Question

Which hormone promotes internode/petiole elongation in deep water rice?

• A. Kinetin
• B. Ethylene
• C. 2, 4-D
• D. GA₃

Answer 1

The Correct Option is B

Correct Answer: Option 2 – Ethylene

The hormone that promotes internode and petiole elongation in deep-water rice is ethylene. Ethylene is a gaseous plant hormone known for its diverse regulatory functions in plant growth, development, and stress responses.

In the case of deep-water rice (Oryza sativa), ethylene plays a crucial role in helping the plant adapt to flooding conditions. When rice fields are submerged, oxygen availability decreases, and ethylene begins to accumulate within plant tissues due to its low diffusion under water.

This increased internal concentration of ethylene triggers a signaling cascade that promotes rapid elongation of internodes and petioles. This adaptive response enables the plant to keep its leaves above water, ensuring continued photosynthesis and survival in submerged environments.

Explanation of Other Options: 

Option 1 – Kinetin: Kinetin is a type of cytokinin that promotes cell division and delays senescence. It does not significantly influence internode elongation in deep-water rice.

Option 3 – 2,4-D: This is a synthetic auxin, mainly used as a herbicide. It can influence plant growth but is not associated with petiole elongation in deep-water rice.

Option 4 – GA₃ (Gibberellic Acid): Gibberellins are involved in stem elongation and seed germination. Although GA₃ contributes to elongation in general, in the specific case of deep-water rice, ethylene is the primary hormone responsible for the elongation response under submerged conditions.

Conclusion: Ethylene is the key plant hormone that enables deep-water rice to adapt to flooding through internode and petiole elongation. This question highlights the importance of hormonal regulation in plant responses to environmental stress, a crucial concept in plant physiology for NEET and other competitive exams.