Abstract 9514239 Klessig Salicylic acid (SA) has been found to play an important role in the activation of defense responses against microbial attack in plants. This laboratory has identified a SA binding protein, which is a catalase, and its activity is blocked by SA. The hypothesis to be tested is that increased levels of H2O2 and other reactive oxygen species induce plant resistance (PR) genes (PR . In this proposal experiments will be done to study the role of catalase and ascorbate peroxidase (another H202 degrading enzyme) inhibition by SA, as well as he induction of PR gene resistant genes. The time course of the levels of SA, H2O2 and PR mRNA will be determined at the sites of infection. Plants made transgenic by the introduction of the nahG gene, which codes for the enzyme that breaks down salicylic acid will be examined and compared in a number of way to the wild type plants. Transgenic plants with suppressed levels of catalase or ascorbate peroxidase, made by introducing antisense to these enzymes will also be examined. These experiments will provide information on how salicyclic acids acts in the plant defense response. ***
