CHILL-INDUCED CHANGES IN THE ACTIVITY AND ABUNDANCE OF THE VACUOLAR PROTON-PUMPING PYROPHOSPHATASE FROM MUNG BEAN HYPOCOTYLS

Changes in the properties of extractable vacuolar H+-pumping pyrophosp hatase (V-PPase) and vacuolar ATPase activities in chilling-sensitive seedlings of mung bean (Vigna radiata) were investigated. Following ch illing at 4 degrees C for 48 h, both hydrolytic and proton-pumping act ivities of the V-PPase increased 1.5- to 2-fold over controls and rema ined elevated even after 72 h at low temperatures. Vacuolar ATPase lev els did not change significantly throughout the chilling regime. Howev er a large increase in alcohol dehydrogenase activity during chilling suggests a shift toward fermentative metabolism, which can be expected to decrease ATPase activity in situ. Western blotting of vacuolar mem brane-enriched fractions from control and treated plants has confirmed that the changes in V-PPase activity are mirrored by increases in the amount of pump protein. Results suggest a specific role for the V-PPa se in protecting chill-sensitive plants from the injurious effects of low temperatures via the maintenance of the proton gradient across the vacuolar membrane.