Clinorotation impacts the plasmalemma lipid bilayer and its functional domains–rafts in plant cells.
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1
Institute of Botany (NAN Ukraine), Ukraine
Currently the presence of functional microdomains, which became known as “lipid rafts”, in the plasmalemma (Pl) of plant cells has been shown. It is supposed that rafts enriched on cholesterol and sphingolipids modulate the protein interrelation and in this way they include in many vitally important cell processes. In this work, we firstly analyzed the composition of fatty acids and sterols both in the Pl isolated from the roots of Pisum sativum seedlings grown during 6 days under slow horizontal clinorotation and in lipid rafts isolated from it. Rafts obtained from the root plasmalemma in the stationary conditions and under clinorotation were similar to those in other plant species. Clinorotation induced changes in the percentage of saturated and unsaturated fatty acids in the Pl and raft fractions. The percentage of cholesterol increased in Pl and especially in rafts under clinorotation. Nevertheless, the plasmalemma unsaturation index was similar to that in control for maintenance of the membrane fluidity necessary for normal cell viability. At the same time, a high level of cholesterol in lipid rafts clearly shows their increased rigidity in simulated microgravity, that can impact membrane activities. This work presents new information for future spaceflight and ground-based experimental designs.
Introduction
Properties and functions of biological membranes, especially plasmalemma (Pl), may consider as the most sensitive indicators of the influence of gravity or altered gravity on a cell. The Pl is one of the most dynamic supramolecular structures in a cell and it is the intermediate link between the cytoplasm and extracellular environment and involved in numerous processes such as transport of metabolites and ions, endocytosis, cell proliferation and differentiation, defence from pathogens. Currently it has been revealed the presence of functional microdomains with the specific localization and content of lipids and proteins in the Pl of plant cells, that became known as “lipid rafts”. It is supposed that rafts enriched on cholesterol and sphingolipids take part in many vitally important cell processes (Brown and London, 1998; Cacas et al., 2012). The investigations of lipid rafts help to explain the biochemiсal processes which occur in cell membrane in the normal conditions and in responses to stress and can’t be explained by using the other models.
It has been experimentally shown that Pl is gravisensitive: changes in the percentage of phospholipids and fatty acids in Pl under clinorotation (Polulyakh, 1988), as well as an impact of gravity on ion channels and fluidity of artificial and cellular membranes (Sieber et al., 2004). At the same time there is no information about the influence of real or simulated microgravity on lipid rafts in plant cells. The purpose of our work was to examine the composition of fatty acids and sterols in Pl and lipid rafts isolated from roots of Pisum sativum seedlings grown during 6 days under slow horizontal clinorotation.
Material and Methods
Roots of pea seedlings grown in 6 days in the stationary conditions and under clinorotation (2 rpm) were used. The Pl fraction was obtained using the two-phase water-polymer system optimized for pea seedling roots. Rafts were separated in the sucrose gradient under height speed centrifugation (31 000 rpm, 16 hours). The fractions of Pl and rafts were obtained with an ultracentrifuge “Optima L-90K” (Beckman Coulter, Germany) and controlled by the electron-microscopic method with a transmission electron microscope JEM 1230 (Jeol, Japan). The composition of saturated and unsaturated fatty acids, and sterols was determined by gas chromatography with a chromatograph HRGC 5300 (Carlo Erba Instruments, Italy).
Results and Discussion
It was shown that lipid rafts from the root PL of pea seedlings grown in the stationary conditions and under clinorotation have the appearance of thin tapes of 80–100 nm in length and 6–13 nm in width (Figure 1), they were similar to those in other plant species on the structure and size, and also enriched with cholesterol and saturated fatty acids. In the stationary conditions, it was found that saturated fatty acids prevailed in the fraction of rafts (64.5%), especially palmitic acid. The percentage of unsaturated fatty acids was 35,5 %, especially linoleic acid.
Under clinorotation, saturated fatty acids also prevailed in the fraction of rafts, and their percentage slightly increased up to 66.67%. Arachidonic acid prevailed among unsaturated fatty acids while the percentage of linoleic acid significantly decreased. The percentage of cholesterol increased 7 times in lipid rafts in comparison with control. Changes in the percentage of individual saturated and unsaturated fatty acids in Pl occurred under clinorotation but the unsaturation index was similar to that in control for maintenance of the membrane fluidity necessary for normal cell viability.
At the same time, the obtained data clearly show the increased rigidity of the lipid domains in the Pl over the stability of the membrane fluidity under simulated microgravity. Since the rafts contain protein complexes necessary for the perception and transduction of external signals, vesicular transport etc. (Lingwood and Simons, 2010), a significant increase in sterols may cause the changes in membrane permeability and functions of respective proteins, that will affect cell vital activity in microgravity.
Figure 1. Rafts obtained from roots of pea 6-day old seedlings (electron transmission microscopy). Arrows indicate rafts.
Acknowledgements
This work was supported by the National Academy of Sciences of Ukraine.
References
Brown, D.A., and London, E. (1998). Functions of lipid rafts in biological membranes. Annu. Rev. Cell Dev. Biol. 14, 111–136.
Cacas, J.-L., Furt, F., Le Guédard, M., Schmitter, J.M., Buré, C., and Gerbeau-Pissot, P. (2012). Lipids of plant membrane rafts. Progress in Lipid Research 51, 272–299.
Lingwood, D., and Simons, K. (2010). Lipid rafts as a membrane-organizing principle. Science 327, 46–50.
Polulyakh, Yu. A. (1988). Phospholipid and fatty acid content in the plasma membrane of pea root cells under clinorotation. Dokladyi AN USSR ser. Biol. 10, 67–69.
Sieber, M., Hanke, W., and Kohn, F.P.M. (2014). Modification of membrane fluidity by gravity. Open J. Biophys. 4, 105–111.
Keywords:
Pisum sativum,
Clinorotation,
plasmalemma,
rafts,
Sterols
Conference:
39th ISGP Meeting & ESA Life Sciences Meeting, Noordwijk, Netherlands, 18 Jun - 22 Jun, 2018.
Presentation Type:
Extended abstract
Topic:
Plants
Citation:
Kordyum
E,
Bulavin
I and
Vorobyova
T
(2019). Clinorotation impacts the plasmalemma lipid bilayer and its functional domains–rafts in plant cells..
Front. Physiol.
Conference Abstract:
39th ISGP Meeting & ESA Life Sciences Meeting.
doi: 10.3389/conf.fphys.2018.26.00012
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Received:
02 Dec 2018;
Published Online:
16 Jan 2019.
*
Correspondence:
Prof. Elizabeth Kordyum, Institute of Botany (NAN Ukraine), Kiev, Ukraine, cellbiol@ukr.net