Influence of silicon on microdistribution of mineral ions in roots of salt-stressed barley as associated with salt tolerance in plants.

Two contrasting barley (Hordeum vulgare L.) cultivars: Kepin No.7 (salt sensitive), and Jian 4 (salt tolerant) were grown hydroponically to investigate the microdistribution of mineral ions in roots as affected by silicon (Si) with respect to salt tolerance. The experiment was undertaken consisting of two treatments with 3 replicates: (i) 120 mmol . L(-1) NaCl alone (referred to as Si-NaCl+), (ii) 120 mmol . L(-1) NaCl + 1.0 mmol . L(-1) Si (as potassium silicate) (referred to as Si+NaCl+). Plant root tips were harvested for microanalysis using an energy dispersive X-ray microanalyzer (EDX) 30 d after transplanting. Higher Cl and Na X-ray peaks were recorded in the root epidermal, cortical and stelar cells of roots for the treatment Si-NaCl+ with the majorities of Na and Cl being accumulated in epidermal and cortical cells, while relatively low K peaks were observed regardless of the barley cultivars used. By contrast, considerably higher K peaks were detected in the epidermal, cortical and stelar cells of the roots for the treatment Si+NaCl+, but lower Cl and Na peaks were also observed for this treatment with both Na and Cl ions being evenly distributed in the epidermal, cortical and stelar cells. These findings directly support our previous finding, which showed that Si depressed the uptake of sodium but enhanced the uptake of potassium by salt-stressed barley. We believe that one of the possible mechanisms involved in Si-enhancement of salt tolerance in barley is attributed to the Si-induced changes in the uptake and microdistribution of mineral ions in plants.