One appraoch to assessing the role of plant growth regulators (PGR) in development is to alter their concentration by exogenous application of of PGRs or inhibitors of their activity. Our system will be quite ammenable to this approach.
Take a 100mm petri plate and put several layers of paper towels in the bottom.
Cover it with a circle of Whatman filter paper.
Pipette Type I water or a PGR solution until the papers are wet but not floating in solution.
Place your seeds in a row.
Close your plate and seal with parafilm.
Place plates vertically in one of four growth boxes:
A = red light
B = blue light
C = far red light
D = green light
Available for your use are10-5 M solutions of indole-3 acetic acid (IAA, a naturally occuring auxin) and 2,3,5-triiodobenzoic acid (TIBA, which blocks auxin transport and thereby interferes with its distribution). These solutions can be used to wet petri plates containing seeds to test the general effect of auxin increase or altered distribution. Use the solution without diluting it. For controls, use Type I water. Be careful not to use the same pipette in different solutions! When considering distribution, keep in mind that auxin generally moves from the shoot tip downward (basipetally).
To collect more information about localized auxin effects, you can make agar blocks with hormones and place them on different places on the hypocotyl. You may also want to consider removing the shoot tip in some of your experiments.
To make agar blocks:
Stir and heat the flasks containing 10-4 M IAA or TIBA plus 1.5% agar on a stir plate.
Once the agar has liquified, pipet a small amount onto a microscope slide and allow it to solidify.
Cut small blocks with a razor blade.
With a weighing spatula or forceps, place the agar block onto your tomato seedling.
Consider using the 1.5% agar solution (without ammenda) for your control.
Carefully design your experiments to test your hypotheses! What are the possible outcomes of your experiment? What would each outcome tell you?
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