Poster: Oxidative Stress

Abs # 138: Chlorophyll metabolism and its physiological significance in plants

Presenter:	Adachi, Masaru , adachim@cc.miyakonojo-nct.ac.jp
Authors	Adachi, Masaru  (A)   Kurata, Rie A (B)   Kurata, Hirofumi  (C)   Shimokawa, Keishi  (C)   Yamaguchi, Tokio  (D)
Affiliations:	(A): Miyakonojo National College of Technology (MNCT) Dept. of Chemistry & Science, (B): National Agriculture reserch center for Kyushu Okinawa region Upland Farming research Lab.of Upland Crop Utilization (C): Fac. Agr., Miyazaki Univ., Miyazaki (D): Dept. Biochem. Gen. Med. Res. Inst., Tokyo Medical and Dental Univ

The chlorophyll (Chl) breakdown takes place not only in the normal turnover of Chl, but also at specific stages of plant development, such as leaf senescence and fruit ripening. These phenomena would suggest that Chl degradation is strictly controlled by environmental and developmental factors (e.g., C₂H₄ and MeJA). However, the physiological function has long been poorly understood especially compared with Chl biosynthesis. cDNAs (chlorophyllase, Chl oxidation cleaving enzyme, RCCR/ACD2) responsible for Chl breakdown were isolated from Arabidopsis thaliana leaves and fruit peels. We previously reported experiments that examine the oxygenolytic ring cleavage mechanism of pheophorbide a derived from Chl a by pheophorbide a monooxygenase. The oxygenolytic cleavage reaction was studied using an in vitro system employing partially purified pheophorbide a oxygenase from senescent A. thaliana leaves. In vitro assays of ¹⁸O₂ incorporation in one of the pheophorbide a derivatives from the reactions show that of the two oxygen atoms inserted into the pigment, only the formyl oxygen originates from dioxygen. At present, Chl catabolic system and its functional analyses are now under going using by anti-bilirubin monoclonal antibody (designated 24G7). We would like to discuss the physiological function of the oxidative Chl catabolic system in the Chl turnover of higher plants. The new physiological function ( the human anticancer activity ) by the Chl metabolite from the tomato is also reported.