Cosuppression of a plasma membrane H+-ATPase isoform impairs sucrose translocation, stomatal opening, plant growth, and male fertility

The plasma membrane H+-ATPase builds up a pH and potential gradient across the plasma membrane, thus activating a series of secondary ion and metaboli te transporters. pma4 (for plasma membrane H+-ATPase 4), the most widely ex pressed H+-ATPase isogene in Nicotiana plumbaginifolia, was overexpressed i n tobacco. Plants that overexpressed PMA4 showed no major changes in plant growth under normal conditions, However, two transformants were identified by their stunted growth, slow leaf initiation, delayed stem bolting and flo wering, and male sterility, Protein gel blot analysis showed that expressio n of the endogenous and transgenic pma4 was cosuppressed. Cosuppression was developmentally regulated because PMA4 was still present in developing lea ves but was not detected in mature leaves. The glucose and fructose content increased threefold, whereas the sucrose content remained unchanged. The r ate of sucrose exudation from mature leaves was reduced threefold and the s ugar content of apical buds was reduced twofold, suggesting failure of sucr ose loading and translocation to the sink tissues. Cosuppression of PMA4 al so affected the guard cells, stomatal opening, and photosynthesis in mature leaves. These results show that a single H+-ATPase isoform plays a major r ole in several transport-dependent physiological processes.