Abstract
H+-pyrophosphatase (H+-PPase) is a proton pump that generates H+ gradient across endomembranes using the energy of phosphoanhydride bond of pyrophosphate. In higher plants, a large amount of H+-PPase exists in vacuolar membranes and maintains vacuolar acidic pH together with V-ATPase. However, it has been reported that H+-PPase is also localized in plasma membrane and involved in auxin transport indirectly.
In this study, we inserted sGFP in cytosolic loop of Arabidopsis thaliana type-I H+-PPase AtVHP1/AVP1 and transformed into wild type or vhp1 plant to identify the expression and localization pattern of the enzyme in various cells. H+-PPase was detected in vacuolar membranes as expected. Furthermore, strong fluorescence was observed in membranes of mobile spherical structure within vacuoles, called 'bulbs'. Histological analysis demonstrated that VHP1 was strongly expressed in almost all tissues, especially in root tips, vesicular bundles, pollens, and water soaked seeds. In conjunction with phenotype of vhp1 plants, we will discuss physiological role of H+-PPase.
