Root Hair Adhesion in Posidonia oceanica (L.) Delile Seedlings: A Numerical Modelling Approach

Abstract

Animals and plants use adhesion to move, to anchor to a substrate, or to disperse seeds and fruits. Some plants developed a root pad as a common strategy to adhere to consolidated substrates. In the marine environment, the seagrass Posidonia oceanica attaches firmly to consolidated substrates via adhesive root hairs, forming a pad structure. We used novel morphological and ultrastructural data to develop a numerical model to study the dynamics of root hair adhesion during contact formation on rough consolidated substrates for this species. Morphological analysis, conducted using Scanning Electron Microscope, highlighted the role of root hair branching in pad formation. Transmission Electron Microscope microscopy allowed us to identify a glue-like substance at the pad/ substrate interface. The numerical model highlighted the role played by the cell wall's elasticity in pad formation and its importance in guaranteeing a firm adhesion. Furthermore, the effectiveness of these mechanisms was assessed at different simulated roughness levels. Increasing knowledge on the adhesion mechanism of seagrass to consolidated substrates could be pivotal in developing advanced seedling-based restoration protocols. The findings of this study could contribute to restoration activities planned to contrast seagrass regression. Transplanting initiatives using seedlings can now better address the search for suitable and low-impact ways to fix germinated plants to the substrate.

Getting a Grip on the Adhesion Mechanism of Epiphytic Orchids – Evidence From Histology and Cryo-Scanning Electron Microscopy

“…This glue-like substance probably helps to hold the root in place. The presence of glue had also been reported in epiphytic ferns (Moran unpublished observation in Zotz et al, 2021a), in climbing figs, root climbers and in seagrasses (Groot et al, 2003;Melzer et al, 2011;Steinbrecher et al, 2011;Huang et al, 2016;Zenone et al, 2020b). Melzer et al (2009) stated that English Ivy's root hairs exude a glue-like substance as roundish excretes.…”

“…In P. tricuspidata, the attachment pads appear to adapt their surface to the substrate geometry and exude an adhesive fluid that fills any space underneath the pad for adhesion to the substrate (Scherge and Gorb, 2001;Steinbrecher et al, 2011). Finally, Zenone et al (2020b) found that the root hair tips of seagrasses branch and form a pad-like structure, increasing the contact area with the corrugated rock surface. Additionally, a glue-like substance fills gaps between the pad base and the substrate, which further enhances contact area and increases adhesion.…”

Holding on or falling off: The attachment mechanism of epiphytic Anthurium obtusum changes with substrate roughness

“…These nanoparticles consist mainly of arabinogalactan proteins, which have very low viscosity, allowing effective wetting of the surface by the ivy adhesive (Huang et al, 2016). For seagrasses, Zenone et al (2020b) hypothesized that the glue could be the first step in securing attachment by facilitating the initial adhesion of the root to the substrate, functioning as a filler to fill the microcrevices of the substrate and enhance real contact area. In this study, the glue‐like substance was perhaps sufficient to fill the remaining spaces between root and substrate, especially so on the smoother substrate, hence providing an enlarged contact area responsible for promoting strong adhesion between the root and substrate.…”

“…It has been described for epiphytic orchids (Tay et al, 2021) and ferns (Testo and Sundue, 2014). Such a substance has also been observed at the root-substrate interface in numerous attachment systems of climbers and seagrasses (e.g., Darwin, 1867;Groot et al, 2003;Melzer et al, 2011;Steinbrecher et al, 2011;Bohn et al, 2015;Zenone et al, 2020b). For example, aerial roots of Syngonium podophyllum secrete a glue-like substance that was a composite of polysaccharides and proteins (Yang and Deng, 2017).…”

“…These nanoparticles consist mainly of arabinogalactan proteins, which have very low viscosity, allowing effective wetting of the surface by the ivy adhesive (Huang et al, 2016). For seagrasses, Zenone et al (2020b) hypothesized that the glue could be the first step in F I G U R E 5 Cryo-SEM micrographs of Anthurium obtusum with its root hairs adhering to the resin of roughness 30 µm. (A, B) Overview of root piece with the underside attached to the resin, after the root was peeled off the resin.…”