lenticel

Before there was much evidence for the existence and functionality of lenticels, the fossil record has shown the first primary mechanism of aeration in early vascular plants to be the stomata.{{Cite journal |last=Matthews |first=Jack S. A. |last2=Vialet-Charbrand |first2=Silvere R. M. |last3=Lawson |first3=Tracy |date=June 2017 |title=Open Access Diurnal Variation in Gas Exchange: The Balance between Carbon Fixation and Water Loss |journal=Plant Physiology |volume=174 |issue=2 |pages=614–623 |doi=10.1104/pp.17.00152 |pmc=5462061 |pmid=28416704}}

However, in woody plants, 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 such parts the entire epidermis may be shed as it is replaced by a suberized periderm or bark in which the respiratory functions of the stomata may be replaced by lenticels, at least until the bark becomes too thick.

The extinct arboreal plants of the genera Lepidodendron and Sigillaria 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, connected the stem's outer and middle cortex to the mesophyll of the leaf. Parichnoi were thought to eventually give rise to lenticels as they helped solve the issue of long-range oxygen transport in these woody plants during the Carboniferous 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.{{Cite journal |last=Wetmore |first=Ralph H. |date=September 1926 |title=Organization and Significance of Lenticels in Dicotyledons. I. Lenticels in Relation to Aggregate and Compound Storage Rays in Woody Stems. Lenticels and Roots |journal=Botanical Gazette |volume=82 |issue=1 |pages=71–78 |doi=10.1086/333634 |jstor=2470894 |s2cid=83645501}} 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 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 in these plants.{{Cite journal |last=Hook |first=Donald D. |date=December 1972 |title=Aeration in Trees |journal=Botanical Gazette |volume=133 |issue=4 |pages=443–454 |doi=10.1086/336669 |jstor=2474119 |s2cid=83842497}}

In plant bodies that produce secondary growth, lenticels promote gas exchange of oxygen, carbon dioxide, and water vapor.{{Cite journal |last=Lendzian |first=Klaus J. |date=July 4, 2006 |title=Survival strategies of plants during secondary growth: barrier properties of phellems and lenticels towards water, oxygen, and carbon dioxide |url=https://academic.oup.com/jxb/article-abstract/57/11/2535/675330 |journal=Experimental Botany |volume=57 |issue=11 |pages=2535–2546 |doi=10.1093/jxb/erl014 |pmid=16820395 |doi-access=free}} Lenticel formation usually begins beneath stomatal 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.{{Cite journal |last=Priestley |first=J. H. |date=December 18, 1922 |title=Physiological Studies in Plant Anatomy V. Causal Factors in Cork Formation |url=https://zenodo.org/record/2380037 |journal=The New Phytologist |volume=21 |issue=5 |pages=252–268 |doi=10.1111/j.1469-8137.1922.tb07603.x |jstor=2428084}} 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).{{cn|date=September 2024}}

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 tissue creates a number of large intercellular spaces between cells. This tissue fills the lenticel and arises from cell division in the phellogen or substomatal ground tissue. Discoloration of lenticels may also occur, such as in mangoes, that may be due to the amount of lignin in cell walls.{{Cite journal |last=Kenoyer |first=Leslie A. |date=Dec 31, 1908 – Jan 2, 1909 |title=Winter Condition of Lenticels |journal=Transactions of the Kansas Academy of Science |volume=22 |pages=323–326 |doi=10.2307/3624744 |jstor=3624744}}{{Cite journal |last=Tamjinda |first=Boonchai |date=1992 |title=Anatomy of Lenticels and The Occurrence of Their Discoloration in Mangoes |url=http://www.lib.ku.ac.th/kujn/TAB451083.pdf |journal=Kasertsart J. |volume=26 |issue=Suppl 5 |pages=57–64}}

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 species, lenticels appear on pneumatophores (specialized roots), where the parenchyma cells that connect to the aerenchyma structure increase in size and go through cell division.{{Cite journal |last=Purnobasuki |first=Hery |date=January 2011 |title=Structure of Lenticels on the Pneumatophores of Avicennia marina: as Aerating Device Deliver Oxygen in Mangrove's root |url=https://www.researchgate.net/publication/216745465 |journal=Biota |volume=16 |issue=2 |pages=309–315 |doi=10.24002/biota.v16i2.113 |s2cid=191198645 |doi-access=free}} In contrast, lenticels in grapes are located on the pedicels and act as a function of temperature. If they are blocked, hypoxia and successive ethanol accumulation may result and lead to cell death.{{Cite journal |last=Xiao |first=Zeyu |last2=Rogiers |first2=Suzy Y. |last3=Sadras |first3=Victor O. |last4=Tyerman |first4=Stephen D. |year=2018 |title=Hypoxia in grape berries: the role of seed respiration and lenticels on the berry pedicel and the possible link to cell death |journal=Experimental Botany |volume=69 |issue=8 |pages=2071–2083 |doi=10.1093/jxb/ery039 |pmc=6018838 |pmid=29415235}}

