Oh man finally, I'm off of work. Now I can go to class and sit, I'm so tired of standing. Today's been a long day but now I have botany class! So here we are at lab and today's focus is about recognizing the tissues within stems and their functions, exploring the diversity of plant stems from different habitats, and seeing the difference between a monocot and a dicot plant. We did multiple cross sections of different types of plants. Let me tell you what! Cross sections are not easy. In order to get the best possible result you need to be able to cut the stem very thin. The problem for me is that my hand shakes too much, so it took me a couple tries to get a perfect cross section. One of my best cross sections is the broad bean stem, which can be seen in figure 1. This image was prepared and stained with Toluidine Blue O (TBO), and that's the reason we are able to see different colors and easily distinguish the different structures in this plant stem. The obvious thing you can notice between Figure 1 and Figure 2 is the complexity of a dicot structure. A distinct separation, that looks like a river that cuts through the forest, is called procambium. This separates the pith and the cortex of the stem. Not only that, comparing Figure 1 to Figure 2, their vascular bundle is very different from each other. In figure 1 you can see a separation between the xylem, which is responsible for transporting water and minerals, and the phloem, which is responsible for transporting food to the rest of the plant. But in figure 2 you can see that they're really close together, almost as if they were one. Now if we look closely at figure 1, you can see a blue stain on top of the phloem. That's what they call sclerenchyma, and we were told in class that this acts as a helmet and protects the phloem .
Now lets look at aquatic plants: Figure 3: These are images of a waterweed (Elodea). This is a cross section of its stem, and was stained with TBO. This image was taken under a compound microscope at about 40x. The second image is a zoomed in version of the first image. (Prepared and photographed by Taylor) The plant structure in land plants compared to aquatic plants is very interesting. I've always thought that since they are all plants, their insides looks the same. I'm obviously wrong. There is a big difference. In aquatic plants I was able to learn that they contain these huge, easily seen air spaces throughout the stem called aerenchyma. Looking at figure 3 above, you can see what I am talking about. These air spaces are very important to aquatic plants because it provides buoyancy and it allows easier circulation of gases. Now after this lab I should be an expert at distinguishing the aquatic plants and terrestrial plants just by looking at their cross sections. Author: John P.
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I think Tuesdays are good days for cross sections. Don’t you feel that urge to perform thin slicing of plant tissue on Tuesdays? Seriously, what could be better than identifying monocots and dicots through vascular bundle arrangements!? I can’t think of any other way I’d rather spend my Tuesday. So lucky for me, this week in Oregon State plant structures lab we did exactly that! By looking at the location of the vascular bundles in plant stems, we were able to identify the plant species as monocot or dicot, assuming this wasn’t already known. Taking a close look at the vascular bundles, distinguishing of the individual components of the vascular bundles as well as the surrounding tissue was pretty clear with proper stain types and methods. Corn (Zea mays) is monocot and is in figure 1 and 2 below. TBO stain was used to provide contrast between cell types depending on the compounds present in the cell. Staining with TBO or Toluidine Blue O, will stain pectin substances pink to reddish purple, and lignin, blue or blue green. The vascular bundles are clearly stained blue which is due to the lignin of the secondary cell wall of the tracheid’s and vessel elements, the components of xylem. Phloem is the other transport tissue type found in the vascular bundles, which is composed of sieve tube elements and its dependable loving friend, the companion cells. I remember xylem and phloem and the way materials generally flow through them by saying 'xylem', in a high, squeaky voice, making me think up, and 'phloem', in a low deep voice for down. Say these words out loud a few times and hopefully it sticks in your memory for years to come like it has for myself. The xylem, transports water and minerals from the roots to the shoots and phloem carries sugars, nutrients, lipids, organics, and sad but true, viruses on a bad day. Surrounding the xylem and phloem is a sheath of sclerenchyma which helps with support and also stains thanks to its lignin found it in. Figure 1 and 2 below both help in identifying the regions referenced above.Figure 1 is a corn stem (Zea mays) cross section with TBO staining. In the image you can see the vascular bundles spread throughout the stem with parenchyma cells filling the space between the bundles and the epidermis encasing the both of them. Because the stem cross section was taken near a shoot, the tissue surrounding the epidermis of the stem is young leaf tissue. This image was taken at 40x magnification with a compound microscope. (Prepared by Lucas and photographed by Taylor) Figure 2 is a corn stem (Zea mays) cross section with TBO staining. This image is actually a more zoomed view of the same image above in figure 1. The larger cells in the vascular bundles are vessel elements. You can see two on the outside of the bundle and one or so at the bottom or top depending on orientation. The one or so at the top or bottom with the darker stained outer walls are dead and have possibly been filled with air making them look like bubbles in the slide. Vessel elements are larger transport tubes than the tracheid’s found in the xylem and are prone to air bubbles if breaks in the water tension occurs. This image was taken at 100x magnification with a compound microscope. (Prepared by Lucas and photographed by Taylor) The meristematic regions of the plant are where the new tissue is formed. There are many locations in the plant this is essentially happening. In the figures 1 and 2 above, a region running through the vascular bundles termed, procambium, creates new cells through mitosis. The procambium promotes radial growth of the plant by providing new vascular tissue to replace the non-functioning xylem and phloem. The secondary xylem and phloem get pushed away from the vascular cambium as primary vascular tissue is created giving the stem girth over time. While the pro-cambium provides lateral growth the apical meristem found at the growing tips of plants, (roots and shoots) generates upward and downward growth. Below in figure 3, you can see where the growth is taking place and the name of the region this is occurring. Figure 3 is a prepared slide of longitudinal section of a Coleus shoot meristem. Staining was used, which is apparent in the dividing cells (purple). In the image the leaf primordia, apical meristem, axillary buds, and vascular bundle are all visible. The image was taken at 40x on a compound microscope. (Pre prepared and photographed by Taylor) Figure 4 is an image under a dissecting microscope of a Coleus shoot meristem. In the shoot apical meristem cells are dividing by mitosis and forming new daughter cells that have yet to undergo differentiation. The swelling of these primary cell vacuoles will cause the shoot to move upwards causing primary growth. At some point these cells will differentiate into dermal, vascular, or ground tissue systems. (Prepared by John and photographed by Taylor) - Taylor Bates In this week’s lab, we examined a celery (Apium graveolens)! A celery has many nutritional benefits. It contains antioxidants and beneficial enzymes, in addition to vitamins and minerals such as vitamin K, vitamin C, potassium, folate and vitamin B6. Within the celery stalk contains a left structure called a petiole. A petiole is a small stalk that attaches to the the leaf blade of the plant to the steam. Unstained cross section of celery petiole. (400x) Ground tissues in celery petiole
This is a photo of that vasular bundles, phloem and xylem taken at 100x magnification Lesson of the day! From this lab, I learned that parachyma cells are very easy to locate because they are most abundant in a cell. For some reason, I had a more difficult time locating the vascular bundles. I really enjoyed this lab and can't wait to see what else we get to see!
-Mylinh Nguyen |
AuthorContent is created by students participating in the Plant Structure course at Oregon State University for Winter 2017. Archives
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