Botany - B.E. Yakubenko 2017

Part One. Plant Anatomy and Morphology
Chapter I. Cytology
Laboratory Session Topic 2.3. Structure of Higher Plant Cells. Cell Wall. Nucleus. Cytoplasm and Vacuole. Cytoplasmic Streaming. Plastids: Chloroplasts, Chromoplasts, Leucoplasts

General Remarks. The Cell Functions both as an independent Organism and as a Structural and biological unit of a multicellular organism or its individual parts. It encompasses an infinitely diverse world of yet-unexplored Organelles and metabolic products. A single cell undergoes up to 2,000 distinct Chemical Reactions and transformations. The entire complex of cellular organelles is referred to as the protoplast. Its physiological processes—Respiration, reproduction, METABOLISM, and irritability—determine the viability of the cell. A hallmark feature of the cellular protoplast is cytoplasmic streaming. Using the leaf of the Canadian waterweed as an example, you will examine the rotational movement of the Cytoplasm.

The vital activity of the protoplast gives rise to its derivatives: The Cell wall, The Vacuolar System, and inclusions. We consider the vacuolar system as a complex of vacuoles interconnected with a portion of The Endoplasmic reticulum, along with its associated Ribosomes and multienzyme systems.

Objects:

1. Epidermis of the fleshy scale of the garden onion (Allium cepa L.)

2. Leaf of the Canadian waterweed (Elodea canadensis Michx.)

3. Leaf of the Virginia spiderwort (Tradescantia virginiana L.)

4. Fruit of the rowan/mountain ash (Sorbus aucuparia L.)

Tasks:

1. Prepare a temporary mount of the garden onion scale epidermis on your own.

2. Study The Structure of The plant cell under low and high microscope magnification.

3. Sketch 2–3 onion epidermal Cells and label their component parts.

4. Prepare a temporary mount of the Canadian waterweed leaf on your own.

5. Study cytoplasmic streaming in the Cells of the central vein of the Canadian waterweed leaf under low and high microscope magnification.

6. Make a detailed close-up drawing of 2–3 cells, indicating their structural components and cytoplasmic streaming.

Equipment and Materials: MBR-1 or Biolam microscope, scalpels, blades, razors, dissecting needles, pieces of fleshy onion scale, leaves, Elodea, Reagents, and other accessories.

Procedure for Preparing the Onion Scale Epidermis Slide. Find a Glass slide in your kit box, hold it with the thumb and index finger of your left hand, and wipe it thoroughly dry and clean on both sides using a wipe in your right hand. Wipe the coverslip with the wipe between your thumb and index finger pads (without applying pressure) and place it to the right on the microscope stage. Place the slide crosswise on the kit box and apply a drop of iodine-potassium iodide solution onto it.

Take a piece of sliced onion scale and peel off the upper epidermis. To do this, first separate the lower epidermis from the inner side of the scale and place it in a Petri dish. The remaining scale will have a crescent shape. Break it in half. Both halves will remain connected by a thin film—the epidermis. Peel one half off (from the middle to the edge) along the other half. In this manner, you will have removed the upper epidermis. Place it, torn side down, into the drop of iodine-potassium iodide solution on the slide. Spread out the epidermis with a dissecting needle and cover it with the coverslip: place the coverslip at an angle into a drop of Water on the slide so that its edge gets wetted, then lower it onto the piece of epidermis, and gently press with a needle or pencil to expel any air and excess liquid from underneath. This will yield a high-quality slide free of air bubbles (Fig. 13). Use pieces of filter paper from your kit box to blot any excess solution on the slide outside the coverslip.

Class="center">

Figure 13. Procedure for preparing the onion fleshy scale slide

Place the slide of the onion scale epidermis prepared in this manner onto the microscope stage so that the target epidermal tissue covers the central part of the aperture and is in the field of view under the low-power microscope objective. Secure the slide on the microscope stage using the stage clips.

Microscopic Examination of the Slide. Examine the cellular STRUCTURE OF THE onion scale epidermis under low microscope magnification. The cellular structure of the specimen is clearly visible. By moving the stage with the slide using the mechanical stage knobs located on both sides of the stage, select 2–3 cells in the field of view where the cell wall, cytoplasm, vacuole, and nuclei appear clearly as small grayish structures (Fig. 14).

