title: The Arabidopsis aba4-1 mutant reveals a specific function for neoxanthin in protection against photooxidative stress.
abstract: The aba4-1 mutant completely lacks neoxanthin but retains all other xanthophyll species. The missing neoxanthin in light-harvesting complex (Lhc) proteins is compensated for by higher levels of violaxanthin, albeit with lower capacity for photoprotection compared with proteins with wild-type levels of neoxanthin. Detached leaves of aba4-1 were more sensitive to oxidative stress than the wild type when exposed to high light and incubated in a solution of photosensitizer agents. Both treatments caused more rapid pigment bleaching and lipid oxidation in aba4-1 than wild-type plants, suggesting that neoxanthin acts as an antioxidant within the photosystem II (PSII) supercomplex in thylakoids. While neoxanthin-depleted Lhc proteins and leaves had similar sensitivity as the wild type to hydrogen peroxide and singlet oxygen, they were more sensitive to superoxide anions. aba4-1 intact plants were not more sensitive than the wild type to high-light stress, indicating the existence of compensatory mechanisms of photoprotection involving the accumulation of zeaxanthin. However, the aba4-1 npq1 double mutant, lacking zeaxanthin and neoxanthin, underwent stronger PSII photoinhibition and more extensive oxidation of pigments than the npq1 mutant, which still contains neoxanthin. We conclude that neoxanthin preserves PSII from photoinactivation and protects membrane lipids from photooxidation by reactive oxygen species. Neoxanthin appears particularly active against superoxide anions produced by the Mehler's reaction, whose rate is known to be enhanced in abiotic stress conditions.
authors.affiliation: Dipartimento Scientifico e Tecnologico, Università di Verona, I-37134 Verona, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Dall'Osto
authors.forename: Stefano
authors.initials: S
authors.lastname: Cazzaniga
authors.forename: Helen
authors.initials: H
authors.lastname: North
authors.forename: Annie
authors.initials: A
authors.lastname: Marion-Poll
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001665:Binding Sites; D002499:Centrifugation, Density Gradient; D002734:Chlorophyll / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects / Q000528:radiation effects; D016166:Free Radical Scavengers / Q000378:metabolism; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000302:isolation & purification / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects / Q000528:radiation effects*; D010788:Photosynthesis / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D011485:Protein Binding / Q000187:drug effects / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D013696:Temperature; D024341:Xanthophylls / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D016166:Free Radical Scavengers; D045342:Light-Harvesting Protein Complexes; C489731:NPQ4 protein, Arabidopsis; D016877:Oxidants; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D017382:Reactive Oxygen Species; D024341:Xanthophylls; D002734:Chlorophyll; C005613:violaxanthin; C011947:neoxanthin