Involved in pyrimidine base degradation. Catalyzes the reduction of uracil to 5,6-dihydrouracil (DHU) by using NADH as a specific cosubstrate and the reduction of thymine to 5,6-dihydrothymine (DHT). Involved in the recycling of nitrogen from nucleobases to general nitrogen metabolism. 5,6-dihydrouracil + NADP(+) = H(+) + NADPH + uracil Amino-acid biosynthesis; beta-alanine biosynthesis. Expressed in roots, leaves, stems, siliques and flowers. Highly expressed ion dry seeds. Up-regulated at days 4 and 5 after germination and during senescence. Up-regulated by nitrogen limitation. No visible phenotype, but impaired degradation of both thymine and uracil (PubMed:19413687, PubMed:21865177). Slower germination and 2 days delay in seedling development (PubMed:21865177). Belongs to the dihydropyrimidine dehydrogenase family.