Catalyzes the key reaction of chlorophyll catabolism, porphyrin macrocycle cleavage of pheophorbide a (pheide a) to a primary fluorescent catabolite (pFCC). Works in a two-step reaction with pheophorbide a oxygenase (PaO) by reducing the C20/C1 double bond of the intermediate, RCC. Belongs to the chlorophyll catabolic enzymes (CCEs). 2 oxidized [2Fe-2S]-[ferredoxin] + primary fluorescent chlorophyll catabolite = 3 H(+) + red chlorophyll catabolite + 2 reduced [2Fe-2S]-[ferredoxin] Porphyrin-containing compound metabolism; chlorophyll degradation. Homodimer (PubMed:19374909, PubMed:20727901). Interacts with HCAR (PubMed:23200839). Interacts with SGR1, NYC1, NOL, PPH, PAO and the LHCII complex (PubMed:22366162). Part of a SGR1-CCE-LHCII complex, which acts in chlorophyll breakdown (PubMed:22366162). And a low amount in mitochondria of 7-day-old seedlings. Expressed in all tissues tested, including roots. Present at all times of development. No change of levels during senescence or pathogen attack. The absence of light completely suppresses cell death in acd2 mutants.