Figure 3.

HA:AtPRA1.F4 OX and atpra1.f4 plants have lower vacuolar Na⁺/K⁺-ATPase and plasma membrane (PM) ATPase activities. A, Effects of HA:AtPRA1.F4 overexpression and AtPRA1.F4 knockdown mutation on vacuolar Na⁺/K⁺-ATPase activity. Vacuolar membrane proteins were prepared from isolated vacuoles and used to measure Na⁺/K⁺-ATPase activity as described in “Materials and Methods.” Control plants harbor the empty pBIB vector. Asterisks indicate statistically significant differences at P ≤ 0.001 (***) between pBIB and HA:AtPRA1.F4 OX plants and at P ≤ 0.05 (*) between wild-type (WT) and atpra1.f4 plants. Error bars represent sd (n = 3). B, Effects of HA:AtPRA1.F4 overexpression and AtPRA1.F4 knockdown mutation on apoplastic pH. Apoplastic fluid samples were prepared and pH was measured as described in “Materials and Methods.” Error bars represent sd (n = 3). Asterisks indicate statistically significant differences at P ≤ 0.01 (**) between pBIB and HA:AtPRA1.F4 OX plants and between wild-type and atpra1.f4 plants. C, Effects of HA:AtPRA1.F4 overexpression and AtPRA1.F4 knockdown mutation on rhizosphere pH. Ten-day-old seedlings grown on one-half-strength MS plates were incubated in one-half-strength liquid MS medium supplemented with 0.005% Bromocresol Purple for 2 d, and the pH of the incubation medium was measured as described in “Materials and Methods.” Error bars represent sd (n = 3). Asterisks indicate statistically significant differences at P ≤ 0.1 (*) between pBIB and HA:AtPRA1.F4 OX plants and at P ≤ 0.001 (***) between wild-type and atpra1.f4 plants. D, Effects of HA:AtPRA1.F4 overexpression and AtPRA1.F4 knockdown mutation on PM ATPase activity. Inside-out vesicles of PM factions were used to measure PM ATPase activity. Asterisks indicate statistically significant differences at P ≤ 0.001 (***) between pBIB and HA:AtPRA1.F4 OX plants and at P ≤ 0.05 (*) between wild-type and atpra1.f4 plants. Error bars represent sd (n = 3).