Apical dominance is the inhibition of the growth of lateral (side) buds by the apical bud at the tip of the shoot. While the apical bud is present, the shoot grows mainly upwards and the lateral buds lower down stay dormant. This helps the plant grow tall quickly towards the light.Apical dominance is caused mainly by auxin produced in the apical bud and transported down the stem.Evidence from experiments
- Plant B, apical bud removed: the lateral buds grow into side shoots.
- Plant C, apical bud removed and replaced with a paste containing auxin (IAA): the lateral buds stay dormant.
- A control with plain paste (no auxin) behaves like plant B, showing that it is the auxin, not the paste, that inhibits the lateral buds.This shows that auxin from the apex inhibits lateral bud growth.Role of other regulatorsCytokinins promote lateral bud growth, so they act antagonistically to auxin. Applying cytokinin directly to a lateral bud can make it grow even when the apical bud is present. The balance of auxin (from the shoot tip) and cytokinin (from the roots) decides whether a bud grows. Abscisic acid in lateral buds may also help keep them dormant.Buds furthest from the tip receive the least auxin, so they are the least strongly inhibited.UsesGardeners pinch out or prune shoot tips to remove apical dominance, so plants become bushier, with more side shoots, flowers and fruit. Hedges grow thicker when they are trimmed for the same reason.
- Plant B, apical bud removed: the lateral buds grow into side shoots.
- Plant C, apical bud removed and replaced with a paste containing auxin (IAA): the lateral buds stay dormant.
- A control with plain paste (no auxin) behaves like plant B, showing that it is the auxin, not the paste, that inhibits the lateral buds.This shows that auxin from the apex inhibits lateral bud growth.Role of other regulatorsCytokinins promote lateral bud growth, so they act antagonistically to auxin. Applying cytokinin directly to a lateral bud can make it grow even when the apical bud is present. The balance of auxin (from the shoot tip) and cytokinin (from the roots) decides whether a bud grows. Abscisic acid in lateral buds may also help keep them dormant.Buds furthest from the tip receive the least auxin, so they are the least strongly inhibited.UsesGardeners pinch out or prune shoot tips to remove apical dominance, so plants become bushier, with more side shoots, flowers and fruit. Hedges grow thicker when they are trimmed for the same reason.