The purpose of this experiment is to examine the movement and pathway of water up an Impatiens stem. In the first part of the experiment, congo red dye will be added to the water to trace the pathway of water up the stem. Cross-sections of the stem demonstrate where in the stem the water is moving and oblique-sections allow identification of the actual cells involved in water transport. The second part of the experiment identifies which parts of the stem, and more specifically, which cells, are lignified. Are the cells involved in water transport lignified? Lets start the experiment and see!!!
Step 1: Impatients have translucent stems (due to the presence of large, thin-walled cells). Therefore, the vascular strands running longitudinally in the stem can be observed directly. Notice the strands in the picture to the right. Click on the picture to label the strands with arrows.
Step 2: Cut the root system from the plant and immediately place the cut surface of the stem in water. Cut off another centimeter of stem under water to ensure there are no air bubbles in the transport tissue that could disrupt water transfer. Click here to see how that was done.
Step 3: Quickly transfer the cut stem to a test tube containing a solution of Congo red and prepare your controls while you wait for water transport to occur up through the stem. Click here to observe the congo red set-up.
Step 4: Two controls are needed for this experiment. Since the purpose of the experiment is to trace the movement of congo red dye to follow the pathway of water transport, it is first necessary to see if any of the cell walls of the plant are already stained red. To do this mount a thinly cut section of stem from the piece cut off in step 2 on a microscope slide and view it under a dissecting microscope. This is control 1. The second control is prepared in the same way, however, this control is to check which parts of the stem Congo red will stain (Congo red stains cellulose). Add a drop of Congo red to a second slide for control 2. Click on the following to observe each each part of step 4.a.Preparation of sections
Step 5: After the dye has moved to the stem apex, cut cross-sections of the stem at various points along the stem. Examine the location of the congo red. Also make longitudinal sections at the same points to identify the cell type. Click on the following to observe each part of step 5.a. Sections at various points along the stem
The purpose of the second part of the experiment is to determine whether or not the cells involved in water transport are lignified. Click on each step to observe the procedure.
Step1:Cut additional cross and longitudinal sections to stain lignified cell walls using phloroglucinol.
Step2:Soak sections in 2-3 drops of phloroglucinol for about 3 minutes.
Step3:Drain the stain off using a paper towel.
Step4:Add 2-3 drops of concentrated HCl. (Lignin stains red)
Step5:Place a cover slip over the sections and examine it under the dissecting microscope.