d. Ethylene :
It is the only gaseous growth regulator. Denny (1924) reported ethylene is effective in fruit ripening. Gane (1934) established that plants naturally synthesize ethylene. Crocker (1930) proposed that ethylene is the plant hormone responsible for fruit ripening. It is a simple gaseous hydrocarbon with essential role in the fruit ripening. The most widely used compound as a source of ethylene is ethephon. It is synthesized in roots, shoot apical meristem, ripening fruits etc.
Physiological effects and application of ethylene :
It promotes ripening of fruits like bananas, apples and mangoes. It stimulates initiation of lateral roots in plants and breaks the dormancy of bud and seed. It accelerates the abscission activity in leaves, flowers and fruits by forming of abscission layer. Ethylene inhibits the growth of lateral buds and causes apical dominance and retards flowering. It is associated with the enhancement of process of senescence of plants organs. It inhibits flowering in most of the plants except pineapple. It causes epinasty (drooping) of leaves and flowers. It increases activity of chlorophyllase enzyme causing degreening effect in banana and Citrus fruits.
