Auxins: Apical dominance is when the growing apical bud at the tip of the shoot inhibits the growth of the lateral buds further down the shoot. Auxins are produced in the tip of the main shoot, and they inhibit the growth of the side shoots. When the tip of the main shoot is removed (e.g. by an animal), the side shoots grow. This shows that auxin produced in the apex of the main shoots and transported to the lateral buds to inhibit their growth.
When there are low concentrations of auxin in the side shoots, their growth is not inhibited, and so they can grow. This is also shown where, as the plant grows taller, the lateral buds at the bottom of the plant start to grow larger - they are further away from the main shoot, so there is a lower concentration of auxin and their growth is less inhibited.
Gibberellins: If genetically dwarf plants are treated with Gibberellic acid, the stems elongate considerably.
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