Hubbry Logo
ThecaThecaMain
Open search
Theca
Community hub
Theca
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Theca
Theca
Theca
View on Wikipedia
from Wikipedia
Strawberry anther with parallel thecae

In biology, a theca (pl.: thecae) is a sheath or a covering.

Botany

[edit]

In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common area of dehiscence called the stomium.[1] Any part of a microsporophyll that bears microsporangia is called an anther. Most anthers are formed on the apex of a filament. An anther and its filament together form a typical (or filantherous) stamen, part of the male floral organ.

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 the microspores, which for seed plants are known as pollen grains.

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 the locules and the cells is called the connective and the parenchyma. Both pollen sacs are separated by the stomium. When the anther is dehiscing, it opens at the stomium.

The outer cells of the theca form the epidermis. Below the epidermis, the somatic cells form the tapetum. 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.

Divergent thecae in Graderia

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

[edit]

In biology, the theca of follicle can also refer to the site of androgen production in females. The theca of the spinal cord is called the thecal sac, and intrathecal injections are made there or in the subarachnoid space of the skull.

In human embryogenesis, the theca cells form a corpus luteum after a Graafian follicle has expelled its secondary oocyte arrested in second meiosis.

Thecal shape is also important in graptolite and pterobranch taxonomy, as well as in many echinoderm groups.

In dinoflagellates that are armoured their covering is made up of thecal plates.

In other taxonomic groups

[edit]

In microbiology and planktology, a theca is a subcellular structural component out of which the frustules of diatoms and dinoflagellates are constructed.

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Theca

View on Grokipedia
from Grokipedia
In , a theca (plural: thecae) is a sheath, case, or covering that encloses and protects an organ, , or , often providing or serving a reproductive function. In , the term commonly refers to the sacs or microsporangia within the anther of a , where grains are produced and stored; these thecae typically occur in pairs per anther lobe, facilitating . In and lower plants, it can denote a case or capsule, such as in mosses, where it encloses spores for dispersal. In animal , particularly reproductive , the forms the outer layers of an in mammals, comprising the vascular theca externa and the endocrine theca interna; these cells produce androgens that serve as precursors for synthesis by granulosa cells, playing a critical role in , , and . Theca cells also provide structural integrity to the follicle and engage in signaling crosstalk with oocytes and surrounding tissues. In protistology and , especially among , the theca is a rigid or protective envelope composed of , silica, or ; for instance, in diatoms it forms one half of the bivalved , while in dinoflagellates and prasinophytes it acts as an armored covering for the cell. This offers mechanical protection and can be involved in locomotion or environmental in unicellular .

General Overview

Definition

In , a theca (plural: ) is a sheath, case, or protective covering that encloses an organ, cell, or structure. Theca structures are typically rigid or fibrous, providing mechanical support and enclosure, and are composed of materials such as or in protists and , or including and fibroblasts in animals. These compositions enable functions like physical protection against environmental stress, structural containment of reproductive elements, and facilitation of developmental processes. The term originates from Latin theca, meaning a case or box, derived from thḗkē (a receptacle or cover), and has been applied broadly in biological taxonomy since the 18th century, particularly through , where it was applied to plant structures like spore capsules. Theca differs from similar terms like "capsule," which often denotes a temporary or loosely attached membranous layer such as the polysaccharide around , and "shell," which typically refers to a hard, in mollusks or other . In contrast, theca emphasizes a more integrated, enveloping layer that is structurally persistent and closely associated with the enclosed entity.

Etymology

The term "theca" originates from the Latin theca, borrowed directly from thḗkē (θήκη), which denotes a case, box, sheath, or receptacle for holding or placing something, derived from the títhēmi (τίθημι), meaning "to place" or "to set." This root reflects a conceptual emphasis on or , as seen in classical usages for containers like scabbards or storage boxes. The word entered the English scientific lexicon in the mid-17th century, with its earliest documented use appearing in 1665 within the Philosophical Transactions of the Royal Society, where it described the protective case (or "theca") enclosing an during from aurelia to . By the late 18th and early 19th centuries, it gained prominence in botanical and zoological literature, particularly through in the , marking its integration into systematic descriptions of . The plural form "thecae" and adjectival derivatives like "thecal" (pertaining to a sheath or case) were retained from Latin conventions in scientific . In medical and anatomical contexts, related terms such as emerged to describe membranous sheaths, extending the root's implication of enclosure. By the mid-19th century, influenced by advancements in , the term solidified as a standard biological reference for protective sheaths and coverings in organisms. This shift paralleled the growing precision in histological studies.

