Fig. 2.

Transgenic tomato plants have increased H⁺-PPase activity. (A) H⁺-PPase and H⁺-ATPase hydrolytic activity was determined from purified vacuolar membrane vesicles from root tissue of two lines of transgenic plants (bar 1 = XAVP1D-1 and bar 2 = XAVP1D-2) and control plants (bar C). Results (means ± SE of four to five replications) are shown as percentage of the control activity. (B) Ca²⁺/H⁺ antiport activity into vacuolar membrane vesicles from root tissue of XAVP1D-1 and control plants. A time course of 10 μM ⁴⁵CaCl₂ uptake was measured after energization by either ATP (H⁺-ATPase dependent) or PP_i (H⁺-PPase-dependent). Uptake was performed in the presence of the Ca²⁺-ATPase inhibitor vanadate. Net results are shown after subtraction of background values (uptake in the presence of the protonophore FCCP).