- Polysaccharides are high-molecular-weight carbohydrates composed of long chains of monosaccharide units linked through glycosidic bonds. In plants, they are among the most abundant biomolecules, serving diverse structural and functional roles. They form the backbone of the plant cell wall, act as storage reserves of energy, and participate in defense, signaling, and interactions with the environment. Plant-derived polysaccharides are of great interest not only in plant biology but also in food, pharmaceutical, and biomaterials industries due to their bioactivity and physicochemical versatility.
- Structurally, plant polysaccharides can be broadly categorized into two main groups: structural polysaccharides and storage polysaccharides. Cellulose is the most abundant structural polysaccharide, consisting of linear chains of β-(1→4)-linked glucose units that assemble into microfibrils, imparting rigidity and tensile strength to the plant cell wall. Hemicelluloses, including xylans, mannans, and glucomannans, form a heterogeneous group of branched polysaccharides that interact with cellulose microfibrils, contributing flexibility and resilience. Pectins, rich in galacturonic acid residues, provide porosity and hydration, enabling cell adhesion and expansion. Together, these structural polysaccharides shape plant morphology and provide mechanical support.
- Storage polysaccharides, by contrast, primarily function as energy reserves. The most well-known is starch, composed of amylose (linear α-(1→4)-linked glucose) and amylopectin (branched α-(1→4) and α-(1→6)-linked glucose). Starch granules accumulate in plastids such as amyloplasts, serving as a vital energy source for plants and humans alike. In addition, certain specialized polysaccharides, like inulin (a fructan stored in roots and tubers of plants such as chicory and Jerusalem artichoke), function as alternative storage forms of carbohydrates. These molecules are notable for their prebiotic and dietary health benefits.
- Beyond their structural and storage roles, plant polysaccharides exhibit a wide range of biological activities that have attracted attention in medicine and biotechnology. Many polysaccharides, such as pectins, arabinogalactans, and β-glucans, demonstrate immunomodulatory, antioxidant, anti-inflammatory, and anticancer properties. Their ability to form viscous gels and interact with gut microbiota also underlies their nutritional value as dietary fibers. Moreover, plant-derived gums such as gum arabic, guar gum, and tragacanth gum are used as stabilizers, emulsifiers, and thickeners in food and pharmaceutical formulations.
