Plant hormones, also known as phytohormones, are chemical messengers that regulate plant growth and development. The five major plant hormones are: Auxins, Gibberellins, Cytokinins, Ethylene, and Abscisic Acid. These hormones control various physiological processes, including cell elongation, cell division, root formation, fruit ripening, and responses to stress.
1. Auxins:
Physiological effects:
Cell elongation, root formation, apical dominance (suppression of lateral bud growth), and inhibition of abscission (leaf or fruit drop).
Function:
Involved in promoting cell elongation, especially in the tips of roots and shoots, and in the formation of roots and flowers.
2. Gibberellins:
Physiological effects: Stem elongation, seed germination, fruit growth, and flowering.
Function: Promote stem growth and flowering, and help break seed dormancy.
3. Cytokinins:
Physiological effects: Cell division, delay of leaf senescence (aging), and shoot growth.
Function: Essential for cell division and leaf expansion, and they can also delay leaf aging.
4. Ethylene:
Physiological effects: Fruit ripening, abscission (leaf or fruit drop), and senescence (aging).
Function: A gaseous hormone that regulates fruit ripening, abscission, and senescence.
5. Abscisic Acid (ABA):
Physiological effects:
Induces dormancy in seeds and buds under stressful conditions, promotes stomatal closure (preventing water loss), and inhibits growth.
Function:
Regulates plant responses to stress, such as drought, and induces dormancy in seeds and buds.