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Locule
Locule
Locule
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A bilocular and a multilocular tomato fruit

A locule (pl.: locules) or loculus (Latin for 'little place'; pl.: loculi) is a small cavity[1] or compartment within an organ or part of an organism (animal, plant, or fungus).

In angiosperms (flowering plants), the term locule usually refers to a chamber within an ovary (gynoecium or carpel) of the flower and fruits. Depending on the number of locules in the ovary, fruits can be classified as unilocular (uni-locular), bilocular, trilocular, or multilocular. The number of locules present in a gynoecium may be equal to or less than the number of carpels. The locules contain the ovules or seeds.

The term may also refer to chambers within anthers containing pollen.[2]

In ascomycetous fungi, locules are chambers within the hymenium in which the perithecia develop.[3]

References

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Locule

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A locule is a small cavity or compartment within an organ or part of an , most commonly referring to chambers in structures such as the of a flower or the anther of a . In botanical contexts, locules house ovules in the or pollen sacs in the anther, playing a key role in and development. In , the number and arrangement of locules vary widely and are important for classifying ovaries as unilocular (one chamber), bilocular (two chambers), or multilocular (many chambers), which influences morphology and . For instance, simple fruits like those of grapes derive from a single carpel with one locule, while simple fruits like oranges feature multiple locules from fused carpels. This structural diversity contributes to evolutionary adaptations in angiosperms, affecting , seed protection, and dispersal strategies. Beyond , locules can describe similar compartments in animal anatomy, though the term is less frequently applied outside . In research, locule characteristics, like number in fruits, are studied for genetic control and breeding improvements to enhance yield and size.

Etymology and Definition

Etymology

The term "locule" originates from the Latin loculus, a of locus meaning "place," thus denoting a "little place" or "small compartment." This Latin root reflects its initial use to describe enclosed spaces, such as compartments in structures. The word entered English in the mid-18th century, with the earliest recorded use in 1751 by English and physician John Hill in a scientific context. It appeared primarily in botanical literature during this period, aligning with the era's advancements in plant classification. Related terms include the Latin singular loculus and the English plural locules, which maintain the sense of compartmentalization. The term is distinct from locus, which broadly indicates a position or site without implying enclosure, and locality, referring to a geographic area or district. Early historical examples trace to 18th-century botanical descriptions, including references in where loculus described structural compartments in plant reproductive organs. By the , it had become established in anatomical and scientific texts for similar partitioned features.

General Definition

A locule, also known as a loculus, is a small cavity, chamber, or compartment within an organ or tissue of , animals, or fungi. This structure serves as a delimited space that organizes internal components, such as cells or reproductive elements, within larger biological tissues. Locules are typically enclosed by walls or , which provide separation from surrounding areas and support functions like containment, protection, and spatial organization of cellular or subcellular elements. These partitions ensure that contents within the locule remain isolated, facilitating specialized physiological processes across diverse organisms. The number of locules in a structure can vary, leading to classifications such as unilocular (containing a single locule), bilocular (two locules), or multilocular (multiple locules), often related to the presence of or other dividing walls./02%3A_Biodiversity_(Organismal_Groups)/2.07%3A_Angiosperm_Diversity/2.7.03%3A_Fruits_and_Dispersal) This variability highlights the role of locules in compartmentalization, applicable to both reproductive structures, like those housing gametes or spores, and non-reproductive tissues that require internal division for functional efficiency.

Contexts in Botany

In Floral Structures

In the ovaries of angiosperm flowers, locules are the internal chambers within the gynoecium or individual carpels that contain and protect developing ovules. These structures form the core of the female reproductive organ, with the number of locules typically corresponding to the fusion state and count of carpels; monocarpellary ovaries are unilocular, featuring a single chamber, while bicarpellary syncarpous ovaries, such as in mustard (Brassica nigra), are bilocular, divided by a central septum. In contrast, apocarpous gynoecia consist of separate carpels, each with its own unilocular ovary, whereas syncarpous fusion can result in multi-loculed ovaries when septa fully develop between carpels. The formation of locules occurs during floral organogenesis from carpel primordia in the floral meristem, where inward growth and fusion establish the chamber architecture early in development. The arrangement and function of ovarian locules are intimately linked to types, which dictate positioning within these chambers and influence reproductive efficiency. Axile placentation positions ovules along a central axis in multi-loculed ovaries, often with separating chambers, as observed in species like . Parietal placentation attaches ovules directly to the ovary walls in unilocular or bilocular ovaries, exemplified by mustard where ovules line the fused carpel margins. Free-central placentation features a single locule with ovules borne on a free-standing central column, common in and lacking , allowing for centralized ovule development. These configurations arise developmentally through directed initiation—acropetal in parietal types or basipetal in free-central—ensuring ovules are accessible for and subsequent fertilization by tubes. In anthers, the male reproductive structures, locules correspond to the microsporangia or pollen sacs that produce and store grains. Angiosperm anthers are typically bilocular, with two locules per lobe forming a tetralocular overall through the division of primary sporogenous tissue during early floral development. Dehiscence mechanisms release from these locules, primarily via longitudinal slits along the anther lobes, driven by hygroscopic contraction of the endothecium layer upon dehydration, which separates the stomium and exposes the for transfer by pollinators. Some monocots, such as (), exhibit distinctly tetralocular anthers with four independent locules, enhancing production capacity. These locules develop from archesporial cells in the anther , maturing to support microspore and wall formation, thereby facilitating ; post-, ovarian locules enclose fertilized ovules, protecting them through early embryogenesis until seed maturation.

