Mechanical and Adhesive Properties of the Cellulosic Seed Mucilage and its Role in Seed Dispersal

Plants have evolved diverse seed structures and properties that aid in their dispersal and protection from environmental influences. One widespread trait among thousands of flowering plants is myxodiaspory, or the ability of seeds, fruits, and diaspores to form mucilaginous coats upon hydration. In many plant species, cellulose nanofibers (CNFs), besides pectins and hemicelluloses, play a crucial role in maintaining the stability of this mucilage and enhance adhesive and mechanical properties. These properties are important for sticking to animal surfaces, such as fur or feathers for dispersal, to various other substrates and surfaces to prevent being carried off and damaged by insects and small vertebrates, protecting the seeds from other environmental influences, and ensuring germination. This thesis examines how CNFs contribute to the mucilage structure, adhesion, and dispersal mechanisms of Ocimum basilicum, Salvia hispanica, Collomia grandiflora, Linum usitatissimum, and Ecballium elaterium seeds. Using advanced imaging methods, such as scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), micro-CT, and high-speed videography, the resulting data were put in context with data from mechanical force measurements. Key findings from these methods include the following: (1) mucilage adhesion and mechanical properties vary within the hydration levels of the seeds, with maximum adhesion achieved, when dried in contact with surfaces. (2) CNFs play a critical role in enhancing the adhesion and mechanical stability of mucilage by contact splitting of the fibers, especially during dehydration, making them the primary component responsible for mucilage adhesion in some species. (3) Some highly specialized dispersal mechanisms, such as ballochory, can work synergistically with mucilage adhesion. 

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