Question

Which one of the following is odd one out?

• A. zeatin
• B. kinetin
• C. IAA
• D. gibberlin

Hint:

When evaluating "odd one out" questions for plant hormones, consider their primary physiological effects. Auxins like IAA are known for promoting apical dominance and inhibiting lateral bud growth, contrasting with cytokinins (Zeatin, Kinetin) and gibberellins, which are involved in breaking dormancy or stimulating growth.

Answer 1

The Correct Option is C

Step 1: Identify the class and primary roles of each substance.
All the given options are plant hormones (phytohormones), which regulate various aspects of plant growth and development.
(A) Zeatin: A naturally occurring plant hormone belonging to the cytokinin class. Cytokinins primarily promote cell division, differentiation, and are known to \textit{overcome apical dominance} and promote lateral bud growth.
(B) Kinetin: A synthetic plant hormone also belonging to the cytokinin class. Like zeatin, it promotes cell division and can \textit{break bud dormancy} and promote lateral bud development.
(C) IAA: Stands for Indole-3-acetic acid. It is the most common and important naturally occurring plant hormone of the auxin class. Auxins are known for promoting cell elongation, apical dominance (which \textit{inhibits} lateral bud growth), and root initiation.
(D) Gibberlin (Gibberellin): A class of naturally occurring plant hormones. Gibberellins are well-known for promoting stem elongation, and most importantly, \textit{breaking seed dormancy} and promoting germination. Step 2: Determine the commonality among three options and identify the "odd one out".
Let's consider the general effect on dormancy or growth from dormant states:
Zeatin (Cytokinin): Promotes the growth of lateral buds by \textit{overcoming apical dominance}, thus breaking bud dormancy.
Kinetin (Cytokinin): Similar to zeatin, it promotes cell division and \textit{lateral bud development}, acting against dormancy.
Gibberellin: Plays a crucial role in in \textit{breaking seed dormancy} and initiating seed germination.
IAA (Auxin): Promotes \textit{apical dominance}, which means it suppresses the growth of lateral buds, effectively maintaining a form of dormancy in these buds. While auxins have diverse roles, their role in apical dominance contrasts with the dormancy-breaking/growth-promoting effects of the other three. Step 3: Conclude the odd one out.
Zeatin, Kinetin, and Gibberellin are all involved in processes that \textit{break dormancy} (bud dormancy for cytokinins, seed dormancy for gibberellins) or promote growth from dormant structures. IAA, on the other hand, is primarily responsible for promoting apical dominance, which \textit{inhibits} lateral bud growth, thus maintaining a dormant state in lateral buds. This functional difference makes IAA the odd one out.