The fall and rise of apical dominance

The plant hormone auxin, synthesised in the shoot apex, moves down the stem and inhibits lateral branching. Auxin does not travel upward into the branches, so it must act indirectly; for example, through a second messenger. However, recent work on auxin transport suggests a possible additional mechanism whereby auxin transport in the stem prevents the establishment of auxin transport out of the branches, inhibiting their growth.