Changes in plasma membrane H+-ATPase activity during aeration of maize roots
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Plasma membrane-enriched vesicles were isolated by density gradient centrifugation from maize roots previously submersed for 2 h with or without aeration in a 1 mmol/L CaSO4 solution, a condition which can modify the rate of ion fluxes in root tissue. The treatments did not significantly modify the composition of the membrane fraction collected at the sucrose gradient interface, as revealed by marker enzyme activities. However, submersion of maize roots for 2 h in aerated CaSO4 before membrane isolation caused a significant increase in both the initial rate of ATP-dependent proton pumping (+99%) and the rate of ATP hydrolysis (+64%) as compared with the vesicles from roots immediately homogenised after being removed from the seedlings. Simple submersion of maize roots without aeration of the solution induced only a small effect on both ATP-hydrolytic activity (+14%) and ATP-dependent H+ transport (-16%). Submersion of root tissue clearly enhanced the apparent passive permeability of isolated membrane vesicles to protons irrespective of the aeration treatment. These results suggest the involvement of plasma membrane H+-ATPase in the response to changes in root environmental conditions, like submersion with or without aeration.