Plant Growth Harmons
Types of phytohormones
There are five types of phytohormones. 1. Auxin 2. Gibberellins 3. Cytokinins 4. Abscissic acid 5. Ethylene
Auxin: It is the most extensively studied phytohormone. They are very weak organic acid having unsaturated ring structure which are capable of promoting cell elongation specially of shoot when present in less concentration. Naturally it is called Indole 3- acetic acid. Auxins are compounds that positively influence cell enlargement, bud formation and root initiation. They also promote the production of other hormones and in conjunction with cytokinins, they control the growth of stems, roots, and fruits, and convert stems into flowers. Auxins, especially 1-Naphthaleneacetic acid (NAA) and Indole-3-butyric acid (IBA), are also commonly applied to stimulate root growth when taking cuttings of plants. The most common auxin found in plants is indole-3-acetic acid or IAA.
Gibberellins: Gibberellins are the second important phytohormones found in plants. They were discovered by a Japanese scientist E. Kurosawa. He observed the rice field and found that certain seedlings grew taller and turned thin and pale. He invented that his seedlings were infected by the fungus Gibberella fujikuroi.
Cytokinins and kinetins: Haberlandt was the first austrilian scientist who discovered the another active growth substances known as cytokinin. It was first obtained from coconut milk now it is naturally occurred. Skoog and his coworkers obtained the cytokinin in tobacoo pith callus. Natural cytokinin were obtained by Letham et al and named ‘ Zeatin’. Another natural cytokinins are dihydrozeatin, ribossylzeatin, methylthiozeatin. Structurally the kinetin is called furfural amino purine.