Ammonia and urea permeability. (A) Growth of ammonium uptake-deficient yeast (31019b; ΔΔΔmep1;2;3) transformed with AtAMT1;2, LjNIP1, LjXIP1, K10 and the empty control plasmid pDR199 on 1 mM ammonium as the only N source at different pH. (B) Growth of urea uptake-deficient yeast (YNVW1; Δdur3) transformed with LjNIP1, LjXIP1, K10 and the empty control plasmid pDR199 on 1 mM urea as the only N source. The ability of mutant yeasts to grow on the two different media was not restored by LjNIP1 or by LjXIP1. Serial dilutions (dil.) of cell suspensions, ranging from 1 to 1 × 10-4, are shown for both pictures.