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- growth stimulants made in cells at tip of roots/shoots, and in meristems, and can travel through plant via transport tissue/cell to cell,
- auxins bind to receptors on apical shoot membrane, which dec pH to 5 (optimal for enzymes to make cell wall more flexible), so stimulates stretching (and therefore growing) as cells mature, auxin destroyed and pH inc so enzymes inactive, and walls now rigid and no longer expand
- apical dominance (main central stem dominant); auxins suppress growth in lateral shoots (shoots further from apical grow better), if apical shoot removed, lateral shoots grow faster, and if auxins reapplied, lateral shoots suppressed
- low concs of auxins promote root growth, the more auxin that reaches roots, the more they grow (to a limit as high auxin concs inhibit root growth), if apical shoot removed, less auxin reaches root so root growth slows, replacing auxin at cut apical shoot restores growth of roots
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