Figure 1.

Expression of Arabidopsis vacuolar pyrophosphatase AVP1 in ena1 mutants. (A) Vector pYES2 (Invitrogen) was introduced into wild-type, ena1, ena1 nhx1, and ena1 gef1 mutants. Plasmid pYes2-AVP1-D (13) was introduced into ena1, ena1 nhx1, and ena1 gef1 mutants. Five-fold serial dilutions (starting at 10⁵ cells) of each strain were plated on YPGAL (1% yeast extract/2% peptone/2% galactose) with or without 0.5 M NaCl and incubated at 30°C for 2 days. (B and C) Intracellular concentrations of Na⁺ and K⁺. Exponentially growing cells (wild-type and ena1 transformed with pYES2 vector and ena1,ena1 nhx1, and ena1 gef1 mutants carrying pYes2-AVP1-D) were exposed to 0.7 M NaCl for 6 h. Total cell extracts were prepared (see Materials and Methods), and Na⁺ and K⁺ concentrations were determined. Values are the mean of two determinations, and bars represent the standard deviations. There is a consistent reduction in total cell Na⁺ in the ena1 AVP-D strain. The reason for this reduction is unknown.