| 1. |
- Aidemark, Mari, et al.
(författare)
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Trichoderma viride cellulase induces resistance to the antibiotic pore-forming peptide alamethicin associated with changes in the plasma membrane lipid composition of tobacco BY-2 cells
- 2010
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Ingår i: Bmc Plant Biology. - : Springer Science and Business Media LLC. - 1471-2229. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Background: Alamethicin is a membrane-active peptide isolated from the beneficial root-colonising fungus Trichoderma viride. This peptide can insert into membranes to form voltage-dependent pores. We have previously shown that alamethicin efficiently permeabilises the plasma membrane, mitochondria and plastids of cultured plant cells. In the present investigation, tobacco cells (Nicotiana tabacum L. cv Bright Yellow-2) were pre-treated with elicitors of defence responses to study whether this would affect permeabilisation. Results: Oxygen consumption experiments showed that added cellulase, already upon a limited cell wall digestion, induced a cellular resistance to alamethicin permeabilisation. This effect could not be elicited by xylanase or bacterial elicitors such as flg22 or elf18. The induction of alamethicin resistance was independent of novel protein synthesis. Also, the permeabilisation was unaffected by the membrane-depolarising agent FCCP. As judged by lipid analyses, isolated plasma membranes from cellulase-pretreated tobacco cells contained less negatively charged phospholipids ( PS and PI), yet higher ratios of membrane lipid fatty acid to sterol and to protein, as compared to control membranes. Conclusion: We suggest that altered membrane lipid composition as induced by cellulase activity may render the cells resistant to alamethicin. This induced resistance could reflect a natural process where the plant cells alter their sensitivity to membrane pore-forming agents secreted by Trichoderma spp. to attack other microorganisms, and thus adding to the beneficial effect that Trichoderma has for plant root growth. Furthermore, our data extends previous reports on artificial membranes on the importance of lipid packing and charge for alamethicin permeabilisation to in vivo conditions.
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| 2. |
- Porsbring, Tobias, 1974, et al.
(författare)
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The pharmaceutical clotrimazole affects marine microalgal communities at picomolar concentrations
- 2009
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Ingår i: SETAC Europe 19th Annual Meeting, Gothenburg, Sweden.
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Konferensbidrag (refereegranskat)abstract
- Clotrimazole is a pharmaceutical that belongs to the group of 14alpha-demethylase inhibiting fungicides. It is widely used and has been identified as a priority pollutant for the marine environment. However, the toxicity of clotrimazole to marine primary producers is largely unknown. We therefore sampled natural microalgal communities (periphyton) and exposed them to concentration series of clotrimazole over 4 days. Already 50 pmol/L clotrimazole caused a concentration-dependent accumulation of C14alpha-methylated sterol precursors, which coincided with a decrease in normal C14-desmethyl sterols. This indicates an inhibition of algal 14alpha-demethylases already at environmental concentrations. A clotrimazole concentration of 500 pmol/L reduced total sterol content to 64% of control level. Clotrimazole concentrations in the picomolar range also reduced biomass of the microalgal community, and interfered with the diatom xantophyll cycling otherwise used for photoadaptation. Concentrations of 10 nmol/L and higher caused large reductions in community growth, and changed community pigment profiles. As clotrimazole concentrations in the marine environment can reach 100 pmol/L, an environmental risk for marine primary producers cannot be excluded.
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| 3. |
- Porsbring, Tobias, 1974, et al.
