Ethylene

d. Ethylene : Ethylene is the only gaseous plant growth regulator. Denny reported in 1924 that ethylene was effective in ripening fruit; Gane established in 1934 that plants themselves naturally synthesise ethylene; and Crocker proposed in 1930 that ethylene is the hormone responsible for fruit ripening. It is a simple gaseous hydrocarbon, synthesised in roots, the shoot apical meristem and ripening fruit; the compound ethephon is the most widely used artificial source of ethylene, releasing the gas when dissolved in water.

Physiological effects and application of ethylene : Ethylene's best-known effect is promoting the ripening of climacteric fruits such as bananas, apples and mangoes. It also stimulates the initiation of lateral roots, breaks the dormancy of buds and seeds, and accelerates abscission -- the shedding of leaves, flowers and fruits -- by promoting the formation of the abscission layer. Ethylene inhibits the growth of lateral buds (reinforcing apical dominance) and retards flowering in most plants, though it uniquely promotes flowering in pineapple. It causes epinasty -- the downward drooping of leaves and flowers -- and hastens senescence generally. It also raises the activity of the enzyme chlorophyllase, which is what produces the 'degreening' effect (the breakdown of green chlorophyll to reveal underlying pigments) seen when ethylene is applied to banana and citrus fruit; commercially, this contro …