Protective fabric . They form the outer limit of plants and are in contact with the environment. It is responsible for protecting the plant from drying out and in turn allowing gas exchange to occur.
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- 1 Types of protective fabrics in vegetables
- 1 Epidermal tissue
- 2 Characteristics of mature epidermal cells
- 1 Cell wall
- 2 Stomatal apparatus or stomata
- 3 Trichomes
- 3 Suberoso fabric
- 4 Characteristics of suberose cells
- 1 Cell wall
- 2 Lenticels
- 5 See also
- 6 Sources
Types of protective fabrics in vegetables
- Epidermal tissue.
- Suberoso fabric (suber or cork).
It corresponds to the superficial layer of cells that covers the entire primary body of the plant: stems, roots, leaves, flowers, fruits and seeds. Some authors refer to the root epidermis as rhizodermis .
It is a primary tissue and originates from the apical meristems , and in particular from the protodermis .
In relation to the multiplicity of its functions, the epidermis contains a wide variety of cell types. The most abundant are the epidermal cells themselves, which can be considered as the least specialized elements and that constitute the fundamental mass of tissue. Scattered among the epidermal cells are the cells of the stomatal apparatus or stomata, and sometimes other specialized cells. The epidermis can produce a wide variety of appendages, trichomes, in the form of hairs or papillae.
Characteristics of mature epidermal cells
The cells are varied in shape: tubular, flattened, etc., arranged closely together without intercellular spaces. They are living cells, with large vacuoles, where water-soluble anthocyanin pigments accumulate, as occurs in many leaves and flowers; they generally do not have chloroplasts, except in the occlusive cells of the stomata and in the epidermal cells of plants that live in shady places, such as ferns.
The most important characteristic of the cell wall of epidermal cells is the presence of a lipid substance, cutin, which permeates the wall (cutinization) and forms the cuticle on the outer surface of the cells. The cuticle varies considerably in thickness in the different plants according to the environmental conditions. The cuticle surface can be smooth, present folds, cracks, etc. Accumulation of wax in the form of granules, hooks, crusts, homogeneous layers, etc. can be observed on the surface of the cuticle. Other surface deposits are resin, oil, or mineral salts in crystalline form. In some cases, lignin, suberin, silica, or mucilage may occur in epidermal cells.
Stomatal apparatus or stomata
They constitute a modification of the epidermal tissue and present as pores or openings surrounded by two occlusive cells. These cells through turgidity changes, control the size of the pore or ostiol .
Stomata are formed by isolated meristematic cell divisions (meristemoids), which become the stem cells of stoppers after various mitotic divisions. Subsequently, these cells become the occlusive cells, among which is the ostiol.
The shape of the occlusive cells is generally kidney-shaped, with thickening of the wall at the upper and lower edges, which when seen in sections resemble horns, and are sometimes absent.
The stomata regulate gas exchange with the atmosphere, the uptake or loss of oxygen and carbon dioxide, and also the loss of water as steam. This phenomenon is known as perspiration .
They are epidermal appendages of diverse shape, structure and functions. They are represented by glandular , protective and support hairs ; by scales, by diverse papillae and by the absorbent hairs of the roots. They can occur in all parts of the plant, and persist throughout the life of an organ or be ephemeral. Some persistent hairs remain alive; others lose the protoplasm and remain dry.
The hairs can be grouped into unicellular and multicellular. In turn, both can be simple or branched. Multicellular cells can consist of one or more rows of cells. Some multicellular hairs have branching, others have branches more or less arranged in one plane (starry hairs).
The cell walls of trichomes are commonly made of cellulose covered by a cuticle; they can also be lignified. Vegetable hairs sometimes produce thick secondary walls; for example, the hairs of cotton seeds. At other times the walls are impregnated with silica and calcium carbonate.
A very important type of trichome in the life of the plant is the absorbent hairs of the roots.
This tissue replaces the epidermis when it dies and falls off, which is a common phenomenon in stems and roots with secondary growth. In plants that have primary growth throughout their development, the remains of the epidermis or external cortical layers suberify their walls, and provide protection to the plant.
It originates from the phylogen, a secondary meristem that in turn originates at different depths from the stem or root structure, outside the cambium ring .
Characteristics of suberose cells
They are approximately prismatic in shape; often somewhat elongated parallel to the longitudinal axis of the stem or root. They are arranged in a compact way, without intercellular spaces.
The cell walls are thickened with suberin, a process that begins before the cells reach their final size. The color of the suberose cells depends on the presence of tannins, resins, and polyterpenes. After their differentiation, the suberose cells lack a protoplast and their cavity is filled with air or colored substances.
In the stems, the suber or cork is interrupted by lenticels , areas characterized by a relatively loose cell arrangement and by the absence of more or less complete suberification. The presence of intercellular spaces in the tissue of the lenticels and the continuity of these spaces with those of the interior of the stem have determined that, like stomata, lenticels are related to gas exchange. The size of the lenticels is variable, from structures not visible to the naked eye, up to 1cm or more in length.
Some authors use the term peridermis to indicate the unity formed by the phylogen, the subber produced by the phylogen towards the outside, and the felodermis, tissue of cortical parenchyma, made up of cells derived from the phylogen towards the inside of the plant.