Auxin (From Greek ‘auxein: to grow) was first isolated from human urine.
They are classifying as follows:
(a) Indole-3 – acetic acid
(b) Indole 3- acetaldehyde
(d) Indole 3- pyruvic acid.
(a) 1-naphthalene acetic acid
(b) 2, 4- dichlorophenoxyacetic acid (2, 4 D)
(c) Indole- 3- butyric acid
(d) 2, 4, 5- trichlorophenoxyacetic acid (2, 4, 5- T).
(e) 2- Naphthyloxyacetic acid.
1. Cell division: Auxins induce cell division under following conditions:
(a) During injury for healing of wound.
(b) During grafting for producing graft union.
(c) During secondary growth by initiating cell divisions in the cambium.
(d) In culture tissue.
2. Root initiation:
Application of Indole acetic acid and some other Auxins to cut end of the stem stimulates the rate of formation and number of root initiated.
3. Shortening of internodes
4. Preventing of lodging:
Application of naphthyl acetamide, induces cell divisions in the cambium. This increases the amount of xylem in the basal part of the stem. It results in thickening and strengthening of the lower plant part, and thus prevents lodging.
6. Initiation of flowering:
Spraying of dilute solution of Auxins like 2, 4-D, and NAA, initiates flowering almost simultaneously. Flowering can be inhibited by spraying high concentration of Auxins.
Fruit development in the absence of pollination and fertilization is called parthenocarpic development and the fruits thus formed are called parthenocarpic fruits
8. Eradication of weeds:
Few synthetic Auxins also act as herbicides and are used to kill weeds.
9. Apical dominance:
Apical meristem suppresses the growth of lateral buds. This condition is known as apical dominance.
10. Abscission and senescence:
Auxins influence the development of abscission or separation layer. Application of Auxins to leaves and fruits can thus prevent their premature falling.