BackgroundLeucine-rich repeat extensins (LRXs) are extracellular proteins consisting of an N-terminal leucine-rich repeat (LRR) domain and a C-terminal extensin domain containing the typical features of this class of structural hydroxyproline-rich glycoproteins (HRGPs). The LRR domain is likely to bind an interaction partner, whereas the extensin domain has an anchoring function to insolubilize the protein in the cell wall. Based on the analysis of the root hair-expressed LRX1 and LRX2 of Arabidopsis thaliana, LRX proteins are important for cell wall development. The importance of LRX proteins in non-root hair cells and on the structural changes induced by mutations in LRX genes remains elusive.ResultsThe LRX gene family of Arabidopsis consists of eleven members, of which LRX3, LRX4, and LRX5 are expressed in aerial organs, such as leaves and stem. The importance of these LRX genes for plant development and particularly cell wall formation was investigated. Synergistic effects of mutations with gradually more severe growth retardation phenotypes in double and triple mutants suggest a similar function of the three genes. Analysis of cell wall composition revealed a number of changes to cell wall polysaccharides in the mutants.ConclusionsLRX3, LRX4, and LRX5, and most likely LRX proteins in general, are important for cell wall development. Due to the complexity of changes in cell wall structures in the lrx mutants, the exact function of LRX proteins remains to be determined. The increasingly strong growth-defect phenotypes in double and triple mutants suggests that the LRX proteins have similar functions and that they are important for proper plant development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0548-8) contains supplementary material, which is available to authorized users.
SUMMARYPlant cell expansion is controlled by a fine-tuned balance between intracellular turgor pressure, cell wall loosening and cell wall biosynthesis. To understand these processes, it is important to gain in-depth knowledge of cell wall mechanics. Pollen tubes are tip-growing cells that provide an ideal system to study mechanical properties at the single cell level. With the available approaches it was not easy to measure important mechanical parameters of pollen tubes, such as the elasticity of the cell wall. We used a cellular force microscope (CFM) to measure the apparent stiffness of lily pollen tubes. In combination with a mechanical model based on the finite element method (FEM), this allowed us to calculate turgor pressure and cell wall elasticity, which we found to be around 0.3 MPa and 20-90 MPa, respectively. Furthermore, and in contrast to previous reports, we showed that the difference in stiffness between the pollen tube tip and the shank can be explained solely by the geometry of the pollen tube. CFM, in combination with an FEM-based model, provides a powerful method to evaluate important mechanical parameters of single, growing cells. Our findings indicate that the cell wall of growing pollen tubes has mechanical properties similar to rubber. This suggests that a fully turgid pollen tube is a relatively stiff, yet flexible cell that can react very quickly to obstacles or attractants by adjusting the direction of growth on its way through the female transmitting tissue.
29Leucine-rich repeat extensins (LRXs)
Bis(2,2‘-bipyridyl)(dihexadecyl-2-[2,2‘-dipyridylmethylene] malonate) ruthenium(II) dihexafluorophosphate, 1, formed multilayered micelles (denoted C16-micelles) upon sonication of aqueous suspensions. The C16-micelles collapsed upon transfer to gold, mica, and silicon surfaces and rearranged to planar bilayers. These bilayers appeared in different arrangements under the atomic force microscope. On graphite, the ruthenium headgroups and the alkyl chains lay flat and were both in direct contact with the substrate. On mica and silicon wafers, upright-standing interdigitated bilayers were found exclusively. Self-assembly of a dodecylsilane layer containing cracks on the silicon surface induced the formation of irregular double and triple layers of 1. Bulk polyethylene or octadecylthiol layers on gold with smooth surfaces did not disrupt the micelles. C18- and C22-micelles made of the corresponding homologues of 1 were much more stable on most surfaces, C14-micelles were destroyed on all surfaces. The variability of micelle−substrate interactions is discussed qualitatively.
πEwiger Traum, da˚man etwas nicht macht, sondern es entsteht™** Einf¸hrungDie spontane Selbstorganisation amphiphiler Lipide f¸hrt in w‰ssriger Lˆsung zu kleinen Molek¸laggregaten wie Micellen, planaren Molek¸ldoppelschichten (Myelin-Figuren), Vesikeln oder biologischen Membranen. Solche Aggregate sind weich und flexibel und verhalten sich wie Fl¸ssig-keiten. Das gilt auch dann, wenn sich die Lipidaggregate bei hˆheren Konzentrationen zu micellaren Rˆhrchen (hexagonale oder kubische Phasen) zusammenlagern oder wenn sie auf festen Substraten verankert werden (Langmuir-Blodgett(LB)-Filme). Der fluide Charakter r¸hrt daher, dass die Lipidaggregate nur von schwachen, ungerichteten Kr‰ften (Van-der-Waals-Kr‰fte, hydrophobe Effekte) zusammengehalten werden und sich die Kopfgruppen gegenseitig absto˚en. [1] Trotzdem sind die kugel-und stabfˆrmigen Micellen und Vesikel in Wasser und die planaren Lipidmonoschichten auf Festkˆrperoberfl‰chen strukturell gut definiert. Die Wirkung dieser ultrad¸nnen Lipidmembranen beschr‰nkt sich allerdings auf die Solubilisierung organischer Molek¸le in Wasser,
Leucine-rich repeat extensins (LRXs) are chimeric proteins containing an N-terminal leucine-rich repeat (LRR) and a C-terminal extensin domain. LRXs are involved in cell wall formation in vegetative tissues and required for plant growth. However, the nature of their role in these cellular processes remains to be elucidated. Here, we used a combination of molecular techniques, light microscopy, and transmission electron microscopy to characterize mutants of pollen-expressed LRXs in Arabidopsis thaliana.Mutations in multiple pollen-expressed lrx genes causes severe defects in pollen germination and pollen tube (PT) growth, resulting in a reduced seed set. Physiological experiments demonstrate that manipulating Ca 2+ availability partially suppresses the PT growth defects, suggesting that LRX proteins influence Ca 2+ -related processes.
Bis(2,2'-bipyridyl)(dioctadecyl-2-[2,2′-dipyridylmethylene] malonate) ruthenium(II) dihexafluorophosphate has been synthesized and was converted to an amphiphilic distearyl ester, 2b. Light-induced charge transfer from ruthenium to the pyridyl ligands occurred preferably to the malonate-type ligand. Its reduction potential was less negative by 400 mV than that of bipyridyl. Whereas the chloroform solution of the dioctadecyl ester 2b did not show any luminescence, the aqueous suspension produced between 30 and 150% of the emission intensity of the symmetrical ruthenium tris(bipyridine) complex in water. Transmission electron microscopy at cryogenic temperature of the sonicated aqueous solution of 2b revealed multilayer spheres without an entrapped water volume. The solid, onion-type sphere is totally filled with interdigitated bilayers of 2b and has therefore the character of a rigid, spherical micelle, not that of a vesicle. The headgroup layer consists of a back-to-back ruthenium complex bilayer; their alkyl chains point inward and outward. The spherical micelles were isolated from water in solid form and were stable on mica and gold surfaces for many hours as was shown by atomic force microscopy. Incorporation of 2b into fluid host vesicles or micelles lead to complete loss of luminescence. Various redox active water-or membrane-soluble agents quenched 30-50% of the emission, which indicates some energy transfer over several layers.
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