Understanding the Role of Silicon in Alleviating Salinity Stress in Grapevine: Insights into Physiological and Molecular Mechanisms

Silicon (Si) has effectively mitigated plant salinity stress and enhanced salt tolerance in grapevine (Vitis vinifera). However, the underlying mechanisms by which Si confers salinity tolerance and its effects on different grape genotypes under salt stress are still not fully understood. This study aims to expose these mechanisms through a hydroponic experiment evaluating the impact of Si on various growth parameters, including dry matter accumulation, photosynthesis rate, sodium (Na⁺) and chloride (Cl⁻) levels, net Na⁺ flux, plasma membrane depolarization, and the expression of putative Si transporter genes. Two grape genotypes were investigated: H6, a salt-tolerant hybrid (V. vinifera cv. GharaUzum × V. riparia cv. Kober 5BB), and GhezelUzum, a salt-sensitive variety. The results showed that salinity stress reduced photosynthesis rates, increased the accumulation of toxic ions, disrupted ion homeostasis, and inhibited growth in both genotypes. Si supplementation significantly alleviated salinity-induced toxicity, although the effects were genotype-dependent. Specifically, Si treatment decreased the Na⁺/K⁺ ratio, enhanced Na⁺ efflux, and reduced Na⁺ influx in both genotypes. Si also improved antioxidant activity, reduced membrane damage, and regulated osmolyte content. Moreover, salinity stress caused plasma membrane depolarization, mitigated by Si treatment. The expression of putative Si transporter genes, VvNIP2;1 and VvArsb, was upregulated with Si application. These findings provide valuable insights into the physiological and molecular mechanisms underlying Si-induced salt tolerance in grapevine genotypes. Future research should explore the practical applications of Si in grapevine cultivation to enhance resilience against salinity stress and optimize grape production in affected regions.