Chilling induces a decrease in pyrophosphate‐dependent H+‐accumulation associated with a ΔpHvac‐stat in mung bean, a chill‐sensitive plant

Abstract

Chilling leads to cytoplasmic acidification in chill-sensitive plants. A possible explanation for this observation is that a DeltapH-stat between the cytosol and vacuole (DeltapH(vac)-stat) is perturbed by chilling. To understand the nature of this DeltapH(vac)-stat, the effect of temperature, between 20 and 0 degrees C, on pyrophosphate (PPi)- or ATP-dependent acidification of vacuolar vesicles, isolated from mung bean hypocotyls, was determined. Over the temperature range investigated, the H+-influx mediated by PPase was balanced with the H+-efflux, which was PPi-dependently suppressed, and consequently a constant pH in vesicles (pH(in)) of ca. 5 was maintained against temperature changes. However, the DeltapH(in) driven by ATP decreased as the temperature dropped. Thus, the PPi-dependent H+-accumulation may function as an essential factor to form a DeltapH(vac)-stat against temperature changes. Next, to study the chilling sensitivity of PPi-dependent H+-accumulation, vacuolar vesicles were isolated from control seedlings or from seedlings chilled at 0 degrees C for 1 d. Chilling treatment resulted in a decrease in the H+-accumulation rate and in the steady-state DeltapH(in) formed by PPi, the causes of which were enhanced by PPi-dependent H+-efflux and reduced by H+-influx driven by PPase. Together, the results suggest that the decrease of PPi-dependent H+-accumulation associated with the DeltapH(vac)-stat could result in cytoplasmic acidification.