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Inbiology,atheca(pl.:thecae) is a sheath or a covering.
Botany
editInbotany,the theca is related to plant's flower anatomy. The theca of anangiospermconsists of a pair ofmicrosporangiathat are adjacent to each other and share a common area ofdehiscencecalled thestomium.[1]Any part of amicrosporophyllthat bears microsporangia is called ananther.Most anthers are formed on the apex of afilament.An anther and its filament together form a typical (or filantherous)stamen,part of the malefloralorgan.
The typical anther is bilocular, i.e. it consists of two thecae. Each theca contains two microsporangia, also known as pollen sacs. The microsporangia produce themicrospores,which forseed plantsare known aspollengrains.
If the pollen sacs are not adjacent, or if they open separately, then no thecae are formed. In Lauraceae, for example, the pollen sacs are spaced apart and open independently.
The tissue between theloculesand the cells is called theconnectiveand theparenchyma.Both pollen sacs are separated by thestomium.When the anther is dehiscing, it opens at the stomium.
The outer cells of the theca form theepidermis.Below the epidermis, thesomaticcells form thetapetum.These support the development of microspores into mature pollen grains. However, little is known about the underlying genetic mechanisms, which play a role in male sporo- and gametogenesis.
The thecal arrangement of a typical stamen can be as follows:
- Divergent: both thecae in line, and forming an acute angle with the filament
- Transverse (or explanate): both thecae exactly in line, at right angles with the filament
- Oblique: the thecae fixed to each other in an oblique way
- Parallel: the thecae fixed to each other in a parallel way
Zoology
editInbiology,thetheca of folliclecan also refer to the site ofandrogenproduction in females. The theca of the spinal cord is called thethecal sac,and intrathecal injections are made there or in the subarachnoid space of theskull.
Inhuman embryogenesis,the theca cells form acorpus luteumafter aGraafian folliclehas expelled its secondaryoocytearrested in secondmeiosis.
Thecal shape is also important ingraptoliteandpterobranchtaxonomy.
Indinoflagellatesthat are armoured their covering is made up ofthecal plates.
In other taxonomic groups
editInmicrobiologyandplanktology,a theca is a subcellular structural component out of which thefrustulesofdiatomsanddinoflagellatesare constructed.
See also
editReferences
edit- ^Larry Hufford,"The origin and early evolution of angiosperm stamens" inThe Anther: form, function, and phylogeny,William G. D'Arcy and Richard C. Keating (editors),Cambridge University Press,1996, 351pp, p.60,ISBN978-0-521-48063-5(fromGoogle Books)
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