Figure 5.

HKT1 confers on yeast cells an enhanced capacity for growth in the presence of high external NH₄⁺ concentrations. A, Growth of WΔ3 yeast cells, defective in K⁺ uptake, and the same cells transformed with HvHAK1 or HKT1 on AP medium supplied with K⁺ 10 μm at two levels of NH₄⁺ addition; 10 μL of progressive dilutions of a 0.1-optical density cell suspension were inoculated on the medium. B, Rb⁺(⁸⁶Rb) uptake mediated by WΔ3 cells expressing HvHAK1 at 100 μm Rb⁺ at increasing levels of NH₄⁺. C, As in B, but for HKT1-expressing WΔ3 cells. In B and C, results are the average values of not less than three experiments. D, Results of a representative experiment showing the accumulation of K⁺ measured as K⁺ removal from a 100 μm K⁺ solution mediated by HKT1-expressing cells in the presence (white symbols) or absence (black symbols) of 5 mm NH₄⁺.