Abscisic Acid and Ethylene Antagonistically Regulate Root Endodermal Suberization to Mitigate Nonuniform Salt Stress in Cotton

The heterogeneity of soil salinity is a critical attribute of saline agricultural environments, particularly for the physiological adaptability of cotton (Gossypium hirsutum L.) plants. However, the mechanisms by which cotton plants acclimate to heterogenous salinity remain poorly understood. To investigate the responses of cotton seedlings to nonuniform salinity, a split-root system using germination paper was employed to replicate spatially variable salinity conditions within the root zone. The root endodermal barriers, consisting of the suberin lamellae and Casparian strip, were found to be enhanced in the roots on the saline side of this system relative to the nonsaline side, playing a crucial role in maintaining ion balance for cotton seedlings under heterogeneous salt environment. Ethylene levels were higher in roots on the nonsaline side, but significantly lower in roots on the saline side. Notably, abscisic acid (ABA) levels increased in roots on both sides. The delicate balance between ABA and ethylene can modify the root endodermal suberization, thereby regulating the adaptability of cotton seedlings to diverse salt environments.