Spore
|
Spores produced in a sporic life cycle. |
A
spore is a
biological term for a
reproductive mechanism, usually
haploid and
unicellular, that is adapted for
dispersion and surviving for extended periods of time in unfavorable conditions. The spore can develop into a new
organism by dividing by
mitosis without
fusing with another cell, producing a
multicellular gametophyte. Produced by
meiosis by the
sporophyte, the spore is considered a part of the
life cycles of
plants or
algae with
alternation of generations. The term derives from the
ancient Greek word σπορα, meaning
seed. Spores can be classified by their function, by their origin in the
life cycle, or by their
motility.
The term may also refer to the dormant stage of some
bacteria, however these are more correctly known as
endospores and are not truly spores in the sense discussed by this article. The term can also be loosely applied to some
animal resting stages. Fungi that produce spores are known as
sporogenous, and those that do not are
asporogenous.
Spores can be classified in several manners.
By function
Diaspores are
dispersal units of
fungi,
mosses,
ferns,
fern allies, and some other
plants. In fungi,
chlamydospores are thick-walled resting spores, and
zygospores are thick-walled resting spores (hypno
zygotes) of
zygomycetous fungi which are produced by sexual gametocystogamy and can give rise to a conidiophore ("zygosporangium") with asexual conidiospores.
By spore-producing structure
In fungi and fungus-like organisms, spores are often classified by the structure in which meiosis and spore production takes place, such as a
telium,
ascus,
basidium, or
oogonium, which produce
teliospore,
ascospores,
basidiospores, and
oospores, respectively. Since fungi are often classified according to their spore-producing structures, these spores are often characteristic of a particular taxon of the fungi, such as
Ascomycota or
Basidiomycota.
Meiospores are the product of
meiosis (the critical cytogenetic stage of
sexual reproduction), meaning that they are
haploid, and will give rise to a haploid daughter cell(s) or a haploid individual. An example is the parent of
gametophytes of the higher vascular plants (
angiosperms and
gymnosperms)—the
microspores (give rise to
pollen) and
megaspores (give rise to ovules) found in
flowers and
cones; these plants accomplish dispersal by means of
seeds.
A
mitospore (
conidium, conidiospore) is an asexually produced propagule, the result of
mitosis. Most
fungi produce mitospores. Mitosporic fungi are also known as anamophic fungi (compare
teleomorph or
deuteromycetes).
Spores can be differentiated by whether they can move or not.
Zoospore can move by means of one or more
flagellum and can be found in some
algae and
fungi.
Aplanospore cannot move, but may potentially grow flagella.
Autospore cannot move and do not have the potential to ever develop any flagella.
Ballistospore are actively discharged from the body of a fungal fruit (such as a
mushroom).
Statismospore are not actively discharged from the fungal fruit body, similarly to a
puffball.
In common parlance, the difference between "spore" and "
gamete" (both together called
gonites) is that a spore will germinate and develop into a
thallus of some sort, while a gamete needs to combine with another gamete before developing further. However, the terms are somewhat interchangeable when referring to gametes.
A chief difference between spores and seeds as
dispersal units is that spores have very little stored food resources compared with seeds, and thus require more favorable conditions in order to successfully germinate. Spores, therefore, are more resistant to harsh conditions and require less
energy to start
mitosis. Spores are usually produced in large numbers to increase the chance of a spore surviving.
The
endospores of certain bacteria are often incorrectly called spores, as seen in the
2001 anthrax attacks where
anthrax endospores were incorrectly called
anthrax spores by the media. Several key differences between bacterial endospores and eukaryotic spores exist: they are primarily a survival mechanism, not a reproductive method, and a bacterium only produces a single endospore.
In the case of spore-shedding
vascular plants such as
ferns, wind distribution of very light spores provides great capacity for dispersal. Also, spores are less subject to animal predation than seeds because they contain almost no food reserve, however they are more subject to fungal and bacterial predation. Their chief advantage is that, of all forms of progeny, spores require the least energy and materials to produce.
Vascular plant spores are always
haploid and vascular plants are either
homosporous or
heterosporous. Plants that are
homosporous produce spores of the same size and type.
Heterosporous plants, such as
spikemosses,
quillworts, and some aquatic ferns produce spores of two different sizes: the larger spore in effect functioning as a "
female" spore and the smaller functioning as a "
male".
Under high
magnification, spores can be categorized as either
monolete spores or
trilete spores. In monolete spores, there is a single line on the spore indicating the axis on which the mother spore was split into four along a vertical axis. In trilete spores, all four spores share a common origin and are in contact with each other, so when they separate each spore shows three lines radiating from a center pole.
*
A video of spores being ejected by fungus*
Alternation of generations*
Sporophyte*
Endospore*
Fern
