Zoospore

Heterokont zoospore of Saprolegnia with tinsel and whiplash flagella.

A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria and fungi to propagate themselves.

Diversity

Flagella types

Zoospores may possess one or more distinct types of flagella: tinsel or "decorated", and whiplash, in various combinations.

Tinsellated (also known as straminipilous^[1]) flagella have lateral filaments known as mastigonemes perpendicular to the main axis which allow for more surface area, and disturbance of the medium, giving it the property of a rudder, that is, the purpose of being used for steering.
Whiplash flagella are straight, to power the zoospore through its medium. There is also the 'default' zoospore, which only has the propelling, 'whiplash' flagella.

Both tinsel and whiplash flagella beat in a sinusoidal wave pattern, but when both are present, the tinsel will beat in the opposite direction of the whiplash, to give 2 axes of control of motility.

Morphological types

Figure 1. Zoospore types. The arrow indicates direction of movement.

In eukaryotes there are four main types of zoospore,^[1] illustrated in Fig. 1 at right:

Opisthokont. Posterior whiplash flagella, a characteristic of Chytridiomycota, and a proposed a uniting trait of the Opisthokonts, a large clade of eukaryotes containing animals and fungi. In most of these, there is a single posterior flagellum (Fig. 1a), but in Neocallimastigales, there are up to 16 (Fig. 1b)
Anisokont. Biflagellate zoospores with two whip type flagella of unequal length (Fig. 1c). These are found in some Myxomycota and Plasmodiophoromycota.
Zoospores with a single anterior flagellum (Fig. 1d) of the tinsel type, characteristic of Hyphochytriomycetes.
Heterokont. Biflagellate zoospores (Fig. 1e, f) with both whiplash and tinsel type flagella attached anteriorly or laterally. These Zoospores are characteristic of Oomycota and other Heterokonts.

Zoosporangium

A zoosporangium is the asexual structure (sporangium) in which the zoospores develop in plants, fungi, or protists (such as the Oomycota)

References

1 2 Webster, John; Weber, Roland (2007). Introduction to Fungi (3rd ed.). Cambridge: Cambridge University Press. pp. 23–24. ISBN 9780521014830.

C.J. Alexopolous, Charles W. Mims, M. Blackwell et al., Introductory Mycology, 4th ed. (John Wiley and Sons, Hoboken NJ, 2004) ISBN 0-471-52229-5

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