Figure 14. Cell Structure

Without moving the slide, switch the microscope to high magnification. To do this, grasp the low- and high-power objectives with two fingers of your left hand and switch from the low-power objective (marked ×8) to the high-power objective (marked ×40). To bring the image into view, look into the eyepiece and turn the coarse adjustment knob toward yourself by a fraction of a micron to raise the microscope tube. Adjust the image clarity using the fine adjustment knob According to the Optical Properties of your eye's lens. At the same time, the slide clearly reveals: a distinctly defined cell wall enclosing the internal Contents of the cell—the protoplast. Within it, the cytoplasm differentiates as a granular mass extending along the cell wall or forming strands that divide the vacuole into several smaller ones. In a mature cell, you will see a single large vacuole, or several vacuoles if it has not yet reached full development. An essential component of the cell is The Nucleus with one or two nucleoli. The nucleus occupies a central or parietal position within the cell, appearing as a spherical, silvery body that stands out against the general Background of the granular cytoplasm. Compare the nucleus with the corresponding chart and examine the fine details of the cell's structural components.

In your laboratory notebook, make a detailed close-up drawing of 3–4 cells and label the distinct PARTS OF THE structures mentioned above. Add a caption to your drawing.

Preparation procedure for an Elodea canadensis leaf slide. Wipe the microscope slide and coverslip clean. Place the clean slide across the pencil case and, using a glass rod, place a few drops of water in the middle of it. Take a sprig of Elodea canadensis from the bacteriological dish and pluck a well-defined middle leaf. Place it into the drop of water on the slide. To stimulate cytoplasmic streaming, gently prick the central vein of the leaf 2—3 times with a needle. Cover the specimen with a coverslip, making sure no air bubbles are trapped underneath. If any air bubbles are present, gently press on the coverslip to remove them. Place the finished slide in the center of the field of view and secure it with stage clips.

Microscopic examination of the slide. Under low magnification, position the slide so that the central vein of the Elodea leaf is in the middle of the field of view. The cellular structure of the leaf is clearly visible due to the distinct boundaries formed by rigid and well-defined cell walls.

The cellular structure and cytoplasmic streaming are best observed under high magnification. To do this, select a field of view at the Base of the central vein, where the cells contain fewer Chloroplasts, making it easier to observe cytoplasmic streaming. Elongated cells with blunt ends are visible on the slide. Locate individual organelles within them. The most prominent feature is the continuous cell wall enclosing the internal content, the protoplast. A thin layer of fine-grained cytoplasm lines the inner surface of the cell wall. Occasionally, in certain areas of the cells, a spherical nucleus of denser consistency can be observed. In addition, numerous green, ellipsoid bodies—chloroplasts—are visible in the cytoplasm. The central part of the cell lacks granularity and consists of a large vacuole.

Upon careful examination of the slide under good sunlight, observe cytoplasmic streaming in individual cells. You will see that the green chloroplasts are passively carried along the cell wall by the cytoplasmic current, meaning you are observing active cytoplasmic streaming within the cells of the central vein. The movement is circular, with the cytoplasm circulating in the parietal layer (Fig. 15).

In your workbook, make a detailed drawing of 2—3 cells, labeling the components described above. Indicate the direction of cytoplasmic streaming with an arrow.

Study of chromoplasts in the fruits of European rowan (Sorbus aucuparia). Prepare a slide of rowan fruit pulp yourself and examine the structure of chromoplasts. In your workbook, make detailed drawings of several cells containing chromoplasts. Add the necessary labels to your drawings.

Figure 15. Cytoplasmic streaming and chloroplast structure:

a — cytoplasmic streaming: 1 — chloroplasts; 2 — cytoplasm; 3 — cytoplasmic streaming; 4 — nucleus; 5 — nucleolus; 6 — vacuole; 7 — cell wall; b — ultrastructure of a chloroplast under an Electron microscope: 8 — outer membrane; 9 — inner membrane; 10 — intermembrane space; 11 — stroma; 12 — granal thylakoids; 13 — stromal thylakoids; 14 — grana; 15 — lamellae; 16 — ribosomes; 17 — primary starch granules; 18 — pores.