(författare)
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Toxicity of the pharmaceutical clotrimazole to marine microalgal communities
- 2009
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Ingår i: Aquatic Toxicology. - : Elsevier BV. - 0166-445X. ; 91, s. 203-211
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Tidskriftsartikel (refereegranskat)abstract
- Clotrimazole belongs to the group of 14α-demethylase inhibiting fungicides. It is widely used in human and veterinary medicine and has been identified as a priority pollutant for the marine environment. However, the toxicity of clotrimazole to marine primary producers is largely unknown. We therefore sampled natural microalgal communities (periphyton) and exposed them to concentration series of clotrimazole over 4 days. 50 pmol/L clotrimazole caused a concentration-dependent accumulation of C14α-methylated sterol precursors, which coincided with a decrease in algal-specific C14-desmethyl sterols. This indicates an inhibition of algal 14α-demethylases already at environmental concentrations. A clotrimazole concentration of 500 pmol/L reduced total sterol content to 64% of control level. Community chlorophyll a content was affected by clotrimazole in a bi-phasic manner with first reductions becoming visible at 500 pmol/L, along with indications of an altered cycling of photoprotective xanthophyll pigments. Concentrations of 10–100 nmol/L and higher caused large reductions in community growth, and changed community pigment profiles in a concentration-dependent monotonous manner. The study further indicated that diatoms use obtusifoliol as a natural substrate for 14α-demethylase, just as higher plants do but also utilize norlanosterol.
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| 4. |
- Andersson, Mats X., 1977, et al.
(författare)
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The plasma membrane and the tonoplast as major targets for phospholipid- to-glycolipid replacement and stimulation of phospholipases in the plasma membrane
- 2005
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Ingår i: Journal of Biological Chemistry. ; 280:30, s. 27578-27586
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Tidskriftsartikel (refereegranskat)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.
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| 5. |
- Larsson, Karin E., 1958, et al.
(författare)
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LysoPC acyltransferase/PC transacylase activities in plant plasma membrane and plasma membrane-associated endoplasmic reticulum
- 2007
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Ingår i: BMC Plant Biology. - 1471-2229.
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Tidskriftsartikel (refereegranskat)abstract
- Background The phospholipids of the plant plasma membrane are synthesized in the endoplasmic reticulum (ER). The majority of these lipids reach the plasma membrane independently of the secretory vesicular pathway. Phospholipid delivery to the mitochondria and chloroplasts of plant cells also bypasses the secretory pathway and here it has been proposed that lysophospholipids are transported at contact sites between specific regions of the ER and the respective organelle, followed by lysophospholipid acylation in the target organelle. To test the hypothesis that a corresponding mechanism operates to transport phospholipids to the plasma membrane outside the secretory pathway, we investigated whether lysolipid acylation occurs also in the plant plasma membrane and whether this membrane, like the chloroplasts and mitochondria, is in close contact with the ER. Results The plant plasma membrane readily incorporated the acyl chain of acyl-CoA into phospholipids. Oleic acid was preferred over palmitic acid as substrate and acyl incorporation occurred predominantly into phosphatidylcholine (PC). Phospholipase A2 stimulated the reaction, as did exogenous lysoPC when administered in above critical micellar concentrations. AgNO3 was inhibitory. The lysophospholipid acylation reaction was higher in a membrane fraction that could be washed off the isolated plasma membranes after repeated freezing and thawing cycles in a medium with lowered pH. This fraction exhibited several ER-like characteristics. When plasma membranes isolated from transgenic Arabidopsis expressing green fluorescent protein in the ER lumen were observed by confocal microscopy, membranes of ER origin were associated with the isolated plasma membranes. Conclusions We conclude that a lysoPC acylation activity is associated with plant plasma membranes and cannot exclude a PC transacylase activity. It is highly plausible that the enzyme(s) resides in a fraction of the ER, closely associated with the plasma membrane, or in both. We suggest that this fraction might be the equivalent of the mitochondria associated membrane of ER origin that delivers phospholipids to the mitochondria, and to the recently isolated ER-derived membrane fraction that is in close contact with chloroplasts. The in situ function of the lysoPC acylation/PC transacylase activity is unknown, but involvement in lipid delivery from the ER to the plasma membrane is suggested.
