FW went experiment on auxin

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 The **Auxin Avena sativa curvature test**, developed by Frits Warmolt Went in 1928, was a pioneering experiment that provided quantitative evidence for the existence of auxin, the first plant hormone to be discovered.


Here's an overview of the experiment:


### Purpose

To demonstrate the existence of a growth-promoting substance (later identified as auxin) produced by the tip of a plant coleoptile and to quantify its effect on growth.


### Organism Used

* **_Avena sativa_ (Oat) Coleoptile:** Went used the coleoptiles (protective sheaths covering the first leaves) of oat seedlings. These were ideal because:

    * They grow rapidly and straight in the dark.

    * Their growth is primarily due to cell elongation, making it easy to observe the effects of growth-promoting substances.

    * The tip is responsible for perceiving light and producing the growth signal.


### Experimental Setup and Procedure


1. **Decapitation:** Went carefully removed the tip (apex) of several oat coleoptiles. This tip is known to be the source of the growth hormone and also the region that perceives light.

2. **Placement of Agar Blocks:** The excised coleoptile tips were placed on small blocks of agar for a period of time. During this period, the growth-promoting substance from the tips diffused into the agar blocks.

3. **Preparation of Decapitated Coleoptiles:** Another set of oat coleoptiles had their tips removed. These were then left in the dark to prevent any phototropic responses.

4. **Placement of Agar Blocks on Decapitated Chololeptiles:** The agar blocks containing the diffused substance were then placed asymmetrically (off-center) on top of the decapitated coleoptiles.

5. **Observation of Curvature:** After a few hours, Went observed that the coleoptiles began to bend away from the side where the agar block was placed. The degree of curvature was directly proportional to the amount of growth substance in the agar block.


### Observations and Results

* **Curvature Induced:** The coleoptiles showed a distinct curvature, bending away from the side where the agar block was placed.

* **Quantitative Relationship:** Went discovered that the angle of curvature was directly proportional to the concentration of the growth substance in the agar block. This allowed for the first quantitative bioassay for a plant hormone.

* **Growth Promotion:** The bending occurred because the cells on the side of the coleoptile receiving the agar block (and thus the growth substance) elongated more rapidly than the cells on the opposite side.


### Significance

* **Proof of Concept:** The experiment definitively showed that a chemical substance produced by the coleoptile tip promotes growth by stimulating cell elongation in the region below the tip.

* **Discovery of Auxin:** It led to the chemical isolation and identification of indole-3-acetic acid (IAA) as the primary natural auxin.

* **Foundation for Plant Hormones:** This experiment laid the groundwork for the study of plant hormones (phytohormones) and their roles in plant development, growth, and responses to environmental stimuli.

* **Bioassay Development:** The Avena curvature test became a standard bioassay for quantifying auxin activity for many years.

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