Lipid asymmetry in plant plasma membranes: phosphate deficiency‐induced phospholipid replacement is restricted to the cytosolic leaflet

Abstract

As in other eukaryotes, plant plasma membranes contain sphingolipids, phospholipids, and free sterols. In addition, plant plasma membranes also contain sterol derivatives and usually <5 mol% of a galactolipid, digalactosyldiacylglycerol (DGDG). We earlier reported that compared to fully fertilized oats (Avena sativa), oats cultivated without phosphate replaced up to 70 mol% of the root plasma membrane phospholipids with DGDG. Here, we investigated the implications of a high DGDG content on membrane properties. The phospholipid-to-DGDG replacement almost exclusively occurred in the cytosolic leaflet, where DGDG constituted up to one-third of the lipids. In the apoplastic (exoplasmic) leaflet, as well as in rafts, phospholipids were not replaced by DGDG, but by acylated sterol glycosides. Liposome studies revealed that the chain ordering in free sterol/phospholipid mixtures clearly decreased when >5 mol% DGDG was included. As both the apoplastic plasma membrane leaflet (probably the major water permeability barrier) and rafts both contain only trace amounts of DGDG, we conclude that this lipid class is not compatible with membrane functions requiring a high degree of lipid order. By not replacing phospholipids site specifically with DGDG, negative functional effects of this lipid in the plasma membrane are avoided.-Tjellström, H., Hellgren, L. I., Wieslander, A., Sandelius, A. S. Lipid asymmetry in plant plasma membranes: phosphate deficiency-induced phospholipid replacement is restricted to the cytosolic leaflet.

Quantification of sterol lipids in plants by quadrupole time-of-flight mass spectrometry

“…At the same time, the content of FS was slightly increased in leaves of phosphate-deprived plants, but this change was not signifi cant, and FS remained unchanged in roots. These fi ndings were in accordance with data previously obtained from phosphate-limited oat ( 22 ). The amounts of SE were significantly increased in phosphate-deprived leaves and phosphate-deprived roots of the pho1 mutant.…”

“…SG and ASG also represent phosphate-free glycolipids and are localized to extraplastidial membranes, in particular to the plasma membrane. Previously, changes in plasma membrane lipid composition were recorded for oat roots ( 22,24 ). After growth on phosphate-defi cient medium, there was an increase in the proportion of SG and ASG relative to the total oat root plasma membrane lipids.…”

“…The role of other glycolipids during phosphate defi ciency, including SGs and ASGs, is less well understood. ASGs were found to be particularly increased in detergent-insoluble membranes of oat root plasma membranes during phosphate deprivation ( 22 ). At present, no data for the molecular species composition of SEs and of ASGs during normal conditions or phosphate deprivation are available.…”

“…Furthermore, no information on molecular species composition can be obtained. An alternative approach includes the separation and isolation of different sterol lipid classes via TLC and the quantifi cation of the sterol moieties by GC after hydrolyzation ( 11,15,22 ). This strategy provides data on the sterol composition of sterol lipid classes but not on the composition of individual molecular species of SEs and ASGs.…”

Lipid Biosynthesis and Protein Concentration Respond Uniquely to Phosphate Supply during Leaf Development in Highly Phosphorus-Efficient Hakea prostrata

“…A decline in phospholipid concentration during leaf senescence in other plant species increases membrane leakiness (Thompson et al, 1998). An extended lifetime for cellular membranes appears to be crucial for prolonging transport functions (Gniazdowska et al, 1999;Rilfors and Lindblom, 2002;Tjellström et al, 2010). This would give Proteaceae spp.…”