Slime cells on the surface of Eragrostis seeds maintain a level of moisture around the grain to enhance germination

Eragrostis is a cosmopolitan genus of the family Poaceae. Several wild species, including E. pilosa (L.) Beauv., are harvested for food, but the only cultivated crop-species is tef [E. tef (Zucc.) Trotter]. Despite its importance as a staple food and its plasticity to diverse environmental conditions, little is known about the structural and physiological strategies that adapt tef seeds to endure diverse and variable moisture regimes. Here, we report the presence of slime cells, a type of modified epidermal cell, covering the fruit of tef and its wild relative, E. pilosa. The slime produced by Eragrostis belongs to the ‘true' slime type, since it is exclusively composed of pectins. Pectin forms uniform layers on the cell wall inner surface, which are confined by a thin cellulose layer to prevent release into the cell lumen. In the presence of water, pectins quickly hydrate, causing swelling of the slime cells. This is followed by their detachment, which may be controlled by a thin cuticle layer on the fruit surface. The ability of slime to absorb and maintain moisture around the grain is thought to be an adaptive feature for Eragrostis growing in dry habitats. This retention of water by slime may create conditions that are suitable for rapid germinatio

The role of mucilage envelope in the endozoochory of selected plant taxa

Myxodiaspory (formation of mucilage envelope around seeds and fruits) is a common adaptation to dry habitats known in many families of Angiosperms. The mucilage envelope of some seeds seems to be also a unique morphological adaptation which protects myxospermatic diaspores while passing through the bird's digestive system. To evaluate the protective potential of mucilage, we fed the diaspores of seven plant species (representing three different mucilage types and three species of non-mucilaginous plants) to pigeons, Columba livia domestica. Twenty-four hours later, we collected the droppings of pigeons and examined a total of 18,900 non-destroyed diaspores to check for mucilage presence and germination ability. Out of all the examined diaspores, 4.5% were mucilaginous seeds. Among them, the highest number (12.2-13.5%) of viable diaspores belonged to the hemicellulosic type of mucilage (from Plantago species). Only 3.7% of germinating diaspores with pectic mucilage (Linum usitatissimum) were collected, and no seeds representing cellulosic mucilage (e.g., Ocimum basilicum). For non-mucilaginous plants, we collected only a few individual seeds (0.1% out of 8100 seeds used). We noted that the mucilaginous seeds found in the droppings were able to germinate; however, the germination ability was generally smaller in comparison to the control (i.e., not digested) seeds. Our results revealed that the presence of mucilage envelope has an impact on diaspore dispersal and survivability. With our experiments, we demonstrated for the first time that the mucilage envelope, especially of the non-cellulosic type, supports endozoochory. We also showed that non-mucilaginous seeds can be occasionally dispersed via endozoochory and are able to germinate. The results of our studies can explain the ways of plants distribution at a small, local scale as well as in long-distance dispersal, e.g., between islands or even continents

Plant Seed Mucilage as a Glue: Adhesive Properties of Hydrated and Dried-in-Contact Seed Mucilage of Five Plant Species

Seed and fruit mucilage is composed of three types of polysaccharides-pectins, cellulose, and hemicelluloses-and demonstrates adhesive properties after hydration. One of the important functions of the mucilage is to enable seeds to attach to diverse natural surfaces. Due to its adhesive properties, which increase during dehydration, the diaspore can be anchored to the substrate (soil) or attached to an animal's body and dispersed over varied distances. After complete desiccation, the mucilage envelope forms a thin transparent layer around the diaspore creating a strong bond to the substrate. In the present study, we examined the mucilaginous seeds of six different plant taxa (from genera Linum, Lepidium, Ocimum, Salvia and Plantago) and addressed two main questions: (1) How strong is the adhesive bond of the dried mucilage envelope? and (2) What are the differences in adhesion between different mucilage types? Generally, the dried mucilage envelope revealed strong adhesive properties. Some differences between mucilage types were observed, particularly in relation to adhesive force (Fad) whose maximal values varied from 0.58 to 6.22 N. The highest adhesion force was revealed in the cellulose mucilage of Ocimum basilicum. However, mucilage lacking cellulose fibrils, such as that of Plantago ovata, also demonstrated high values of adhesion force with a maximum close to 5.74 N. The adhesion strength, calculated as force per unit contact area (Fad/A0), was comparable between studied taxa. Obtained results demonstrated (1) that the strength of mucilage adhesive bonds strongly surpasses the requirements necessary for epizoochory and (2) that seed mucilage has a high potential as a nontoxic, natural substance that can be used in water-based glues

Current distribution of Pilularia globulifera L. in Poland : changes of geographical range and habitat preferences

Pilularia globulifera is a subatlantic European fern threatened with extinction. In Poland, it reaches the eastern border of its continuous range. Up to the end of the 20th century, it was observed here in 21 stands; only 2 of them existed by the second half of the century, so the species was categorized as critically endangered. Five new locations have been found in western and northwestern Poland during the last 10 years. Abundant and permanent populations grow in 3 locations, while 2 stands were ephemeral. All the current stands are situated in anthropogenic habitats with spontaneous vegetation, in oligotrophic to eutrophic waters. One of the new localities is about 280 km distant from the eastern range of the limit known previously. Pilularia forms its own plant community Pilularietum globuliferae, enters plots of Ranunculo-Juncetum bulbosi and occurs in mesotrophic to eutrophic rushes of Eleocharis palustris, Phragmites australis, Typha angustifolia and Equisetum fluviatile. Specimens are vigorous and regularly produce sporocarps

The micro- and nanoscale spatial architecture of the seed mucilage-Comparative study of selected plant species.

