Periderm


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Periderm

A group of tissues which replaces the epidermis in the plant body. Its main function is to protect the underlying tissues from desiccation, freezing, heat injury, mechanical destruction, and disease. Although periderm may develop in leaves and fruits, its main function is to protect stems and roots. The fundamental tissues which compose the periderm are the phellogen, phelloderm, and phellem.

The phellogen is the meristematic portion of the periderm and consists of one layer of initials. These exhibit little variation in form, appearing rectangular and somewhat flat in cross and radial sections, and polygonal in tangential sections.

The phelloderm cells are phellogen derivatives formed inward. The number of phelloderm layers varies with species, season, and age of the periderm. In some species, the periderm lacks the phelloderm altogether. The phelloderm consists of living cells with photosynthesizing chloroplasts and cellulosic walls.

The phellem, or cork, cells are phellogen derivatives formed outward. These cells are arranged in tiers with almost no intercellular spaces except in the lenticel regions. After completion of their differentiation, the phellem cells die and their protoplasts disintegrate. The cell lumens remain empty, excluding a few species in which various crystals can be found. The remarkable impermeability of the suberized cell walls is largely due to their impregnation with waxes, tannins, cerin, friedelin, and phellonic and phellogenic acids.

Lenticels are loose-structured openings that develop usually beneath the stomata and that facilitate gas transport through the otherwise impermeable layers of phellem. See Sclerenchyma

Periderm

 

the protective tissue on the stems, roots, tubers, and rhizomes of perennial and, less frequently, annual plants; it consists of cork (phellem), phelloderm, and phellogen (cork cambium). The periderm is tissue of secondary origin. Its middle part, the phellogen, arises from the epidermis (apple and willow stems), the subepidermal layer (birch, linden, and elder stems), the deeper layers of the primary cortex (barberry and pine stems), the pericycle (raspberry, currant, and spirea stems; the roots of the majority of plants), or the phloem (grape stems).

As a result of division of phellogen cells, a multilayer cork— the protective tissue proper—is formed on the outside, while one or more layers of phelloderm cells are formed beneath. The latter consists of living cells that differ from the parenchymatous cells of the cortex in their radial distribution. Sometimes the phelloderm is absent (raspberry, bittersweet).

Cork cells are dead and are impervious to air and water. The cavities of the dead cells fill up with air, thus intensifying the heat-insulating properties of cork tissue. (Gas exchange and evaporation in plants are accomplished through lenticels in the periderm.)

Several periderms usually develop in plant organs; each successive one occurs beneath the preceding layer. The formation of only one periderm is relatively rare (aspen, alder, perennial herbs). In time, the outer periderms and the tissues enclosed between them die, forming bark on the surface of the organ.

M. A. GULENKOVA

periderm

[′per·ə‚dərm]
(botany)
A group of secondary tissues forming a protective layer which replaces the epidermis of many plant stems, roots, and other parts; composed of cork cambium, phelloderm, and cork.
(embryology)
The superficial transient layer of epithelial cells of the embryonic epidermis.
References in periodicals archive ?
The metaphyll's petiole shows similarity with the eophyll, except for the presence of trichomes, periderm on both sides (mainly at the base and on the adaxial side), idioblasts with druses, and primordium fibers on the phloematic region.
After 24 h of incubation, cell walls of the periderm showed weak coloring.
In trial 3 (T3) where the wounding treatment penetrated the tuber periderm there were no significant differences recorded between the clones A380 andTC-RB8 and the parent (Table 1).
This suggests that Jag2 is the ligand responsible for activation of Notch1 and oral periderm differentiation.
Skin development begins at 36 days of gestational age, with the formation of an epidermis consisting only of a basal layer of cells and a superficial periderm. Less than 8 months later--assuming normal development--the newborn emerges with soft, moist, resilient skin that provides an excellent barrier that adapts rapidly to the change from immersion in liquid to air and light exposure.
The layers that are part of the outer bark are collectively referred to as the periderm. The outmost periderm layer--made up of cork cells that die soon after their protective qualities have developed--is the visible, touchable surface of smooth-barked trees.
It occurs, in a smaller amount, in the periderm, associated to suberin and acting as a barrier against pathogens (Browning, 1967; GuimarAes et al., 2003).
The root segments selected varied in diameter and in possession of an epidermis versus periderm; thus they varied in age.
Many could grow up to 50 metres tall but the main stem - the "trunk" - had very little wood and mostly consisted of bark-like tissue called periderm. This tissue could grow quickly, allowing the plants to reach their full height in as little as 25 years.
9) extended from the periderm to the secondary xylem, exposing partially the latter (Fig.
Collectively the cork cambium and the cells it produces--the cork cells and phelloderm--make up the periderm, a tissue that replaces the epidermis as the protective outer covering.