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plant growth

Raymond Shillito TMBG42A at prodigy.com
Wed Jan 4 22:49:24 EST 1995

The classic experiment is to put the auxin in an agar gel, and place this 
on one half of a cut oat seedling.  This will also work on stems of 
cucumbers. I think you can do it in the light, alsthough it is a long 
time since I had to demonstrate this.  The auxin causes cell expansion 
which means the stem will lean away from the side which has the agar 

Another expt is to take roots of dandelion.  Cut them into 1-2 inch 
pieces (remember which way is up.)  Auxin transport downwards related to 
the original orientation of the root will cause root formation (Root-tone 
is just auxin).  

The effects of gravitropism and bending towards the light, although 
mediated via auxin, are caused by sensors (such as phytochromes) sensing 
the light, which then affect the auxin transport/ production/breakdown to 
decrease the auxin content on the side near the light. 
In the dark, the phytochrome does not sense light, so the auxin 
concentration remains high and the cells elongate.  On seeing light, 
other sensing phytochromes etc. come into play, and leaf development and 
expansion is triggered.

I hope I got this right.  Hopefully there are some other plant biologists 
out there who can add more....

Ray Shillito
shillitor at am.abru.cg.com
Any opinions expressed are private and not the policy of my employers 
(standard disclaimer)

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