Converts salicylic acid (SA) to both 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-DHBA in vitro but only 2,3-DHBA in vivo. Component of a negative feedback regulation system of SA levels during senescence. Regulates both onset and progression of leaf senescence (PubMed:23959884). Negative regulator of defense against Hyaloperonospora arabidopsidis (PubMed:25376907). (Microbial infection) Confers susceptibility to the downy mildew pathogen Hyaloperonospora arabidopsidis. H(+) + NADH + O2 + salicylate = 2,3-dihydroxybenzoate + H2O + NAD(+) Binds 1 Fe(2+) ion per subunit. Optimum pH is 6. Optimum temperature is 40 degrees Celsius. Induced by the powdery mildew pathogen Erysiphe cichoracearum (PubMed:12920300). Accumulates upon infection with the downy mildew Hyaloperonospora arabidopsidis, the powdery mildew Erysiphe orontii, and the bacterium Pseudomonas syringae. Present only in or around the main veins of cotyledons and leaves infected by H. arabidopsidis (PubMed:25376907). Induced by salicylic acid (SA) (PubMed:23959884, PubMed:25376907). Accumulates in senescing leaves (PubMed:23959884). Impaired production of 2,3-DHBA sugar conjugates but accumulation of salicylic acid (SA) and its sugar conjugates. Precocious senescence. Enhanced expression of senescence-associated and defense-related genes. Belongs to the iron/ascorbate-dependent oxidoreductase family.