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

Abstract

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 PP‐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 PP‐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 PP‐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.