Measurement of K+ concentrations
First, 0.05 g dry weight tomato roots was added to a 10-mL centrifuge tube containing 2 mL of 0.5 M hydrochloric acid. Samples were incubated for 3 days, after which, 5 mL deionised water was added to each centrifuge tube, and the mixture was filtered. The filtered stock solution was diluted 10 times, and the K+concentration was measured with a flame photometer. Each sample was evaluated with three biological replicates.