Mucilage secretion: an adaptive mechanism to reduce seed removal by soil erosion?

Seed mucilage as a defense against granivory is influenced by substrate characters

Many seeds are consumed by granivores despite numerous adaptations to prevent detection or exploitation. The environment can influence the efficacy of these defensive traits. Understanding the mechanisms by which environmental factors modify defensive efficacy is important for understanding spatial patterns of granivory and seed recruitment. Seed mucilage is a sticky coating that binds imbibed seeds to substrates; this attachment has been demonstrated to lessen exploitation by granivores. Seed mucilage as a defense has been recognized for decades, though rarely studied. Here, we investigated whether the environment alters this seed defense by addressing two questions: (1) Does substrate particle size affect attachment strength? (2) Does a change in particle size lead to changes in granivore-related mortality? In the field experiment, ants removed more seeds from finer substrates than their coarser counterparts. Across that same grit range, seeds took less force to dislodge when mucilage-bound to fine sandpaper; however, an investigation across a wider range of grits demonstrated nonlinearities occurred for many species, probably due to structural and chemical mucilage properties. Small differences in substrate grit lead to differential mortality in mucilaginous seeds due to alterations in attachment strength, suggesting that the defensive efficacy of this trait differs across the landscape. This work paves the way for a more integrative look at mucilaginous seeds. Seed mucilage is a widespread trait that is easily studied and has important demographic implications. It represents an ideal system to examine dispersal, germination, and granivory to gain a more holistic view of seed ecology.

Purification effects show seed and root mucilage's ability to respond to changing rhizosphere conditions

Mucilage, a polysaccharide-containing hydrogel, is hypothesized to play a key role in the rhizosphere as a self-organized system because it may vary its supramolecular structure with changes in the surrounding solution. However, there is currently limited research on how these changes are reflected in the physical properties of real mucilage. This study examines the role of solutes in maize root, wheat root, chia seed, and flax seed mucilage in relation to their physical properties. Two purification methods, dialysis and ethanol precipitation, were applied to determine the purification yield, cation content, pH, electrical conductivity, surface tension, viscosity, transverse 1 H relaxation time, and contact angle after drying of mucilage before and after purification. The two seed mucilage types contain more polar polymers that are connected to larger assemblies via multivalent cation crosslinks, resulting in a denser network. This is reflected in higher viscosity and water retention ability compared to root mucilage. Seed mucilage also contains fewer surfactants, making them better wettable after drying compared to the two root mucilage types. The root mucilage types, on the other hand, contain smaller polymers or polymer assemblies and become less wettable after drying. However, wettability not only depends on the amount of surfactants but also on their mobility, as well as the strength and mesh size of the network structure. The changes in physical properties and cation composition observed after ethanol precipitation and dialysis suggest that the polymer network of seed mucilage is more stable and specialized in protecting the seeds from unfavorable environmental conditions. In contrast, root mucilage is characterized by fewer cationic interactions and its network relies more on hydrophobic interactions. This allows root mucilage to be more flexible in responding to changing environmental conditions, facilitating nutrient and water exchange between root surfaces and the rhizosphere soil.

Anchorage by seed mucilage prevents seed dislodgement in high surface flow: a mechanistic investigation

BACKGROUND AND AIMS

Seed mucilage is a common and highly diverse trait shared among thousands of angiosperm species. While it has long been recognized that mucilage allows seeds to anchor to substrates (antitelechory), resisting abiotic and biotic dislodgement, we still lack a mechanistic understanding of this process.

METHODS

We propose a mechanistic model of how mucilage affects substrate anchorage and fluid resistance, ultimately contributing to dislodgement resistance. To test this model, we subjected mucilaginous seeds of 52 species, varying in eight measured seed traits, to 7 d of continuous water flow at a range of dislodgement potentials.

KEY RESULTS

Supporting our model, mucilage mass increased the force necessary to dislodge both dry and wet seeds; our measurement of the dislodgement force of dry mucilage explained time to dislodgement well. The effect size was remarkably large; increasing the standardized mucilage mass by 1 s.d. resulted in a 280-fold increase in the time to dislodgement. Fluid resistance was largely dependent on the speed of water flow and the seed's modified drag coefficient, but not seed traits. Neither mucilage expansion speed nor mucilage decay rate explained dislodgement potential well.

CONCLUSIONS

Our results suggest that the degree of anchorage to a substrate, measured with a simple dislodgement force assay, is highly predictive of mucilaginous seed retention in highly erosive environments. In contrast, we found that other seed and mucilage traits are of lesser importance to anchorage.

