title: Ubiquity and quantitative significance of detoxification catabolism of chlorophyll associated with protistan herbivory.
abstract: Chlorophylls are essential components of the photosynthetic apparati that sustain all of the life forms that ultimately depend on solar energy. However, a drawback of the extraordinary photosensitizing efficiency of certain chlorophyll species is their ability to generate harmful singlet oxygen. Recent studies have clarified the catabolic processes involved in the detoxification of chlorophylls in land plants, but little is understood about these strategies in aquatic ecosystem. Here, we report that a variety of heterotrophic protists accumulate the chlorophyll a catabolite 13(2),17(3)-cyclopheophorbide a enol (cPPB-aE) after their ingestion of algae. This chlorophyll derivative is nonfluorescent in solution, and its inability to generate singlet oxygen in vitro qualifies it as a detoxified catabolite of chlorophyll a. Using a modified analytical method, we show that cPPB-aE is ubiquitous in aquatic environments, and it is often the major chlorophyll a derivative. Our findings suggest that cPPB-aE metabolism is one of the most important, widely distributed processes in aquatic ecosystems. Therefore, the herbivorous protists that convert chlorophyll a to cPPB-aE are suggested to play more significant roles in the modern oceanic carbon flux than was previously recognized, critically linking microscopic primary producers to the macroscopic food web and carbon sequestration in the ocean.
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan. chiro@fc.ritsumei.ac.jp
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Kashiyama
authors.forename: Akiko
authors.initials: A
authors.lastname: Yokoyama
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kinoshita
authors.forename: Sunao
authors.initials: S
authors.lastname: Shoji
authors.forename: Hideaki
authors.initials: H
authors.lastname: Miyashiya
authors.forename: Takashi
authors.initials: T
authors.lastname: Shiratori
authors.forename: Hisami
authors.initials: H
authors.lastname: Suga
authors.forename: Kanako
authors.initials: K
authors.lastname: Ishikawa
authors.forename: Akira
authors.initials: A
authors.lastname: Ishikawa
authors.forename: Isao
authors.initials: I
authors.lastname: Inouye
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Ishida
authors.forename: Daiki
authors.initials: D
authors.lastname: Fujinuma
authors.forename: Keisuke
authors.initials: K
authors.lastname: Aoki
authors.forename: Masami
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Shinya
authors.initials: S
authors.lastname: Nomoto
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D005075:Biological Evolution; D002734:Chlorophyll / Q000378:metabolism*; D060434:Herbivory; D010788:Photosynthesis; D010944:Plants / Q000378:metabolism*
chemical_list: D002734:Chlorophyll