Phototransformation of protochlorophyllide (Pchlide) to chlorophyllide (Chlide). PORA may also function as a photoprotectant during the transitory stage from dark to light. Functions in skotomorphogenesis, photomorphogenesis and throughout the plant life under specific light conditions. chlorophyllide a + NADP(+) = H(+) + NADPH + protochlorophyllide a Porphyrin-containing compound metabolism; chlorophyll biosynthesis. Forms large complexes including TOC33, pPORA and OEP161 during pPORA import into plastids at the plastid envelope membrane. Interacts with CPP1 during plastid import (PubMed:25901327). Expressed in young seedlings. Not detected in leaves. Etiolated seedlings. Down-regulated by light. Lethal under normal growth conditions and light-green stunted plants when grown in presence of sucrose. The presence of TOC33 is not required for the import of PORA into plastids. Belongs to the short-chain dehydrogenases/reductases (SDR) family. POR subfamily.