Plant Growth Regulators

 

 

Gibberellic Acids:

Gibberellic Acids are naturally occurring plant hormones. Gibberellic Acids are used in agriculture as plant regulators to stimulate both cell division and cell elongation that affect leaves as well as stems (eventually affecting fruit development and fruit set). Applications of Gibberellic Acids can also hasten plant maturation and seed germination. Gibberellic Acids are applied to growing crops (field crops, small fruits, vines and tree fruits), ornamental and shade tress, and ornamental plants, shrubs and vines.

 

Gibberellic acid will promote growth and elongation of cells. It affects decomposition of plants and helps plants grow if used in small amounts. Gibberellic acid is a very potent hormone whose natural occurrence in plants controls their development. Since GA regulates growth, applications of very low concentrations can have a profound effect.

 

 

 

 

 

 

Indole 3-butyric Acid:

The term auxin is derived from the Greek word auxein which means to grow. The first know auxin found in plants is Indole Acetic Acid (IAA). IAA is known to break apart in the presence of light. Other compounds with simular auxin effects have been proposed. The compounds currently used  as substitutes for IAA are Indole Propanoic Acid (IPA) and Indole Butyric Acid (IBA).

 

 

Action and Mechanism:

Auxins are absorbed through seed coats, roots, stems, and leaves. The Physiological actions Auxins are known to promote are:

• Stimulate cell elongation in roots and stems.

• Stimulate cell division in the cambium.

• Stimulate differentiation of phloem and xylem

• Promote root initiation on stem cuttings and lateral root development.

• Mediate the bending in response to gravity and light.

• Suppress growth of lateral buds.

• Delay leaf senescence

• Can inhibit or promote (via ethylene stimulation from high applied concentrations) leaf and fruit abscission.

• Can induce fruit setting and growth in some plants.

• Involved in assimilate movement toward auxin possibly by an effect on phloem transport.

• Delay of fruit ripening.

• Promotes (via ethylene production) femaleness in dioecious flowers.

• Stimulates the production of ethylene at high concentrations.

 

 

 

Kinetin:

Cytokinins are a class of growth regulators discovered in the 1950s. Cytokinins were extracted from yeast in 1955 by Miller and Skoog at the University of Wisconsin. Cytokinins promote cell differentiation and cell division in tobacco marrow. Later, scientists crystallized 6-furanmethyladenine (named kinetin) from DNA hydrolysis, and then chemically synthesized it. In 1963, Letham isolated and purified zeatin from immature corn seeds. Zeatin was also chemically synthesized. After 1963, more than 10 cytokinins were isolated from plants and microorganisms.