| Building Bodies from Slime: Plasmodia |
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The pictures above show a computer Pov-Ray model of a slime-mould plasmodium. These creatures form a sheet of
mobile slime, only a couple of millimetres thick at most but up to one metre in more diameter. The remarkable things
is, that despite their large size, these creatures are single cells! They resemble single giant animal cells, but are
protoctistans, as is the single-celled amoeba which they resemble. Amoebae are normally one millimetre across at
most, but the plasmodium slime-mould is in essence a giant amoeba. The plasmodium actually begins its life as a
tiny amoeba, but grows and grows! Like an animal cell, the plasmodium consists of cytoplasm enclosed by a 'skin'
called the plasma-membrane. Whereas a typical animal cell contains one nucleus, however, a plasmodium contains
many thousands of nuclei (as required to maintain its large size). The plasmodium is able to slowly crawl along the
surface, at about one centimetre per hour, in which case it assumes a fan-shape, with the broad margin leading as
the front end, though it can easily change shape and start moving in another direction.
To facilitate this movement, the plasmodium forms a network of vessels to transport its cytoplasm from one end to
the other. Plasmodia vary in colour, depending upon species, though most are either transparent or bright yellow or
white, some are reddish, green or even blue in colour. Although they occur in most habitats, they are most likely
encountered crawling in the leaf litter and inside rotting logs in damp woods. They feed by smothering their food and
absorbing it directly (a process called phagocytosis). They engulf bacteria, fungi, and decaying organic matter and
can home-in on potential food by responding to its odour. I have heard stories of people keeping small plasmodia in
petri dishes, and entertaining people by placing food atone end of the dish, and then watching the slim slowly crawl
over to eat the food!
I once found two translucent plasmodia (almost totally transparent) crawling across a felled log in a damp
Devonshire woodland. Each was about the size of a human hand. Pressing one of the veins, it was surprisingly rigid,
but squeezing it showed the cytoplasm inside squirt along the vein in either direction from the point of pressure.
Cytoplasm ordinarily moves back and forth along these veins in oscillations lasting about one minute, with cytoplasm
streaming along at up to 1.3 millimetres per second. Superimposed on these oscillatory movements is a general net
movement of cytoplasm toward the leading edge.
The diagram below shows the structure of a small plasmodial slime-mould.
mobile slime, only a couple of millimetres thick at most but up to one metre in more diameter. The remarkable things
is, that despite their large size, these creatures are single cells! They resemble single giant animal cells, but are
protoctistans, as is the single-celled amoeba which they resemble. Amoebae are normally one millimetre across at
most, but the plasmodium slime-mould is in essence a giant amoeba. The plasmodium actually begins its life as a
tiny amoeba, but grows and grows! Like an animal cell, the plasmodium consists of cytoplasm enclosed by a 'skin'
called the plasma-membrane. Whereas a typical animal cell contains one nucleus, however, a plasmodium contains
many thousands of nuclei (as required to maintain its large size). The plasmodium is able to slowly crawl along the
surface, at about one centimetre per hour, in which case it assumes a fan-shape, with the broad margin leading as
the front end, though it can easily change shape and start moving in another direction.
To facilitate this movement, the plasmodium forms a network of vessels to transport its cytoplasm from one end to
the other. Plasmodia vary in colour, depending upon species, though most are either transparent or bright yellow or
white, some are reddish, green or even blue in colour. Although they occur in most habitats, they are most likely
encountered crawling in the leaf litter and inside rotting logs in damp woods. They feed by smothering their food and
absorbing it directly (a process called phagocytosis). They engulf bacteria, fungi, and decaying organic matter and
can home-in on potential food by responding to its odour. I have heard stories of people keeping small plasmodia in
petri dishes, and entertaining people by placing food atone end of the dish, and then watching the slim slowly crawl
over to eat the food!
I once found two translucent plasmodia (almost totally transparent) crawling across a felled log in a damp
Devonshire woodland. Each was about the size of a human hand. Pressing one of the veins, it was surprisingly rigid,
but squeezing it showed the cytoplasm inside squirt along the vein in either direction from the point of pressure.
Cytoplasm ordinarily moves back and forth along these veins in oscillations lasting about one minute, with cytoplasm
streaming along at up to 1.3 millimetres per second. Superimposed on these oscillatory movements is a general net
movement of cytoplasm toward the leading edge.
The diagram below shows the structure of a small plasmodial slime-mould.
Above: the structure of a plasmodial slime mould (redrawn from Fleischer and
Wohlfarth-Bottermann, 1975). CFC, circular fibrils in cross-section; CFL, circular
fibrils in longitudinal section; ECC, ectoplasm in cross-section; ECL, ectoplasm in
longitudinal section; ENC, endoplasm in cross-section; ENL, endoplasm in
longitudinal section; PI, plasma-membrane invagination;PL, plasma-membrane
(plasmalemma) and PS, pseudopod.
Wohlfarth-Bottermann, 1975). CFC, circular fibrils in cross-section; CFL, circular
fibrils in longitudinal section; ECC, ectoplasm in cross-section; ECL, ectoplasm in
longitudinal section; ENC, endoplasm in cross-section; ENL, endoplasm in
longitudinal section; PI, plasma-membrane invagination;PL, plasma-membrane
(plasmalemma) and PS, pseudopod.
