Plasma membrane ATPase and H+ transport activities in microsomal membranes from mycorrhizal tomato roots

ATPase activity, ATP-dependent H⁺ transport and theamount of antigenic tomato plasma membrane H⁺-APTasehave been analysed in membrane vesicles isolated from Glomusmosseae- or Glomus intraradices-colonizedroots and from non-mycorrhizal tomato roots. Microsomal protein content washigher in mycorrhizal than in control roots. The specific activity of theplasma membrane H⁺-ATPase was not affected bymycorrhizal colonization, although this activity increased in membranesisolated from mycorrhizal roots when expressed on a fresh weight basis.Western blot analysis of microsomal proteins using antibodies raisedagainst the Arabidopsis thaliana plasma membraneH⁺ - ATPase showed that mycorrhizal colonization didnot change the relative amount of tomato plasma membrane ATPase in themicrosomes. However, on a fresh weight basis, there was a greater amount ofthis protein in roots of mycorrhizal plants. In addition, mycorrhizalmembranes showed a higher specific activity of the vanadate-sensitiveATP-dependant H⁺ transport than membranes isolatedfrom control roots. These results suggest that mycorrhiza might regulatethe plasma membrane ATPase by increasing the coupling efficiency betweenH⁺ transport and ATP hydrolysis. The observedeffects of mycorrhizal colonization on plasma membraneH⁺-ATPase were independent of the AM fungal speciescolonizing the root system.