Dehiscence (botany) - AbsoluteAstronomy.com

Dehiscence is the opening, at maturity, in a pre-defined way, of a plant structure, such as a fruit

Fruit

In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...

, anther, or sporangium

Sporangium

A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...

, to release its contents. 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 or predation to release the contents.

A similar process to dehiscence occurs in some flower buds (e.g. Platycodon, Fuchsia
Fuchsia
Fuchsia is a genus of flowering plants that consists mostly of shrubs or small trees. The first, Fuchsia triphylla, was discovered on the Caribbean island of Hispaniola in 1703 by the French Minim monk and botanist, Charles Plumier...

), but this is rarely referred to as dehiscence unless circumscissile dehiscence is involved; anthesis

Anthesis

Anthesis is the period during which a flower is fully open and functional. It may also refer to the onset of that period.The onset of anthesis is spectacular in some species. In Banksia species, for example, anthesis involves the extension of the style far beyond the upper perianth parts...

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

Abscission

Abscission is a term used in several areas of biology. In plant sciences it most commonly refers to the process by which a plant drops one or more of its parts, such as a leaf, fruit, flower or seed...

. The lost structures are said to be caducous.

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 of the agronomically important plants have been bred for reduced shattering.

Explosive dehiscence is a ballistic form of dispersal

Biological dispersal

Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...

that flings seeds or spores far from the parent plant. This rapid plant movement

Rapid plant movement

Rapid plant movement encompasses movement in plant structures occurring over a very short period of time, usually under one second. For example, the Venus Flytrap closes its trap in about 100 milliseconds. The Dogwood Bunchberry's flower opens its petals and fires pollen in less than 0.5 milliseconds...

can achieve limited dispersal without the assistance of animals. A notable example is the Sandbox Tree

Sandbox Tree

Hura crepitans , the Sandbox tree, also known as Possumwood and Jabillo, is an evergreen tree of the spurge family , native to tropical regions of North and South America in Amazon Rainforest. It is recognized by the many dark, pointed spines and smooth brown bark...

(Hura crepitans), which can fling seeds 100 meters (300 ft) and has been called the "Dynamite tree" due to the loud sound of its explosive dehiscence. Another example is Impatiens
Impatiens
Impatiens is a genus of about 850–1,000 species of flowering plants, widely distributed throughout the Northern Hemisphere and tropics. Together with the puzzling Hydrocera triflora, this genus makes up the family Balsaminaceae...

, whose explosive dehiscence is triggered by being touched, leading it to be called the "touch-me-not." Explosive dehiscence of sporangia is a characteristic of Sphagnum
Sphagnum
Sphagnum is a genus of between 151 and 350 species of mosses commonly called peat moss, due to its prevalence in peat bogs and mires. A distinction is made between sphagnum moss, the live moss growing on top of a peat bog on one hand, and sphagnum peat moss or sphagnum peat on the other, the...

.

Poricidal dehiscence

Dehiscence through a small hole (pore) is referred to as poricidal dehiscence. The pore may have a cover (operculate poricidal dehiscense or operculate dehiscence) that is referred to as an operculum
Operculum (botany)
An operculum, in botany, is a term generally used to describe a structure within a plant, moss, or fungus acting as a cap, flap, or lid. In plants, it may also be called a bud cap.Examples of structures identified as opercula include:...

or it may not (inoperculate poricidal dehiscense 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

Myxogastria

Myxogastria is a class of Mycetozoa, itself a grouping of slime molds, that contains 5 orders, 14 families, 62 genera, and 888 species. Notable examples within Myxogastria include the genus Stemonitis and the species Physarum polycephalum...

). Poricidal anthers of various flowers are associated with buzz pollination

Buzz pollination

Sonication or buzz pollination is a technique used by some bees to release pollen which is more or less firmly held by the anthers, which makes pollination more efficient. The anther of buzz-pollinated species of plants is typically tubular, with an opening at only one end, and the pollen is inside...

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 locule

Locule

A locule is a small cavity or compartment within an organ or part of an organism ....

s of each theca

Theca

A theca refers to any case, covering, or sheath.In botany, the theca of an angiosperm consists a pair of microsporangia that are adjacent to each other and share a common area of dehiscence called the stomium. Any part of a microsporophyll that bears microsporangia is called an anther. Most...

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

Septum

In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...

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 tension

Tension (mechanics)

In physics, tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object on another object. It is the opposite of compression. As tension is the magnitude of a force, it is measured in newtons and is always measured parallel to the string on which it applies...

s 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.

Dehiscence of flower buds

Flower buds of Eucalyptus
Eucalyptus
Eucalyptus is a diverse genus of flowering trees in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia...

and related genera open with circumscissile dehiscence. A small cap separates from the remainder of the bud along a circular horizontal zone.

Fruit dehiscence

There are many different types of fruit dehiscence, that involve different types of structures. Some fruits are indehiscent, and not open to disperse the seeds. Xerochasy is dehiscence that occurs upon drying, and hygrochasy is dehiscence that occurs upon wetting. Dehiscent fruits that are derived from one carpel are follicles

Follicle (fruit)

In botany, a follicle is a dry unilocular many-seeded fruit formed from one carpel and dehiscing by the ventral suture in order to release seeds, such as in larkspur, magnolia, banksia, peony and milkweed....

or legumes, and those derived from multiple carpels are capsules

Capsule (fruit)

In botany a capsule is a type of simple, dry fruit produced by many species of flowering plants. A capsule is a structure composed of two or more carpels that in most cases is dehiscent, i.e. at maturity, it splits apart to release the seeds within. A few capsules are indehiscent, for example...

or silique

Silique

A silique or siliqua is a fruit of 2 fused carpels with the length being more than three times the width. The outer walls of the ovary usually separate when ripe, leaving a persistent partition...

s.

One example of a dehiscent fruit is the silique

Silique

A silique or siliqua is a fruit of 2 fused carpels with the length being more than three times the width. The outer walls of the ovary usually separate when ripe, leaving a persistent partition...

. This fruit develops from a gynoecium composed of two fused carpels, which, upon fertilization, grow to become a silique that contains the developing seed

Seed

A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...

s. After seed maturation, dehiscence takes place, and valves detach from the central septum 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 mechanical properties of the drying cells.

Sporangium dehiscence in Bryophytes

Endothecium tissue found in moss

Moss

Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...

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 fern

Eusporangiate fern

Eusporangiate ferns are vascular spore plants, whose sporangia arise from several epidermal cells and not from a single cell as in leptosporangiate ferns...

s do not generally have specialized dehiscence mechanisms.