Cell wall structural changes lead to separation and shedding of biofouled epidermal cell wall layers by the brown alga A
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ORIGINAL ARTICLE
Cell wall structural changes lead to separation and shedding of biofouled epidermal cell wall layers by the brown alga Ascophyllum nodosum Laryssa Halat 1,2
&
Moira E. Galway 1
&
David J. Garbary 1,3
Received: 16 November 2019 / Accepted: 18 March 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Marine plants control the accumulation of biofouling organisms (epibionts) on their surfaces by various chemical and physical means. Ascophyllum nodosum is a perennial multicellular brown alga known to shed patches of epidermal material, thus removing epibionts and exposing unfouled surfaces to another cycle of colonization. While surface shedding is documented in multiple marine macroalgae, the cell and developmental biology of the phenomenon is almost unexplored. A previous investigation of Ascophyllum not only revealed regular cycles of epibiont accumulation and epidermal shedding but also stimulated the development of methods to detect the corresponding changes in epidermal (meristoderm) cells that are reported here. Confocal laser scanning microscopy of cell walls and cytoplasm fluorescently stained with Solophenyl Flavine 7GFE (Direct Yellow 96) and the lipophilic dye Rhodamine B (respectively) was combined with light and electron microscopy of chemically fixed or freeze-substituted tissues. As epibionts accumulated, epidermal cells generated thick, apical cell walls in which differentially stained central layers subsequently developed, marking the site of future cell wall separation. During cell wall separation, the outermost part of the cell wall and its epibionts plus the upper parts of the anticlinal walls between neighboring cells detached in a layer from multiple epidermal cells, exposing the remaining inner part of the cell wall to new colonizing organisms. These findings highlight the dynamic nature of apical cell wall structure and composition in response to colonizing organisms and lay a foundation for further investigations on the periodic removal of biofouling epibionts from the surface of Ascophyllum fronds. Keywords Ascophyllum nodosum . Cell wall . Biofouling . Epidermis shedding . Phaeophyceae
Introduction Like other marine organisms, the surfaces of multicellular marine macroalgae host diverse, dynamic, and interacting populations of epibionts, including bacteria, algae, protists, yeasts, and filamentous fungi, which may have neutral, beneficial or harmful effects on the basibiont (Wahl 1989; Wahl Handling Editor: David McCurdy * Moira E. Galway [email protected] 1
Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
2
Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
3
Jack McLachlan Laboratory of Aquatic Plant Resources, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
et al. 2012; Egan et al. 2012; Da Gama et al. 2014). Together, the epibionts and their basibiont host seaweed might be considered as an integrated community of organisms,
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