WOUND SIGNALING IN TOMATO PLANTS - EVIDENCE THAT ABA IS NOT A PRIMARYSIGNAL FOR DEFENSE GENE ACTIVATION

The effects of abscisic acid (ABA) on the accumulation of proteinase i nhibitors I (Inh I) and II (Inh II) in young, excised tomato (Lycopers icon esculentum L.) plants were investigated. When supplied to excised plants through the cut stems, 100 mu M ABA induced the activation of the ABA-responsive le4 gene. However, under the same conditions of ass ay, ABA at concentrations of up to 100 mu M induced only low levels of proteinase-inhibitor proteins or mRNAs, compared with levels induced by systemin or jasmonic acid over the 24 h following treatment. In add ition, ABA only weakly induced the accumulation of mRNAs of several ot her wound-response proteins. Assays of the ABA concentrations in leave s following wounding indicated that the ABA levels increased preferent ially near the wound site, suggesting that ABA may have accumulated be cause of desiccation. The evidence suggests that ABA is not a componen t of the wound-inducible signal transduction pathway leading to defens e gene activation but is likely involved in the general maintenance of a healthy plant physiology that facilitates a normal wound response.