Image:Sterappel.jpg

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.{{Cite web |last=Krewer |first=Gerard |last2=Bertrand |first2=Paul |title=Home garden pears |url=http://www.caes.uga.edu/Publications/pubDetail.cfm?pk_ID=6366 |access-date=18 January 2014 |website=CAES Publications |publisher=University of Georgia College of Agricultural and Environmental Sciences}}{{Cite news |last=Pyzner |first=John |date=19 April 2005 |title=Pick pears before completely ripe, advises LSU AgCenter horticulturist |url=http://www.lsuagcenter.com/news_archive/2004/News+You+Can+Use/Pick+Pears+Before+Completely+Ripe+Advises+LSU+AgCenter+Horticulturist.htm |url-status=dead |archive-url=https://web.archive.org/web/20060115191508/http://www.lsuagcenter.com/news_archive/2004/news%2Byou%2Bcan%2Buse/pick%2Bpears%2Bbefore%2Bcompletely%2Bripe%2Badvises%2Blsu%2Bagcenter%2Bhorticulturist.htm |archive-date=15 January 2006 |work=Louisiana State University Agricultural Center website}} Certain bacterial and fungal infections can penetrate fruits through their lenticels, with susceptibility sometimes increasing with its age.Irtwange, S. V. (February, 2006.) [http://cigr-ejournal.tamu.edu/submissions/volume8/Invited%20overview%20Irtwange(2)%2027Feb2006.pdf "Application of modified atmosphere packaging and related technology in postharvest handling of fresh fruits and vegetables"] {{Webarchive|url=https://web.archive.org/web/20061011155443/http://cigr-ejournal.tamu.edu/submissions/volume8/Invited%20overview%20Irtwange(2)%2027Feb2006.pdf |date=2006-10-11 }}. Agricultural Engineering International: the CIGR Ejournal. Invited Overview No. 4. Vol. VIII, page 8. Retrieved on 2007-10-11.

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 (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, and other epidermal breaks that usually occur in the early development of young pome fruits. The closing of pome lenticels can arise when the cuticle 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 availability during the early stages of development of each apple type.{{Cite journal |last=Clements |first=Harry F. |date=September 1935 |title=Morphology and Physiology of the Pome Lenticels of Pyrus malus |journal=Botanical Gazette |volume=97 |issue=1 |pages=101–117 |doi=10.1086/334539 |jstor=2471695 |s2cid=84144735}}

"Lenticel breakdown" is a global skin disorder of apples in which lenticels develop dark 1–8 mm diameter pits shortly after processing and packing.{{Cite journal |last=Curry |first=Eric A. |last2=Torres |first2=Carolina |last3=Neubauer |first3=Luis |year=2008 |title=Preharvest lipophilic coatings reduce lenticel breakdown disorder in 'Gala' apples. |url=http://horttech.ashspublications.org/content/18/4/690.full |journal=HortTechnology |volume=18 |issue=4 |pages=690–696 |doi=10.21273/HORTTECH.18.4.690 |doi-access=free}}{{Cite journal |last=Turketti |first=S.S. |last2=Curry |first2=E. |last3=Lötze |first3=E. |year=2012 |title=Role of lenticel morphology, frequency and density on incidence of lenticel breakdown in 'Gala' apples |journal=Scientia Horticulturae |volume=138 |pages=90–95 |doi=10.1016/j.scienta.2012.02.010 |issn=0304-4238|doi-access=free }} It is most common on the 'Gala' (Malus × domestica) variety, particularly the 'Royal Gala', and also occurs in 'Fuji', 'Granny Smith', 'Golden Delicious', 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.

Lenticels are also present on potato tubers.{{Cite journal |last=Adams |first=M. J. |year=1975 |title=Potato tuber lenticels: Development and structure |journal=Annals of Applied Biology |volume=79 |issue=3 |pages=265–273 |doi=10.1111/j.1744-7348.1975.tb01582.x}}

Prunus serrula bark lenticels, Dawyck Botanic Gardens.JPG|Lenticels on Prunus serrula

Wild Cherry bark lenticels.JPG|Lenticels on wild cherry or gean

Alder bark and callus.JPG|Alder bark (Alnus glutinosa) with characteristic lenticels and abnormal lenticels on callused areas

Pommes de terre Monalisa.png|Lenticels on potatoes of the Monalisa variety

Poires williams Vertes et Rouges Savoie.jpg|Lenticels on Williams pear varieties

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• Complementary cells

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• {{Cite book |last=Raven |first=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}}

Category:Plant morphology

Category:Trees