Seed Mucilage: Biological Functions and Potential Applications in Biotechnology

In plants, the diaspore (seed dispersal unit) may include a seed coat and/or pericarp to protect the embryo and assist in dispersion. In many species, the seed coat and/or pericarp secrete a gelatinous mixture of cell wall polysaccharides known as mucilage. In several species, mucilage synthesis, secretion and modification have been studied extensively as model systems for the investigation of plant cell wall structure and function. Despite this, efforts toward understanding the role of mucilage have received less attention. Mucilage has been hypothesized to impact seed dispersal through interaction with soil, protecting the seed in the gut following ingestion by animals or affecting the ability of seeds to sink or float in water. Mucilage has been found to influence seed germination and seedling establishment, most often during abiotic stress, probably by maintaining seed hydration when water is scarce. Finally, mucilage has been documented to mediate interactions with various organisms. Advances in transgenic technology should enable the genetic modification of mucilage structure and function in crop plants. Cells synthesizing mucilage may also be a suitable platform for creating custom polysaccharides or proteins with industrial applications. Thus, in the near future, it is likely that research on seed mucilage will expand well beyond the current focus. Here we summarize our understanding of the biological functions of mucilage and provide an outlook on the future of mucilage research.

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.

Seed Biology of Lepidium apetalum (Brassicaceae), with Particular Reference to Dormancy and Mucilage Development

Lepidium apetalum (Brassicaceae) is an annual or biennial weed widely distributed in Asia and Europe. The outer surface of L. apetalum seeds produces a large amount of mucilage. The primary aim of this study was to explore the dormancy characteristics and to determine how mucilage develops. The role of mucilage in water absorption/dehydration, the effects of after-ripening, gibberellin acid (GA₃), cold stratification and seed coat scarification on germination, the role of mucilage in germination and seedling growth during drought, and the progress of mucilage production during seed development were investigated. The results indicate that the best temperature regime for germination was 10/20 °C. After-ripening, GA₃ and seed coat scarification helped to break dormancy. Light promoted germination. Seedling growth of mucilaged seeds were significantly higher than those of demucilaged seeds at −0.606 and −1.027 MPa. Anatomical changes during seed development showed that mucilage was derived from the outer layer of the outer integument cells. Our findings suggest that seeds of L. apetalum exhibited non-deep physiological dormancy. The dormancy characteristics along with mucilage production give seeds of L. apetalum a competitive advantage over other species, and thus contribute to its potential as a weed. Effective control of this weed can be achieved by deep tillage.

Investigation of the Biodynamic Commands Use Effect on Mucilage Content and Germination Behavior in Three Ecotypes of Basil (<i>Ocimum</i> Sp.)

One of the most popular and useable of Aromatic plants are kinds of Basilica (Ocimumsp., Lamiaceae). This genius has different characteristics in behavior germination. Biodynamic agriculture is a new science in the research and especially, the position of stars and planet relative to each other, position of moon around the earth and seasonal change and Solar and lunar eclipses. We must to demonstrative of this theory. In this experiment, we want to record the effect of based on two calendars (biodynamic and Astronomic) on 3 ecotype of Basilica seed germination. The based on this experiment randomized block design with 3 replications. We use 50 seeds in Falcon tube (value=15ml) and record the weight and value of seed in tube. Then added 5ml of water in tube and shacked after moisturized and control and record of Mucilage value and another behavior of seed germination in lab condition. Results showed that different position of some planets such as moon and Mars and Jupiter had the highest effect, positive and significant effect on mucilage percent (p>95%), germination speed and length of root. Therefore, we could be express the lunar position had the highest effect on root length of local type and the lowest effect on purple basil. Mucilage percentage of seed coat in green basil had the highest content relative to another ecotype and this content was significant (p>95%). Then, the best suggest for produce of mucilage from the basil seeds, the best time is the first quadrature of moon.

Histological Features of the Olive Seed and Presence of 7S-Type Seed Storage Proteins as Hallmarks of the Olive Fruit Development

The production of olive oil is an important economic engine in the Mediterranean area. Nowadays, olive oil is obtained mainly by mechanical processes, by using the whole fruit as the primary raw material. Although the mesocarp is the main source of lipids contributing to olive oil formation, the seed also contributes to the olive oil composition and attributes. The olive seed is also becoming an interesting emerging material itself when obtained after alternative processing of the olive fruit. Such seed is used for the production of differential oil and a unique flour among other bioactive products, with increasing uses and applications in cosmetics, nutrition, and health. However, olive seed histology has been poorly studied to date. A complete description of its anatomy is described for the first time in the present study by using the 'Picual' cultivar as a model to study the development of the different tissues of the olive seed from 60 to 210 days after anthesis. A deep analysis of the seed coats, endosperm storage tissue and the embryo during their development has been performed. Moreover, a panel of other olive cultivars has been used to compare the weight contribution of the different tissues to the seed, seed weight variability and the number of seeds per fruit. In addition to the histological features, accumulation of seed storage proteins of the 7S-type (β-conglutins) in the seed tissues has been assessed by both biochemical and immunocytochemical methods. These hallmarks will help to settle the basis for future studies related to the location of different metabolites along the olive seed and mesocarp development, and therefore helping to assess the appropriate ripening stage for different commercial and industrial purposes.