title: The giant kelp Macrocystis pyrifera presents a different nonphotochemical quenching control than higher plants.
abstract: Here the mechanisms involved in excitation energy dissipation of Macrocystis pyrifera were characterized to explain the high nonphotochemical quenching of chlorophyll a (Chla) fluorescence (NPQ) capacity of this alga. We performed a comparative analysis of NPQ and xanthophyll cycle (XC) activity in blades collected at different depths. The responses of the blades to dithiothreitol (DTT) and to the uncoupler NH4Cl were also assayed. The degree of NPQ induction was related to the amount of zeaxanthin synthesized in high light. The inhibition of zeaxanthin synthesis with DTT blocked NPQ induction. A slow NPQ relaxation upon the addition of NH4Cl, which disrupts the transthylakoid proton gradient, was detected. The slow NPQ relaxation took place only in the presence of de-epoxidated XC pigments and was related to the epoxidation of zeaxanthin. These results indicate that in M. pyrifera, in contrast to higher plants, the transthylakoid proton gradient alone does not induce NPQ. The role of this gradient seems to be related only to the activation of the violaxanthin de-epoxidase enzyme.
authors.affiliation: Departamento de Oceanografía Biológica, Centro de Investigación Científica y de Educación Superior de Ensenada, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC, México CP 22860.
authors.forename: Ernesto
authors.initials: E
authors.lastname: García-Mendoza
authors.affiliation: Departamento de Oceanografía Biológica, Centro de Investigación Científica y de Educación Superior de Ensenada, Km 107 Carretera Tijuana-Ensenada, Ensenada, BC, México CP 22860.
authors.forename: María Florencia
authors.initials: MF
authors.lastname: Colombo-Pallotta
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D003624:Darkness; D004229:Dithiothreitol / Q000494:pharmacology; D005453:Fluorescence; D044662:Macrocystis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000378:metabolism; D024341:Xanthophylls / Q000378:metabolism; D065146:Zeaxanthins
chemical_list: D045332:Photosystem II Protein Complex; D024341:Xanthophylls; D065146:Zeaxanthins; D000643:Ammonium Chloride; D002734:Chlorophyll; D004229:Dithiothreitol; D000077194:Chlorophyll A