title: Involvement of zeaxanthin and of the Cbr protein in the repair of photosystem II from photoinhibition in the green alga Dunaliella salina.
abstract: A light-sensitive and chlorophyll (Chl)-deficient mutant of the green alga Dunaliella salina (dcd1) showed an amplified response to irradiance stress compared to the wild-type. The mutant was yellow-green under low light (100 micromol photons m(-2) s(-1)) and yellow under high irradiance (2000 micromol photons m(-2) s(-1)). The mutant had lower levels of Chl, lower levels of light harvesting complex II, and a smaller Chl antenna size. The mutant contained proportionately greater amounts of photodamaged photosystem (PS) II reaction centers in its thylakoid membranes, suggesting a greater susceptibility to photoinhibition. This phenotype was more pronounced under high than low irradiance. The Cbr protein, known to accumulate when D. salina is exposed to irradiance stress, was pronouncedly expressed in the mutant even under low irradiance. This positively correlated with a higher zeaxanthin content in the mutant. Cbr protein accumulation, xanthophyll cycle de-epoxidation state, and fraction of photodamaged PSII reaction centers in the thylakoid membrane showed a linear dependence on the chloroplast 'photoinhibition index', suggesting a cause-and-effect relationship between photoinhibition, Cbr protein accumulation and xanthophyll cycle de-epoxidation state. These results raised the possibility of zeaxanthin and Cbr involvement in the PSII repair process through photoprotection of the partially disassembled, and presumably vulnerable, PSII core complexes from potentially irreversible photooxidative bleaching.
authors.affiliation: Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA.
authors.forename: E S
authors.initials: ES
authors.lastname: Jin
authors.forename: J E
authors.initials: JE
authors.lastname: Polle
authors.forename: A
authors.initials: A
authors.lastname: Melis
mesh_terms: D002338:Carotenoids / Q000032:analysis; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D000460:Chlorophyta / Q000235:genetics* / Q000254:growth & development / Q000302:isolation & purification; D004591:Electrophoresis, Polyacrylamide Gel; D018506:Gene Expression Regulation, Plant; D008027:Light; D045342:Light-Harvesting Protein Complexes; D009687:Nuclear Proteins / Q000032:analysis / Q000378:metabolism; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism* / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D020524:Thylakoids / Q000378:metabolism / Q000528:radiation effects; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism*
chemical_list: C076679:Cbr protein, Dunaliella; D045342:Light-Harvesting Protein Complexes; D009687:Nuclear Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D002734:Chlorophyll; D002338:Carotenoids