Abstract
Activation of the hypersensitive response (HR) triggers localized acquired resistance (LAR) and systemic acquired resistance (SAR). Recently we found that Arabidopsis thaliana lesion initiation 3 (len3) plants develop lesions on leaves without pathogen attack, constitutively express PR genes, and accumulate elevated levels of SA. Hence we hypothesized that a signal important for LAR and SAR accumulates in the intercellular fluids (IFs) of the len3 plants. Infiltration of the IF from len3 plants induced PR-2 expression in local leaves but not in the systemic leaves of the wild type plants, suggesting that the elicitor activity of the IF contributes to LAR but not to SAR. Induction of PR-2 was dependent on SA signaling and ET signaling, and the elicitor in the IF was associated with molecules in the range of >100 kDa. These results suggest that len3 plants accumulate the elicitor in the IF, and that this might play a role in the establishment of LAR.
