BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VII. PLANT TISSUES

In multicellular Algae, Functions may be distributed among the Cells of the thallus, but they do not form true Tissues. Tissue differentiation is characteristic of higher plants, whose vegetative body is divided into roots and shoots.

Interconnected cells of common origin that have the same Structure and perform identical functions are called tissues.

Organs in higher plants are built of tissues, which constitutes the tissue-organ level of Organization of living systems in the plant world. Organs, in turn, are interconnected and ensure the functioning of the plant as a single Organism. METABOLISM/2.html">THE CONCEPT OF "tissue" was introduced by the English botanist N. Grew, who divided it into parenchyma, formed by isodiametric cells, and prosenchyma, consisting of elongated cells.

The modern system of plant tissues is physiological and anatomical. According to this Classification, plant tissues are divided into meristematic (or meristem), dermal (protective), ground (or parenchyma), mechanical (supporting), vascular (conducting), and secretory.

Tissues can be simple, consisting of a single Cell type, or complex, built from several tissue types (periderm, phloem, xylem).

Meristematic Tissues

Meristematic tissue, or meristem, consists of small isodiametric (less commonly elongated) cells capable of division. Most of its protoplast consists of The Nucleus, as well as proplastids, Mitochondria, Endoplasmic reticulum, Golgi apparatus, and Ribosomes. There are many small vacuoles. Due to the ability of cells to divide, the meristem ensures the formation and growth of tissues and organs.

Meristematic tissue consists of parenchymatous or prosenchymatous cells devoid of intercellular spaces. Based on their function and properties, meristem cells are divided into initials and derivatives. Initial cells have an isodiametric shape. They retain The ability to divide continuously throughout the plant's life. Derivative cells stop dividing after a few divisions. They have a parenchymatous or prosenchymatous shape.

The number and arrangement of initial cells depend on the organ and the taxonomic affiliation of the plant. Thus, in the ROOT tip of clubmosses, horsetails, and ferns, there is only a single initial cell, whereas in dicotyledonous plants, the root tip contains three rows of initial cells, with 1-4 cells in each. Derivative cells are formed from the initial cells and eventually transform into permanent root tissues. Initial cells of the first row turn into root cap cells and dermatogen, from which the protoderm is formed, and subsequently the epiblema. Initial cells of the second row form the periblema, and from it the ground meristem, which differentiates into the cells of the primary root cortex. The third row of initial cells forms the plerome, from which the pericycle and procambium develop. They transform into the stele (the central axial cylinder of the root).

The SHOOT apical meristem of angiosperms contains two, or from one to four rows of initial cells that are part of the tunica. They surround a group of initial cells that make up the corpus. The outer layer of tunica cells transforms into the protoderm, which is the primordial epidermis. The inner layer of tunica cells, or occasionally the outer cells of the corpus, gives rise to the ground meristem, from which storage (assimilation) or primary mechanical Tissues of the primary cortex are formed. Initial cells of the corpus give rise to the procambium. The cells of the latter differentiate into cells of the phloem, xylem, mechanical tissues, and parenchyma, which are Components of the central axial cylinder, or stele (Fig. 47).

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Fig. 47. Apical Meristems in angiosperms:

A - shoot apical meristem (1 - tunica, 2 - corpus); B - root apical meristem

(1 - root cap, 2 - dermatogen, 3 - periblema, 4 - plerome).

Meristematic tissues are classified according to their origin and Location in plant organs.

According to their origin, meristems are divided into Primary and secondary.

The primary or embryonic meristem is present as early as in the seed embryo. During organ growth, it transforms into primary permanent tissue, forming its Primary Structure. In plant organs, the primary meristem is represented by the root and shoot apical meristems, pericycle, procambium, and intercalary meristem.

Secondary meristems appear during the growth of plant organs. They are formed from the procambium or living parenchymatous cells. Secondary meristems provide Secondary Growth and the Formation of secondary permanent tissue and secondary organ structure. Secondary meristems include the cambium, fascicular and interfascicular cambium, and cork cambium (phellogen).

According to their location in plant organs, meristems are classified into apical, lateral, intercalary, and traumatic (wound).

Apical meristems are represented by the root and shoot apices. They give rise to the root and shoot, respectively.

Lateral meristems are located in the axial organs of plants parallel to their surface. They include the pericycle, procambium, cambium, and phellogen.

Intercalary meristems are located at the base of stem internodes or leaf bases. They provide intercalary growth in length in grasses and horsetails, as well as intercalary leaf growth in seed plants.

Traumatic (wound) meristems appear in the event of organ damage; in this case, living (undamaged) cells divide intensively and form a callus—a tumor of undifferentiated cells. After a certain period of growth, callus cells, influenced by neighboring cells, differentiate into the corresponding permanent tissue. Thus, during grafting, the vascular tissue of the rootstock and scion connects, or when the bark is damaged, the protective and other tissues are restored.

Meristematic tissue is rich in phytohormones (Cytokinins, Auxins), Nucleic Acids, purine and pyrimidine bases, Vitamins (B1, B2, PP, E, carotenoids), and Enzymes. For example, pine and birch buds are rich in Essential Oils, Tannins, phytoncides, and Glycosides, which is why they are used in medicine.