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Dehiscence is the splitting of a mature plant structure along a built-in line of weakness to release its contents. This is common among
fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...
s, anthers and sporangia. Sometimes this involves the complete detachment of a part. Structures that open in this way are said to be dehiscent. Structures that do not open in this way are called indehiscent, and rely on other mechanisms such as decay, digestion by herbivores, or predation to release the contents. A similar process to dehiscence occurs in some flower buds (e.g., '' Platycodon'', '' Fuchsia''), but this is rarely referred to as dehiscence unless circumscissile dehiscence is involved; anthesis is the usual term for the opening of flowers. Dehiscence may or may not involve the loss of a structure through the process of abscission. The lost structures are said to be
caducous Dehiscence is the splitting of a mature plant structure along a built-in line of weakness to release its contents. This is common among fruits, anthers and sporangia. Sometimes this involves the complete detachment of a part. Structures that op ...
.


Association with crop breeding

Manipulation of dehiscence can improve crop yield since a trait that causes seed dispersal is a disadvantage for farmers, whose goal is to collect the seed. Many agronomically important plants have been bred for reduced shattering.


Mechanisms


Explosive dehiscence

Explosive dehiscence is a ballistic form of dispersal that flings seeds or spores far from the parent plant. This rapid plant movement can achieve limited dispersal without the assistance of animals. A notable example is the sandbox tree ('' Hura crepitans''), which can fling seeds 100 meters (300 ft) and has been called the "boomer plant" due to the loud sound it generates. Another example is '' Impatiens'', whose explosive dehiscence is triggered by being touched, leading it to be called the "touch-me-not". '' Ecballium elaterium'', the "squirting cucumber", uses explosive dehiscence to disperse its seeds, ejecting them from matured fruit in a stream of mucilaginous liquid. Explosive dehiscence of sporangia is a characteristic of ''
Sphagnum ''Sphagnum'' is a genus of approximately 380 accepted species of mosses, commonly known as sphagnum moss, also bog moss and quacker moss (although that term is also sometimes used for peat). Accumulations of ''Sphagnum'' can store water, since ...
''.


Septicidal and loculicidal dehiscence

In loculicidal dehiscence, the locule wall splits between the septa, leaving the latter intact, while in septicidal dehiscence the split is at the septum that separates the loculi. Septicidal and loculicidal dehiscence may not be completely distinct; in some cases both the septa and the walls of the locules split. File:Rhododendron tomentosum 004.JPG, Septicidal dehiscence. The septa between the locules of '' Ledum palustre'' capsules split as the fruit opens, and the seeds are released. File:Crepe myrtle 1.jpg, Loculicidal dehiscence. The locules of '' Lagerstroemia'' capsules split as the fruit opens, and the septa remain intact. File:Peganum harmala Baikonur 09.jpg, Loculicidal dehiscence in '' Peganum harmala'' File:Hibiscus trionum 3.jpg, A complex form of dehiscence. The calyx of '' Hibiscus trionum'' has opened apically to reveal the capsule (ovary) inside. The capsule has split vertically in the centre, as well as through the locule walls.


Types

Dehiscence occurs through breakage of various parts of the enclosing structure; the mechanisms can be classified in various ways, but intermediate forms also occur. File:Anther morphology dehiscence transverse.png, Transverse dehiscence of a pair of anthers File:Anther morphology dehiscence longitudinal.png, Longitudinal dehiscence of a pair of anthers File:Anther morphology dehiscence valvular.png, Valvular dehiscence of a pair of anthers File:Anther morphology dehiscence poricidal.png, Poricidal dehiscence of a pair of anthers


Poricidal dehiscence

Dehiscence through a small hole (pore) is referred to as poricidal dehiscence. The pore may have a cover (operculate poricidal dehiscence or operculate dehiscence) that is referred to as an operculum or it may not (inoperculate poricidal dehiscence or inoperculate dehiscence). Poricidal dehiscence occurs in many unrelated organisms, in fruit, causing the release of seeds, and also in the sporangia of many organisms (flowering plants, ferns, fungi,
slime molds Slime mold or slime mould is an informal name given to a polyphyly, polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myx ...
). Poricidal anthers of various flowers are associated with buzz pollination by insects.


Circumscissile dehiscence

Circumscissile dehiscence involves a horizontal opening that causes a lid to separate completely. This type of dehiscence occurs in some fruit and anthers and also in some flower buds.


