Question

Where are auxins synthesized in plants? Mention any two of their uses.

Answer 1

Hint: The term auxin has been derived from the Greek word “auxein” which means “to grow”. It is known to be the first plant hormone that was discovered.

Complete answer:
Auxins are a group of compounds that include indole-3-acetic acid (IAA), and other natural and synthetic compounds that have certain growth-regulating properties. They are one of the various plant growth regulators(PGRs). They are generally produced by the growing apices of the stems and roots; from where they migrate to the other regions of their action. Auxins can be natural or synthetic. Indole Acetic Acid(IAA) and indole butyric acid (IBA) are some natural auxins that have been isolated from plants.
Some synthetic auxins include NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) which are used for various purposes.
Functions:
Physiological-
Cell Elongation - Auxin promotes elongation and growth of stems and roots and enlargement of fruits by overall enlargement of cells in all directions,
Apical Dominance - In many plants, the apical bud grows while the lower axillary buds are suppressed. This is an effect of the auxin(IAA) of the axillary bud. This can be proven but removing the apical bud which then results in the growth of lateral buds.
Control abscission layer - Auxin inhibits the abscission of young leaves and fruits in normal amounts. An abscission layer is produced only when the auxin content is reduced below the minimum level which ultimately leads to the fall of ripe fruits.
There are many other uses:-
Rooting - Auxin stimulates root formation in woody stem cuttings.
Flowering - The dilute solutions of synthetic auxins are sprayed on fruits like litchi and pineapple which induce flowering in them. However, in most plants, flowering will be inhibited by spraying high concentration of auxins.
Parthenocarpy - Auxins in diluted form can be used to produce parthenocarpic or seedless fruits. It has been proven that naturally parthenocarpic fruits like bananas and grapes have higher internal production of auxins.
Weedicides – Spraying synthetic auxins like 2,4-D is a procedure commonly used as weedicides. They are used to remove many broad-leaved weeds or dicotyledonous weeds while sparing the monocot plants.

Note: -Except for auxin, there are four other plant hormones called gibberellins, cytokinin, abscisic acid, and ethylene. Together they are called Plant Growth Regulators (PGRs).
-Some of them cause the plants to grow, while others like abscisic acid promote senescence. i.e. promote falling of leaves and fruits.Ethylene is the only gaseous hormone.