Last Tuesday in lab we studied about exploring the stomatal complexes of monocot leaf vs dicot leaf. We also learned about the internal structures of different leaves as well as their primary functions such as photosynthesis and transpiration. Stomatal Complexes of Monocot vs. Dicot Wheat cat grass is known Tritium vulgare, is monocot plant. Stomata of the wheat "cat-grass" (Tritium vulgare) consist of four cells, two guard cells and two subsidiary cells. The guard cells are specialized cells in the epidermis of leaves, stems and other organs that are used to control gas exchange. They are produced in pairs with a gap between them that form a stomatal pore. Broad bean is known Vicia faba, which is the dicot plant. Stomata plays a vital role in openings in the epidermal layer that allow for the exchange of gases. They allow for a plant to balance water inside and outside the cells. Guard cells allow for the opening or closing of the stomata with the internal hormone stimuli as well as external environmental factors. Pavement cells are simple cells with no real functions other than protecting the cells below them. Moreover, they help decrease water loss, and maintain an internal temperature. The most significant difference between the stomata of the monocots and the dicots is the shape of the guard cells. The monocot leaf has the narrow, dumbbell-shaped guard cells; whereas the dicot leaf has the pair-of-sausage shaped guard cells. Moreover, the monocot has the guard cells arranged in regular arrays, but the dicot has different paving. The monocot has stomata on both the upper and lower surface of the leaf. However, the dicot has stomata on the lower surface. Cross-Section of Corn Leaf (Zea mays) Corn leaf (Zea mays) is monocot, has parallel veins. Moreover, spongy mesophyll is composed of parenchyma cells that contain chloroplast for photosynthesis. It also has air spaces for gas exchange and produces carbohydrates by photosynthesis. The upper and lower epidermis protect the leaf from water, sealing water inside and preventing parasite's attack. Xylem transports water into the leaf while phloem begins the sugar transport down to the roots. Veins is consisted of xylem and phloem, and a surrounding bundle sheath. The internal structures of the monocot plants compared to the dicot plants made me surprised because I've always thought that their insides looks the same. However, there is a big difference. Guard cells of the monocot are narrow, dumbbell-shaped; but they are crazy-paving arrangement in the dicot. Stomata are located on both the upper and lower surface of the monocot leaf; whereas they are located only on the lower surface of the dicot leaf. During the lab, I felt difficulties in doing the cross-section of corn leaf because it needs a good skill technique to cut the cross-section. Finally, TA help me to finish the slide; the one I got that make me happy.
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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.
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 Good evening! This week in Botany 313, we got to do some super interesting things. After talking things over with my lab partner and the other group doing a blog this week, I was given the responsibility of posting the epidermises of Tradescantia and a section of coleus (Plectranthus scutellarioides), so this post will focus mainly on those topics. In order to get a slide of the epidermises for Tradescantia, I started off with a leaf from the plant and with a little bending, snapping, and peeling I was able to successfully get a slide with both the upper and lower epidermises present. As shown in the images below, the stomata, guard cells, and pavement cells can clearly be seen on the lower epidermis. On the upper epidermis, only pavement cells can be seen as this type of plant does not have stomata on the upper epidermis. Stomata (plural of stoma) are openings in the outmost epidermal layer in plants that allow for the exchange of gases. They allow for a plant to retain water in times of drought or to increase rate of water loss in times when there is an excess of water. Guard cells allow for the opening or closing of the stomata with the aid of internal signaling (i.e. hormones), as well as external (i.e. The sun or rain). Pavement cells are simple cells with no real function other than protecting the cells below them. The purple pigmentation in these epidermal peels are from naturally occurring pigmentation within the plant. Taking a longitudinal section of coleus and finding the lignified tracheary elements was a bit more challenging. Simply getting sections that were thin enough requires some practice, and finding the tracheary elements, even more so. They are very easy to miss even with the stain! With a little patience, and maybe some help from Dr. L-P, I was able to find a few examples, as shown below. Tracheary elements, such as tracheids, aid in the conduction of water and minerals through the plant. Lower epidermis of Tradescantia with no stains. Wet mount. Epidermal Peel. Arrow shown in image is from compound microscope. Arrow is pointing to stoma flanked by guard cells. The green dots in guard cells are chloroplasts. Cells surrounding guard cells are pavement cells. Photo credit: Michael Billard. Slide Prep credit: Michael Billard. Upper epidermis of Tradescantia leaf with no stains. Wet mount. Epidermal Peel. Arrow shown is from compound microscope pointing to a pavement cell. Purple pigment shown is from naturally occurring pigments within the plant. No stomata can be seen on upper epidermis of plant leaf. Photo Credit: Michael Billard. Slide prep credit: Michael Billard. Lesson Learned: Even with stains and a compound microscope, finding lignified tracheary elements can be very difficult. It can require cycling all the way through (and sometimes back) a focusing cycle, and even then, can be very easy to miss!
Author: Michael Billard |
AuthorContent is created by students participating in the Plant Structure course at Oregon State University for Winter 2017. Archives
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