They are produced in the stem, buds, and root tips. Auxin is a plant hormone produced in the stem tip that promotes cell elongation. Auxin moves to the darker side of the plant, causing the cells there to grow larger than corresponding cells on the lighter side of the plant. This produces a curving of the plant stem tip toward the light, a plant movement known as phototropism . Auxin also plays a role in maintaining apical dominance.
Buds are embryonic meristems maintained in a dormant state.
Auxin maintains this dormancy. As long as sufficient auxin is produced by the apical meristem , the lateral buds remain dormant. This will cause the lateral buds to break their dormancy and begin to grow. In effect, the plant becomes bushier. When a gardener trims a hedge, they are applying apical dominance.