title: Monogalactosyldiacylglycerol deficiency in Arabidopsis affects pigment composition in the prolamellar body and impairs thylakoid membrane energization and photoprotection in leaves.
abstract: Monogalactosyldiacylglycerol (MGDG) is the major lipid constituent of chloroplast membranes and has been proposed to act directly in several important plastidic processes, particularly during photosynthesis. In this study, the effect of MGDG deficiency, as observed in the monogalactosyldiacylglycerol synthase1-1 (mgd1-1) mutant, on chloroplast protein targeting, phototransformation of pigments, and photosynthetic light reactions was analyzed. The targeting of plastid proteins into or across the envelope, or into the thylakoid membrane, was not different from wild-type in the mgd1 mutant, suggesting that the residual amount of MGDG in mgd1 was sufficient to maintain functional targeting mechanisms. In dark-grown plants, the ratio of bound protochlorophyllide (Pchlide, F656) to free Pchlide (F631) was increased in mgd1 compared to the wild type. Increased levels of the photoconvertible pigment-protein complex (F656), which is photoprotective and suppresses photooxidative damage caused by an excess of free Pchlide, may be an adaptive response to the mgd1 mutation. Leaves of mgd1 suffered from a massively impaired capacity for thermal dissipation of excess light due to an inefficient operation of the xanthophyll cycle; the mutant contained less zeaxanthin and more violaxanthin than wild type after 60 min of high-light exposure and suffered from increased photosystem II photoinhibition. This is attributable to an increased conductivity of the thylakoid membrane at high light intensities, so that the proton motive force is reduced and the thylakoid lumen is less acidic than in wild type. Thus, the pH-dependent activation of the violaxanthin de-epoxidase and of the PsbS protein is impaired.
authors.affiliation: Department of Plant and Environmental Sciences, University of Gothenburg, SE-405 30 Gothenburg, Sweden. henrik.aronsson@dpes.gu.se
authors.forename: Henrik
authors.initials: H
authors.lastname: Aronsson
authors.forename: Mark A
authors.initials: MA
authors.lastname: Schöttler
authors.forename: Amélie A
authors.initials: AA
authors.lastname: Kelly
authors.forename: Christer
authors.initials: C
authors.lastname: Sundqvist
authors.forename: Peter
authors.initials: P
authors.lastname: Dörmann
authors.forename: Sazzad
authors.initials: S
authors.lastname: Karim
authors.forename: Paul
authors.initials: P
authors.lastname: Jarvis
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism; D004553:Electric Conductivity; D038983:Galactolipids / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D010088:Oxidoreductases / Q000378:metabolism; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D011521:Protochlorophyllide / Q000378:metabolism*; D018892:Proton-Motive Force; D020524:Thylakoids / Q000378:metabolism*; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D038983:Galactolipids; D045342:Light-Harvesting Protein Complexes; C489731:NPQ4 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D024341:Xanthophylls; C009909:monogalactosyldiacylglycerol; D011521:Protochlorophyllide; D010088:Oxidoreductases; C023290:violaxanthin de-epoxidase