Botany - B.Ye. Yakubenko 2017

Part One. Plant Anatomy and Morphology
Chapter II. Histology
Laboratory Class Topic 4.6. Meristematic Tissues

General Remarks. Meristematic Tissues give rise to all other tissue types. This property is due to the Cells' ability to divide, which in turn leads to an increase in Cell number, differentiation, and specialization into a specific tissue, and ultimately into the plant itself. A key feature of meristematic cells is their viability, Abundance of nutrients and energetic reserves, as well as an enrichment in Genetic information that ensures their high plasticity and the transmission of hereditary traits throughout ontogeny.

Objects:

1. A twig of Canadian waterweed (Elodea canadensis Michx.)

2. ROOT tip of a wheat seedling (Triticum aestivum L.)

Tasks:

1. Using a hand lens and a Microscope, examine the meristematic Tissues of the SHOOT and root apex on a self-prepared slide.

2. Draw The Structure of the root and shoot apex, labeling their component parts.

Equipment and Materials: MBR-1 or Biolam microscopes, twigs of Canadian waterweed, fixed wheat seedlings, dissecting needles, scalpels, razor blades, charts, Reagents, and other accessories.

Procedure for Preparing a Slide of the Shoot Apex of Canadian Waterweed. Place a Glass slide across a pencil case and apply a drop of Water or a weak iodine-potassium iodide solution in the center.

Using forceps and a dissecting needle, isolate the leaves from a twig of Canadian waterweed, working from bottom to top. Place the isolated leaves in the exact order in which you remove them. This will allow you to trace the Developmental Stages of the leaves, from the primordial apical leaves to the well-defined and fully developed lower leaves. The structurally simplest apical leaf primordia near the top of the stem transform into fairly distinct bumps, which are replaced even higher up by a smooth contour apex. This very structure constitutes the shoot apex, which represents a delicate, transparent stem tip where new cells are formed. Next, carefully detach it along with the lower bumpy region using a scalpel or razor blade and place it into the drop of water or iodine solution on the glass slide. Cover the preparation with a coverslip. Examine it carefully using a hand lens. You will clearly distinguish the rounded apex, leaf remnants, and individual bumps of varying size and shape.

For a more detailed Study of the shoot apex, take the shoot tip of Elodea, insert it into a slit made in a cut piece of elderberry pith, and use a razor blade or scalpel to make a longitudinal section. It is advisable to cut a series of thin sections and select the thinnest and most complete one. It must necessarily capture the shoot tip. Place it in a drop of water and cover with a coverslip.

Microscopic Examination of the Elodea canadensis Slide. Under low magnification of the microscope, observe the general appearance of the slide. In the lower part of the twig section, nodes and internodes are clearly visible, which gradually shorten toward the top. Normally developed large leaves, arranged in whorls of three at each node, give way to primordial leaves at various Selection/3.html">Stages of development, which in turn transform into leaf bumps, in the axils of which lie vegetative and generative bud primordia. The undifferentiated shoot tip serves as the shoot apex (Fig. 25).

Under high magnification, In addition to the previously noted parts, a Cytology/practical/54.html">Longitudinal section of the shoot apex reveals an outer layer of cells—the tunica—and the corpus, which comprises the remaining Cells of the meristematic tissue. These parenchymatous cells are living, with dense cytoplasmic contents, nearly isodiametric, tightly packed without intercellular spaces. They possess thin, delicate walls that do not hinder their growth. No METABOLISM/14.html">Chloroplasts were detected in the cells.

Draw the shoot apex under high magnification in your lab notebook and label its component parts.

Procedure for Preparing a Slide of the Young Root Apex of a Wheat Seedling. Place a drop of water on a glass slide. Place the tip of a young wheat seedling root into it. Using a hand lens, check whether the root cap is present at the tip and whether root hairs are visible. If these features are observed, the slide has been prepared correctly. Add another drop of water and cover with a coverslip. Secure the slide on the microscope stage with clips.

For a more detailed study of root Meristems, a longitudinal section of the root tip must be prepared. To do this, take a piece of elderberry pith, make a slit about 1 cm deep, and gently insert the tip of the wheat root horizontally using forceps. Level The surface of the pith, and only then proceed to make the necessary sections of the root tip. Sections should be made with a very sharp razor or blade. It is best to produce a series of sections. Select the most successful ones that are best preserved and most complete, and place them in a drop of water or iodine-potassium iodide solution. Using a hand lens or low microscope magnification, make sure that the root cap and root hairs are preserved on the preparations. Moisten the specimen once more with water or iodine solution and cover with a coverslip. Secure the finished slide on the microscope stage with clips.

Microscopic Examination of the Wheat Root Slide. Under low magnification, examine the object and sketch the structural diagram of the wheat seedling root. On the diagram, outline and indicate the following zones: the root cap covering the apex; the division zone, 2–4 mm long, located just above the root cap; the elongation zone, extending to the first root Hair primordia; the root hair zone, or absorption zone; and the maturation zone (or zone of lateral roots), located above the root hair zone.

Under high magnification, note that in the division zone, an outer layer of large cells oriented perpendicular to the root surface stands out. This is the dermatogen, which forms the epiblema in the root hair zone, thereby giving rise to a permanent absorptive tissue.

Beneath the dermatogen towards the center lie 3–7 layers of elongated periblem cells. These are living meristematic cells whose division forms the primary cortical tissues in the maturation zone.

In the center of the section, 4–8 rows of vertically elongated living cells stand out, forming the plerome. Through the division of these cells in the division zone, along with the subsequent elongation and root hair zones, the tissues of the central cylinder are formed, some of which are clearly visible (Fig. 26).

Pay special attention to the group of root cap cells located in the center, directly adjacent to the apex. They are somewhat larger, with dense, living cytoplasmic contents. These are the cells of the calyptrogen, a specific meristematic tissue of the root cap. Through the division of these cells, new root cap cells are replenished to replace the outer dead cells that periodically become mucilaginous and slough off, thereby facilitating the penetration of the root into the soil.

Draw the wheat root apex and label all the constituent parts noted above, comparing them with the provided illustrations.

Conclusion. Meristematic tissues possess a high capacity for Cell Division, enabling plants to grow in length and thickness. Meristematic tissues give rise to all other permanent tissues; they are localized in specific Regions of the plant and are classified as primary or secondary according to their origin.

Self-Assessment Questions

1. Where are apical meristems located?

2. What distinguishes the shoot apex from the root apex?

3. Based on their position, what type of meristematic tissue do the shoot and root apices belong to?