ABSCISIC-ACID DOES NOT MEDIATE NACL-INDUCED ACCUMULATION OF 70-KDA SUBUNIT TONOPLAST H-ATPASE MESSAGE IN TOMATO()

There is an increased accumulation of message for the catalytic (70-kD a) subunit of the tonoplast H+-ATPase in leaves of tomato (Lycopersico n esculentum L.) plants responding to NaCl. To determine if abscisic a cid (ABA) mediates this response, message accumulation was examined in treatments designed to separate exposure to NaCl from increases in en dogenous ABA. Under three different experimental conditions, salt-indu ced changes in the accumulation of 70-kDa message were unrelated to an y change in endogenous ABA. The results were as follows: (i) under dro ught stress, plants accumulated levels of ABA similar to those measure d in salt-treated plants; however, no increase in 70-kDa subunit messa ge was observed; (ii) the ABA-deficient mutant sitiens exhibited an in creased accumulation of message despite the absence of NaCl-induced ac cumulation of ABA; and (iii) the inhibitor of general isoprenoid biosy nthesis, Lovastatin, blocked NaCl-induced accumulation of ABA but did not alter NaCl-induced accumulation of message. In addition to these t hree experimental responses, application of exogenous ABA increased en dogenous ABA levels without any comparable increase in message accumul ation. Based on these results, it is concluded that ABA does not media te the NaCl-induced accumulation of 70-kDa subunit tonoplast H+-ATPase message accumulation in tomato.