Plant hormone
Plant Hormone
A Plant Hormone (pronunciation: /plɑːnt ˈhɔːrmoʊn/), also known as a phytohormone, is a chemical substance produced naturally in plants that regulates growth and development.
Etymology
The term "Plant Hormone" is derived from the Greek words "phyto" meaning plant and "hormone" meaning to excite or stimulate.
Definition
Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cells locally and, when moved to other locations, in other locations of the plant.
Types of Plant Hormones
There are five major types of plant hormones: Auxins, Gibberellins, Cytokinins, Ethylene, and Abscisic Acid. Each of these hormones has a unique role in the growth and development of plants.
- Auxins are the main hormones responsible for cell elongation in phototropism and gravitropism. They also control the differentiation of meristem into xylem and phloem.
- Gibberellins are responsible for stem elongation, germination, dormancy breaking, flowering, sex expression, enzyme induction.
- Cytokinins promote cell division and shoot formation.
- Ethylene is a gaseous hormone that promotes fruit ripening and opposes auxins in its actions.
- Abscisic Acid is generally known as a stress hormone as it induces dormancy and closes stomata.
Related Terms
- Phototropism - The orientation of a plant or other organism in response to light, either towards the source of light (positive phototropism) or away from it (negative phototropism).
- Gravitropism - The orientation of a plant or other organism in response to gravity, either towards the source of gravity (positive gravitropism) or away from it (negative gravitropism).
- Meristem - The undifferentiated tissue from which new cells are formed, as at the tip of a stem or root.
- Stomata - Tiny openings or pores in plant tissue that allow for gas exchange.
External links
- Medical encyclopedia article on Plant hormone
- Wikipedia's article - Plant hormone
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