Converts proline to delta-1-pyrroline-5-carboxylate. a quinone + L-proline = (S)-1-pyrroline-5-carboxylate + a quinol + H(+) Amino-acid degradation; L-proline degradation into L-glutamate; L-glutamate from L-proline: step 1/2. Ubiquitous. Highest expression in pollen grains, in the stigma and in developing embryos. Down-regulated by salt or drought stress. Up-regulated by proline, hypoosmolarity or rehydration (PubMed:17106685, PubMed:20403182, PubMed:9003320, PubMed:9847097). Activated by BZIP53 (PubMed:16810321). No visible phenotype when grown under normal conditions. Proline hypersensitivity. Belongs to the proline oxidase family.