Figure 5.

(A) LePT1 shows enrichment in the plasma membrane of roots. The microsomal membranes (MM) obtained from roots of P_i-starved tomato plants were further fractionated into plasma membranes (PM) and other membranes (OM) by the aqueous two-phase extraction procedure (15). Equal quantities (5 μg) of membrane proteins from these fractions were analyzed by Western blotting. M, molecular mass markers. (B) Activities of marker enzymes in different membrane fractions. Specific activities of vanadate-sensitive ATPase (a plasma membrane marker), nitrate-sensitive ATPase (a tonoplast membrane marker), and oligomycin-sensitive ATPase (a mitochondrial membrane marker) were determined for each of the membrane fractions to assess their purity. The PM fraction is enriched in vanadate-sensitive ATPase activity.