Evolution of chlorophyll degradation: The significance of RCC reductase

In angiosperms the key process of chlorophyll breakdown in senescing leaves is catalyzed by pheophorbide a oxygenase and RCC reductase which, in a met abolically channeled reaction, cleave the porphyrin macrocycle and produce a colourless primary catabolite, pFCC. RCC reductase is responsible for the reduction of the C20/C1 double bond of the intermediary catabolite, RCC De pending on plant species, RCC reductase produces one of the two C1 stereois omers, pFCC-1 or pFCC-2, Screening of a large number of taxa for the type o f RCCR revealed that the isomer produced is uniform within families, It als o revealed that type RCCR-2 is predominant; RCCR-1 seems to represent a rec ent derivation which in unrelated lineages has evolved independently from R CCR-2. A third type of pFCC was produced by RCCR from basal pteridophytes a cid some gymnosperms; its structure is unknown, Collectively, the data sugg est that the pathway of chlorophyll breakdown is very conserved in vascular plants. RCCR appears to represent a decisive addition to the catabolic pat hway: it allows terrestrial plants to metabolize the porphyrin part of the chlorophyll molecule to photodynamically inactive final products that are s tored in the vacuoles of senescing mesophyll cells.