I believe the polysaccharide that provides rigidity and strength in plants would be cellulose. As this is one of the essential components found in the cell wall of plant cells.
Cellulose can be defined as the polysaccharide that provides plant stiffness and strength. Cellulose stands out for being an insoluble carbohydrate and resistant to various chemical reactions. Moreover, it is the major component of the plant cell cell wall, representing about 30% of the dry mass in primary walls and 50% to 80% in secondary walls.
Cellulose is part of the constitution of the cell wall. Here it ensures stiffness as it forms a large system of interwoven fibers. Although it is formed by the same starch compound, cellulose is not used as an energy source for the vegetable.
Only some organisms are capable of breaking down cellulose molecules for their use, such as bacteria, fungi and some animals. In ruminants, cellulose is used as a source of energy due to the presence of microorganisms in its digestive tract that can break down this product.
