`star` Auxin
`star` Gibberellins


● `color{Auxins}"Auxins"` (from Greek ‘auxein’ : to grow) was first isolated from `color{violet}"human urine"`.

● The term ‘auxin’ is applied to the `color{violet}"indole-3-acetic acid (IAA)"`, and to other natural and synthetic compounds having certain `color{violet}"growth regulating properties"`.

● They are generally produced by the `color{violet}"growing apices"` of the stems and roots, from where they `color{violet}"migrate to the regions"` of their action.

● Auxins like `color{violet}"IAA and indole butyric acid (IBA)"` have been isolated from plants.

● `color{violet}"NAA (naphthalene acetic acid)"` and `color{violet}"2, 4-D (2, 4-dichlorophenoxyacetic)"` are synthetic auxins.

● All these auxins have been used extensively in `color{violet}"agricultural and horticultural practices."`

● They help to `color{violet}"initiate rooting"` in stem cuttings, an application widely used for `color{violet}"plant propagation"`.

● Auxins `color{violet}"promote flowering"` e.g. in pineapples.

● They help to `color{violet}"prevent fruit and leaf drop"` at early stages but promote the `color{violet}"abscission"` of older mature leaves and fruits.

● In most higher plants, the `color{violet}"growing apical bud"` inhibits the growth of the lateral (axillary) buds, a phenomenon called `color{Brown}"apical dominance"`.

● `color{violet}"Removal of shoot tips"` (`color{Brown}"decapitation"`) usually results in the growth of lateral buds.

● It is widely applied in `color{violet}"tea plantations, hedge-making"`.

● Auxins also `color{violet}"induce parthenocarpy"`, e.g., in tomatoes.

● They are widely used as `color{violet}"herbicides. 2, 4-D,"` widely used to `color{violet}"kill dicotyledonous weeds"`, does not affect mature monocotyledonous plants.

● It is used to prepare `color{violet}"weed-free lawns"` by gardeners.

● Auxin also `color{violet}"controls xylem differentiation"` and helps in cell division.


● Gibberellins are another kind of `color{violet}"promoter PGR"`.

● There are more than `color{violet}"100 gibberellins"` reported from widely different organisms such as `color{violet}"fungi and higher plants"`.

● They are `color{violet}"denoted"` as `GA_1`, `GA_2`, `GA_3` and so on.

● However, `color{violet}"Gibberellic acid"` (`GA_3`) was one of the `color{violet}"first gibberellins"` to be discovered and remains the
most intensively studied form.

● All GAs are `color{violet}"acidic"`.

● They produce a wide range of `color{violet}"physiological responses"` in the plants.

● Their ability to cause an `color{violet}"increase in length"` of axis is used to increase the length of grapes stalks.

● Gibberellins, cause fruits like `color{violet}"apple to elongate"` and `color{violet}"improve its shape"`.

● They also `color{violet}"delay senescence"`.

● Thus, the fruits can be left on the `color{violet}"tree longer"` so as to extend the `color{violet}"market period."`

● `GA_3` is used to speed up the `color{violet}"malting process"` in brewing industry.

● Sugarcane stores carbohydrate as `color{violet}"sugar in their stems"`.

● Spraying sugarcane crop with gibberellins increases the `color{violet}"length of the stem"`, thus increasing the yield by as much as `color{violet}"20 tonnes per acre."`

● Spraying juvenile conifers with GAs `color{violet}"hastens the maturity period"`, thus leading to early seed production.

● Gibberellins also promotes `color{violet}"bolting (internode elongation"` just prior to flowering) in `color{violet}"beet, cabbages"` and many plants with rosette habit.