Tonoplast H+ pumps are activated during callus formation of tuber tissues of Jerusalem artichoke (Helianthus tuberosus)

Changes in tonoplast H+-ATPase (EC 3.6.1.3) and H+-PPase (EC 3.6.1.1) activities were examined during the early period of callus formation in tuber tissues of Jerusalem artichoke (Helianthus tuberosus L.). In callus-forming tissues cultured on a medium containing 2,4-D, the ATP-dependent H+-translocation activity of tonoplast vesicles increased 3-fold after a 2-day lag phase, while the ATP-hydrolytic activity and amount of tonoplast H+-ATPase protein were relatively constant after the lag phase. In the control tissue disks cultured on a medium free of 2,4-D, large declines in ATP-hydrolytic and ATP-dependent H+-translocation activities were observed. By contrast, the PPi-dependent H+-translocation activity of tonoplast vesicles increased about 8-fold during the first 3 days of culture without any lag phase, and regardless of the presence of 2,4-D in the culture medium. However, the PPi-hydrolytic activity and amount of H+-PPase protein did not change during the culture period, independently of callus formation. Transfer of the control tissue disks to the 2,4-D-containing medium, however, resulted in a further rapid stimulation of PPi-dependent H+-translocation as well as an activation of ATP-dependent H+-translocation, These results suggest that both tonoplast H+ pumps are involved in callus formation of tuber tissues of Jerusalem artichoke.