Ethylene (plant hormone)
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Ethylene (or Ethene) functions as a plant hormone in plants. It stimulates the ripening of fruit, the opening of flowers, and the abscission of leaves. Its biosynthesis starts from methionine with 1-aminocyclopropane-1-carboxylic acid (ACC) as a key intermediate.
Ethylene was discovered when the byproducts of gas burning street lamps were shown to cause plant senescence in a greenhouse.
Location, Characteristics and Occasions for Synthesis Induction
- Directly induced by high levels of Auxin
- Found in germinating seeds
- Induced by root flooding
- Induced by drought
- Synthesized in nodes of stems
- Synthesized in tissues of ripening fruits
- Synthesized in response to shoot environmental, pest, or disease stress
- Synthesized in senescent leaves and flowers
- Rapidly diffuses
- Inhibiting effects of Ethylene on shoot growth (more specifically on stem elongation) reduced in the presence of light. Also Ethylene levels are decreased by light
- Released in mature cells when they do not have enough minerals and water to support both themselves and any dependent cells
- Released by all cells when they are experiencing conditions which would normally cause a mature shoot cell to produce Ethylene
Effects
- Stimulates leaf and flower senescence
- Induces leaf abscission mainly in older versus younger leaves.
- Induces seed germination
- Induces root hair growth – this increases the efficiency of water and mineral absorption
- Stimulates Epinasty – leaf petiole grows out, leaf hangs down and curls into itself
- Stimulates fruit ripening
- Induces the growth of adventitious roots during flooding
- Usually inhibits growth - just shoot growth
- Affects neighboring individuals
- Disease/wounding resistance
- Triple response when applied to seedlings – root ? and shoot growth inhibition and pronounced hypocotyl hook bending
- Inhibits stem swelling ? (Contradictory to the finding below – contradictory sources)
- Stimulates cell broadening (and lateral root growth)
- Interference with Auxin transport (when hormone levels are increasing)
- Directly or indirectly induces Auxin at high levels
- Inhibits the rate of metabolism of cells in the shoot (who are not already at their lowest metabolism rates) in response to an decrease in the levels minerals and/or water
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Auxins - Cytokinins - Ethylene - Gibberellins - Abscisic acid - Brassinosteroids - Jasmonates - Salicylic acid |