Langmuir monolayers of chloroplast membrane lipids

The present work explores the interactions between chloroplast membrane lipids in model experiments. Chloroplast membrane is characterized by a high proportion of galactolipids: MGDG — monogalactosyldiacylglycerol and DGDG — digalactosyldiacylglycerol. Since cadmium is known to be one of the most toxic heavy metal causing plant stress appearing e.g. as a reduction in plant growth, its influence on MGDG/DGDG monolayers was examined. For that reason the surface pressure–mean molecular area isotherms of these galactolipids and their mixtures on pure water and water solution of cadmium chloride (CdCl₂) were recorded. A classical thermodynamic analysis was performed on those isotherms, which involved calculating excess free energies of mixing to determine the miscibility properties. The strongest interactions between MGDG and DGDG are found at MGDG/DGDG stoichiometry corresponding to the composition of natural chloroplast membrane (MGDG:DGDG 2:1). Addition of CdCl₂ unfavourably influences these interactions.