Write an explanatory note on Ethylene.

(N/A) Ethylene is a simple gaseous $PGR$.
It is synthesized in large amounts by tissues undergoing senescence and ripening fruits.
Influences of ethylene on plants include horizontal growth of seedlings,swelling of the axis,and apical hook formation in dicot seedlings.
Ethylene promotes senescence and abscission of plant organs,especially of leaves and flowers.
Ethylene is highly effective in fruit ripening.
It enhances the respiration rate during the ripening of fruits.
This rise in the rate of respiration is called respiratory climacteric.
Ethylene breaks seed and bud dormancy,initiates germination in peanut seeds,and sprouting of potato tubers.
Ethylene promotes rapid internode/petiole elongation in deep-water rice plants.
It helps leaves/upper parts of the shoot to remain above water.
Ethylene also promotes root growth and root hair formation,thus helping the plants to increase their absorption surface.
Ethylene is used to initiate flowering and for synchronizing fruit-set in pineapples.
It also induces flowering in mango.
Since ethylene regulates so many physiological processes,it is one of the most widely used $PGR$ in agriculture.
Ethephon in an aqueous solution is readily absorbed and transported within the plant and releases ethylene slowly.
Ethephon hastens fruit ripening in tomatoes and apples and accelerates abscission in flowers and fruits (thinning of cotton,cherry,walnut).
It promotes female flowers in cucumbers,thereby increasing the yield.