Ascorbate oxidase involved in a redox system involving ascorbic acid (AsA) (PubMed:27255930). The oxidation of AsA represses responses to high salinity and oxidative stress conditions such as vegetative growth and seed production reductions (By similarity). Negative regulator of defense responses toward incompatible Turnip mosaic virus (TuMV strain UK1) by preventing jasmonic acid (JA)- dependent accumulation of ascorbic acid (AsA, AS) and dehydroascobic acid (DHA) (PubMed:27255930). 4 L-ascorbate + O2 = 2 H2O + 4 monodehydro-L-ascorbate radical Binds 4 Cu cations per monomer. Cofactor degradation; L-ascorbate degradation. Dimer. Repressed progressively during incompatible Turnip mosaic virus (TuMV) infection (strain UK1) in resistant cultivars (e.g. cv. Aki-masari) but not in susceptible cultivars (e.g. cv. Yukihime-kabu) (PubMed:27255930). When the plant is infected by a compatible TuMV strain (UK1 m2), the down-regulation is transient and last two days (PubMed:27255930). Induced by jasmonic acid (JA) and hydrogen peroxide H(2)O(2) treatments (PubMed:27255930). Belongs to the multicopper oxidase family.