Ethylene-enhanced chlorophyll catabolism in radish (Raphanus sativus L.) cotyledons

The mechanism of ethylene action on degreening of intact radish (Raphanus sativus) cotyledons was studied using inhibitors of protein and nucleic acid synthesis. Ethylene treatments enhanced the degreening and increased Chl-oxidative enzyme activity of cotyledons held in the dark. Cycloheximide, an inhibitor of cytoplasmic protein synthesis, and actinomycin D, an inhibitor of nuclear RNA synthesis, completely inhibited the effects of ethylene, but chloramphenicol, an inhibitor of plastid RNA synthesis, did not. These results suggest that ethylene appears to enhance the degreening of the radish cotyledons through de novo synthesis of Chl-oxidative enzyme(s). Furthermore, an inverse correlation between the contents of total Chls or Chi a, of radish cotyledons and Chl-oxidative enzyme activity was obtained, indicating that Chl-oxidative enzyme(s) is the key enzyme in the degreening process.