Catalyzes the oxidation of L-aspartate to iminoaspartate. Can complement nadB-deficient E.coli mutant. Plays a role in stomatal immunity. L-aspartate + O2 = H2O2 + iminosuccinate Binds 1 FAD per subunit. Cofactor biosynthesis; NAD(+) biosynthesis; iminoaspartate from L-aspartate (oxidase route): step 1/1. Interacts in vitro with QS (PubMed:18978034). Embryonic lethality when homozygous. The viable mutant fin4 (T-DNA insertion in the promoter) is impaired in the RBOHD-dependent pathogen-associated molecular pattern (PAMP)-induced reactive oxygen species (ROS) burst and stomatal closure. Belongs to the FAD-dependent oxidoreductase 2 family. NadB subfamily.