Reproduction and Development of Blastocladiella emersonii
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License | CC Attribution - NoDerivatives 3.0 Germany: You are free to use, copy, distribute and transmit the work or content in unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
Identifiers | 10.3203/IWF/C-1959eng (DOI) | |
IWF Signature | C 1959 | |
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Production Year | 1993 |
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IWF Technical Data | Video ; F, 11 min |
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Transcript: English(auto-generated)
00:10
The mud-inhabiting aquatic fungus Blastocladiella emersonii forms reddish-brown resting sporangia and also colourless zoosporangia.
00:22
Here, a young thallus about 100 micrometres in diameter is growing. At its base is a tuft of rhizoids. On media deficient in carbon dioxide, a thin-walled, colourless sporangium develops within 24 hours. The thallus is divided by an incomplete septum into two portions.
00:52
The upper develops into a sporangium from which exit papillae will protrude.
01:04
The cytoplasm is in active movement but becomes homogeneous shortly before the zoospores are differentiated. Vacuoles appear and enlarge. The release of the zoospores is due to increasing pressure.
01:20
Zoospores have already differentiated in this sporangium. A mucilage plug which blocks the exit tube dissolves, allowing the zoospores to escape, shown here in real time. The papillae elongate and zoospores move into them.
01:42
After dissolution of the plug, the zoospores are expelled. Each one squeezes singly through the exit pore. Sometimes one is caught by its trailing flagellum as the next zoospore temporarily blocks up the opening.
02:01
Each is propelled by a single posterior flagellum. The whiplash flagellum beats by means of a sine wave. This electron micrograph shows the organelles of the zoospore.
02:26
Nuclear cap, nucleus, nucleolus. The single basal mitochondrion surrounds the flagellum base and distributed throughout the cytoplasm,
02:41
lipid droplets as an energy reserve and gamma particles concerned with synthesis of chitin which makes up the cell wall. The same cell organelles can be made visible by special techniques using high magnification phase contrast.
03:13
In flattened preparations, the zoospores show amoeboid movement with frequent change of form.
03:22
After a time, their movement slows down. Spores then rotate, an indication that they will soon insist. Before insistment, the flagellum is withdrawn.
03:55
Flagellum withdrawal, speeded up 25 times.
04:04
Some zoospores have already insisted. Others are settling nearby, for instance to the right of the centre. The nuclear cap dissolves after the flagellum has been withdrawn.
04:24
Zoospores often come to rest in groups. They germinate to form thallae which grow and produce sporangia which then release zoospores. Development in a medium pore in carbon dioxide shown again diagrammatically.
04:45
Zoospore, cyst, thallus, thin-walled sporangium. This developmental cycle takes about 24 hours and is repeated when the carbon dioxide concentration stays low.
05:04
On carbon dioxide-rich media, morphologically distinct thallae and sporangia, resting sporangia develop. The thallae develop resting sporangia over a period of about 7 days. The resting sporangia can survive adverse conditions for several months.
05:25
Zoospores are released when free water is available.
05:42
The resting sporangial thallus is divided into a lower compartment from which rhizoids extend and an upper compartment containing the thick-walled resting sporangium. Resting sporangium development is induced by high CO2 or bicarbonate concentration. New metabolic pathways lead to the synthesis of melanin.
06:03
The brown pigment melanin is deposited in the wall of the resting sporangium. When free water is available, zoospore production is initiated. Motile zoospores are visible through the sporangium wall.
06:24
Before zoospore discharge occurs, the resting sporangia take up water and inner wall swells, cracking open the thick rust-coloured outer wall. These processes are demonstrated by time-lapse photography.
06:46
Exit tubes develop from the thin inner wall of the sporangium. Their tips dissolve, allowing zoospores to escape.
07:00
On release of zoospores, the resting sporangium wall shrinks, separating from the thallus wall which surrounds it. Zoospores from resting sporangia contain abundant lipid droplets with dissolved γ-carotene giving a golden brown colour.
07:24
They are similar to zoospores from thin-walled sporangia, in amoeboid movement and structural details. They come to rest and insist.
07:41
In young thallae, nuclear divisions occur. During germination, rhizoids form. These anchor the thallus to the substrate. The sac-shaped part of the thallus enlarges.
08:09
In the upper part of the young thallus, a spherical resting sporangium develops. Its wall already has the characteristic reddish colour.
08:25
After seven to ten days, the resting sporangia are fully developed. Again, in the diagram, the two alternative pathways are compared.
08:46
If zoospores from thick-walled sporangia are placed on a medium deficient in carbon dioxide, they germinate and develop zoosporangia. If, on the other hand, zoospores from thin-walled sporangia
09:04
germinate on a carbon dioxide-rich medium, they develop thick-walled resting sporangia. It is obvious that morphogenesis is determined by an external factor.
09:34
Resting sporangia predominate in old cultures because crowding causes a rise in carbon dioxide.
09:45
Each cluster of resting sporangia has probably developed from a single sporangium. Resting sporangia are structures which enable blastocladiella emersonii to survive adverse conditions.