BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

IV. PLANT ANATOMY AND MORPHOLOGY

Secondary Plant Metabolites

Glycosides

Compounds in which a sugar molecule is linked to a non-carbohydrate moiety. They readily hydrolyze into a sugar (glycone) and various non-carbohydrate components (aglycone). The bond between the glycone and the aglycone can be formed via oxygen atoms (O-Glycosides), nitrogen atoms (N-glycosides), sulfur atoms (S-glycosides, or thioglycosides), or carbon atoms (C-glycosides).

The Classification of glycosides is based on the Chemical Structure of their aglycone. The following groups are distinguished: monoterpene glycosides (bogbean, dandelion), cardenolides and bufadienolides (foxglove, pheasant's eye, lily of the valley), triterpene saponin glycosides (licorice, Greek valerian, ginseng, field horsetail), steroidal saponin glycosides (yam, devil's club), phenolic glycosides, phenol-oxy acids, and phenolic alcohols (bearberry, cowberry, roseroot), anthraquinone glycosides (aloe, buckthorn, purging buckthorn, rhubarb, horse sorrel), Flavonoids (hawthorn, motherwort, tansy, Water-pepper, knotweed), Coumarins and coumarin glycosides (parsnip, dill, mountain parsley), Tannins (smoke tree, sumac, thick-leaved bergenia, English oak, great burnet, tormentil, bird cherry, bilberry, grey alder), various Phenolic Compounds (male fern, chaga mushroom), thioglycosides (Sarepta mustard and black mustard), and cyanogenic (nitrile) glycosides (bitter almond, apricot seeds, apple trees, olive). Among glycosides, flavonoids and tannins (tanning agents) deserve special attention.

Flavonoids feature a sugar-conjugated molecule consisting of two benzene rings and one oxygen-containing heterocyclic ring. Most flavonoids are brightly colored in blue, red, or yellow. They are predominantly water-soluble and occur within The Cell sap of vacuoles. Flavonoids are responsible for the coloration of plants and include anthocyanidins, flavonols, Chalcones, and Aurones.

Anthocyanidins change their color depending on pH: in acidic solutions, their hue shifts from orange-red through bluish-red to pinkish-mauve; in neutral solutions (pH 7.0), they appear violet; and in alkaline solutions (pH 7.3–8.0), they turn blue.

Flavonols, chalcones, and aurones form a group of yellow plant pigments. The flavonol syringetin imparts a yellow color to the petals of meadow pea; isorhamnetin colors the petals of marigolds; gossypetin is found in cotton and primrose; and quercetagetin occurs in marigolds.

Chalcones and aurones are also referred to as anthochlor pigments. They impart a yellow coloration to the petals of carnations and garden snapdragons.