Mucilage secretion in seeds of Mediterranean species: hypotheses about its origin and function
An outstanding modification of the diaspore surface structure in many species of the Angiosperms is the presence of a mucilaginous layer. In these species, when the dry seed coat or the pericarp comes in contact with water, imbibes the outer cell wall completely and release a mucilaginous substance; a phenomenon known as myxospermy. Mucilage is composed of polysaccharides, mostly of pectins, and forms a gel like envelop around the diaspore that holds a considerable amount of water due to its hydrophilic nature. The seed weight as well as the volume increases significantly once the mucilage is released. Once it dries up, mucilage becomes stiff then gluing the diaspore to the surface on which it settles. There are differences in mucilage composition depending on the species. However, the main component of the mucilage of the pericarp and seed coat in all species are pectins. The polysaccharide and acidic qualities of mucilage make them very hydrophilic so in the presence of water they hydrate rapidly, thus forming super absorbent hydrogels. After water absorption, the mucilage breaks through the cell wall forming the mucilaginous envelope surrounding the seed. In addition to pectin, mucilage in some species also contains strands of elementary fibrils of cellulose of different widths embedded in the pectin envelope. Mucilage can therefore be distinguished in “true” mucilage consisting almost exclusively of pectin, and “cellulosic” mucilage, which, additionally to pectin, also contains cellulose fibrils. Cellulosic mucilage seems to add an additional strength to the pectin mucilage layer and has been hypothesized that it prevents mucilage of being washed away from the seed coat or fruit pericarp making the mucilage more rigid and thus, resulting in an enhanced adhesion of the mucilage to the diaspore.
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| Format: | tesis doctoral biblioteca |
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Universidad Complutense de Madrid
2014-05-06
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| Online Access: | http://hdl.handle.net/10261/141274 http://dx.doi.org/10.13039/501100003339 http://dx.doi.org/10.13039/501100004837 |
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