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....
shillitor at am.abru.cg.com
Any opinions expressed are private and not the policy of my employers