Head and stalk structures of soybean vacuolar membranes.

Highly purified tonoplast fractions isolated by preparative free-flow electrophoresis from hypocotyls of etiolated soybean (Glycine max L. (Merr.)) were examined by negative-staining electron microscopy, and many but not all vesicles were found to exhibit head and stalk structures resembling the 9-nm stalked F1 ATPase particles reported previously for Neurospora (Bowman et al., 1989, J. Biol. Chem. 264, 15606-15612). The structures show distinguishing characteristics similar to those for Neurospora. These include a cleft in the particle not exhibited by mitochondrial F1 ATPase and a tendency to disappear from the membrane when treated with nitrate plus Mg(-2+)-ATP-containing solutions. The position of the stalked ATPase structures, indicates that some of the tonoplast vesicles were oriented cytoplasmic side out whereas others were oriented cytoplasmic side in.