title: Salicylic acid is a reducing substrate and not an effective inhibitor of ascorbate peroxidase.
abstract: This communication describes the interactions of salicylic acid (SA) with plant ascorbate peroxidase (APX). Contrary to a recent report (Durner, J., and Klessig, D. F. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 11312-11316) we show conclusively that ascorbate oxidation by APX is not inhibited by SA (10 mM), but that SA is a slow reducing substrate of this enzyme. The suggestion that SA-dependent inhibition of APX in planta may result in the elevation of H2O2 levels, which in turn acts as a second messenger in systemic acquired resistance signaling, is therefore not tenable. We conclude that APX remains a key antioxidant during systemic acquired resistance following pathogenic infection of plants. The transient products of SA oxidation by APX appear to be SA free radicals that undergo subsequent chemistry. APX-dependent oxidation of SA could be essential for diminishing the detrimental effects of this phenolic acid on plant cells.
authors.affiliation: Nitrogen Fixation Laboratory, John Innes Centre, Norwich, NR4 7UH, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Kvaratskhelia
authors.forename: S J
authors.initials: SJ
authors.lastname: George
authors.forename: R N
authors.initials: RN
authors.lastname: Thorneley
mesh_terms: D060387:Ascorbate Peroxidases; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000037:antagonists & inhibitors*; D010940:Plant Proteins / Q000378:metabolism; D012459:Salicylates / Q000378:metabolism* / Q000494:pharmacology; D020156:Salicylic Acid; D013056:Spectrophotometry, Ultraviolet; D013662:Tea
chemical_list: D010940:Plant Proteins; D012459:Salicylates; D013662:Tea; D010544:Peroxidases; D060387:Ascorbate Peroxidases; D020156:Salicylic Acid