In Fruits

In fruits, locules represent the mature chambers derived from the ovarian locules of the flower following fertilization, where they continue to enclose and contain the developing . These structures form as the walls thicken into the pericarp, maintaining the compartmentalization established in the while adapting to support seed maturation and protection. Fruits are often classified based on the number of locules, which reflects the original carpel arrangement and influences overall morphology in relation to the pericarp layers. Unilocular fruits, such as those in ( family), feature a single chamber surrounded by the pericarp, typically dehiscing along two sutures to release seeds. In contrast, multilocular fruits like tomatoes ( lycopersicum) possess multiple chambers—often two to ten—embedded within the fleshy pericarp, contributing to larger size and varied shapes. This locule count directly interacts with pericarp development, where the endocarp, mesocarp, and exocarp layers form around or between locules to provide . Locules play key functional roles in seed protection by isolating within pericarp-enclosed compartments, shielding them from environmental stresses and herbivores, while also shaping types that facilitate dispersal. For instance, in schizocarps, the fruit splits at maturity into separable mericarps, each derived from a single locule, allowing targeted seed release by or animals. Examples include bilocular capsules in opium poppy (), where the two locules dehisce poricidally to disperse numerous small via , an evolutionary adaptation enhancing colonization in disturbed habitats. Similarly, trilocular berries in some , such as chili peppers ( spp.), feature three locules with axile , promoting animal-mediated dispersal through colorful, fleshy pericarps that attract birds and mammals./02%3A_Biodiversity_(Organismal_Groups)/2.07%3A_Angiosperm_Diversity/2.7.03%3A_Fruits_and_Dispersal) Variations in locule development, such as or fusion, significantly affect morphology and taxonomic . Locule occurs when certain chambers fail to develop fully, often due to limitations, resulting in empty or reduced compartments that alter fruit symmetry, as seen in some varieties where aborted locules lead to irregular shapes. Fusion of locules, arising from incomplete septa between carpels, produces seemingly unilocular fruits from multicarpellary ovaries, exemplified in cucurbit fruits like squash ( spp.), where three carpels fuse to form a single large cavity. These variations not only influence dispersal efficiency but also serve as diagnostic traits in , helping delineate genera and families based on reproductive adaptations.

Contexts in Mycology

In Ascomycetous Fungi

In ascomycetous fungi, particularly within the class (formerly classified as Loculoascomycetes), a locule refers to a cavity or pocket formed within a stroma or ascostroma, serving as the site where bitunicate asci and ascospores develop. These structures are characteristic of ascolocular development, where the locule precedes ascus formation, distinguishing them from the developmental pattern seen in many other ascomycetes, where asci form before the cavity. The developmental sequence in these fungi begins with the formation of a solid stroma composed of pseudoparenchymatous tissue from interwoven hyphae, followed by the lysigenous creation of one or more locules through the dissolution of internal cells. Asci then arise from fertile hyphae lining the locule walls, developing as bitunicate, often fissitunicate structures that enable forceful ascospore discharge. Multilocular stromata, containing multiple such locules, are common, with walls typically formed from compressed pseudoparenchyma providing . These locules often contribute to perithecium-like bodies known as pseudothecia or ascostromata, which externally resemble true perithecia but differ in : true perithecia develop around preformed asci, whereas pseudothecia feature preformed locules lined by asci. For instance, in the Venturia, such as V. inaequalis causing , locules within pseudothecia house up to 100 bitunicate asci, each containing eight ascospores that serve as primary inoculum. Similarly, in Pleospora , multilocular ascostromata develop locules that protect maturing ascospores, aiding in the fungus's role as a plant pathogen. Ecologically, locules in these fungi provide a protective environment for and ascospore maturation, shielding them from and environmental stressors during development, which is crucial for many as aggressive plant pathogens affecting crops and forests. This enhances viability and dispersal, contributing to the pathogens' success in infecting hosts like apple trees or cereals.

