Brassinosteroids seed-priming to enhance Sorghum bicolor salt tolerance

Crop productivity and ecosystem survival is constantly and increasingly threatened by the soil salinization phenomenon (Atta et al., 2023). Climate change is reducing traditional European cereal crops productivity year by year, Sorghum bicolor is a salt-tolerant crop mainly cultivated in arid and semi-arid regions of the world and could be an interesting alternative for European agriculture. Despite its natural resistance to osmotic stress, there are differences in salt-tolerance among genotypes (Peduzzi et al., 2024) so it is necessary to find a way to help the more sensitive genotypes to cooperate with salt stress without harming the environment. Brassinosteroids (BRs) are known to be involved in plant responses to many stresses, including salt stress. These steroidal hormones could be exogenously applied to enhance crops resistance using many techniques and one of the most promising is the seed-priming technique (Neha et al., 2022). Seed-priming provides a double advantage to the crop, both economic and ecological: the direct application on the seed allows the use of a reduced quantity of the compound and avoids its spreading into the environment. In this study, we tested the efficacy of seed priming with 24-epibrassinolide, a bioactive BR precursor, to reduce the negative effects of 150 mM of NaCl in two sorghum hybrids, a tolerant and a sensitive one, namely Bianca and Tonkawa.The seedlings were analysed at two different time points: 6 days and 10 days after sowing. We studied the germination rate of the seeds, the morphology of the root system, the adventitious roots anatomy, the gene expression for the main vacuolar sodium transporter (SbNHX2) both in root and shoot with RT-qPCR and the sodium inside the root cells was localized with confocal microscopy. The germination rate was significantly increased by the priming for the Tonkawa genotype in presence of salt. The morphological analyses revealed that the priming implemented the number of adventitious roots and lateral roots primordia in both genotypes. The organization of the root tissues of the sensitive genotype under salt stress was restored by the priming treatment. The relative expression of the main sodium transporter was enhanced in both genotypes by the priming treatment, in presence of salt stress. The localization of sodium in the root cells confirmed that there was a difference between the two genotypes in the ability of sequestrate Na+ in the vacuole and that the priming helped the sensitive one deal with this task.