title: Enhanced alpha-tocopherol quinone levels and xanthophyll cycle de-epoxidation in rosemary plants exposed to water deficit during a Mediterranean winter.
abstract: Photosynthesis operates in a constantly shifting balance between efficient capture of solar energy and its rapid dissipation when captured in excess. In an attempt to better understand the role of alpha-tocopherol in plant photoprotection, we examined the changes in alpha-tocopherol quinone (alpha-TQ), in parallel with those of other low-molecular-weight antioxidants, in rosemary plants exposed to water deficit during a Mediterranean winter. Relative leaf water content (RWC) decreased from about 85% to approximately 65% in drought, but plants did not show symptoms of oxidative damage, as indicated by constant Fv/Fm ratios and malondialdehyde (MDA) levels. alpha-TQ was present at concentrations of 20 mmol per 100 mol of chlorophyll, and represented less than 1% of total tocopherol content in non-stressed leaves. Although alpha-tocopherol levels were not significantly altered, alpha-TQ reached up to 36 mmol per 100 mol of chlorophyll under stress (under both high light and after exposure to increasing water deficit at lower light intensities). Furthermore, both alpha-TQ and xanthophyll cycle de-epoxidation were strongly negatively correlated with the relative efficiency of photosystem II photochemistry (phiPSII) at midday. The biological significance of alpha-tocopherol and alpha-TQ in the network of photo- and antioxidative protection mechanisms evolved by plants to withstand stress is discussed.
authors.affiliation: Departament de Biologia Vegetal, Universitat de Barcelona, Facultat de Biologia, Avinguda Diagonal 645, 08028 Barcelona, Spain.
authors.forename: Maren
authors.initials: M
authors.lastname: Müller
authors.forename: Iker
authors.initials: I
authors.lastname: Hernández
authors.forename: Leonor
authors.initials: L
authors.lastname: Alegre
authors.forename: Sergi
authors.initials: S
authors.lastname: Munné-Bosch
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D003080:Cold Temperature; D008027:Light; D010788:Photosynthesis / Q000502:physiology; D027542:Rosmarinus / Q000502:physiology*; D024505:Tocopherols / Q000378:metabolism; D014867:Water / Q000502:physiology*; D024341:Xanthophylls / Q000378:metabolism*; D024502:alpha-Tocopherol / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D000975:Antioxidants; D024341:Xanthophylls; D014867:Water; C024838:alpha-tocopherol quinol; D002338:Carotenoids; D024502:alpha-Tocopherol; D024505:Tocopherols