role or function of auxin

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 Here’s a concise and exam-ready note on the Role / Functions of Auxin 🌱 — perfect for semester preparation 👇

🌿 Role / Functions of Auxin

🔹 1. Cell Elongation

  • Auxin promotes elongation of cells in shoots and coleoptiles.

  • It increases the plasticity of the cell wall, allowing cell expansion.

  • This is the primary function of auxin and explains phototropism and geotropism.

🔹 2. Apical Dominance

  • The apical bud suppresses the growth of lateral (axillary) buds due to high auxin concentration at the apex.

  • Removing the tip (decapitation) allows lateral buds to grow — showing apical dominance.

🔹 3. Root Initiation

  • Auxin stimulates the formation of adventitious and lateral roots.

  • Synthetic auxins like IBA (Indole-3-butyric acid) and NAA (Naphthalene acetic acid) are used to promote rooting in cuttings.

🔹 4. Tropic Movements

  • Auxin causes unequal growth on two sides of an organ, leading to bending movements:

    • Phototropism: towards light (shoots)

    • Geotropism: towards gravity (roots)

🔹 5. Vascular Differentiation

  • Auxin helps in the formation of xylem and phloem tissues during secondary growth and wound healing.

🔹 6. Fruit Development and Parthenocarpy

  • Auxin promotes fruit growth after fertilization.

  • Application of synthetic auxins can produce seedless fruits (e.g., tomato, banana).

🔹 7. Delay of Abscission

  • Auxin delays leaf and fruit drop by preventing abscission layer formation.

  • When auxin levels drop, abscission occurs.

🔹 8. Flower Initiation

  • In some plants, auxin promotes flowering (e.g., pineapple).

🔹 9. Callus Formation

  • Auxin, when combined with cytokinin, helps in callus formation in tissue culture.

🔹 10. Weed Control (Herbicidal Action)

  • Synthetic auxins like 2,4-D and 2,4,5-T are used as selective herbicides to kill broad-leaved weeds.

🧠 Summary Table:

FunctionEffect of Auxin
Cell elongationGrowth of stem and coleoptile
Apical dominanceInhibits lateral buds
Root initiationPromotes adventitious roots
Fruit developmentStimulates parthenocarpic fruits
Vascular differentiationPromotes xylem and phloem
Abscission controlDelays leaf and fruit drop
Herbicidal useKills weeds (broad-leaved)

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