Galactolipids in Plant Membranes

Abstract

Photosynthetic membranes of plants contain high amounts of galactolipids (monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)) that are indispensable for the efficiency of photosynthetic light reactions. Galactolipids make up the bulk of the thylakoid membranes, and they are also found as integral constituents of the photosystems I and II. The presence of galactolipids is conserved from cyanobacteria and green algae to plants, in accordance with the endosymbiont theory. However, cyanobacteria and plants use different pathways for the synthesis of galactolipids. The ratio of MGDG to DGDG in the thylakoids is crucial for the stabilisation of the membrane bilayer. Under freezing and drought stress, a certain proportion of MGDG is converted into DGDG and oligogalactolipids to prevent fissions and fusions of chloroplast membranes. When plants are grown under phosphate‐limiting conditions, phospholipids are partially replaced by galactolipids in plastidial and extraplastidial membranes, thereby releasing phosphate for other essential cellular processes. Key Concepts: Galactolipids are phosphorous‐free glycoglycerolipids in plants. Galactolipids make up the bulk of photosynthetic membranes. Oxygenic photosynthesis in cyanobacteria and plants depends on the presence of galactolipids. The ratio of the two galactolipids carrying one or two galactoses in the head group is crucial for the maintenance of membrane integrity during stress. Phospholipids in plants are replaced by galactolipids during phosphate deprivation.

Insights Into Oxidized Lipid Modification in Barley Roots as an Adaptation Mechanism to Salinity Stress

“…The decrease of these plastidial lipids and inhibition of galactosyl transferases combined with impairment of plastid/ chloroplast membranes has been reported for salt stress before (Müller and Santarius, 1978;Shu et al, 2013;Bejaoui et al, 2016). The MGDG/DGDG ratio is associated with the physical state of plastid envelope membranes, and a higher MGDG/DGDG ratio suggests that a proportion of liquid-crystalline membranes are transformed into a hexagonal II (HII) non-bilayer phase (Dörmann and Benning, 2002;Dörmann, 2013). Lipids in the HII non-bilayer phase are organized into inverted micelles with the polar head groups on the inside and the hydrophobic tails on the outside (Jouhet, 2013).…”

“…GL including MGDGs/MGMGs, DGDGs/DGMGs, SQDGs, and GlcADGs are synthesized and mainly present in plastidial membranes (Dörmann, 2013;Okazaki et al, 2013). Compositional changes of these plastidial glycerolipids occur in response to drought, cold, freezing, and salinity, all of which can induce osmotic stress (Moellering et al, 2010;Tarazona et al, 2015).…”

Weathering the Cold: Modifying Membrane and Storage Fatty Acid Composition of Seeds to Improve Cold Germination Ability in Upland Cotton (Gossypium hirsutum L.)

“…As major components of plant membranes, lipids create hydrophobic barriers that separate cells from their environment and prevent diffusion of organelle contents in and out of a cell. Lipids are composed of a hydrophilic, polar head attached to a glycerol backbone and a hydrophobic tail composed of two fatty acids [25,26]. Membrane lipids in plants are synthesized via two distinct pathways, i.e., the prokaryotic and the eukaryotic pathways.…”

Beta galactosidases in Arabidopsis and tomato–a mini review

“…In plants, β-D-linked galactosyl residues are found in glycolipids (e.g. monogalactosyldiacylglycerol, MGDG [22]), proteoglycans (e.g. arabinogalactan proteins [23]) and cell wall polysaccharides (e.g.…”