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

Combined phosphorus and potassium starvation increases root Na+ content in tomato plants by 2-fold versus single K+ deficiency, and this Na+ uptake is mediated by HKT1;1.

• Why it matters: Beneficial Na+ accumulation is linked to K+ deficiency, but how other nutrient shortages alter Na+ uptake and which transporters mediate it remains unclear for crop physiology.
• What they did: Tomato plants were grown under -K, -P, and combined -K -P conditions, with electrophysiology and growth tests assessing coupling between Pi uptake and Na+; HKT1;1 and HKT1;2 were functionally tested via silencing.
• The result: In -K -P plants, HKT1;1-silenced tomato lines show a 40–45% reduction in root Na+ content, while HKT1;2 does not contribute, implying HKT1;1 specifically supports Na+ uptake under combined deficiency.

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