Lemna Bioassay System

Duckweed (Lemna gibba) is used for legally-binding assays of contaminants in soil and water all over the world... usually in expensive automated systems using microtitre plates. Over the next three weeks you will become familiar with this system by first doing a simple test involving sodium chloride. Then you will use the system to estimate the concentration of an unknown amount of herbicide (glyphosate).

Today you will be preparing growth media with increasing concentrations of NaCl and observing the effect on Lemna or Spirodela growth over a seven day period (Spirodela is a close relative of Lemna).

After you have prepared and set up your cultures, take a JPEG photograph of your plate.

In seven days you will take another photograph and analyze the differences using J_image.

Make sure you take the photo in the same orientation each week!!! Make sure you know the concentrations of each well in the photo!!!

From the data you will prepare a dose response curve for NaCl and your plant type. You will also have gained the skills necessary to ask more sophisticated questions with this system.

Important Note: This is an upper-division lab. You and your partner will be required to think about and plan your experiments!

Schematic of lab:

1. What is the molecular weight of NaCl?
2. How much solution will be needed for each well?
3. How will you prepare 0.05 M, 0.1 M, 0.2 M, 0.4 M, & 0.8 M NaCl in Lemna Growth Medium?
4. What is your control in this dose-response experiment?
5. How many plants should you use per well?
6. What are the parameters you should record for this experiment?
7. The photograph is probably the most important part of this experiment. What do you need to think about when taking the photo?
8. Should the micro-titre plates be covered or uncovered?
9. Be sure to record every step you take in order to prepare a good discussion for your write-up.

1. Title as question.
2. Introduction - very brief, why does salt harm plants? Why do different plants have different responses to salt? What question did you ask in this experiment? Why do scientists use Lemna to answer these types of questions?
3. Methods - details on how you answered the question including a description of the software and how you used it (which functions).
4. Materials - what chemicals, organisms, and equipment did you use?
5. Data/Results - should include two photos with captions of the plates you prepared. You should also have a table of Image J data from all the photos in the class, with title and caption, Line graph of growth relative to the control with legend, title and caption. Since there will be five class data points for each concentration (treatment), you should prepare error bars for your line graph.
6. Discussion - should include prose description of results as well plausible explanations for the results, should also include suggestions for further experimentation.

Due Thursday, March 16th, together with the Glyphosate report.