41. Other examples of gravitropic mutants include those affecting the transport or response to the hormone auxin . 42. Apical dominance occurs because the shoot apical meristem produces auxin which prevents axillary buds from growing. 43. Several mathematical models making different assumptions on the way auxin influences PIN localisation explain different observations. 44. Some models assume PIN proteins polarize towards the neighbouring cell containing the highest cytosolic auxin concentration. 45. "' Fluroxypyr "'is an herbicide in the class of synthetic auxins . 46. In grafting, auxin promotes callus tissue formation, which joins the surfaces of the graft together. 47. To cause growth in the required domains, auxins must of necessity be active preferentially in them. 48. The " direct inhibition hypothesis " posits that these effects result from the cytokinin to auxin ratio. 49. This biotype was determined to have cross resistance to other auxin -like herbicides, especially clopyralid. 50. As a result, the PIN proteins generate a directional flow of auxin at the cellular scale.
