Pit connection
Encyclopedia
In Plant anatomy
, a pit connection is a hole in the septum
between two algal cells, and is found only in the red algae
- specifically, all orders except the Porphyridiales and haploid Bangiales. They are often stoppered with "pit plugs". They are in fact neither pits, nor connections, yet the term remains in use due to its longevity. By contrast, many fungi (only ascomycetes and basidomycetes, as other groups lack septa) contain septal pores - an unrelated phenomenon.
Pit connections come in many varieties: the micropores of the zygomycetes; the simple, Woronin body
-bearing pores of the ascomycetes, and the dolipores of the holobasidiomycetes and phragmobasidiomycetes. Simple, unornamented, pores are also associated with the teliomycetes, where they are accompanied by "pulley wheel occlusions". "Munk pores" are found in the walls of some Sordariales
and are surrounded by a raised rim. Dolipores too have a thick wall surrounding their opening, which prevents the movement of cell organelles between adjoining cells, while permitting the sharing of cell fluids. These may be further covered by septal pore caps.
The dolipores of the Agaricomycotina
(basidomycetes) are often surrounded by bracket-shaped structures called parenthesome
s - but other basidomycetes have differently structured pores.
Secondary connections, by contrast, occur between unrelated cells, and serve a role in transferring cell contents and nutrients. They may even form between cells of different species, as in the parasite Holmsella.
Plant anatomy
Plant anatomy or phytotomy is the general term for the study of the internal structure of plants. While originally it included plant morphology, which is the description of the physical form and external structure of plants, since the mid-20th century the investigations of plant anatomy are...
, a pit connection is a hole in the septum
Septum
In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...
between two algal cells, and is found only in the red algae
Red algae
The red algae are one of the oldest groups of eukaryotic algae, and also one of the largest, with about 5,000–6,000 species of mostly multicellular, marine algae, including many notable seaweeds...
- specifically, all orders except the Porphyridiales and haploid Bangiales. They are often stoppered with "pit plugs". They are in fact neither pits, nor connections, yet the term remains in use due to its longevity. By contrast, many fungi (only ascomycetes and basidomycetes, as other groups lack septa) contain septal pores - an unrelated phenomenon.
Characteristics
A sieve-like membrane may cover the pit in living algae, but in the majority of algae a plug forms, limiting the transfer of metabolites between neighbouring cells.Pit connections come in many varieties: the micropores of the zygomycetes; the simple, Woronin body
Woronin body
A Woronin body is a peroxisome-derived, dense core microbody with a double membrane found near the septae that divide hyphal compartments in filamentous Ascomycota. One established function of Woronin bodies is the plugging of the septal pores after hyphal wounding, which restricts theloss of...
-bearing pores of the ascomycetes, and the dolipores of the holobasidiomycetes and phragmobasidiomycetes. Simple, unornamented, pores are also associated with the teliomycetes, where they are accompanied by "pulley wheel occlusions". "Munk pores" are found in the walls of some Sordariales
Sordariales
Sordariales are an order of fungi within the class Sordariomycetes , subphylum Pezizomycotina, phylum Ascomycota....
and are surrounded by a raised rim. Dolipores too have a thick wall surrounding their opening, which prevents the movement of cell organelles between adjoining cells, while permitting the sharing of cell fluids. These may be further covered by septal pore caps.
The dolipores of the Agaricomycotina
Agaricomycotina
The subphylum Agaricomycotina, also known as the hymenomycetes, is one of three taxa of the fungal division Basidiomycota . The Agaricomycotina contain some 20,000 species, and about 98% of these are in the class Agaricomycetes: most of the fungi known as mushrooms, including the bracket fungi and...
(basidomycetes) are often surrounded by bracket-shaped structures called parenthesome
Parenthesome
Within the cells of basidiomycete fungi are found microscopic structures called parenthesomes or septal pore caps. They are shaped like parentheses and found on either side of pores in the dolipore septum which separates cells within a hypha. Their function has not been established, and their...
s - but other basidomycetes have differently structured pores.
Formation
Primary pit connections are formed between cells in the same filament, derived from the same parent cell by its division. Such connections are always single, and usually circular; this is a result of their method of formation. The septa is formed as the walls of a filament grow inwards, dividing the cell; this results in a hole in the middle of the tube where the walls don't quite merge. Thus connections are visible in the youngest of septa, widening as the septum thickens, until in some cases they may ultimately occupy the entire septum.Secondary connections, by contrast, occur between unrelated cells, and serve a role in transferring cell contents and nutrients. They may even form between cells of different species, as in the parasite Holmsella.
External links
- Transverse SEM images of pit connections in the coralline SynarthrophytonSynarthrophytonSynarthrophyton is a genus of thalloid alga comprising eight species. The monomerous, crustose thalli are composed of a single system of filaments which grow close to the underlying surface. Synarthrophyton reproduces by means of flask-shaped multiporate conceptacles; it produces tetraspores and...
can be seen in Figs. 54 & 60 in- (Lower quality) transverse SEM images of pit connections in the coralline PhymatolithonPhymatolithonPhymatolithon is a genus of nongeniculate coralline red alga, known from the UK and Australia. It is encrusting, flat, and unbranched; it has tetrasporangia and bisporangia borne in multiporate conceptacles...
are available on page 138 at .
- (Lower quality) transverse SEM images of pit connections in the coralline Phymatolithon