Auxin was the first discovered plant hormone. It is certainly unknown the auxin producing area of a plant. The most active centers of auxin synthesis are shoot apical meristems, young leaves, and fruits. It is present in root tips but is believed to be transported there from the shoot rather than being synthesized there.
Auxin is responsible for the Abscission suppression, apical dominance, cell elongation; formation of roots in cuttings, fruit maturation, tropisms and xylem differentiation. This is the reason auxin is present in the tip region of the plant eg. root tips, shoot tips, buds. Auxin may not be produced in these regions but transport thereafter production.
Indole acetic acid (IAA) is the first auxin examined. Any substance in the plant reacts like IAA or resemble IAA called auxin. IAA (Auxin) can be produced artificially under certain conditions and applied to plants for desirable results. Some studies also showed that some compounds in the plants are converted into the IAA (AUXIN). In current present studies also mention that phenylacetic acid and chlorinated IAA are directly used in the plant as growth hormones.
It also needs to know that only natural occurring compounds are called hormone not artificially produced. Naphthaleneacetic acid is an artificially produced auxin is used for propagation of plants from leaf and stem cuttings.
Auxin growth hormone, as well as the concentration of particular hormone, in an area, is also important. Because hormones are active only at a particular concentration. If they are present in higher concentration, they become toxic to plant.