Plants have cells as their basic unit, which are organized into tissues, which are then organized into organs. The internal structure of different organs in a plant differs. The monocots and dicots of angiosperms are also anatomically distinct. Internal structures exhibit environmental adaptations as well.
Plant anatomy is primarily concerned with the structure and study of tissue organization. A tissue is defined as “a collection of similar or dissimilar cells that share a common origin and perform a specific function.” Secretory tissue, Permanent tissue, and Meristematic tissues or Meristems are the three main types of tissues. There are two types of tissue in plants: Meristematic tissues or Meristems and Permanent tissue.
Meristematic Tissues
- Meristematic tissues contain living cells of various shapes. They have a large nucleus that lacks the vacuole. The cells have no intercellular space between them. These cells can be found in the meristem.
- Meristematic tissue cells can actively divide to form specialized structures such as buds of leaves and flowers, tips of roots and shoots, and so on. These cells contribute to the plant’s length and bulkiness.
- The term “meristem” was coined by Carl Wilhelm von Nägeli. Meristematic tissue contains undifferentiated cells, which serve as the foundation for specialized plant structures.
- Meristematic tissue cells divide actively to form specialized structures such as buds of leaves and flowers, tips of roots and shoots, and so on. These cells contribute to the plant’s overall length and width.
- Meristematic tissues are made up of living cells of various shapes. Meristem is the zone where these cells exist.
- Plant growth is largely restricted to specialized regions of active cell division known as meristems.
- The root apical meristem is located at the tip of the root, whereas the shoot apical meristem is located at the farthest region of the stem axis.
- Apical meristems are meristems that form at the tips of roots and shoots and produce primary tissues.
- Intercalary meristem is a type of meristem that occurs between mature tissues and is found in grasses and regenerated parts.
- Some cells ‘left behind’ from the shoot apical meristem during leaf formation and stem elongation form the axillary bud, which is present in the axils of leaves and forms a branch or a flower.
- Both apical and intercalary meristems are primary meristems because they appear early in a plant’s life and help to form the primary plant body.
- The secondary or lateral meristem is the meristem that appears later than the primary meristem in the mature regions of roots and shoots of many plants.
Fascicular vascular cambium, interfascicular cambium, and cork-cambium are a few examples. - Particular areas of the apical meristem produce vascular tissues, ground tissues, and dermal tissues during the development of the main plant body.
- After cell division in both primary and secondary meristems, newly formed cells become specialized and lose their ability to divide; these cells are referred to as permanent or mature cells, and they comprise the permanent tissues.
Classification of Meristematic Tissues
The meristematic tissue can be classified into different types according to its function, position, and origin.
Based on position
Lateral Meristem
- It is found on the lateral side of the stems and roots.
- It increases the plant’s thickness.
- The two lateral meristems are vascular cambium and cork cambium.
- These divide either pre-clinically or radially, resulting in an increase in secondary permanent tissues.
Apical meristem
- These are found at the tips of the roots and shoots and aid in the growth of the plant’s height.
- Cell divisions of various types aid in the growth of cells in the roots and shoots. and promote cellular growth
- The apical meristem is divided into two parts:
- The promeristem zone is made up of dividing cells (apical initials)
- Protoderms (epidermis), procambium (primary vascular tissue), and ground meristem are all found in the meristematic zone (cortex and pith).
Intercalary Meristem
- It is found at the intercalary position within the leaves and internodes.
- These contribute to the lengthening of the internode.
- It is surrounded by grass, monocots, and pines.
- It is a component of the apical meristem and contributes to the plant’s peak.
Based on Origin
Primordial meristem
- Because the promeristem develops from the embryo, it is also known as the primordial or embryonic meristem. It is found in areas where an organ or a part of the plant body is developing.
- Promeristem is a group of initial cells that form the foundation of an organ or plant part. This group is made up of a small number of cells that divide repeatedly to give rise to primary meristem. All other meristems, including the primary meristem, are derived from the promeristem.
