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

IV. PLANT ANATOMY AND MORPHOLOGY

Secondary Plant Metabolites

Phytohormones

Physiologically active substances synthesized in one plant organ and transported to other parts, where they stimulate or inhibit specific processes and Functions, are called phytohormones. They include growth stimulators (Auxins, Gibberellins, Cytokinins) and inhibitors (Abscisic acid, Ethylene). The former can accelerate or enhance certain processes within the Organism (such as plant growth), whereas the latter slow down chemical, biochemical, and physiological reactions (for instance, plant growth inhibitors suppress Cell elongation and expansion).

Auxins are produced by SHOOT and ROOT apices. They stimulate cell elongation and organ growth, and promote adventitious root formation in cuttings.

Gibberellins are produced by Fungi of the genus Gibberella and, in smaller quantities, by higher plants. They stimulate and accelerate Plant Growth and flowering, as well as parthenocarpy (The Development of seedless fruits).

Cytokinins activate Cell Division. Chemically, they are derivatives of Purines.

Abscisic acid inhibits growth, accelerates leaf abscission (leaf fall), and delays seed germination. High concentrations of abscisic acid are found in mature leaves, ripe fruits, buds, and dormant seeds. It inhibits both cell division and elongation. Ethylene accelerates the ripening and senescence of all plant Organs.

Certain plant-derived substances exert effects on Human and Animal organisms similar to those of animal Hormones. For example, Insulin-like substances have been detected in the leaves of chicory, dandelion, centaury, walnut, mistletoe, stinging nettle, and corn silk (stigmas), while sex-hormone-like substances are found in the leaves of common sage, field pennycress, and bittercress.

A constituent component of the thyroid hormone thyroxine is diiodotyrosine, which has been discovered in Iceland moss, dyer's greenweed, and spiny cocklebur. This hormone stimulates METABOLISM, growth, and tissue differentiation in humans and animals.