Botanical Applications

In Bryophytes and Pteridophytes

In bryophytes, the theca refers to the spore-producing region of the capsule, or , which develops at the apex of the in the generation. This structure is characterized by walls composed primarily of and typically dehisces through an operculum, a lid-like that detaches to allow release. The theca encloses spore mother cells that undergo to produce haploid , facilitating the transition back to the phase in the . The developmental process of the theca begins following fertilization within the of the female , where the divides to form the diploid , including the and theca. As the matures, the theca differentiates into a fertile zone surrounding a central sterile , with the outer layers forming the capsule wall. This process underscores the life cycle, where the dependent relies on the photosynthetic for nutrition while producing spores essential for dispersal and propagation. In mosses such as those in the genus , the theca features a —a ring of teeth-like structures at the capsule mouth—that regulates dispersal by hygroscopic movements in response to environmental , preventing premature release and aiding in dispersal. By contrast, in species, the theca lacks a true ; instead, internal pressure builds to 4-6 atmospheres upon drying, explosively ejecting the operculum and s through a specialized pseudostome for efficient long-distance dispersal in habitats. These adaptations highlight the theca's role in optimizing liberation under varying moisture conditions. In pteridophytes, particularly ferns, the theca denotes an individual , typically clustered in sori on the undersurface of fertile fronds, serving as the site for production via . The theca wall is a single layer of thin-walled cells in leptosporangiate ferns, and dehiscence is driven by an annulus—a ring of thickened, lignified cells on one side—that contracts unevenly upon drying, creating tension to split the longitudinally and propel . This mechanism ensures precise timing for spore release, often synchronized with favorable conditions for colonization. The formation of the theca in pteridophytes also originates from fertilization in the of the free-living , leading to sporophyte development where multiple () arise from sporophylls. In the life cycle, these thecae play a pivotal role by generating large numbers of spores—often thousands per —to compensate for high mortality rates during dispersal and germination. For instance, in species, each theca is supported by a short pedicel (stalk) and features specialized lip cells at the dehiscence slit, which thin during maturation to facilitate clean rupture without damaging adjacent structures in the sorus.

In Angiosperms

In angiosperms, the theca refers to the specialized chambers within the anther where occurs, producing grains essential for . The typical angiosperm anther is dithecous, featuring two lobes joined by a central connective, with each lobe housing one theca composed of two microsporangia or pollen sacs, resulting in a total of four microsporangia per anther. These microsporangia are enclosed by four wall layers: the outer , the fibrous endothecium responsible for dehiscence mechanics, a transient middle layer, and the innermost tapetum, which lines the theca and provides nutrients and enzymes for maturation. This bilocular structure of each theca ensures compartmentalized development and protection of male gametophytes. Development of the theca begins early in stamen primordia, derived primarily from the L2 layer of the floral meristem, with archesporial cells differentiating into primary parietal and sporogenous tissues. The sporogenous cells develop into microspore mother cells, which undergo meiosis to produce tetrads of haploid microspores; these microspores are released from the tetrad callose wall and proceed through microgametogenesis to form mature pollen grains, often binucleate or trinucleate depending on the species. The tapetum plays a critical role by secreting sporopollenin precursors for the pollen exine and degrading to nourish free microspores, while the endothecium develops fibrous thickenings for tension during dehiscence. At maturity, the stomium—a thin-walled region at the junction of the two thecae—facilitates longitudinal splitting of the anther along the connective, releasing pollen at anthesis. Variations in theca structure and orientation occur across angiosperm lineages, reflecting evolutionary adaptations to syndromes. Thecae may be oriented parallel to each other and the filament in most monocots and basal , or divergent, forming an acute angle, as seen in genera like Graderia (), which enhances presentation in specialized flowers. Other orientations include transverse, where thecae align at right angles to the filament, or oblique, though less common; these configurations influence dispersal efficiency. For instance, in (), the anther exhibits a standard dithecous structure with parallel thecae and four microsporangia, supporting entomophilous through exposed release. The primary function of the theca is to contain, nourish, and safeguard developing grains from environmental stresses until dehiscence, ensuring viable microgametophytes for fertilization. By isolating microsporogenesis within its walls, the theca optimizes resource allocation and prevents premature exposure, with dehiscence timed to coincide with flower opening for access. This protective role is vital in diverse habitats, where theca integrity contributes to in over 300,000 angiosperm species.

