Apoplastic Na+ in Vicia faba Leaves Rises After Short‐Term Salt Stress and Is Remedied by Silicon

Salinity primarily affects plants by inhibiting shoot growth. Salt‐sensitive plants have been suggested to accumulate Na⁺ within their leaf apoplast under salinity, leading to a reduced water status. Evidence related to apoplastic Na⁺ accumulation is still enigmatic. We have focused on the effect of a short‐term salt treatment by using the salt‐sensitive Vicia faba. Moreover, we have examined the role of silicon in alleviating sodium accumulation in the apoplast. Salt‐sensitive field beans have been subjected to increasing levels of salinity, with and without the addition of silicon under hydroponic conditions. We have demonstrated that the dicot Vicia faba exhibits a rise in Na⁺ concentration in the leaf apoplast at higher salinity levels; this is significantly ameliorated by the addition of silicon. Further, enhanced shoot growth under high salt treatment in the presence of added silicon is correlated with a significant decrease in Na⁺ concentration in the leaves. The novelty of the current study is the detection of a high Na⁺ concentration in the leaf apoplast of the salt‐sensitive dicot field bean. Our results support Oertli's hypothesis that extracellular salt accumulation can lead to wilting leaves, plant growth reduction and cell death.