strombulifera specifically accumulated castasterone, indicating species-specific BR biosynthesis. Exogenous ABA enhanced BR accumulation, particularly under Na₂SO₄ stress, but was insufficient to restore water balance, pointing to impaired stomatal regulation under sulfate toxicity. The presence of Na2SO4 disrupts hormonal homeostasis more severely than NaCl, likely through interference with sulfur metabolism and BR and ABA interplay. Their iso-osmotic mixture buffered the effects and promoted more balanced physiological responses. The species-specific hormonal patterns observed provide insights into adaptive strategies to saline environments and suggest potential targets for enhancing the tolerance. Future research should focus on identifying sulfate-sensitive components of BR and ABA interplay to inform the development of salt tolerance plants.