Zoological Applications

In Ovarian Follicles

In ovarian follicles, the theca forms a specialized layer surrounding the granulosa cells, comprising two distinct sublayers: the theca interna and theca externa. The theca interna consists of steroidogenic endocrine cells, vascular endothelial cells, and immune cells, providing a highly vascularized network essential for delivery and transport to support follicular development. The theca externa, in contrast, is a fibrous layer of fibroblast-like cells that offers structural integrity and mechanical support to the growing follicle. The primary function of theca interna cells is the production of androgens, such as and testosterone, in response to (LH) stimulation, which are subsequently aromatized into by granulosa cells via the two-cell, two-gonadotropin model of steroidogenesis. These androgens not only drive estrogen synthesis but also contribute to follicular maturation, oocyte development, and overall reproductive endocrine balance. Additionally, theca cells provide metabolic support, including the transfer of substrates like for steroid hormone biosynthesis, and their vascularization facilitates within the follicle. Theca cells originate from mesenchymal precursors in the ovarian stroma, differentiating in response to signals from developing follicles, such as granulosa cell-derived factors. A 2023 study using single-cell sequencing identified three discrete subtypes of theca cells—structural, androgenic, and perifollicular—each with lineage-specific roles in follicle support and production. Following , theca interna cells transform into small luteal cells within the , where they express LH receptors and contribute significantly to progesterone synthesis, maintaining early until placental takeover. Clinically, excessive stimulation of theca cells by high levels of (hCG) during can lead to theca lutein cysts, benign bilateral enlargements of the ovaries filled with clear fluid, which typically regress spontaneously postpartum without intervention. Dysregulation of theca cell androgen production is a hallmark of (PCOS), where hyperplastic theca cells exhibit intrinsic defects leading to elevated androgens, contributing to , ovulatory dysfunction, and metabolic complications.

In Other Animal Structures

In , theca often refers to protective casings or tubular structures that enclose colonial or individual organisms. In extinct , colonial hemichordates from the era, thecae were chitinous, tube-like cups arranged along branching stipes, each housing a and providing for the rhabdosome . Similarly, in living pterobranchs, such as species in the Rhabdopleura, thecae form tubular sheaths secreted by , enabling colonial growth through budding and offering enclosure within a shared tube . In scleractinian corals, the theca is a calcareous wall surrounding the polyp's calyx, composed of , which protects the soft-bodied polyp and contributes to framework formation. Among echinoderms, the theca serves as a central skeletal element. In , including stalked sea lilies, the theca—also termed the calyx—consists of interlocked forming a cup-shaped body that houses the digestive organs and supports radiating arms for filter feeding. In sea urchins (Echinoidea), the theca is equivalent to the , a rigid, globular shell of fused that encases the Aristotle's lantern and other viscera, providing mechanical protection against predators. In vertebrates, a prominent thecal structure is the , an extension of the lining the , which encloses the , , and for cushioning and nutrient transport. In insects, which are , the pupal theca denotes the hardened case or surrounding the during , often chitinous and formed from the larval exuvium, shielding the transforming tissues from desiccation and predation. These animal thecae primarily function in mechanical support and environmental protection, stabilizing colonial arrays in and pterobranchs or safeguarding internal organs in solitary forms like echinoderms and vertebrates.

