Robust, universal, and persistent bud secretion adhesion in horse-chestnut trees

Abstract

Buds of horse-chestnut trees are covered with a viscous fluid, which remains sticky after long-term exposure to heat, frost, radiation, precipitation, deposition of aerosols and particles, attacks by microbes and arthropods. The present study demonstrates that the secretion does not dry out under arid conditions, not melt at 50 °C, and not change significantly under UV radiation or frost at a microscopic level. It is slightly swellable under wet conditions; and, it universally wets and adheres to substrates having different polarities. Measured pull-off forces do not differ between hydrophilic and lipophilic surfaces, ranging between 58 and 186 mN, and resulting in an adhesive strength up to 204 kPa. The mechanical and chemical properties of secretion resemble those of pressure-sensitive adhesives. The Raman, infrared, and nuclear magnetic resonance spectra show the clear presence of saturated aliphatic hydrocarbons, esters, free carboxylic acids, as well as minor amounts of amides and aromatic compounds. We suggest a multi-component material (aliphatic hydrocarbon resin), including alkanes, fatty acids, amides, and tackifying terpenoids embedded in a fluid matrix (fatty acids) comprising nonpolar and polar portions serving the universal and robust adhesive properties. These characteristics matter for ecological-evolutionary aspects and can inspire innovative designs of multifunctional, biomimetic pressure-sensitive adhesives and varnishes.

The water-soluble fraction of extracellular polymeric substances from a resource recovery demonstration plant: characterization and potential application as an adhesive

“…The underlying mechanism of the adhesive property of the EPS fraction remains unknown. Interestingly, reported studies suggested that some proteins, glycoconjugates (e.g., glycoproteins and lipopolysaccharides), and amino acids can be used as adhesives ( Abu-Lail and Camesano, 2003 ; Willett et al, 2005 ; Patel et al, 2013 ; Voigt et al, 2020 ; Heinritz et al, 2023 ).…”

The Plant Leaf: A Biomimetic Resource for Multifunctional and Economic Design

“…For example, colleters are multicellular secretory hair-like structures [ 90 ] that occur, for example, on the bud scales (modified leaves) of species of Aesculus (horse chestnut). They produce highly adhesive substances (mucilaginous secretions) that apparently protect developing plant organs [ 91 ]. Moreover, the secreted mucilaginous compounds may deliver a nourishing medium for symbiotic bacteria as in some species of Rubiaceae and Myrsinaceae [ 90 ].…”

Colleters, Extrafloral Nectaries, and Resin Glands Protect Buds and Young Leaves of Ouratea castaneifolia (DC.) Engl. (Ochnaceae)

“…The protective roles of some bud secretions have long been studied, as attested by the reports made by Groom [ 8 ], who stated that “ many buds have a great protective auxiliary in the secretion which covers and fills them. This secretion consists of gummy mucilage or resin, or both together; it is secreted by the general epidermis, by colleters, or by “leaf-teeth ”.” The substances present in bud secretions can protect vegetative and reproductive buds against several environmental stresses ([ 9 , 10 ] and references therein). These substances act complementary to the protection provided by enveloping shoot apical meristems by superimposing cataphylls and undeveloped leaves [ 11 ].…”

“…This secretion consists of gummy mucilage or resin, or both together; it is secreted by the general epidermis, by colleters, or by "leaf-teeth"." The substances present in bud secretions can protect vegetative and reproductive buds against several environmental stresses ( [9,10] and references therein). These substances act complementary to the protection provided by enveloping shoot apical meristems by superimposing cataphylls and undeveloped leaves [11].…”