Effectiveness of exogenous silicon and proline on mediating grapevine ‘castellana negra’ responses to salt stress

Salinity is a significant challenge for grapevines growing in arid and semiarid regions. In this study, 'Castellana Negra' plants were subjected to NaCl stress (90 mM) for 75 days and treated with silicon (Si) and proline to evaluate their potential in mitigating the effects of salinity. Si was administered through irrigation, while proline was applied as a foliar spray. Analysis of the results (P < 0.05) indicated that salt stress reduced leaf fresh weight (75%), but Si and proline limited this reduction (57% and 54%, respectively, compared to control). Also, Si improved total chlorophyll (chl t, 46%) and carotenoids (car, 49%), while proline increased chl t (72%) and car (52%), compared to their levels in only NaCl-stressed plants. Additionally, salt stress increased abscisic acid (ABA) in 39%, but Si maintained its levels, and proline reduced it (42%) in comparison to control. Similar trends were observed for salicylic acid and jasmonic acid, where Si and proline helped normalize their levels. Moreover, salt exposure raised Na⁺ concentrations; however, Si and proline reduced this accumulation. Overall, data show that Si and proline can regulate hormonal, nutritional and physiological processes, and may be considered promising tools for enhancing grapevine resilience to salinity.