The seed coat mucilage envelope is formed just after hydration and surrounds the seed as a gel-like, transparent capsule. The mucilage envelope represents a special type of modified cell wall with all of the typical polysaccharides i.e. cellulose, pectins and hemicelluloses. The chemical composition of the mucilage is well-recognized but its structural organization remains unclear. In the presented study, we visualized the spatial architecture of the seed mucilage envelope of selected taxa which produce cellulose mucilage. Using critical point drying (CPD) and scanning electron microscopy (SEM) imaging, we demonstrated the structural details of the mucilage from the micro- down to the nanoscale. The mucilage, after CPD, had a visibly spatial structure which differed between the studied taxa; for example, a tangled organization in Arabidopsis thaliana and a more ordered arrangement in Ocimum basilicum were revealed. In general, the mucilaginous fibrillary components formed network made of long, unbranched, thicker cellulose fibrils together with shorter, thinner and, often branched other polysaccharides. Cellulose fibrils built a kind of scaffold for the rest of the components which were spread between them and/or covered their surface. The cellulose fibrils were attached to the seed surface, and therefore prevent the loss of the mucilage envelope during mechanical impacts. The loose architecture and special chemical composition of the mucilaginous cell wall is important for water binding and storage, which are crucial for the proper functioning of the seed mucilage envelope

Mucilage morphology.

<p>A-D <i>Ocimum basilicum</i> mucilage envelope. A. Unstained mucilage with visible small granules-starch grains; B-C. Staining with safranin revealed ‘tubule’-like structure of mucilage (arrows) with spirally-coiled cellulose fibrils which are closed on the top with the disc-like structure (arrow); D. <i>Ocimum basilicum</i>—dark color indicates starch grains stained with I in KI; E <i>Salvia sclarea</i> stained with safranin. Visible thick, partially uncoiled wavy, cellulose threads; F. <i>Artemisia annua</i> mucilage envelope stained with safranin with observable cellulose threads. <b>Abbreviations</b>: ct–cellulose threads, d—disc, sg–starch grains <b>Scale bars:</b> A, B– 100 μm, C, E– 50 μm, D– 20 μm, F– 200 μm.</p

Mucilage spatial architecture after hydration and CPD-drying visualized in SEM.

<p>A-C. <i>Arabidopsis thaliana</i>. A. The seed surface tightly covered with the mucilage; B. Mucilage components organized in a tightly-tangled net-like structure; C. Thicker cellulose fibrils (arrow) cross-linked by shorter chains (arrowhead); D-F. <i>Lepidium sativum</i>. D. The abundant mucilage envelope; E. Delicate fibrils form a densely-organized mucilage envelope; F. The main, unbranched cellulose fibrils (arrows) cross-linked by shorter chains (arrowhead). G-J. <i>Ocimum basilicum</i>. G. Mucilage forms an uneven envelope densely-covering the seed surface; H. Mucilage material organized in ‘tubules’ (arrows) attached to the seed surface (remainders of the cell wall of mucilage secreting cells); I. The site where the cellulose fibrils are attached to the seed surface, the ‘base of the tubule’; J. Cellulose fibrils (arrows) with other components (cross-linking polysaccharides) (arrowheads) spread between the fibrils; K-M. <i>Salvia sclarea</i>. K. The surface of the seed is covered with dense mucilage layer; L. The ‘tubules’ (arrows) structure of the mucilage envelope at higher magnification; M. The net-like structure at the site, where the cellulose fibrils constitute the main scaffold and where they are cross-linked by other components (matrix polysaccharides; arrowheads); N-P. <i>Artemisia annua</i>. N. Very delicate mucilage envelope; O. Parallel organization of the cellulose fibrils; P. Net-like structure of the mucilage with visible cellulose fibrils (arrows), granules covering their surface and crosslinking components (arrow heads); Q-S. <i>Artemisia leucodes</i>. Q. Very abundant mucilage envelope around the seed; R. Organization of the mucilage components in ‘tubules’ attached to the seed surface (arrows); S. The cellulose fibrils (arrows) very tightly covered with granules and cross-linked by shorter chains (arrowheads). <b>Abbreviations</b>: cf–cellulose fibrils, csp–crosslinking polysaccharides, cfb–cellulose fibril bundles, t–‘tubules’, ss–seed surface <b>Scale bars</b>: A, N, R– 500 μm, B, F, J– 1 μm, C, P, S– 500 nm, D, G, K, Q– 1 mm, E, I– 5 μm, H, L– 100 μm, M, O– 2 μm, K– 5 μm.</p