Algal Cell Walls

Abstract Algae represent a diverse group of mostly photosynthetic eukaryotes that are profoundly important to Earth's ecosystems and human economy. These organisms possess a variety of extracellular matrix (ECM) components that are critical for multiple life functions. The most well‐studied ECMs are cell walls that are common to the green algae, red algae and brown algae. The typical cell wall consists of crystalline fibrillar polysaccharides (e.g. cellulose) that interact with a surrounding matrix of polysaccharides and proteoglycans. The matrix polysaccharides may be sulfated or acidic and some can complex various cations to form hard surfaces. Other distinct cell wall‐like coverings are found in algae including glycoprotein walls of volvocalean flagellates and silica‐complexed frustules of diatoms. Other noncell wall ECM types of algae include the amphiesma or dinoflagellates and the coccosphere of haptophytes. Key Concepts Algae possess a variety of extracellular matrices including cell walls. Most green, red and brown algae have cell walls consisting of a composite of a fibrillar polysaccharide framework associated with a polysaccharide/protein matrix. Unique cell walls are found in some algal groups including crystalline glycoprotein cell walls of volvocalean green algae and silica‐complexed cells walls of diatoms. Many algae do not have cell walls but have coverings made of complex scales and plates. The cell wall is synthesised and deposited externally through the coordinated action of the endomembrane and cytoskeletal systems.