Anther dehiscence

Anther dehiscence is the final function of the anther that causes the release of pollen grains. This process is coordinated precisely with pollen differentiation, floral development, and flower opening. The anther wall breaks at a specific site. Usually this site is observed as an indentation between the locules of each theca and runs the length of the anther, but in species with ''poricidal'' anther dehiscence it is instead a small pore. If the pollen is released from the anther through a split on the outer side (relative to the center of the flower), this is extrorse dehiscence, and if the pollen is released from the inner side, this is introrse dehiscence. If the pollen is released through a split that is positioned to the side, towards other anthers, rather than towards the inside or outside of the flower, this is latrorse dehiscence. The stomium is the region of the anther where dehiscence occurs. The degeneration of the stomium and
septum In biology, a septum (Latin language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Hum ...
cells is part of a developmentally timed cell-death program. Expansion of the endothecial layer and subsequent drying are also required for dehiscence. The endothecium tissue is responsible for the tensions that lead to splitting of the anther. This tissue is usually one to several layers thick, with cells walls of uneven thickness due to uneven lignification. The cells lose water, and the uneven thickness causes the thinner walls of the cells to stretch to a greater extent. This creates a tension that eventually leads to the anther being split along its line of weakness and releasing pollen grains to the atmosphere. image:Milk Pea dehiscence.jpg, Before/During images of anther dehiscence in the common Milk Pea image:Solanum anther-terminal-pores.jpg, Poricidal anther dehiscence image:Anther dehiscence in Lilium.jpg, Longitudinal latrorse anther dehiscence


Flower buds

Flower buds of ''
Eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...
'' and related genera open with circumscissile dehiscence. A small cap separates from the remainder of the bud along a circular horizontal zone. image:Eucalyptus ficifolia dehiscent flower bud.jpg, '' Corymbia ficifolia'' image:Eucalyptus_globulus_-_Köhler–s_Medizinal-Pflanzen-147.jpg, '' Eucalyptus globulus''


Fruit dehiscence

There are many different types of fruit dehiscence involving different types of structures. Some fruits are indehiscent, and do not open to disperse the seeds. Xerochasy is dehiscence that occurs upon drying, and hygrochasy is dehiscence that occurs upon wetting, the fruit being hygroscopic. Dehiscent fruits that are derived from one carpel are follicles or legumes, and those derived from multiple carpels are capsules or siliques.Esau, K. 1977. ''Anatomy of seed plants''. John Wiley and Sons, New York. One example of a dehiscent fruit is the silique. This fruit develops from a
gynoecium Gynoecium (; ; : gynoecia) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl (botany), whorl of a flower; it consists ...
composed of two fused carpels, which, upon fertilization, grow to become a silique that contains the developing
seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...
s. After seed maturation, dehiscence takes place, and valves detach from the central
septum In biology, a septum (Latin language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Hum ...
, thus freeing the seeds. This is also known as shattering and can be important as a seed dispersal mechanism. This process is similar to anther dehiscence and the region that breaks (dehiscence zone) runs the entire length of the fruit between the valves (the outer walls of the ovary) and the replum (the persisting septa of the ovary). At maturity, the dehiscence zone is effectively a non-lignified layer between two regions of lignified cells in the valve and the replum. Shattering occurs due to the combination of cell wall loosening in the dehiscence zone and the tensions established by the differential hygro-responsive properties of the drying cells. image:Pavot.JPG, Poppy fruit showing poricidal dehiscence; the seeds exit through pores beneath the "crown" image:Peanut 9417.jpg,
Peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), goober pea, pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible seeds. It is widely grown in the tropics and subtropics by small and large ...
s: an indehiscent subterranean legume fruit image:Thlaspi arvense ENBLA05.jpg, '' Thlaspi arvense'', with fruit that are dehiscent siliques image:Illustration Ledum palustre0.jpg, '' Rhododendron'' capsules have septicidal dehiscence; the fruit splits through the septa between the carpels image:Starr 071024-0245 Unknown iridaceae.jpg, Iridaceae capsules have loculicidal dehiscence; the fruit splits through the ovary wall of each carpel, allowing the seeds to exit directly from the locule image:Anagallis spp Sturm60.jpg, '' Anagallis'' fruits open with circumscissile dehiscence. A small cap separates from the remainder of the fruit along a circular horizontal zone. image:Lysimachia arvensis pyxis.jpg, ''Anagallis'' fruit, circumscissile dehiscence image:Spathoglottis plicata (Philippine ground orchid) capsule dehisced.jpg, '' Spathoglottis plicata'' capsules, like in most
orchid Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Orchids are cosmopolitan plants that are found in almost every habitat on Eart ...
s, split longitudinally along three to six slits while remaining closed at both ends


Sporangium dehiscence in bryophytes

Endothecium tissue found in
moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
capsules functions in a similar way in dehiscence to the endothecium in the walls of anthers (see above).


Sporangium dehiscence in ferns

Many leptosporangiate ferns have an annulus around the sporangium, which ejects the spores. Eusporangiate ferns do not generally have specialized dehiscence mechanisms. image:Botrychium lunaria-matricariae nf.jpg, Sporangium dehiscence through a horizontal slit in ''Botrychium'', a eusporangiate fern.


Sporangium dehiscence in fungi and myxomycetes

image:Haeckel Mycetozoa.jpg, Various sporangia of myxomycetes that dehisce in varied ways


See also

* Abscission—separation of structures that leads to their loss * Anthesis—the opening of flowers * Elaters—structures that form inside a sporangium and aid in spore dispersal of horsetails, liverworts, and hornworts * Loment—a type of fruit that breaks apart but is not dehiscent * Schizocarp—a type of fruit that breaks apart and may or may not be dehiscent.


References


Bibliography

*


External links

* * {{cite web , title=Anther dehiscence , url=https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dehiscence , access-date=25 March 2024 Fruit morphology Plant physiology Plant morphology