Ascorbate oxidase involved in a redox system involving ascorbic acid (AsA) (PubMed:15883131, PubMed:27255930). The oxidation of AsA represses responses to high salinity and oxidative stress conditions such as vegetative growth and seed production reductions (PubMed:15883131). 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) (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). Impaired ascorbate oxidase activity and reduced apoplastic hydrogen peroxide H(2)O(2) and ascorbate peroxidase accumulation, especially in high salinity (PubMed:15883131). Short stems and late flowering (PubMed:15883131). Slightly increased ascorbate (AsA) contents in the apoplasm but lower monodehydroascorbate (DHA) contents (PubMed:15883131, PubMed:27255930). Increased tolerance for high salinity during vegetative growth, seed production and seed germination (PubMed:15883131). Higher resistance to oxidative stress agents such as methyl viologen (MV) and hydrogen peroxide H(2)O(2) (PubMed:15883131). Enhanced resistance to Turnip mosaic virus (TuMV) associated with an increased accumulation of ascorbic acid (AsA, AS) and dehydroascobic acid (DHA) due to a reduction of AS oxidation and activation of AS recycling (PubMed:27255930). Belongs to the multicopper oxidase family.