Lenticel
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A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the
bark Bark may refer to: Common meanings * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Arts and entertainment * ''Bark'' (Jefferson Airplane album), ...
of woody stems and roots of
gymnosperm The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...
s and
dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, ...
ous flowering plants. It functions as a pore, providing a pathway for the direct exchange of gases between the internal tissues and atmosphere through the bark, which is otherwise impermeable to gases. The name lenticel, pronounced with an , derives from its lenticular (
lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
-like) shape. The shape of lenticels is one of the characteristics used for tree identification.


Evolution

Before there was much evidence for the existence and functionality of lenticels, the
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
record has shown the first primary mechanism of
aeration Aeration (also called aerification or aeriation) is the process by which air is circulated through, mixed with or dissolved in a liquid or other substances that act as a fluid (such as soil). Aeration processes create additional surface area in t ...
in early
vascular plants Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue ( ...
to be the
stomata In botany, a stoma (: stomata, from Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange between the internal air spa ...
. However, in
woody plants A woody plant is a plant that produces wood as its structural tissue and thus has a hard stem. In cold climates, woody plants further survive winter or dry season above ground, as opposed to herbaceous plants that die back to the ground until s ...
, while the respiratory function of stomata is retained in the living epidermis of leaves and green stems, that function is lost where the epidermis of trunks and branches is displaced by vascular and cork cambial activity and by
secondary growth In botany, secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips ...
. In such parts the entire epidermis may be shed as it is replaced by a suberized periderm or
bark Bark may refer to: Common meanings * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Arts and entertainment * ''Bark'' (Jefferson Airplane album), ...
in which the respiratory functions of the stomata may be replaced by lenticels, at least until the bark becomes too thick. The extinct
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...
plants of the
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
'' Lepidodendron'' and ''
Sigillaria ''Sigillaria'' is a genus of extinct, spore-bearing, Lepidodendrales, arborescent lycophyte, known from the Carboniferous and Permian periods. It is related to the more famous ''Lepidodendron'', and more distantly to modern Isoetes, quillworts. ...
'' were the first to have distinct aeration structures that rendered these modifications. "Parichnoi" (singular: parichnos) are canal-like structures that, in association with foliar traces of the
stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...
, connected the stem's outer and middle
cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...
to the mesophyll of the
leaf A leaf (: leaves) is a principal appendage of the plant stem, stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leav ...
. Parichnoi were thought to eventually give rise to lenticels as they helped solve the issue of long-range
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
transport in these woody plants during the
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
period. They also acquired secondary connections as they evolved to become transversely elongated to efficiently aerate the maximum number of vertical rays as well as the central core tissue of the stem. The evolutionary significance of parichnoi was their functionality in the absence of cauline stomata, where they can also be affected and destroyed by pressure similar to what can damage to stomatal tissue. Evidently, in both
conifers Conifers () are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All e ...
and Lepidodendroids, the parichnoi, as the primary lenticular structure, appear as paired structures on either side of leaf scars. The development and increase in the number of these primitive lenticels were key to providing a system that was open for aeration and
gas exchange Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a b ...
in these plants.


Structure and development

In plant bodies that produce
secondary growth In botany, secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips ...
, lenticels promote gas exchange of oxygen,
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
, and
water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...
. Lenticel formation usually begins beneath
stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...
tal complexes during primary growth preceding the development of the first periderm. The formation of lenticels seem to be directly related to the growth and strength of the shoot and on the hydrose of the tissue, which refers to the internal
moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Moisture is defined as water in the adsorbed or absorbed phase. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some comme ...
. As stems and roots mature lenticel development continues in the new periderm (for example, periderm that forms at the bottom of cracks in the bark). Lenticels are found as raised circular, oval, or elongated areas on stems and roots. In woody plants, lenticels commonly appear as rough, cork-like structures on young branches. Underneath them,
porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
tissue creates a number of large intercellular spaces between cells. This tissue fills the lenticel and arises from
cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...
in the phellogen or substomatal
ground tissue The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. This tissue system is present between the dermal tissue and forms the main bulk of t ...
. Discoloration of lenticels may also occur, such as in mangoes, that may be due to the amount of
lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidit ...
in cell walls. In oxygen deprived conditions, making respiration a daily challenge, different species may possess specialized structures where lenticels can be found. For example, in a common
mangrove A mangrove is a shrub or tree that grows mainly in coastal saline water, saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen a ...
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
, lenticels appear on pneumatophores (specialized
root In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often bel ...
s), where the
parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...
cells that connect to the
aerenchyma Aerenchyma or aeriferous parenchyma or lacunae, is a modification of the parenchyma to form a spongy tissue that creates spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and ...
structure increase in size and go through cell division. In contrast, lenticels in
grapes A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began approximately 8,0 ...
are located on the
pedicels In botany, a pedicel is a stem that attaches a single flower to the inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branch ...
and act as a function of
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
. If they are blocked, hypoxia and successive
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
accumulation may result and lead to
cell death Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as di ...
.


