Question

……….. is a plant hormone which is volatile in nature ?
A) Gibberellin
B) Ethylene
C) Abscisic acid
D) None of the above

Answer 1

Hint: Gaseous plant hormone is a growth-inhibiting phytohormone, mainly involved in the ripening of fruits, a few bacteria, several fungi, and all seed-plants produce it. Algae are not known to synthesize this hormone.

Complete answer:
Ethylene is the only gaseous growth hormone. It is a volatile, unsaturated hydrocarbon gas, present in the atmosphere as a component of smoke and other industrial gases. Denny observed that ethylene gas was highly effective in inducing fruit ripening. Zimmerman et al., found that it induces leaf abscission. Subsequent physiological studies led to the discovery of ethylene as a natural product of fruit ripening. It is now well established that ethylene is synthesized in ripening fruits, flowers, leaves, and even roots. It is synthesized from the amino acid methionine with the help of a number of enzymes. High concentrations of auxins promote ethylene production. Ethylene is usually present in minute quantities and causes marked effects. Although ethylene is a gaseous compound, it will not freely move through intercellular spaces. Its water-soluble precursor has been shown to move from roots to shoot along xylem transport.
-Ethylene prevents the elongation of stem and roots in the longitudinal direction. Ethylene inhibits the growth of lateral buds, promoting apical dominance.
-It is stated that auxins cause apical dominance in association with ethylene. It promotes flowering in some plants and triggers the ripening of fruits.
-Ethylene stimulates the formation of a separation layer, or abscission zone, in leaves, flowers, and fruits.

So, the correct answer is 'Ethylene'.

Note:
- A commercial compound ethephon is applied to stimulate the flow of latex in rubber plants
-This layer stimulates abscission by promoting the formation of hydrolases. Ethylene is responsible for breaking the dormancy of buds and seeds.
-Ethylene is applied to induce flowering in pineapple and mango and to hasten the ripening of tomatoes and citrus fruits. Ethylene treatment is done to increase the production of female flowers and fruits in some monocots.