Ethylene is a volatile gaseous compound that stimulates transverse growth but retards longitudinal growth.
- Cousins confirmed its presence in ripened oranges, that hastened the ripening of stored unripe bananas.
- Formed in all parts of the plant i.e., roots, leaves, flowers, seeds.
- Maximum synthesis occurs in ripening fruits & tissues undergoing senescence.
- Synthesized from Methionine.
- Excess of auxin induces synthesis of ethylene.
- Biologically active at low concentration.
Physiological effects of ethylene:
- Causes horizontal growth of seedling, swelling of axis & apical hook formation in dicot seedling.
Horizontal growth of seedling
- Climacteric is increase in the rate of respiration in ripening fruits due to the production of ethylene. Loosening fruits. To prevent fruits from ripening oxygen must be eliminated from the environment in which the fruits are stored.
- Promotes senescence & abscission of leaves, flowers & fruits.
- Can break dormancy of buds, seeds & storage organs. E.g., peanut & sprouting of potato tubers.
- Causes elongation of internodes of deepwater rice plants, helping the upper part to remain above the water level.
- It promotes root growth & root hair formation thus increasing the surface area for absorption.
- Interferes with geotropic responses of seedlings.
- Promotes flowering in pineapple & mango. Helps in synchronizing fruit set.
- It is widely used in agriculture as it affects a range of physiological processes.
- Source of ethylene in agriculture is Ethephon, as it is readily absorbed in aqueous solution, transported to the various parts of the plant & releases ethylene slowly.
- It hastens fruit ripening in tomato, apple, banana.
- Accelerates abscission of excess flowers & fruits in cotton, cherry & walnut.
- Promotes the formation of female flowers in Cucumber.
- Rhizome, corm, tubers, seeds & storage organs can be made to sprout.