Hi. Over the course of 12 weeks I have conducted a chemistry experiment for school on the effect that the auxin Indole-3-acetic-acid has on plant growth (tommy toe tomato plant). This is because IAA is meant to increase plant growth by promoting cell division, expansion etc. We also created a nutrient solution. However, I found that instead of increasing plant growth, yeast precipitates have formed within the solution taking all the nutrients from the plant and effectively killing it. My question therefore is this, in terms of chemistry, why is the addition of Indole-3-acetic-acid producing yeast?

You mean there is a fungal infection, or how did you determine that a) there was yeast and b) that the adverse effect was by nutrient competition? The reasoning is likely to be off, indoles do not "produce" yeast. There are plenty of sources very fungi can come from, especially if you do not work under sterile condition. However, if you did your own nutrient solution under non-sterile condition, there is a good chance that you accidentally cultivated fungi in it and then infected the plant with it.

Adding too much Indole-3-acetic-acid will have a herbicidal effect. Plants should generate chemical signals on an as needed basis. Otherwise they will be out of control.

 

If you add "nutrients" to any given situation you have a large probability of generating some sort of micro-organism. This happens frequently when germinating seeds. Anyways, the herbicidal effects on the plant are essential opening the plants vascular system and it is leaking. This provides the fuel for the micro-organisms.