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| 6. |
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| 7. |
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| 8. |
- Tjellström, Henrik, 1974
(författare)
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Interplay Between Phospholipids and Digalactosyldiacylglycerol in Phosphate Limited Oats
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phosphate is an essential nutrient. In most soils it is limiting, which has resulted in that phosphate is supplied as fertilizer to increase crop yield. Through evolution, plants have adapted several mechanisms to increase phosphate uptake from the soil and to household with acquired phosphate. A recent discovered house-holding mechanism is that plants utilize the phosphate bound in the headgroups of phospholipids: under phosphate-limiting conditions, phospholipids can be replaced by the non-phosphate containing lipid digalactosyldiacylglycerol (DGDG), previously assumed to reside in plastid membranes. The extra-plastidial phospholipid-to-DGDG replacement occurs in plasma membrane, tonoplast and mitochondria and has led to discoveries of new enzymes and metabolic pathways in plants. This thesis reports that phosphate limitation-induced biochemical and lipid compositional changes in oat root plasma membranes occur prior to any morphological changes in the oat. The phospholipase kinetics suggests that the plasma membrane is continuously supplied with phospholipids and that the products of plasma membrane lipase activities, phosphatidic acid and diacylglycerol, both are removed from the membrane. Furthermore, the phospholipid-to-DGDG replacement is reversible and when phosphate is resupplied the proportion of phospholipids increases and DGDG decreases in the oat root plasma membrane. Membrane lipids are more than a two dimensional liquid where membrane proteins reside. The specific lipid composition and distribution enables the membrane to function as a barrier to solutes and the interactions between lipids and proteins are important for the correct function. The lateral and transversal lipid distribution in oat root plasma membranes shows that DGDG does not replace phospholipids molecule for molecule; whereas phospholipids occur in both leaflets of the plasma membrane, DGDG is almost exclusively localized in the cytosolic leaflet. Model membrane studies suggests that one of the reasons that DGDG is absent in the apoplastic leaflet is its incompatibility to properly interact with the high sterol content of this leaflet. The oat seed contains enough phosphate to complete an entire generation without any exogenously supplied phosphate. The overall seed yield is much lower in phosphate-limited oat compared to fully fertilized oat, but the seed quality (starch, b-glucan, lipid, soluble protein) is very similar, including that the phospholipids-to-DGDG replacement is absent from the mature oat seeds, here membrane lipid composition is conserved. Oat thus produce a few seeds of acceptable quality rather than more seeds of poor quality.
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| 9. |
- Tjellström, Henrik, 1974, et al.
(författare)
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Lipid asymmetry in plant plasma membranes : phosphate deficiency-induced phospholipid replacement is restricted to the cytosolic leaflet
- 2010
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Ingår i: The FASEB Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 24:4, s. 1128-1138
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Tidskriftsartikel (refereegranskat)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 > 5mol% 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.
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| 10. |
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| 11. |
- Tjellström, Henrik, 1974, et al.
(författare)
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Membrane phospholipids as a phosphate reserve: the dynamic nature of phospholipid-to-digalactosyl diacylglycerol exchange in higher plants.
- 2008
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Ingår i: Plant Cell & Environment. ; 31:10, s. 1388-1398
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Tidskriftsartikel (refereegranskat)abstract
- ABSTRACT It is well established that phosphate deficiency induces the replacement of membrane phospholipid with non-phosphorous lipids in extra-plastidial membranes (e.g. plasma membrane, tonoplast, mitochondria). The predominant replacement lipid is digalactosyl diacylglycerol (DGDG). This paper reports that the phospholipid-to-DGDG replacement is reversible, and that when oat seedlings are re-supplied with radio-labelled phosphate, it is initially recovered primarily in phosphatidylcholine (PC). Within 2 d, the shoot contains more than half of the lipid-associated radiolabel, reflecting phosphate translocation. Oat was also cultivated in different concentrations of phosphate and the DGDG/PC ratio in roots and phospholipase activities in isolated plasma membranes was assayed after different times of cultivation. The DGDG/PC ratio in root tissue correlated more closely with plasma membrane-localized phospholipase D, yielding phosphatidic acid (PA), than with plasma membrane-localized PA phosphatase, the activity that results in a decreased proportion of phospolipids. The lipid degradation data did not reflect a significant involvement of phospholipase C, although a putative phospholipase C analogue, non-specific phospholipase C4 (NPC4), was present in oat roots. The correlation between increased phospholipase D activity and DGDG/PC ratio is consistent with a model where phospholipid-to-DGDG replacement involves formation of PA that readily is removed from the plasma membrane for further degradation elsewhere.
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