Applications in Protists and Algae

In Dinoflagellates

In dinoflagellates, the theca refers to a rigid cell covering composed of interlocking plates, known as thecal plates, which form an armored structure in many species. These plates are housed within membrane-bound vesicles called amphiesmal vesicles beneath the plasma membrane, providing a supportive framework for the cell. The theca is divided into two main regions: the epitheca, which forms the anterior (apical) portion of the cell, and the hypotheca, the posterior portion. A transverse groove called the cingulum encircles the cell near its , housing one , while a longitudinal sulcus runs from the cingulum to the posterior end, accommodating the other ; these grooves enable the characteristic spinning of dinoflagellates. The primary functions of the theca include imparting that facilitates efficient through water columns via the flagella's coordinated action, which produces a tumbling spiral motion. Additionally, the thecal plates serve as a protective armor, deterring predation by grazers such as through their tough, interlocking design. The arrangement of these plates is described by a standardized , which varies by species but often follows the Kofoid system; for instance, in the freshwater Peridinium, a typical formula is Po, cp, X, 4', 3a, 7'', 6c, 5s, 5''', 2'''', where Po denotes the pore plate, primes (') indicate apical plates, double primes ('') anterior intercalary plates, and so on for other series. This tabulation not only supports locomotion but also contributes to species-specific morphology, such as the elongated, horned thecae in Ceratium species, which further enhance hydrodynamic efficiency and defense. Dinoflagellates are classified into thecate (armored) and athecate (naked) forms based on the presence of this cellulose-based theca; thecate species possess these plates, while athecate ones lack them and rely on a flexible outer . This distinction is crucial for taxonomic identification, as thecal tabulation patterns are highly conserved within genera. Ecologically, the theca plays a key role in harmful algal blooms, such as red tides caused by species like Ceratium furca, where it provides structural integrity during dense populations and may aid in containing potent neurotoxins produced by many thecate dinoflagellates, preventing premature release until cell . Recent studies since 2020 have elucidated the formation of thecal plates through thecal vesicles, revealing that amphiesmal vesicle trafficking and Golgi apparatus involvement are essential for deposition during , offering insights into evolutionary adaptations for bloom persistence.

In Diatoms

In diatoms, the theca refers to the siliceous , or , which encases the cell and provides structural support while allowing permeability. The consists of two overlapping : the larger epitheca and the smaller hypotheca, joined by a flexible series of girdle bands that permit expansion during . Each is a perforated silica plate featuring intricate patterns of nanopores known as areolae, which are often arranged in radial or parallel striae and covered by cribrum membranes; these areolae enable the of nutrients, gases, and exudates across the , enhancing uptake efficiency in nutrient-limited environments. The formation of the theca occurs through biosilicification within specialized intracellular compartments called silica deposition vesicles (SDVs), where dissolved is polymerized into amorphous silica under acidic conditions. The SDV expands laterally as silica ribs and pore fields form, guided by local variations in membrane curvature and contact sites with the plasma membrane, rather than rigid templates; this process results in species-specific nanopatterns, with morphogenesis completing in about 30-60 minutes. In pennate diatoms, a distinctive longitudinal slit called the raphe forms in the face, lined with mucilage-secreting pores that facilitate across substrates via adhesive propulsion. Recent studies highlight the role of proteins such as dAnk1-3 in controlling cribrum pore patterning within the SDV membrane, linking genetic regulation to the precise hexagonal and radial architectures observed in the theca. Diatoms are classified into two major groups based on theca symmetry: centric diatoms exhibit radial patterns with circular or polygonal valves, while pennate diatoms display bilateral symmetry with elongated, lanceolate forms. For instance, species in the genus Navicula possess elongated pennate thecae with parallel striae and a central raphe, enabling benthic locomotion. Ecologically, diatom thecae play a pivotal role as diatoms comprise up to 45% of oceanic primary production and dominate the biological silica cycle by incorporating approximately 240 teramoles of silicon annually into sinking frustules, which export silica to deep ocean sediments and regulate nutrient availability for phytoplankton communities. This "silica pump" mechanism sustains carbon sequestration while influencing global biogeochemical fluxes, with theca dissolution rates affected by factors like ocean acidification.

