Combined Phosphorus and Potassium Starvation Upregulates Sodium Accumulation by HKT1;1 in Tomato Plants

Na + can substitute K + under K + deficiency conditions, which is denominated as beneficial Na + . Despite its relevance at the physiological level and its interest in agriculture, the mechanisms allowing its uptake and use by plants remain unclear. The accumulation of beneficial Na + has been associated with K + deficiency, but the deficiency of other mineral nutrients could also affect this process. In this study, we observed that the combined deficiency of K + and P (−K −P) resulted in a 2‐fold increase in the root Na + content in tomato plants with respect to the single K + deficiency (−K). Such a response was observed also in quinoa and barley but not in Arabidopsis, wheat, rice, soybean and Solanum pennellii , evidencing natural variability for this trait. Pi uptake in −K −P plants was not coupled to Na + as deduced from electrophysiology and plant growth experiments. Finally, we show that the Na + channel HKT1;1, but not HKT1;2, contributes to Na + uptake in tomato plants, in particular, in the −K −P condition where a 40‐45% reduction in root Na + content is observed in HKT1;1 ‐silenced lines. Therefore, the information acquired on HKT1;1 is crucial for boosting Na + uptake in plants.