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Seed mucilage envelope as a new structural model in cell wall research

Periodic Reporting for period 1 - MuCellWall (Seed mucilage envelope as a new structural model in cell wall research)

Reporting period: 2016-09-01 to 2018-08-31

In the present project the mucilage envelope was investigated as a specific anatomical structure at the cell level, where it represents a modified secondary cell wall possessing specific chemical composition, structure and properties. Mucilaginous cell wall is composed of three main groups of polysaccharides i.e. pectins, hemicelluloses and cellulose, where pectins constitute very often the main component. All of the polysaccharides are interacting to each other by means of diverse bonds (hydrogen, covalent or ion). The cell wall has been an important area for many different research disciplines however many studies concentrated mostly on (bio)chemical or genetic analysis. Our detailed knowledge about the cell wall architecture is still limited. The structural studies were mostly based on various invasive techniques such as enzymatic or chemical treatments, which can destroy and/or influence the cell wall organization and its individual components. The issue of this project was addressed to visualization of the spatial architecture of the mucilaginous cell wall in its almost native stage by using less invasive methods which should not destroy its structure and allow to detect and to observe the individual polysaccharides, their shape, size and distribution. The results coming from this project, including applied research techniques, can be significant for the broad society as well as for the industry.
The morphological studies revealed that the mucilage envelope was organized as a thick, continuous, evenly distributed layer on the seed surface (e.g Plantago ovata) or thin layer spread unevenly (e.g. Linum usitatissimum). The biochemical analysis demonstrated differentiation in the chemical composition between the diaspores representing divers taxa. The presence of selected pectins, hemicelluloses and structural protein was proved for the mucilage envelope. The obtained results will allow, among them, to follow through the evolution of the changes in the cell wall composition and morphology. Many of mucilaginous diaspores are commercially used because of the mucilage envelope presence and its value as food additive or diet supplement. Therefore the results obtained in this project can also be exploit e.g. in the seed/food industry and can help to estimate of the mucilaginous seeds and fruits quality or storage methods.
Work performed on the mucilage architecture demonstrated significant differences in the structure and composition within and between diverse taxa e.g. stronger concentration of polysaccharides in the polyploids. It was revealed that the presence of cellulose microfibrils caused the attachment of mucilage to the seed surface and that the matrix polysaccharides were spread on the surface of microfibrils or between them. The results concerning spatial architecture of the mucilaginous cell wall can also be exploit in the bioenergy research e.g. wood technology to analyze the modifications of the cell wall in order to increase the biomass production (caloric value of firewood), in the textile production to analyze (at nano-level) the texture and structure of e.g. commercially obtained fibers.
The performed in this project experiments delivered also the data which demonstrated that the mucilage can help in the diaspore dispersal. It can be suppose that the specific mucilage composition, can be responsible for the dispersal success. The results can be exploit e.g. in the global studies of the seeds and fruits dispersion by animals. They can also be helpful in the environmental protection, agriculture or horticulture e.g. in predicting/preventing the potential of distribution of (invasive) plants which could endanger local floras or cultivations.
The work performed on the physical characteristic of mucilage demonstrated its strong adhesive properties. As it was observed the adhesion seems to depend on the mucilage biochemical composition and architecture. These data can be exploit e.g. in the production of ecological, biodegradable binding materials.
The morphology, genetic and (bio)chemical composition of the mucilage envelope has been recognized mainly for diaspores of Arabidopsis thaliana wild form and mutants. Whereas mucilaginous diaspores are known for more than 50 different families among them for plants with e.g. important medical or pharmaceutical value. There has been still lacking the information about the spatial arrangement and structure of the polysaccharides within the mucilage envelope (mucilaginous cell wall). In the present project the obtained results delivered clear evidences allowed for the first time to describing the mucilage spatial architecture. The obtained results revealed that the mucilage envelope is forming loosely organized net-like structure where the cellulose fibrils stay attached to the seed surface and constitute the main skeleton for the rest of the components (pectins, hemicelluloses and structural protein). Special preparation method i.e. Critical Point Drying (CPD) and visualization with Scanning Electron Microscopy (SEM), allowed to achieve the significant progress in the structural studies of the mucilaginous cell wall. For the first time it was possible to visualize and describe the shape, size and organization of the components within the mucilage envelope at the nanoscale. The standard microscopic techniques as well as diverse (bio)chemical or genetic analysis cannot provide such detailed structural information. This part of the project, including the applied combination of two techniques (CPD and SEM), can be exploit for elementary studies of the cell wall structure and function in different plant organisms. They can be use in the structural analysis of cell wall modifications or adaptations to diverse biotic or abiotic conditions. The described biochemical composition and spatial architecture of mucilage of diverse diaspores also demonstrated that these features can have an influence on the mucilage envelope ecological and physical properties. The results obtained in this project allowed to make a progress particularly in the studies concerning the mucilage envelope biochemical composition, spatial structure and physical features as well as in the mucilage ecology. The final conclusions coming from this project will be important in different ways allowing e.g.: 1. to follow through the evolution and adaptation of plants (cell wall structure) to different habitats, 2. to study and redesign the cell wall for industry - for the production of textile, timber, paper and biofuel, 3. to study the spatial structure and biomechanical features of the cell wall after diverse mutations and changes in the chemical composition which can be use e.g. in timber production and manufacturing, 4. to make new concepts in the nano-industrial technologies e.g. in the production of cellulose (nano)fibers, glues based on the natural components or in medicine for the production of bandages based on the mucilage envelope.