The plasma membrane H+-ATPase of maize embryos localizes in regions that are critical during the onset of germination

The H+-ATPase is a plasma membrane enzyme that hydrolyzes ATP and translocates protons from the cytosol to the apoplast space. The resulting acidification is used to promote stomata opening, pH homeostasis, secondary transport of nutrients, and cell elongation. The latter two processes are critical in germination, since radicle protrusion, requires the growth of embryo cells. Earlier studies have shown that the plasma membrane H+-ATPase is already active during the first hours of imbibition. Here, the localization of this enzyme was studied in maize embryos by histochemical and immunochemical techniques at 2 h of imbibition. The enzyme is mainly located in regions of the embryo that require high transport activity or that participate in cell elongation: the scutellum, the root and the plumule. The cells that were more immunolabeled were those located in the epidermis, in the parenchyma and in the elements of the vascular bundles. These results suggest that the plasma membrane H+-ATPase levels present in the first hours of imbibition are preserved and/or are newly synthesized to fulfill the demands of transport and elongation of the embryo on the onset of seed germination.