Cytokinins help overcome the (A)____.they promote (B)____whch helps in the delay of leaf senescence.

Answer

**Step-by-Step Solution:**

1. **Identify the Role of Cytokinins:** Cytokinins are plant hormones that play a crucial role in various aspects of plant growth and development. They are particularly known for their ability to promote cell division and delay aging in plants.

2. **Fill in the First Blank (A):** The first part of the question asks what cytokinins help overcome. The correct answer is "apical dominance." Apical dominance refers to the phenomenon where the growth of the main shoot (apical bud) inhibits the growth of lateral buds. Cytokinins help in overcoming this by promoting the growth of lateral buds.

3. **Explain Apical Dominance:** Apical buds produce hormones that suppress the growth of lateral buds. When cytokinins are applied, they can help to promote the growth of these lateral buds, allowing for a bushier plant structure.

4. **Fill in the Second Blank (B):** The second part of the question asks what cytokinins promote that helps delay leaf senescence. The answer is "nutrient mobilization." Cytokinins help in the mobilization of nutrients within the plant, which can delay the aging process of leaves.

5. **Explain Leaf Senescence:** Leaf senescence is the process of aging in leaves, which often leads to their eventual shedding. Cytokinins help to transfer nutrients to leaves that are low in nutrients, thereby delaying their senescence and preventing them from falling off prematurely.

6. **Final Answers:**
- (A) Apical dominance
- (B) Nutrient mobilization