Auxins
Auxins, derived from the Greek word 'auxein' meaning 'to grow', are key plant hormones that regulate various growth and developmental processes in plants. The most commonly referenced auxin is indole-3-acetic acid (IAA), alongside synthetic options such as naphthalene acetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D).
Discovery and Production
Auxins were first isolated from human urine and are synthesized mainly at the tips of shoots and roots. These hormones play vital roles in directing growth responses such as phototropism (growth toward light) and gravitropism (growth in response to gravity).
Physiological Effects
Auxins affect multiple physiological processes:
- Root Development: Auxins promote rooting in cuttings, making them crucial for horticultural practices.
- Apical Dominance: They inhibit the growth of lateral buds, ensuring that the main shoot continues to grow. When the apical bud is removed, lateral buds can grow more freely.
- Fruit Development: Auxins can induce parthenocarpy, resulting in seedless fruits, such as certain tomato varieties.
- Leaf and Fruit Abscission: They help prevent early drop of immature fruits and leaves but promote the abscission of older ones.
- Herbicides: Synthetic auxins like 2,4-D are used in agriculture to selectively kill dicotyledonous weeds without harming monocots.
In summary, auxins are essential for plant growth regulation and have significant applications in agriculture, making them a focal point for enhancing plant productivity.