Abstract
The vacuole of higher plant cells contains two H+-pumping enzymes, H+-translocating adenosine triphosphatase (V-ATPase; EC 3.6.1.3) and H+- translocating inorganic pyrophosphatase (V-PPase; EC 3.6.1.1), across its membrane. These two enzymes produce proton gradient for homeostasis of the cell at the expense of ATP and PPi hydrolysis. Both enzymes regulate cell turgor, cytoplasmic homeostasis, the storage of metabolites, signal transduction, and protein turnover. They generate approximately equal proton gradients through the vacuolar membrane. In this study, we investigated the effects of high-temperature on these two enzymes in etiolated mung bean seedling. Using electrolyte leakage and pH assay, we observed that there were no obvious injury on the cell membrane at 38℃ for various time periods. In the Northern blotting analysis, we found that the amount of mRNA of V-ATPase declined but then increased at 38℃ for 4 h heat treatment. However, that of V-PPase decreased rapidly after heat treatment. Hydrolytic and proton-pumping activities of V- ATPase were maximum under high temperature treatment for 1 h and then decreased. V-PPase showed a similar pattern upon heat treatment. Hydrolytic and proton-pumping activities of V-PPase at heat treatment increased 1.3- and 1.4-fold over control at 38 ℃ for 1 h, respectively. We observed that V-ATPase was sensitive to high temperature. It is proposed that V-PPase plays an important role in the survival strategies of plant under high temperature stress.