Abstract
Cytosolic K + retention is a key determinant of salinity tolerance, and H + transport can support K + homeostasis under salt stress. Silicon (Si) often improves plant performance under salinity, but its short-term mechanisms remain debated. We tested whether Si pretreatment reduces early NaCl-induced K + efflux in barley roots via modulation of H + transport. Net K + and H + fluxes were measured in vivo and in real-time in the mature root zone (at 10–20 mm from the tip) of barley ( Hordeum vulgare var. Esperanza) using microelectrode ion flux estimation (MIFE) technique. Seedlings were treated with 0, 1, or 2 mM Si supplied as Na 2 SiO 3 from germination and exposed to 80, 160, or 320 mM NaCl. Flux responses were analyzed during the first 30 min, emphasizing the 15–20 min post-treatment window. Longer-term effects were assessed by K + leakage (2 h) and Na + accumulation (24 h) assays. NaCl induced a rapid, dose-dependent K + efflux peaking within 15–20 min. Si pretreatment reduced NaCl-induced K + loss in a concentration-dependent manner and was consistently associated with stimulation of H + efflux in the mature root zone. Si rapidly modulates root ion transport under salinity by enhancing H + efflux, which likely supports membrane potential, limits NaCl-induced depolarization, and/or facilitates Na + management, thereby improving early cytosolic K + retention.