Secondary Meristem
- Secondary meristems get their name because they develop from permanent cells.
- Secondary meristems in the plant body produce secondary tissues and add new cells for effective protection and repair.
- A good example of a secondary meristem is phellogen or cork cambium.
Primary Meristem
- A promeristem gives rise to a primary meristem, which retains its meristematic activity. It is found at the apex of roots, stems, and leaf primordial, for example, Apical meristem and Intercalary meristem.
Based on Function
Ground Meristem
- The cells are quite large and have thick walls.
- It contributes to the formation of the cortex, pericycle, and pith.
- Meristematic tissue is found in the apices of root systems and shoots and divides continuously.
Protoderm
- It is the epidermis, the tissue that covers the outside of the plant.
- It protects the plants from mechanical shocks.
Procambium
- It is the innermost tissue that gives rise to the xylem and phloem.
- It aids in the transport of water and nutrients to various parts of the plant.
Based on the Plane of Division
Mass Meristem
- It divides into all planes, forming a mass of cells, such as endosperm.
Rib meristem
- It divides in a single plane, resulting in a row of cells. Cortex, for example.
Plate Meristem
- It divides into two planes, forming a cell plate. For example, epidermis and epiblema.
Characteristics of Meristematic Tissues
- They have a small number of vacuoles.
- Meristematic tissue is alive and thin-walled, with the ability to self-renew.
- When a cell divides, one cell remains identical to the parent cell, while the others develop specialized structures.
- The protoplasm of the cells is very dense, and the meristematic tissues heal an injured plant’s wounds.
- Meristematic tissue cells are immature and young.
- They do not store food and have a high metabolic rate.
Uses of Meristematic Tissues
- They’re alive, and they’re composed of a swarm of rapidly dividing cells.
- Tissue is composed of totipotent (all-powerful) cells.
- Indefinitely, the cells remain embryonic (immature) and unspecialized.
- Vacuoles are typically absent or extremely small if present and cells can be spherical, polygonal, or rectangular in shape.
- The nucleus is large and can be found in divisions’ interphase and subphases.
- With the exception of mitochondria, other cell organelles are absent or in a non-functional state.
- The cell wall is composed of cellulose, which is a homogeneous component, and the cells have a large nucleus and a large number of protoplasms.
- Do not keep reserved food materials if orgastic chemicals are missing.
FAQs on Meristematic Tissues
Question 1: What exactly are meristematic tissues?
Answer:
Meristematic tissue is plant tissue that can divide actively throughout its life. Nageli coined the term meristem (1858). Meristems are found in plant apex, root, leaf primordia, vascular cambium, cork cambium, and so on.
Question 2: What are apical meristems?
Answer:
These are found in the tips of roots and shoot at opposite ends of the plant axis. Cell division and subsequent cellular enlargement in these areas extend the plants above and below ground parts. Meristems also influence the shapes of mature plants because they lay down the patterns for subsequent growth.
Question 3: What exactly is a primary meristem?
Answer:
The cells produced by apical meristem divisions quickly differentiate into three zones of distinct tissues that differentiate below the apical meristems. The protoderm, procambium, and ground meristem are the primary meristems, also known as transitional meristems. They give rise to the primary plant body’s tissue systems.
Question 4: What are some of the characteristics of meristematic tissues?
Answer:
- Because when a cell divides, one cell remains identical to the parent cell while the others divide to produce specialized structures, it has the ability to self-renew.
- They have the fewest number of vacuoles.
- Meristematic tissues are thin-walled, living tissues.
Question 5: What is the Apical Cell Theory?
Answer:
Nageli proposed this theory (1858). The shoot apical meristem, according to this theory, is made up of a single apical cell. This theory applies to higher algae, bryophytes, and many pteridophytes but not to higher plants (i.e., gymnosperms and angiosperms).