ALDH4A1 and infection: It is worth noting that the P5C dehydrogenase (P5CDH) mutant of A. thaliana showed higher proline dehydrogenase (ProDH) and ornithine aminotransferase (OAT) activity, as well as higher levels of ornithine and proline when challenged with exogenous proline, or infection with the bacterial pathogen Pseudomonas syringae pv.