Contexts in Zoology

In Animal Anatomy

In animal anatomy, a locule refers to a small enclosed cavity or compartment within an organ, tissue, or structure, often serving purposes such as organization, secretion, or attachment. These compartments are typically found in invertebrates, particularly in parasitic forms, where they facilitate specialized functions like host adhesion. A prominent example occurs in cestodes, or tapeworms, where the scolex—the anterior attachment organ—features loculi as shallow, sucker-like depressions or subdivided chambers on bothria (grooves) or phyllidea (leaf-like structures). These loculi, acting passively like cups, enable the parasite to grip the host's intestinal wall securely, enhancing attachment efficiency during feeding and locomotion. For instance, in Cyathocephalus species, the scolex bears a single loculus, while Echeneibothrium exhibits four phyllidea, each armed with numerous loculi for increased surface contact. Similarly, in the caryophyllidean cestode Isoglaridacris mackiewiczi, the scolex is broadly ovoid to deltoid with three flat to almost indistinct loculi on both dorsal and ventral surfaces, aiding in its parasitic lifestyle within hosts. Such locules are less common in free-living but appear in other parasitic groups, like certain , where they form part of the haptor (posterior attachment organ) to secure the worm to host tissues such as gills or . In vertebrates, locules are rare in normal anatomy, with the term more often applied in pathological contexts rather than structural organization. Evolutionarily, these compartments represent adaptations for compartmentalization in complex or parasitic body plans, allowing efficient division of functions like adhesion and nutrient uptake in invertebrate lineages.

References

  1. https://people.uncw.edu/chandlerg/documents/FlowersandFlowerTerminology.pdf
  2. https://open.lib.umn.edu/horticulture/back-matter/glossary-of-terms/
  3. https://home.csulb.edu/~rodrigue/geog330/fruitsseeds.html
  4. https://bio.libretexts.org/Bookshelves/Botany/The_Science_of_Plants_-_Understanding_Plants_and_How_They_Grow_(Michaels_et_al.)/08%3A_Fruit/8.01%3A_Fruit_Morphology
  5. https://employees.csbsju.edu/ssaupe/biol308/Lecture/flowers.htm
  6. https://www.merriam-webster.com/dictionary/locule
  7. https://pmc.ncbi.nlm.nih.gov/articles/PMC6607973/
  8. https://www.oed.com/dictionary/locule_n
  9. https://academic.oup.com/aob/article/104/3/365/227255
  10. https://www.dictionary.com/browse/locule
  11. https://www.oxfordreference.com/display/10.1093/oi/authority.20110803100111957
  12. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/locule
  13. https://www.cambridge.org/core/books/introduction-to-fungi/loculoascomycetes/22E858577E345F310FBA7F5F5C63330F
  14. https://sweetgum.nybg.org/science/glossary/glossary-details/?irn=37
  15. https://www.idtools.org/tools/1060/index.cfm?packageID=2246&entityID=57851
  16. https://open.lib.umn.edu/horticulture/chapter/8-1-fruit-morphology/
  17. https://pmc.ncbi.nlm.nih.gov/articles/PMC8252473/
  18. https://gobotany.nativeplanttrust.org/species/papaver/somniferum/
  19. https://www.researchgate.net/figure/Fruit-of-three-fused-carpels-with-axile-placentation-trilocular_fig9_263041480
  20. https://onlinelibrary.wiley.com/doi/10.1111/btp.70008
  21. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dothideomycetes
  22. https://www.mycosphere.org/pdf/MYCOSPHERE_11_1_13.pdf
  23. https://www.sciencedirect.com/science/article/pii/B9780123877314000086
  24. https://www.sciencedirect.com/science/article/pii/B9780323850421000082
  25. https://encyclopediaofarkansas.net/entries/cestodes-8360/
  26. http://www.biology.ualberta.ca/parasites/ParPub/themes/attach/l080205.htm
  27. http://www.biology.ualberta.ca/parasites/ParPub/themes/attach/l080101.htm
  28. https://www.nature.com/articles/s41598-025-02828-9
  29. https://www.sciencedirect.com/topics/medicine-and-dentistry/monogenea
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