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

ATPase activity, ATP-dependent H+ transport and the amount of antigenic tomato plasma membrane H+-ATPase have been analysed in membrane vesicles isolated from Glomus mosseae- or Glomus intraradices-colonized roots and from non-mycorrhizal tomato roots. Microsomal protein content was higher in mycorrhizal than in control roots. The specific activity of the plasma membrane H+-ATPase was not affected by mycorrhizal colonization, although this activity increased in membranes isolated from mycorrhizal roots when expressed on a fresh weight basis. Western blot analysis of microsomal proteins using antibodies raised against the Arabidopsis thaliana plasma membrane H+-ATPase showed that mycorrhizal colonization did not change the relative amount of tomato plasma membrane ATPase in the microsomes. However, on a fresh weight basis, there was a greater amount of this protein in roots of mycorrhizal plants. In addition, mycorrhizal membranes showed a higher specific activity of the vanadate-sensitive ATP-dependent H+ transport than membranes isolated from control roots. These results suggest that mycorrhiza might regulate the plasma membrane ATPase by increasing the coupling efficiency between H+ transport and ATP hydrolysis. The observed effects of mycorrhizal colonization on plasma membrane H+-ATPase were independent of the AM fungal species colonizing the root system.