BIO-0014 Lecture 16: What Auxin is and what it does

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1. Auxin as a signal molecule
a.
i. Signalling molecules are able to transmit information about the
environment to other parts of the plant
b.
i. Discovered by Darwin wife and son
ii. Used a corn seedling
1. Realized they were bending towards light
2. When he cut off the top, no bending
a. The top 3 mm of the plant
3. When he blocked the top with an aluminum cap, no bending
a. The top 3 mm of the plant
4. Wrote about it in 1880 that a growth stimulus is produced in the
coleoptile tip and is transmitted to the growth zone
iii. Follow up experiment occurred in 1913
1.
2. Discovered that growth stimulus passes through gelatin
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3. But not through water-impermeable barriers such as mica
4. The signal could go through the agar bridge
a. They could take out the signal that got caught in the agar
block and analyze it
b. Compound was named Auxin
5.
6. Definition of auxin: any compound that allows seedling cells to
enlarge in darkness
a.
b. Enlarged cells on the left side, causing the curving
c. Class of compounds
d. Higher concentration of auxin leads to more bending
c.
i. Chemical compound of auxin
1. Don’t have to memorize this structure
2. Has acetic acid side chain
3. IAA: Indole-3-acetic acid
a. Auxin found in plants
b. ONLY auxin that is naturally made
4. Needed to be broken down after the growth has occurred
ii. Synthetic Auxins
1. Created artificially by scientists
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