EFFECTS OF VANADATE ON THE ATP CONTENT, ATPASE ACTIVITY AND PHOSPHATEABSORPTION CAPACITY OF MAIZE ROOTS

Although the sensitivity of the plasma membrane H+-ATPase to vanadate is well known, the metabolic response of plant cells to vanadate is le ss well characterised in vivo and its use as an inhibitor in whole pla nt experiments has had mixed success. Experiments with maize (Zea mays , L.) roots and with purified plasma membrane fractions from the same tissues showed that exposure to vanadate caused: (i) a reduction in th e capacity for phosphate uptake; (ii) a reduction in the extractable A TPase activity from the tissue; and (iii) a significant increase in th e ATP level. The measurements on the extractable ATPase activity and t he ATP level showed that the effect of vanadate developed slowly, appa rently reflecting the slow accumulation of intracellular vanadate. The marked effect of vanadate on the ATP level-exposure to 500 mu M vanad ate for 5 h doubled the ATP content of the roots tips-indicates that t here is no stringent control over the ATP level in the roots and that the plasma membrane H+-ATPase activity is likely to have a significant role in determining the ATP level under normal conditions.