References

  1. https://www.dictionary.com/browse/theca
  2. https://dictionary.cambridge.org/us/dictionary/english/theca
  3. https://sweetgum.nybg.org/science/glossary/glossary-details/?irn=3365
  4. https://www.sciencedirect.com/topics/medicine-and-dentistry/theca-cell
  5. https://www.nature.com/articles/s42003-022-04384-8
  6. https://pmc.ncbi.nlm.nih.gov/articles/PMC7401757/
  7. https://www.oxfordreference.com/display/10.1093/oi/authority.20110803103631239
  8. https://www.dcceew.gov.au/science-research/abrs/online-resources/glossaries/algae
  9. https://academic.oup.com/biolreprod/article/93/2/26%2C%25201-1/2434188
  10. https://www.pnas.org/doi/10.1073/pnas.1614842114
  11. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/theca
  12. https://www.mobot.org/mobot/latindict/keyDetail.aspx?keyWord=tTeca
  13. https://www.britannica.com/science/bacteria/Capsules-and-slime-layers
  14. https://www.oed.com/dictionary/theca_n?tl=true
  15. https://digitalcommons.mtu.edu/context/bryophyte-ecology1/article/1001/viewcontent/Chapter_2___Life_Cycles_and_Morphology.pdf
  16. https://www.anbg.gov.au/bryophyte/sexual-reproduction.html
  17. https://www.biologydiscussion.com/plants/plant-kingdom/bryophytes-characters-and-functions-plant-kingdom/52175
  18. https://digitalcommons.mtu.edu/context/bryophyte-ecology1/article/1003/viewcontent/Chapter_4___Adaptive_Strategies.pdf
  19. https://www3.botany.ubc.ca/bryophyte/sem/sphagnum_sporophyte_w_calyp.html
  20. https://academiccommons.columbia.edu/doi/10.7916/h8eg-4k10/download
  21. http://artemis.austincollege.edu/acad/bio/gdiggs/NCTX%2520pdf/FNCT%25201353-1456.pdf
  22. https://archive.org/download/monographofgenus01chri/monographofgenus01chri.pdf
  23. https://pmc.ncbi.nlm.nih.gov/articles/PMC5807095/
  24. https://pmc.ncbi.nlm.nih.gov/articles/PMC10305830/
  25. https://www.ncbi.nlm.nih.gov/books/NBK278951/
  26. https://pmc.ncbi.nlm.nih.gov/articles/PMC9812973/
  27. https://pmc.ncbi.nlm.nih.gov/articles/PMC6895843/
  28. https://pmc.ncbi.nlm.nih.gov/articles/PMC9525056/
  29. https://pmc.ncbi.nlm.nih.gov/articles/PMC6855291/
  30. https://geosci.uchicago.edu/~foote/PALEO/2007/Labs/Geos223Lab8.pdf
  31. https://onlinelibrary.wiley.com/doi/10.1111/ede.12394
  32. https://cdhc.noaa.gov/coral-biology/coral-skeleton/
  33. https://libguides.nova.edu/crinoids/calyx
  34. https://www.journals.uchicago.edu/doi/full/10.1086/721915
  35. https://radiopaedia.org/articles/spinal-canal?lang=us
  36. https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1021&context=onlinedictinvertzoology
  37. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dinophysiales
  38. https://fmp.conncoll.edu/silicasecchidisk/LucidKeys3.5/Keys_v3.5/Carolina35_Key/Media/Html/Dinoflagellates.html
  39. https://bio.libretexts.org/Courses/Norco_College/BIO_5%253A_General_Botany_%28Friedrich_Finnern%29/19%253A_Protists/19.06%253A_Dinoflagellates
  40. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dinoflagellate
  41. https://ucmp.berkeley.edu/protista/dinoflagmm.html
  42. https://www1.bio.ku.dk/english/research/mbs/daugbjerg-lab/pdf/2011b_craveiro_et_al.pdf
  43. https://www.mdpi.com/1660-3397/21/2/70
  44. https://pmc.ncbi.nlm.nih.gov/articles/PMC7658998/
  45. https://www.int-res.com/articles/ame/24/a024p287.pdf
  46. https://pmc.ncbi.nlm.nih.gov/articles/PMC11385223/
  47. https://www.pnas.org/doi/10.1073/pnas.2211549119
  48. https://www.nature.com/articles/s42003-024-06889-w
  49. https://phytoplankton.eoas.ubc.ca/research/phytoplankton/diatoms/pennate/navicula/navicula_spp.html
  50. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002GB002018
  51. https://www.nature.com/articles/s41586-022-04687-0
Add your contribution
Related Hubs
User Avatar
No comments yet.