In deep water rice plants, it is crucial for the leaves and upper parts of the shoot to remain above water. Which of the following plant growth regulators specifically promotes the rapid internode or petiole elongation required for this adaptation?

Step-by-step solution

According to NCERT, ethylene promotes rapid internode or petiole elongation in deep water rice plants. This specific physiological effect helps the leaves and upper parts of the shoot to remain above water. While gibberellic acid is generally known for causing internode elongation (such as in sugarcane or bolting in rosette plants), the rapid elongation in deep water rice is a specific function of ethylene. Auxin is involved in apical dominance and general stem growth, and cytokinin promotes cell division and delay