title: Digalactosyl-diacylglycerol-deficiency lowers the thermal stability of thylakoid membranes.
abstract: We investigated the effects of digalactosyl-diacylglycerol (DGDG) on the organization and thermal stability of thylakoid membranes, using wild-type Arabidopsis thaliana and the DGDG-deficient mutant, dgd1. Circular-dichroism measurements reveal that DGDG-deficiency hampers the formation of the chirally organized macrodomains containing the main chlorophyll a/b light-harvesting complexes. The mutation also brings about changes in the overall chlorophyll fluorescence lifetimes, measured in whole leaves as well as in isolated thylakoids. As shown by time-resolved measurements, using the lipophylic fluorescence probe Merocyanine 540 (MC540), the altered lipid composition affects the packing of lipids in the thylakoid membranes but, as revealed by flash-induced electrochromic absorbance changes, the membranes retain their ability for energization. Thermal stability measurements revealed more significant differences. The disassembly of the chiral macrodomains around 55°C, the thermal destabilization of photosystem I complex at 61°C as detected by green gel electrophoresis, as well as the sharp drop in the overall chlorophyll fluorescence lifetime above 45°C (values for the wild type-WT) occur at 4-7°C lower temperatures in dgd1. Similar differences are revealed in the temperature dependence of the lipid packing and the membrane permeability: at elevated temperatures MC540 appears to be extruded from the dgd1 membrane bilayer around 35°C, whereas in WT, it remains lipid-bound up to 45°C and dgd1 and WT membranes become leaky around 35 and 45°C, respectively. It is concluded that DGDG plays important roles in the overall organization of thylakoid membranes especially at elevated temperatures.
authors.affiliation: Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands. sashka@bio21.bas.bg
authors.forename: Sashka Boychova
authors.initials: SB
authors.lastname: Krumova
authors.forename: Sergey Petrovich
authors.initials: SP
authors.lastname: Laptenok
authors.forename: László
authors.initials: L
authors.lastname: Kovács
authors.forename: Tünde
authors.initials: T
authors.lastname: Tóth
authors.forename: Arie
authors.initials: A
authors.lastname: van Hoek
authors.forename: Gyozo
authors.initials: G
authors.lastname: Garab
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002942:Circular Dichroism; D038983:Galactolipids / Q000378:metabolism*; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011744:Pyrimidinones / Q000378:metabolism; D013696:Temperature; D020524:Thylakoids / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D038983:Galactolipids; D045342:Light-Harvesting Protein Complexes; D011744:Pyrimidinones; C007388:digalactosyldiacylglycerol; C003954:merocyanine dye; C119967:DGD1 protein, Arabidopsis; D005700:Galactosyltransferases