Dehiscence (botany)

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. 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). 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 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 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. One example of a dehiscent fruit is the silique. This fruit develops from a gynoecium composed of two fused carpels, image:Pavot.JPG|Poppy fruit showing poricidal dehiscence; the seeds exit through pores beneath the "crown" image:Peanut 9417.jpg|Peanuts: an indehiscent subterranean legume fruit image:Microthlaspi perfoliatum 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 orchids, split longitudinally along three to six slits while remaining closed at both ends == Sporangium dehiscence in bryophytes ==

Endothecium tissue found in moss 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 ==