Digalactosyl-diacylglycerol-deficiency lowers the thermal stability of thylakoid membranes.
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.
Krumova
Sashka Boychova
SB
Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands. sashka@bio21.bas.bg
Laptenok
Sergey Petrovich
SP
Kovács
László
L
Tóth
Tünde
T
van Hoek
Arie
A
Garab
Gyozo
G
van Amerongen
Herbert
H
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*
D029681:Arabidopsis Proteins; D038983:Galactolipids; D045342:Light-Harvesting Protein Complexes; D011744:Pyrimidinones; C007388:digalactosyldiacylglycerol; C003954:merocyanine dye; C119967:DGD1 protein, Arabidopsis; D005700:Galactosyltransferases