IMMUNOFLUORESCENT LOCALIZATION OF PLASMA-MEMBRANE H+-ATPASE IN BARLEY ROOTS AND EFFECTS OF K-NUTRITION

The plasma membrane H+-ATPase (PM-H+-ATPase) of barley (Hordeum vulgare L. cv Klondike) roots was assayed by cross-reaction on western blots and cryosections with an antibody against the PM-H+-ATPase from corn roots. Under conditions of reduced K availability, which have previously been shown to increase K influx by greater than 25-fold, there were only minor changes detected in PM-H+-ATPase levels. Antibody labeling of cryosections showed the relative distribution of PM-H+-ATPase among cell types in root tips and mature roots. Epidermal cells, both protoderm and mature root epidermis, including root hairs, had high levels of antibody binding. In mature roots, the stelar tissue showing the highest antibody binding was the companion cells of the phloem, followed by pericycle, xylem parenchyma, and endodermis.