1999 Volume 68 Issue 6 Pages 1139-1145
Ethylene enhanced the degreening and increased the chlorophyll (Chl)-oxidative enzyme activity in intact radish (Raphanus sativus L.)(Rs) cotyledons kept in the dark. The catabolism of Chl α-porphyrin in plants was investigated by using crude proteins from ethylene-induced degreening radish cotyledons. The enzyme catalyzes the degradation of Chl α in the presence of H2O2 and 2, 4-dichlorophenol (DCP), or p-coumaric acid. Analysis by HPLC and HPTLC revealed the appearance of C-132-hydroxy (HO)Chl α. The reaction of C-132-HO Chl α formation was inhibited completely by ascorbate (2mM) or KCN (2mM), but it was not under an anoxygenic condition. These results suggest that C-132-HO Chl α forming enzyme is aperoxygenase and/or peroxygenase-like peroxidase, the peroxidase-catalyzed oxygen transfer from H2O2. Moreover, the 3-dimensional (3-D) fluorescence spectral measurements showed that a colorless fluorescent Chl catabolite (FCC : Ex 350 nm/Em 455 nm) was produced with a concomitant decrease in Chl α level. The production of C-132-HO Chl α and colorless Rs-FCC was inhibited by heating the extracts. It appears that Chl α-porphyrin is catabolized by the proteins prepared from Raphanus sativus cotyledons via the following reaction : Chl α→C-132-HO Chl α→→colorless Rs-FCC (Chl-porphyrin oxygenolytic cleavage catabolite).
