Question

Which growth regulator promotes fruit ripening?

• A. Auxin
• B. Gibberellin
• C. Cytokinin
• D. Ethylene

Hint:

Ethylene is the only gaseous plant hormone.
It exhibits both growth-promoting and growth-inhibiting activities, but it acts primarily as an inhibitor of growth processes (senescence and abscission) while actively promoting fruit ripening.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
This question is from Plant Physiology, specifically the chapter "Plant Growth and Development" in the NCERT Class 11 curriculum.
We are asked to identify the plant hormone (growth regulator) that is responsible for promoting the ripening of fruits.

Step 2: Key Concept or Approach:
Ethylene ($\text{C}_2\text{H}_4$) is a simple, gaseous plant growth regulator that plays a major role in regulating physiological processes associated with aging, senescence, and the ripening of fruits.

Step 3: Detailed Explanation:

• Ethylene is synthesized in large quantities by tissues undergoing senescence and by fruits during the ripening phase.

• It acts as an autocatalytic trigger that accelerates the chemical breakdown of starches into sugars, the softening of cell walls, and the development of pigments and volatile compounds that give ripe fruits their flavor and aroma.

• During ripening in climacteric fruits (such as bananas, apples, and tomatoes), ethylene induces a dramatic increase in the rate of respiration, a phenomenon known as the respiratory climacteric.

• Let us review the functions of the other options:
-

Auxin: Promotes apical dominance, cell elongation, and root initiation.
-

Gibberellin: Promotes stem elongation, bolting, and seed germination.
-

Cytokinin: Promotes active cell division, delays senescence, and induces shoot formation.

• In commercial agriculture, Ethephon (an aqueous source of ethylene) is widely used to artificially and uniformly ripen fruits.



Step 4: Final Answer:
The plant growth regulator that promotes fruit ripening is Ethylene, which matches option (D).