Epidermis (botany)
The epidermis (from the
Description
The epidermis is the outermost cell layer of the primary plant body. In some older works the cells of the leaf epidermis have been regarded as specialized
The cells of the epidermis are structurally and functionally variable. Most plants have an epidermis that is a single cell layer thick. Some plants like Ficus elastica and Peperomia, which have a periclinal cellular division within the protoderm of the leaves, have an epidermis with multiple cell layers. Epidermal cells are tightly linked to each other and provide mechanical strength and protection to the plant. Particularly, wavy pavement cells are suggested to play a pivotal role in preventing or guiding cracks in the epidermis.[4] The walls of the epidermal cells of the above-ground parts of plants contain cutin, and are covered with a cuticle. The cuticle reduces water loss to the atmosphere, it is sometimes covered with wax in smooth sheets, granules, plates, tubes, or filaments. The wax layers give some plants a whitish or bluish surface color. Surface wax acts as a moisture barrier and protects the plant from intense sunlight and wind.[5]
The epidermal tissue includes several differentiated cell types: epidermal cells,
In plants with secondary growth, the epidermis of roots and stems is usually replaced by a periderm through the action of a cork cambium.
Stoma complex
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The leaf and stem epidermis is covered with pores called
- The guard cells are bean-shaped in surface view, while the epidermal cells are irregular in shape
- The guard cells contain chloroplasts, so they can manufacture food by photosynthesis (The epidermal cells of terrestrial plants do not contain chloroplasts)
- Guard cells are the only epidermal cells that can make sugar. According to one theory, in sunlight, the concentration of potassium ions (K+) increases in the guard cells. This, together with the sugars formed, lowers the water potential in the guard cells. As a result, water from other cells enters the guard cells by osmosis so they swell and become turgid. Because the guard cells have a thicker cellulose wall on one side of the cell, i.e. the side around the stomatal pore, the swollen guard cells become curved and pull the stomata open.
At night, the sugar is used up and water leaves the guard cells, so they become flaccid and the stomatal pore closes. In this way, they reduce the amount of water vapor escaping from the leaf.
Cell differentiation in the epidermis
The plant epidermis consists of three main cell types:
Trichomes develop at a distinct phase during
Arabidopsis thaliana uses the products of inhibitory genes to control the patterning of trichomes, such as TTG and TRY. The products of these genes will diffuse into the lateral cells, preventing them from forming trichomes and in the case of TRY promoting the formation of pavement cells.
Expression of the gene MIXTA, or its
Stomatal patterning is a much more controlled process, as the stoma affects the plant's water retention and
Stomata are pores in the plant epidermis that are surrounded by two guard cells, which control the opening and closing of the aperture. These guard cells are in turn surrounded by
Stomata begin as stomatal meristemoids.[
Because stomata play such an important role in the plants' survival, collecting information on their differentiation is difficult by the traditional means of genetic manipulation, as stomatal mutants tend to be unable to survive. Thus the control of the process is not well understood. Some genes have been identified. TMM is thought to control the timing of stomatal initiation specification and FLP is thought to be involved in preventing the further division of the guard cells once they are formed.
Environmental conditions affect the development of stomata, in particular, their
See also
- Bark
- Cork cambium
- Periderm
References
- ^ Hill, J. Ben; Overholts, Lee O; Popp, Henry W. Grove Jr., Alvin R. Botany. A textbook for colleges. Publisher: MacGraw-Hill 1960
- ^ "9.3: Plant Tissues". Biology LibreTexts. 29 February 2020. Retrieved 19 July 2023.
- ISBN 978-0-471-73843-5
- PMC 10719271.
- OCLC 222047616
- PMID 10938806.
External links
- Plant tissue systems Archived 2007-12-05 at the Wayback Machine