Abstract
We recently reported that cultivation of oat (Avena sativa L.) without phosphate resulted in plasma membrane phosphoglycerolipids being replaced to a large extent by digalactosyldiacylglycerol (DGDG) (Andersson, M. X., Stridh, M. H., Larsson, K. E., Liljenberg, C., and Sandelius, A. S. (2003) FEBS Lett. 537, 128-132). We report here that DGDG is not the only non-phosphorous-containing lipid that replaces phospholipids but that also the content of glucosylceramides and sterolglycosides increased in plasma membranes as a response to phosphate starvation. In addition, phosphate deficiency induced similar changes in lipid composition in the tonoplast. The phospholipid-to-glycolipid replacement apparently did not occur to any greater extent in endoplasmic reticulum, Golgi apparatus, or mitochondrial inner membranes. In contrast to the marked effects on lipid composition, the polypeptide patterns were largely similar between root plasma membranes from well-fertilized and phosphate-limited oat, although the latter condition induced at least four polypeptides, including a chaperone of the HSP80 or HSP90 family, a phosphate transporter, and a bacterial-type phosphoesterase. The latter polypeptide reacted with an antibody raised against a phosphate deficiency-induced phospholipase C from Arabidopsis thaliana (Nakamura, Y., Awai, K., Masuda, T., Yoshioka, Y., Takamiya, K., and Ohta, H. (2005) J. Biol. Chem. 280, 7469-7476). In plasma membranes from oat, however, a phospholipase D-type activity and a phosphatidic acid phosphatase were the dominant lipase activities induced by phosphate deficiency. Our results reflect a highly developed plasticity in the lipid composition of the plasma membrane and the tonoplast. In addition, phosphate deficiency-induced alterations in plasma membrane lipid composition may involve different sets of lipid-metabolizing enzymes in different plant tissues or species, at different stages of plant development and/or at different stages of stress adjustments.
Highlights
We recently reported that cultivation of oat (Avena sativa L.) without phosphate resulted in plasma membrane phosphoglycerolipids being replaced to a large extent by digalactosyldiacylglycerol (DGDG)
We previously suggested that the plasma membrane was the major target for the phospholipids-to-DGDG replacement [9]
Because separation by two-phase partition relies on surface properties [15], this result reflects that the composition of the apoplast-facing leaflet of the plasma membrane had been affected by cultivation under phosphate-limited conditions
Summary
Materials—Polyethylene glycol 3350 (Ultra) and lipid standards were from Sigma. TLC plates, organic solvents, inorganic salts, and other chemicals were from Merck. The 20.00-g two-phase systems used for microsomal membranes from 30 – 40 g of oat root tissue contained 6.2% (w/w) each of Dextran T500 and polyethylene glycol 3350 for membranes from well-fertilized tissue but 6.6% (w/w) of each polymer for membranes from phosphate-limited material. After a three-step two-phase partition [14], the plasma membrane-rich upper phase was diluted with 10 mM HEPES/KOH, pH 7.5, 0.25 M sucrose, and 10 mM KCl; pelleted twice at 100,000 ϫ gmax for 30 min; and resuspended in the same buffer. The peptides eluted in 3.5 l of 0.1% (v/v) formic acid in acetonitrile:water (1:1, by volume) analyzed by nano-LC-FTISR on a Thermo Finnigan LTQ-FT operated in data-dependent mode with pre-separation of the peptides on a C18 capillary column [21]. The data represent mean values Ϯ S.D. of three independent experiments
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