- A A sharp rise in cytokinin levels delivered from the root system
- B Decreased auxin and increased ethylene and ABA
- C An isolated drop in ambient temperature unaccompanied by hormonal change
- D An increase in available soil water supply to the root system
Correct answer: B. Decreased auxin and increased ethylene and ABA
Explanation: Leaf senescence: triggered by decrease in auxin/cytokinin and increase in ethylene and ABA. Chlorophyll breaks down, nutrients are reclaimed.
Concept context
Phases of plant growth, the five classical plant hormones plus newer ones, photoperiodism, vernalization, and seed dormancy.