Lenticels: Characteristics And Functions

The lenticels are specialized structures located at the felodermis, whose function is to ensure the entry of oxygen and gas exchange. They are superficial accumulations of loose cells with little suberification in lenticular form (biconvex lens).

These small elongated circular structures are open spaces that allow active communication with the environment. In addition to maintaining a continuous flow of gases between the plant and the environment, they facilitate evapotranspiration and the absorption of surface water.

Its appearance appears as a transverse or longitudinal elongated mass, composed of loose cells around a slit in the peridermis. In this case, the peridermis functions as a protective tissue in stems and roots that show adventitious growth.

The presence of lenticels is limited to the felodermis, where the felogen is very active and produces tissues with large intercellular spaces. In fact, the phellogen around the lenticel has numerous intercellular spaces.

The tissues that make up the lenticels with wide intercellular spaces are of the aerenchymal type, being the place where gas exchange occurs. As plants grow and thicken, the lenticels do not widen, but new structures develop.

General  characteristics

The size of the lenticels is determined by the size of the structure of the plant where it occurs. There are tiny (1-3 mm) in grape fruits ( Vitis vinifera ) or 6-8 cm in the bark of Balsam ( Myroxylon balsamum ).

They are circular or elongated, and arranged transversely or longitudinally on the surface of roots, stems and branches. It is white, creamy or yellowish in color, with a central space similar to a dark colored cut.

Lenticels are located on the surfaces of young tissues or lignified tissues, in roots, stems, leaves and even fruits. Likewise, they are observed in woody plants, on the súber and the cork that externally covers developed trees.

The area where the lenticel is formed has a partially weak cellular development, with a low level of suberification. This tissue has a large number of intercellular spaces, which is why they are related to gas exchange.

Origin

Lenticels are formed in a specific area of ​​lenticular or circular shape that emerges from the peridermis. The lenticular pore is present in the central area, below which parenchymal cells with large intercellular spaces are located.

These structures frequently originate under the stomata from the parenchymal cells that line the substomatic chamber. The division of these cells produces the felogen, which generates felodermis towards the inside and filling cells towards the outside.

The filler cells produced by the phellogenic meristematic tissue pile up, tear the epidermis and emerge outwards. The area where the lenticel forms is characterized by having an active suberous cambium that produces a greater amount of intercellular spaces.

In some species such as ivy ( Hedera helix ) the lenticels originate from tissue independent of the stomata. From the peridermis originating from the inner layers of the stem, a part of the fellogen produces filler cells that emerge as lenticels.

Location

These small protrusions develop mainly in the meristematic tissues, in the stems in growths and young leaves; also in herbaceous dicotyledons. In fruits as dissimilar as apple, avocado (avocado), mango or grapes, it is common to find lenticels.

In woody trees, such as the white poplar ( Populus alba ), the presence of bumps or lenticels around the entire surface of the stem is common. Likewise, they are located in the main or secondary roots, arranged in pairs, one on each side.

On the smooth surface of species such as cannelloni ( Rapanea laetevirens ), they appear as an agglomeration of cells that emerge from the peridermis. In the bark of woody plants they develop on the surface under the scales or in the fissures of the furrows.

Similarly, in plants with extensive suberous tissue, they form along the surface. In the cork or protective plant tissue of some species, the lenticels appear radially across their surface.

Types of lenticels

In Gymnosperms, lenticels are made up of cells similar to the suber, elongated, with a thin wall and large intercellular spaces. In Dicotyledons they are classified depending on the layer of suberized cells that cover them.

No closure layer

Lenticel is characterized by being formed by suberized cells, grouped and with intercellular spaces. Its development in various species can be annual. Typical in avocado ( Persea americana ) and magnolias ( Magnolia grandiflora ).

With a closure layer

There is a layer of suberized cells that covers a set of loose filling cells and with wide intercellular spaces. This structure is usually formed at the end of the season. They are frequent in oak ( Quercus robur ) and elderberry ( Sambucus peruviana ).

With several layers of closure

It occurs in specialized lenticels of species such as peach ( Prunus persica ) and beech ( Fagus sylvatica ). The suberized layers are formed annually, and are associated with loose non-suberized fabrics. These layers are one or two cells thick and cover loose multi-cell tissue.

Function

Basically the function of lenticels is the gas exchange between the internal tissues of the plant and the surrounding air. These openings allow oxygen to enter the internal parenchymal tissues of the plant for cellular respiration.

The internal tissues of the stem show a constant metabolic activity, so they require the exchange of gases with the air. Likewise, the internal tissues of the roots obtain oxygen and gases from the localized pore space between the soil particles.

Lenticels are structures made up of numerous intercellular spaces that facilitate gas exchange. In trees, in the autumn and winter seasons, when the plant loses its leaves, lenticels facilitate gas exchange.

In the same way, in specialized roots such as tubers, lenticels allow the loss of water and gases, facilitating maturation. Fruits continually require fresh air to breathe and ripen properly, in fact, lenticels in fruits fulfill this function.

References

    1. Evert Ray F, & Eichhonrn Susan E. (1992) Plant Biology. Editorial Reverté. SA ISBN 84-291-1843-8.
    2. Lenticels. Secondary Structure of the Stem (2013) Morphology of Vascular Plants. Faculty of Agricultural Sciences, Sgt. Cabral 2131. Available at: biologia.edu.ar
    3. Megías Manuel, Molist Pilar, and Pombal Manuel A. (2017) Atlas of Animal and Plant Histology. Vegetable Tissues. Protection. Department of Functional Biology and Health Sciences. Faculty of Biology. University of Vigo.
    4. Peridermis. Plant Tissues (2018) Atlas of Plant and Animal Histology. Available at: mmegias.webs.uvigo.es

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