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 Introduction This past week in lab was all about learning and exploring the simple and complex tissues of plants. Our objectives were to recognize the three tissue systems of the plant body (ground, vascular, and dermal tissues), compare and contrast parenchyma, collenchyma, and sclerenchyma, identify water-conducting cells of the vascular tissue system and relate their structural features with their functions, and describe the characteristics of the epidermis, which we consider as a complex tissue. My primary focus for this lab was to prepare slides and observe the sclerenchyma fibers of a snake plant (Sansevieria trifasciata) by taking a cross-section and logitudinal-section of a leaf and observe the brachysclereids and tracheary elements of a wax pant (Hoya carnosa). Sclerenchyma Fibers of Snake Plant (Sansevieria trifasciata), Cross Section In order to examine the sclerenchyma fibers, a leaf was taken off of the snake plant. Using a razor blade, several thin cross-sections were taken from the leaf. A cross-section of the leaf was then stained in Toluidine Blue O (TBO) for about two minutes and then removed with a Kim wipe. Ethanol was added to the cross-section and then replaced with 20% CaCl and a cover slip. The reason the cross-section was stained with TBO was to observe the thickened secondary walls, which will be stained blue or blue-green in the presence of lignin. Vascular bundles, photosynthetic parenchyma cells of the mesophyll, and epidermis cells might have been also observed under the microscope (Figure 1). Once the cross-section was observed, a longitudinal-section was cut from the leaf and prepared on a slide stained in TBO. Observing the longitudinal-section of the snake plant leaf we were able to observe the elongated shape of the fibers, located in bundles. We were also able to see lignified water -conducting cells (Figure 2). Tracheary Elements, Sclerids, and Parenchyma Tissue of Wax Plant (Hoya carnosa) In order to examine the tracheary elements, sclerids, and parenchyma tissue in the wax plant, thin cross-sections of the stem were taken. These cross-sections were then stained with CVA. Observing the cross-section of the stem under a microscope, the CVA stained the sclerids and the water-conducting cells (tracheary elements) violet/blue . The outer ground tissue is made up of the parenchyma cells in the cortex and the ground tissue inside the ring of vascular tissue is called the pith. The parnechyma cells and the pith are differentiated into brachysclereids (Figure 3). Author: Austin Wriggle |
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