Glycosides

Glycosides, class of complex chemical compounds in plants. They are broken down by plant enzymes into sugars, among which glucose is generally included, and into other substances. The term glucoside is often used synonymously with glycoside, but in its more specific meaning it refers to glycosides that yield glucose.

Each glycoside in a plant is hydrolyzed (converted in a reaction with water) by an enzyme, usually a specific enzyme found in the same plant. The enzyme emulsin, however, causes hydrolysis of several glycosides. The enzymes and glycosides are stored in separate plant cells until the reaction products of the glycosides are needed and the enzymes are activated.

Glycosides are believed to serve several purposes in the plant. Glycosides are bitter tasting, and it is believed that they help keep birds and insects from eating seeds and fruit before they are fully grown, by which time the glycosides have been converted to sweet sugars. When a plant tissue is bruised, the enzymes hydrolyze the glycosides into products, such as phenol compounds and acids that have an antiseptic action and prevent decay of the damaged tissues.

Glycosides are soluble in water and are obtained from plants by water extraction. They are mostly colorless crystalline solids with a bitter taste. Simple glycosides have been synthesized in the laboratory, and several hundred glycosides have been extracted from plants and used for many purposes. Among the important glycosides are indican (see Indigo Plant), used for dyeing; digitalin (see Digitalis), used in medicine; and the saponins, foaming agents used industrially and medicinally.