ABSCISIC ACID-DEFICIENT PLANTS DO NOT ACCUMULATE PROTEINASE-INHIBITOR-II FOLLOWING SYSTEMIN TREATMENT

The role of systemin in Pin2 gene expression was analyzed in wild-type plants of potato (Solanum tuberosum L.) and tomato (Lycopersicon escu lentum Mill.), as well as in abscisic acid (ABA)-deficient tomato (sit iens) and potato (droopy) plants. The results showed that systemin ini tiates Pin2 mRNA accumulation only in wild-type tomato and potato plan ts. As in the situation after mechanical wounding, Pin2 gene expressio n in ABA-deficient plants was not activated by systemin. Increased end ogenous levels of jasmonic acid (JA) and accumulation of Pin2 mRNA wer e observed following treatment with alpha-linolenic acid, the precurso r of JA biosynthesis, suggesting that these ABA mutants still have the capability to synthesize de novo JA. Measurement of endogenous levels of ABA and JA showed that systemin leads to an increase of both phyto hormones (ABA and JA) only in wild-type but not in ABA-deficient plant s.