UBC Theses and Dissertations
A biochemical and microscopic analysis of adhesion in the kelp Alaria marginata Musor, Maisie
Adhesion is a critical first step in the successful recruitment of seaweeds. Kelp (Laminariales) sporophytes secrete adhesives from specialized rhizoid cells to anchor themselves to the substrate and withstand immense forces applied by waves. The composition of macroalgal adhesive has primarily been described in the Fucales as a “modified extension of the cell wall”, but the extent to which kelp adhesives are compositionally similar to fucoids is unknown. Moreover, the cellular organization of the attachment interface of kelps is poorly understood. To address this, rhizoid cells and adhesive from developing Alaria marginata sporophytes were examined with brightfield, fluorescence, and scanning electron microscopy to describe the organization of the attachment interface and biochemical composition of adhesives and walls in developing holdfasts. The primary holdfast is composed of elongated, thick-walled cortical cells and a meristoderm layer. New rhizoids appear to differentiate from meristoderm cells by modification of the meristoderm outer wall and elongation by tip growth. Rhizoid cells contain small spherical plastids distributed evenly along the length of the cell. Physodes are found along their length and phenolics localize in rhizoid walls. The highest resolution chemical analysis of kelp adhesives to date was provided by confocal microscopy, demonstrating adhesives are composed of fucose containing sulfated polysaccharides (FCSPs), alginate, and phlorotannins and dominated by BAM3 and BAM4 epitopes, not alginates as expected. Adhesives are biochemical extensions of the cell wall with distinct but variable stoichiometries, suggesting adhesives are more complex and dynamic than expected. Chemical analysis demonstrated that adhesives are likely underestimated in their complexity and identified weak points in our current understanding of kelp adhesives, for example calling into question the roles of phenolics and proteins. Finally, these results provide a baseline understanding of adhesive composition in kelps and establish biochemical methods to allow further examination of the developmental, ecological, and evolutionary dynamics of adhesion.
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