Apical dominance

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  Araucaria heterophylla in New Zealand

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  Weeping larch

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  Beckley Park topiary garden

Apical Dominance

Apical dominance is a phenomenon in plant physiology where the main, central stem of the plant is dominant over other side stems; it is the suppression of the growth of lateral buds by the apical bud. This dominance is maintained by the production of auxins, a class of plant hormones, by the apical bud.

Mechanism

The apical bud, located at the tip of the plant, produces auxins that are transported down the stem. These auxins inhibit the growth of lateral buds, which are located at the nodes along the stem. The concentration of auxins decreases as they move further from the apical bud, allowing lateral buds further down the stem to grow more freely. This gradient of auxin concentration is crucial for maintaining the plant's growth pattern.

Role of Auxins

Auxins are primarily responsible for the regulation of apical dominance. They are synthesized in the apical meristem and transported basipetally (from the top downwards) through the plant. Auxins promote cell elongation in the stem and inhibit the growth of lateral buds. This hormonal control ensures that the plant grows vertically, optimizing light capture and resource allocation.

Other Hormones Involved

While auxins play a central role in apical dominance, other plant hormones such as cytokinins and gibberellins also influence this process. Cytokinins, which are produced in the roots and transported upwards, can promote lateral bud growth and counteract the effects of auxins. Gibberellins can also promote stem elongation and influence bud growth.

Environmental Factors

Environmental factors such as light, water, and nutrient availability can affect apical dominance. For example, in low light conditions, plants may exhibit reduced apical dominance, allowing lateral buds to grow and increase the plant's surface area for light capture. Similarly, nutrient availability can influence hormone levels and thus affect the degree of apical dominance.

Practical Applications

Understanding apical dominance is important in horticulture and agriculture. Pruning, a common horticultural practice, involves cutting the apical bud to reduce apical dominance and encourage the growth of lateral branches. This can lead to bushier plants and increased fruit production. In agriculture, manipulating apical dominance can optimize crop yields and improve plant architecture.

Related Pages

• Auxin
• Cytokinin
• Gibberellin
• Plant hormone
• Pruning