Question

What is apical dominance? How do auxin and cytokinin interact in determining the growth of lateral buds??

Short answer

Apical dominance is a phenomenon in plant growth where the apical bud inhibits the growth of lateral buds, allowing the plant to focus on upward growth. The plant hormones auxin and cytokinin play crucial roles in this process. Auxin is produced in the shoot apical meristem and inhibits lateral bud growth, while cytokinin is produced in the root tips and promotes lateral bud growth. The interaction between these hormones and their relative levels determine the growth patterns of lateral buds. In the release of apical dominance, auxin levels decrease when the apical bud is removed, allowing cytokinin levels to stimulate lateral bud growth and branch development.

Step-by-step solution

Understanding Apical Dominance

Apical dominance is a phenomenon in plant growth where the main shoot, or apical bud, inhibits the growth of lateral buds. This mechanism helps the plant to primarily focus on upward growth and conserve energy. The key hormones involved in this process are auxin and cytokinin.

Role of Auxin in Apical Dominance

Auxin is a plant hormone that is primarily produced in the shoot apical meristem, which is the tip of the growing shoot. This hormone has several functions in the plant, one of which is promoting cell elongation and thus the upward growth of the plant. Auxin moves downwards from the apical meristem with a higher concentration at the apex and reducing as we move downwards. In the context of apical dominance, auxin inhibits the growth of lateral buds, thus suppressing their development and allowing the apical bud to grow more. So, when the auxin level is high, lateral bud growth is suppressed.

Role of Cytokinin in Apical Dominance

Cytokinin is another plant hormone that plays a crucial role in promoting cell division and growth. Unlike auxin, cytokinin is predominantly produced in the root tips and moves upwards in the plant. Cytokinin has an opposite effect on lateral buds compared to auxin, i.e., it promotes the growth of lateral buds. Therefore, when cytokinin levels are high, the growth of lateral buds is stimulated.

Interaction between Auxin and Cytokinin in Determining Lateral Bud Growth

Both auxin and cytokinin have opposing effects on the growth of lateral buds, making their interaction in the plant important for controlling lateral bud growth. A high level of auxin inhibits lateral bud growth, whereas a high level of cytokinin stimulates it. In most plants, the apical bud produces large amounts of auxin that moves downwards and leads to apical dominance and the inhibition of lateral bud growth. However, if the apical bud is removed (e.g., by pruning), the auxin level in the plant decreases, and the balance between auxin and cytokinin shifts. In this case, the cytokinin levels become more significant, promoting lateral bud growth and leading to the development of branches. This phenomenon is known as the release of apical dominance. In conclusion, apical dominance in plants involves the regulation of lateral bud growth by the hormones auxin and cytokinin. Auxin, produced in the apical bud, suppresses lateral bud growth, whereas cytokinin, produced in the roots, promotes it. The interaction between these two hormones and their relative levels in the plant determine the overall growth patterns of lateral buds.