Catalyzes the conversion of monodehydroascorbate (MDA) to ascorbate, oxidizing NADH in the process. Can also use 2,4,6-trinitrotoluene (TNT) and 1-chloro-2,4-dinitrobenzene (CDNB) as substrates, but not 1-chloro-4-nitrobenzene (CNB). H(+) + 2 monodehydro-L-ascorbate radical + NADH = 2 L-ascorbate + NAD(+) Redox regulation of the activity by thioredoxin TRXy1. Interacts in vitro with TRXy. No visible phenotype, but enhanced 2,4,6-trinitrotoluene (TNT) tolerance. The main mechanism for TNT toxicity in plants is the production of superoxide in the mitochondria by MDAR5 with TNT as a substrate. Inactivation of MDAR5 enhance TNT tolerance, thus enabling revegetation and remediation of explosives-contaminated sites. The use of alternative transcription starts causes dual targeting of the same mature MDAR protein to both mitochondria and chloroplast. Belongs to the FAD-dependent oxidoreductase family.