Slide preparation procedure. Take a microscope slide from the pencil case and a coverslip from the bacteriological dish, and wipe them thoroughly clean and dry. Place the slide across the pencil case and put a drop of water on it. Take a rowan fruit and, using a dissecting needle, tear and peel back the Skin of the pericarp. Take a small amount of fruit pulp from beneath the skin onto the tip of the needle and place it into the drop of water on the slide. Use the needle to tease the piece of pulp into a homogeneous mass. Add a drop of water to it and cover with a coverslip. Place the finished slide on the microscope stage and secure it with the clips.

Microscopic examination of the slide. First, examine the slide under low magnification. You will see A large number of separated, irregularly shaped cells. Select 2—3 cells with the most clearly defined structure. In these cells, your attention is drawn to the orange or reddish coloration of interconnected filamentous, cylindrical, and other shaped structural bodies. These orange bodies are chromoplasts. Carefully observe their shape, structure, and arrangement. They are distributed within the granular cytoplasm located along the cell wall. The cells typically contain several vacuoles separated by cytoplasmic strands. Somewhere to the side within the cytoplasm, locate the nucleus—a spherical, grayish body—with a nucleolus (Fig. 16).

In your workbook, make a detailed drawing of 2—3 cells and label the identified components.

Preparation procedure for a Tradescantia virginiana leaf slide. Prepare a slide of Tradescantia leaf epidermis yourself and study the structure of Stomata and leucoplasts. Wipe the microscope slide clean and dry. Wipe the coverslip in the same manner. Place the slide across the pencil case and put a drop of water on it.

Take a Tradescantia leaf or previously cut leaf pieces and wrap it around the index finger of your left hand so that the lower side of the leaf faces upward. Using a sharp scalpel or razor blade, very carefully—so as not to cut your finger—slice and peel off a piece of the epidermis without the green leaf mesophyll. If this fails, cut away a piece of the epidermis. A piece a few millimeters in size is sufficient. Place it into the drop of water on the slide. Moisten it slightly, cover it with a coverslip, and push out any trapped air. Remove excess water using filter paper. Place the slide on the microscope stage and secure it with the clips.

Figure 16. Chromoplasts in cells of fruit from various plant species:

a — dog rose; b — lily of the valley; c — rowan; d — hawthorn; 1 — cell wall;

2 — cytoplasm; 3 — nucleus; 4 — chromoplasts; 5 — vacuole.

Microscopic examination of the slide. First, examine and study the slide under low magnification. The cellular structure of the epidermis is clearly visible on it. Select an area where all the Components of the object are most distinctly visible. Position them in the center of the field of view.

Next, examine the object under high magnification. Note that the epidermis is formed by living, polygonal, tightly packed cells. The following elements stand out clearly in their structure: 1) the cell wall surrounding the cell protoplast; 2) the cytoplasm, located along the cell wall as a continuous layer or as cytoplasmic strands separating individual vacuoles; 3) the nucleus with one or two nucleoli; 4) leucoplasts (Fig. 17)—silvery, spherical bodies that are most often arranged around the nucleus like a silvery wreath.

Figure 17. Leucoplasts in Tradescantia leaf cells:

1 — cell wall; 2 — cytoplasm; 3 — nucleus; 4 — leucoplasts; 5 — vacuole

In your workbook, make a detailed drawing of 2—3 cells containing leucoplasts.

Conclusions. 1. Plastids are an essential component of plant cells, distinguishing them from animal cells.

2. During the course of evolution, plastids and their internal structure develop in ADAPTATION TO ENVIRONMENTAL conditions.

3. Plastids mediate The process of Photosynthesis: the synthesis and accumulation of Organic compounds, and the enrichment of the atmosphere with oxygen, which is essential for The Development of highly organized animals and humans.

Review Questions:

1. What types of plastids do you know?

2. What is the ultrastructure of chloroplasts under an electron microscope?

3. What is THE ORIGIN OF plastids?

4. What is the Cytology/cytology/26.html">Structure of Different types of plastids?

5. Name the pigments found in plastids.

6. In which plastids are starch grains deposited?

7. What Methods of plastid reproduction do you know?

8. What are the Similarities and differences between chloroplasts and chromoplasts?

9. What type of starch is stored in chloroplasts?

10. What are the plastids that store starch called?

11. What kind of starch is deposited in leucoplasts?

12. In which plant Organs are chloroplasts concentrated?

13. Which plant organs contain chromoplasts?

14. Are carotene and xanthophyll components of chloroplasts?