Fruits

Lenticels are also present on many fruits, quite noticeably on many apples and pears. On European pears, they can serve as an indicator of when to pick the fruit, as light lenticels on the immature fruit darken and become brown and shallow from the formation of cork cells. Certain bacterial and fungal infections can penetrate fruits through their lenticels, with susceptibility sometimes increasing with its age. While the term lenticel is usually associated with the breakage of periderm tissue that is associated with gas exchange, it also refers to the lightly colored spots found on
apples An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...
(a type of pome fruit). "Lenticel" seems to be the most appropriate term to describe both structures mentioned in light of their similar function in gas exchange. Pome lenticels can be derived from no longer functioning stomata, epidermal breaks from the removal of
trichomes Trichomes (; ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant ...
, and other epidermal breaks that usually occur in the early
development Development or developing may refer to: Arts *Development (music), the process by which thematic material is reshaped * Photographic development *Filmmaking, development phase, including finance and budgeting * Development hell, when a proje ...
of young pome fruits. The closing of pome lenticels can arise when the
cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
over the stomata opening or the substomatal layer seals. Closing can also begin if the substomatal cells become suberized, like cork. The number of lenticels usually varies between the species of apples, where the range may be from 450 to 800 or from 1500 to 2500 in Winesap and Spitzenburg apples, respectively. This wide range may be due to the
water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
availability during the early stages of development of each apple type. "Lenticel breakdown" is a global skin disorder of apples in which lenticels develop dark 1–8 mm diameter pits shortly after processing and packing. It is most common on the '
Gala Gala may refer to: Music * ''Gala'' (album), a 1990 album by the English alternative rock band Lush * Gala (singer), Italian singer and songwriter *'' Gala – The Collection'', a 2016 album by Sarah Brightman * GALA Choruses, an association of ...
' (''Malus'' × ''domestica'') variety, particularly the '
Royal Gala Gala is an apple cultivar with a sweet, mild flavor, a crisp but not hard texture, and a striped or mottled orange or reddish appearance. Originating from New Zealand in the 1930s, similar to most named apples it is Cloning#Horticultural, clonal ...
', and also occurs in ' Fuji', '
Granny Smith The Granny Smith is an List of apple cultivars, apple cultivar that originated in Australia in 1868. It is named after Maria Ann Smith, who Fruit tree propagation, propagated the cultivar from a chance seedling. The tree is thought to be a Hybri ...
', '
Golden Delicious Golden Delicious is a cultivar of apple. It is one of the 15 most popular apple cultivars in the United States. It is not closely related to Red Delicious. History Golden Delicious arose from a chance seedling, possibly a hybrid of Grimes ...
', and 'Delicious' varieties. It is more common in arid regions, and is thought to be related to relative humidity and temperature. The effect can be mitigated by spraying the fruit with lipophilic coatings prior to harvest.


Tubers

Lenticels are also present on potato tubers.


Gallery

Prunus serrula bark lenticels, Dawyck Botanic Gardens.JPG, Lenticels on ''
Prunus serrula ''Prunus serrula'', called birch bark cherry, birchbark cherry, paperbark cherry, or Tibetan cherry, is a species of cherry native to China, and is used as an ornamental in many parts of the world for its striking coppery-red bark. Description ...
'' Wild Cherry bark lenticels.JPG, Lenticels on wild cherry or gean Alder bark and callus.JPG, Alder bark (''
Alnus glutinosa ''Alnus glutinosa'', the common alder, black alder, European alder, European black alder, or just alder, is a species of tree in the family (biology), family Betulaceae, native plant, native to most of Europe, southwest Asia and northern Africa. ...
'') with characteristic lenticels and abnormal lenticels on callused areas Pommes de terre Monalisa.png, Lenticels on
potato The potato () is a starchy tuberous vegetable native to the Americas that is consumed as a staple food in many parts of the world. Potatoes are underground stem tubers of the plant ''Solanum tuberosum'', a perennial in the nightshade famil ...
es of the Monalisa variety Poires williams Vertes et Rouges Savoie.jpg, Lenticels on
Williams pear The Williams' bon chrétien pear, commonly called the Williams pear, or the Bartlett pear in the United States and Canada, is a cultivar (cultivated variety) of the species ''Pyrus communis'', commonly known as the European pear. The fruit has a ...
varieties


See also

* Complementary cells


Notes


References

* {{Cite book , last1=Raven , first1=Peter H. , title=Biology of Plants 7th Ed. , last2=Ray F. Evert , last3=Susan E. Eichorn , publisher=W. H. Freeman and Company Publishers , year=2005 , isbn=0-7167-1007-2 , pages=586–587 Plant morphology Trees