Physiological, Biochemical and Transcriptomic Mechanisms Underlying the Mitigation of Salt Stress in Cabernet Sauvignon Grapevine Seedlings by Foliar Application of a Seaweed-Based Biostimulant (Jinmei Extract)

Salt stress is one of the major abiotic constraints limiting the growth of grapevine (Vitis vinifera L.). Although seaweed-based biostimulants have been widely reported to enhance plant stress tolerance, the physiological and molecular mechanisms underlying their foliar application-mediated alleviation of salt stress in grapevine remain poorly understood. In this study, 1-year-old grapevine (‘Cabernet Sauvignon’) seedlings were grown to the 15–20 leaf stage prior to treatment. The seedlings were then exposed to 200 mmol·L−1 NaCl with foliar spraying of three doses of seaweed-based biostimulant: low (SLF, 1:1200 dilution), medium (SMF, 1:800 dilution), and high (SHF, 1:500 dilution) concentrations of a seaweed-based biostimulant via foliar spraying. Physiological and biochemical parameters were determined, and transcriptomic analysis was performed to elucidate the regulatory mechanisms involved. The results showed that the low-concentration treatment exhibited the most pronounced mitigating effect, significantly reducing malondialdehyde and hydrogen peroxide contents by 35.47% and 27.53%, respectively, while markedly enhancing the activities of superoxide dismutase, catalase, and ascorbate peroxidase. In addition, SLF treatment effectively maintained Na+/K+ ionic homeostasis and preserved the normal functioning of the photosynthetic system under salt stress. Transcriptomic analysis revealed that 1482 differentially expressed genes (DEGs) were identified between the SLF and salt-stressed groups, including 593 upregulated and 869 downregulated genes. These DEGs were significantly enriched in pathways related to photosynthesis, hormone signal transduction, and antioxidant detoxification, indicating their active involvement in salt stress responses. Furthermore, weighted gene co-expression network analysis identified several candidate genes closely associated with these physiological processes, including VvAOC4, VvGBSS1, and VvARR9, suggesting a strong linkage between transcriptional regulation and physiological alleviation effects. Overall, this study provides novel insights into the coordinated physiological and molecular mechanisms by which foliar application of a seaweed-based biostimulant enhances salt stress tolerance in grapevine seedlings.