Zoospores are composed of a microtubular cytoskeleton base which extends from the base of the flagellum. The complexity and structure of this cytoskeleton is variable and is largely dependent on volume and size.[2] One common feature of zoospores is their asymmetrical shape; a result of the ventral grove housing the flagella base. Certain zoospores progress through different phases, the first phase commonly referred to as 'the initial'.[2] Others form cysts that vary tremendously in volume (14-4905 cubic micrometers) and shape, each with distinctive hair structures.[2]
Zoospores may possess one or more distinct types of flagella - tinsel or "decorated", and whiplash, in various combinations.
Tinsellated (straminipilous[3]) flagella have lateralfilaments known asmastigonemes perpendicular to their main axis, which allow for more surface area, and disturbance of the medium, giving them the property of arudder, that is, used for steering.
Whiplash flagella are straight, to power the zoospore through its medium. Also, the "default" zoospore only has the propelling, whiplash flagella.
Both tinsel and whiplash flagella beat in asinusoidal wave pattern, but when both are present, the tinsel beats in the opposite direction of the whiplash, to give two axes of control ofmotility.
Attachment to the base of the zoospore is variable between taxa and may help with identification of species.[2]
Figure 1. Zoospore types. The arrow indicates direction of movement.
Ineukaryotes, the four main types of zoospore are[3] illustrated in Fig. 1 at right:
Posterior whiplash flagella are a characteristic of theChytridiomycota, and a proposed uniting trait of theopisthokonts, a large clade of eukaryotes containing animals and fungi. Most of these have a single posterior flagellum (Fig. 1a), but theNeocallimastigales have up to 16 (Fig. 1b).
Anisokonts are biflagellated zoospores with two whip types flagella of unequal length (Fig. 1c). These are found in some of theMyxomycota andPlasmodiophoromycota.
Zoospores with a single anterior flagellum (Fig. 1d) of the tinsel type are characteristic ofHyphochytriomycetes.
Heterokont are biflagellated zoospores (Fig. 1e, f) with both whiplash (smooth) and tinsel type (fine outgrowths called mastigonemes) flagella attached anteriorly or laterally. These zoospores are characteristic of theOomycota and otherheterokonts.
Zoosporangia and zoospores ofPhytophthora agathidicida
A zoosporangium is the asexual structure (sporangium) in which the zoospores develop in plants, fungi, or protists (such as theOomycota). Developing sporangia of oomycetes go through a process of cleavage in which aprotein kinase, in the case ofPhytophthora infestans, induces the sporangial cytoplasm to split and release the various zoospores.[4] Release of the spores can occur either inside of the zoosporangium (intrasporangial zoosporogenesis) or exteriorly (extrasporangial zoosporogenesis).[2] Spores absorb water and travel through thecell membrane for excretion.[2]
Different fungal zoospores may infect different taxa of organisms. Due to zoospores' aquatic lifestyle,[1] fish and amphibians are ideal hosts. Some colonize exposed injuries in fish which may causeepidermal damage, leading to death in certain cases.[5] Others may utilize species of frogs (such asBufo marinus andRana catesbieana) as carriers, allowing extended ranges of travel.[1]
^abcdO’Rourke, Dorcas P.; Rosenbaum, Matthew D. (2015),"Biology and Diseases of Amphibians",Laboratory Animal Medicine, Elsevier, pp. 931–965, retrieved2023-11-08
^Fox, James G.; Anderson, Lynn C.; Otto, Glen M.; Pritchett-Corning, Kathleen R.; Whary, Mark T. (2015).Laboratory animal medicine. American College of Laboratory Animal Medicine series. American college of laboratory animal medicine (3rd ed.). Amsterdam: Elsevier/Academic Press.ISBN978-0-12-409527-4.
Alexopoulos, C. J.; Mims, Charles W.; Blackwell, M.; et al. (2004).Introductory Mycology (4th ed.). Hoboken, New Jersey: John Wiley and Sons.ISBN0-471-52229-5.
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