The plant tissues are groups of specialized cells that form the various plant organs. The main plant tissues are the meristems or growth tissues, the fundamental tissues, the vascular systems and the epidermal ones.
When the embryo is growing, new cells are formed, which are grouped into tissues and these in turn form organs. As the plant develops, this characteristic of indefinite growth or permanently “young” tissues is restricted to the meristems.
The fundamental tissue is divided into parenchyma, collenchyma, and sclerenchyma. These structures have support functions and are involved in the photosynthetic and respiration process. Vascular systems include the tissues responsible for conducting water, salts, nutrients and sap, called xylem and phloem .
Finally, the epidermal tissues have protective functions and are located in the most external parts of the plant. The epidermis can be replaced in secondary growth.
Tissues can also be classified based on the type of cells that compose them. The parenchyma is considered a simple tissue because it is made up of a unique type of cells. In contrast, the rest of the tissues are complex because they are made up of different cell types.
The conglomerates of plant cells that form the different tissues in plants are characterized mainly by the presence of a solid cell wall that protects the cell from osmotic stress. In addition, these have special organelles – chloroplasts – where photosynthetic events take place .
However, each type of plant tissue has its unique characteristics. In the next section we will describe each fabric in detail.
Classification and functions
Botanists have always recognized the existence of an organization in conspicuous units within the body of plants . These tissue systems are present both in the root, as well as in the leaves and stems.
In the three mentioned structures, the tissues show a basic similarity that allows the continuity of the plant body.
There are three main tissue systems: the fundamental system, the vascular system, and the epidermal system. Each tissue system originates from the development of the embryo with the meristems.
The fundamental system is made up of three types of tissues: the parenchyma – which is the most predominant – the collenchyma and the sclerenchyma.
The vascular system is made up of conducting structures called xylem and phloem. Finally, the tissue system is made up of the epidermis (which is replaced by the peridermis in secondary growth).
Meristems are essentially characterized by their permanent ability to divide. The apical and lateral meristems are classified.
The apical meristems are responsible for the extension of the plant body (called primary growth) and are located in the terminal portions of stems and roots.
In contrast, the lateral meristem is associated with the production of secondary tissues. It consists of the vascular cambium and the suberogenous cambium. The vascular is responsible for producing the vascular tissues that are the xylem and phloem and the suberogen produces the suber or cork.
However, there are other tissues that also undergo cell division such as protodermis, procambium and fundamental tissue.
Parenchyma, collenchyma, and sclerenchyma are simple tissues because they are made up of only one type of cells.
The parenchyma is the precursor to all the remaining tissues. It is characterized by forming masses in the different structures of the plants, including the fruits.
These parenchymal cells are grouped into elements called rays. Parenchymal cells are polyhedral, alive, and capable of dividing. Thanks to this ability, they participate in the regeneration processes.
The functions of the parenchyma are storage and healing. In addition, it participates in metabolic processes such as photosynthesis and respiration.
Collenchyma is also being formed by living cells in its maturity. The cells are elongated, with thick, shiny walls. They are found forming cords in the epidermis, in the petioles and in the veins of the dicotyledons. Its main function is support.
Finally, the sclerenchymal tissue is characterized by its firmness, thanks to the lignification of its thick and irregular cell walls.
They are divided into two cell types: the fibers are long and fine, some are economically important, such as Manila hemp; and the sclereids, mainly branched. It takes care of the support, thanks to its thickened texture.
The vascular system is a set of tubes whose main function is the transport of substances. In plants it is made up of two conductive elements: phloem and xylem. The movement of substances through this system is called translocation.
In vascular plants (club mosses, ferns, conifers and angiosperms), the phloem is responsible for the transport of nutrients. Its origin can be primary and is called protofloem or secondary origin. The cells that are part of its structure are the sieving elements, a term that refers to the presence of pores.
In contrast, the xylem is responsible for conducting water, salts and minerals from the soil to the aerial regions of the plant. In addition to conduction, the xylem also participates in the support of the plant, since – in some cases – its walls contain lignin.
The forces that allow the movement of substances vary in both tissues. Xylem uses perspiration and radical pressure, while phloem uses active transport mechanisms.
The epidermis forms the tissue tissue and is generally grouped into a single layer of cells. It is the outermost layer of the plant and is found in leaves, in flower elements, in fruits, in seeds, and in roots. Epidemic cells vary widely in terms of their morphology and function.
Cells may have a special coating that reduces or completely prevents water loss. Said protective covering can be formed of waxes, suberin, among others.
Some epidermal cells may have stomata, some type of appendage or trichomes. Stomata are responsible for mediating gas exchange between the plant and its environment.
- Beck, CB (2010). An introduction to plant structure and development: plant anatomy for the twenty-first century . Cambridge University Press.
- Campbell, NA (2001). Biology: Concepts and relationships . Pearson Education.
- Curtis, H., & Schnek, A. (2006). Invitation to Biology . Panamerican Medical Ed.
- Raven, PH, Evert, RF, & Eichhorn, SE (1992). Plant Biology (Vol. 2). I reversed.
- Sadava, D., & Purves, WH (2009). Life: The Science of Biology. Panamerican Medical Ed.
- Thorpe, STE (2009). The Pearson General Studies Manual 2009, 1 / e . Pearson Education India.