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

Abstract

plants, including many agricultural important crop species (Barea et al., 1993). The fungi biotrophically colonize the ATPase activity, ATP-dependent H+ transport and the cortex of the root to obtain carbon compounds from the amount of antigenic tomato plasma membrane H+- host plant, while assisting the plant with the supply of ATPase have been analysed in membrane vesicles isol- phosphate and other mineral nutrients that the external ated from Glomus mosseae -o rGlomus intraradices- fungal mycelium takes up from the soil (Harley and colonized roots and from non-mycorrhizal tomato Smith, 1983). The transfer mechanisms between symroots. Microsomal protein content was higher in mycor- bionts are of considerable interest and are likely to involve rhizal than in control roots. The specific activity of the specific alterations in membrane transport processes. plasma membrane H+-ATPase was not affected by Woolhouse was the first to suggest that the controlled mycorrhizal colonization, although this activity in- transfer of nutrients required for a functional mycorrhizal creased in membranes isolated from mycorrhizal roots symbiosis is carried out by means of active transport when expressed on a fresh weight basis. Western blot processes ( Woolhouse, 1975). analysis of microsomal proteins using antibodies raised In many cellular systems, transport of solutes into and against the Arabidopsis thaliana plasma membrane H+- out of the cell involves processes driven by the H+ ATPase showed that mycorrhizal colonization did not electrochemical gradient generated by the plasma memchange the relative amount of tomato plasma mem- brane H+-ATPase, which pumps protons out of the cell brane ATPase in the microsomes. However, on a fresh (Serrano, 1989). Therefore, the hypothesis of an active weight basis, there was a greater amount of this protein transport in mycorrhizal symbioses requires the presence in roots of mycorrhizal plants. In addition, mycorrhizal of a H+ pumping activity. This hypothesis has been membranes showed a higher specific activity of the supported by cytochemical, electrophysiological and biovanadate-sensitive ATP-dependent H+ transport than chemical data. In particular, cytochemical studies (Marx membranes isolated from control roots. These results et al., 1982; Smith and Smith, 1990; Gianinazzi-Pearson suggest that mycorrhiza might regulate the plasma et al., 1991) have shown that in arbuscular mycorrhizas membrane ATPase by increasing the coupling effici- ATPase activity is associated with both plant and fungal ency between H+ transport and ATP hydrolysis. The membranes of the arbuscular interface, which is consistent observed effects of mycorrhizal colonization on plasma with active transport processes occurring at this location. membrane H+-ATPase were independent of the AM ATPases represent proton pumps that establish proton motive forces and drive the uptake of P i or hexose against