CHANGES IN PROTEIN-COMPOSITION AND THE H+-ATPASE ACTIVITY OF THE PLASMA-MEMBRANE DURING INDUCTION OF CALLUS FROM TUBER TISSUES OF JERUSALEM-ARTICHOKE

Changes in composition and synthesis of the proteins in plasma membranes during early periods of induction of callus from tuber tissues of Jerusalem artichoke were examined in relation to analogous changes in H+-ATPase activity. By the 12th h of culture, vanadate-sensitive ATPase activity had increased more than 3.5-fold. The level of a polypeptide with a molecular mass of 97 kDa, which putatively corresponded to a subunit of the plasma membrane H+-ATPase, also showed a similar increase. Increases in ATPase activity and in the level of the 97-kDa polypeptide occurred independently of the presence of 2,4-D in the culture medium but the rate of increase in both cases was slightly higher for tissue disks cultured with 2,4-D than for the control disks in medium without 2,4-D for the first 12 h of culture. The increase in the level of the 97-kDa polypeptide may be ascribed predominantly to synthesis de novo during the early period of culture. Enhanced synthesis of the 97-kDa polypeptide in the cultured tissues may have resulted in the increases in ATPase activity. Since auxin itself may stimulate H+ -ATPase activity, the activated H+-ATPase may be further stimulated in tissue disks cultured with 2,4-D. The H+-ATPase activated in this way may produce conditions that facilitate the induction of callus from tuber tissues of Jerusalem artichoke during the early period of culture.