Brassinosteroid seed priming enhances tolerance in a salt-sensitive sorghum through membrane, cell wall and Na⁺ regulation

Sorghum is generally considered a moderately salt-tolerant crop, although substantial variations in salt tolerance exist among grain sorghum genotypes. Moreover, the mechanisms underlying salt tolerance in this species remain poorly understood compared with those of other crops. Brassinosteroids (BRs) regulate numerous developmental processes and stress responses and their exogenous application, also via seed priming, has been shown to mitigate the negative effects of salinity in several plant species, including sorghum. However, the role of BR seed priming in root development and the biochemical, cellular, and molecular responses to salt stress remains unclear. Seeds of the salt-tolerant sorghum genotype Bianca and the salt-sensitive genotype Tonkawa were primed with 1μM of 24-epibrassinolide and then cultured in vitro in the presence or absence of 150 mM NaCl. Root system morphology, lipid peroxidation levels, Raman spectral profiles associated with membrane and cell wall components, cytosolic K+ levels and vacuolar Na+ compartmentalization were evaluated. BR seed priming enhanced root system architecture under salt stress, promoting adventitious and lateral root formation, and reducing lipid peroxidation, particularly in the salt-sensitive Tonkawa. In this genotype, BR seed priming had a long-lasting effect, inducing Na+ sequestration in root cell vacuoles, modulating membrane and cell wall components, and improving root system branching, thereby ensuring adequate water uptake as a protective mechanism against high soil salinity. Overall, the results demonstrate the efficacy of BR seed priming in enhancing salt tolerance in sorghum, highlighting its potential as a sustainable strategy for improving crop performance under saline conditions.