Catalyzes the interconversion of ornithine to glutamate semialdehyde. a 2-oxocarboxylate + L-ornithine = an L-alpha-amino acid + L-glutamate 5-semialdehyde Amino-acid biosynthesis; L-proline biosynthesis; L-glutamate 5-semialdehyde from L-ornithine: step 1/1. Part of the rocDEF operon. Expression is sigma L dependent, induced by arginine, ornithine, ctirulline or proline. Ammonium and glutamine strongly repress induction of the rocD by proline, and only glutamine represses weakly induction by arginine. Cells lacking this gene do not grow in minimal medium containing either arginine or ornithine as sole nitrogen source. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family. OAT subfamily.