First, it should be noted, that in a plasmodium of at least moderate size, the network of vessels are much more
complex than depicted either in the computer model or in the diagram above - many finer vessels branch and
ramify to form a lattice-like network, rather like the veins in a leaf, especially toward the leading edge where the
finer veins are denser.
Notice that each vein consists of two concentric cylinders inside the plasma-membrane sheath (PL) - the outer
ectoplasm and the inner endoplasm. The ectoplasm is stiff and gelatinous and contains longitudinal and circular
fibrils (and also radial fibrils which are not shown) which are composed principally of rods of a protein called actin.
Actin is a component of the cell skeleton and is capable of exerting tension and ordering water in the cytoplasm to
form a stiff gel, such as the ectoplasm. The endoplasm is free of these stiffening actin rods and much more watery.
The actin fibrils in the ectoplasm contract in sequence, squeezing the fluid endoplasm along the veins, rather like
squeezing toothpaste along a tube. This transports cytoplasm from the rear of the creature to the advancing edge.
When the time comes, ectoplasm can be mobilised by simply dissolving the actin cytoskeleton and turning the
ectoplasm into endoplasm. Actin has the remarkable property of being able to assemble rods (columns or struts) or
dissolving into fluid, as and when required! The pseudopods (literally 'false feet') absorb any food on the substrate
as the slime crawls along and are also assembled and disassembled as required.
Plasmodia have some remarkable properties. If you cut one into several smaller pieces, no matter, each fragment
will continue to move and crawl as an individual organism, but if it encounters another piece of its former self, then
the two will fuse back together again! If, however, a foreign plasmodium (differing genetically) is encountered, then
the bigger will usually devour the smaller!
Finally, when the plasmodium has fed sufficiently, it will crawl out from hiding and ascend a tall structure (if one is
available) stop moving and then transform into a spore-producing structure. This is when plasmodia are most often
seen - as foam-like material on grass or the trunks of trees. In this non-motile state, the fan-like shape with its veins
disappears and the whole resembles a foamy mass which easily fragments on touch, rather like shaving foam. (It is
also cool to the touch and has a subtle slightly minty odour in my opinion, an odour which is unmistakable). I once
saw a specimen about 30 cm long and 5 cm wide streaked vertically along the outside of an old oak trunk, about 2
metres from the ground. This state is modelled in the computer graphics below.
complex than depicted either in the computer model or in the diagram above - many finer vessels branch and
ramify to form a lattice-like network, rather like the veins in a leaf, especially toward the leading edge where the
finer veins are denser.
Notice that each vein consists of two concentric cylinders inside the plasma-membrane sheath (PL) - the outer
ectoplasm and the inner endoplasm. The ectoplasm is stiff and gelatinous and contains longitudinal and circular
fibrils (and also radial fibrils which are not shown) which are composed principally of rods of a protein called actin.
Actin is a component of the cell skeleton and is capable of exerting tension and ordering water in the cytoplasm to
form a stiff gel, such as the ectoplasm. The endoplasm is free of these stiffening actin rods and much more watery.
The actin fibrils in the ectoplasm contract in sequence, squeezing the fluid endoplasm along the veins, rather like
squeezing toothpaste along a tube. This transports cytoplasm from the rear of the creature to the advancing edge.
When the time comes, ectoplasm can be mobilised by simply dissolving the actin cytoskeleton and turning the
ectoplasm into endoplasm. Actin has the remarkable property of being able to assemble rods (columns or struts) or
dissolving into fluid, as and when required! The pseudopods (literally 'false feet') absorb any food on the substrate
as the slime crawls along and are also assembled and disassembled as required.
Plasmodia have some remarkable properties. If you cut one into several smaller pieces, no matter, each fragment
will continue to move and crawl as an individual organism, but if it encounters another piece of its former self, then
the two will fuse back together again! If, however, a foreign plasmodium (differing genetically) is encountered, then
the bigger will usually devour the smaller!
Finally, when the plasmodium has fed sufficiently, it will crawl out from hiding and ascend a tall structure (if one is
available) stop moving and then transform into a spore-producing structure. This is when plasmodia are most often
seen - as foam-like material on grass or the trunks of trees. In this non-motile state, the fan-like shape with its veins
disappears and the whole resembles a foamy mass which easily fragments on touch, rather like shaving foam. (It is
also cool to the touch and has a subtle slightly minty odour in my opinion, an odour which is unmistakable). I once
saw a specimen about 30 cm long and 5 cm wide streaked vertically along the outside of an old oak trunk, about 2
metres from the ground. This state is modelled in the computer graphics below.
Above: the plasmodium is preparing to spore. This is the form that most people see slime moulds in, and they
usually mistake them for foam that some one has sprayed! This is the type of structure formed by the large
Physarum polycephalum species. Actually, many species do not form these structures, but instead form one or
more rounded nodules or clusters of tiny stalked sporangia, very similar to those produced by cellular slime moulds
but usually occurring in groups rather than singly. These stalked structures are easily seen on rotting logs, but are
missed by most people because of their small size - they are slimy and usually brightly coloured and much smaller
than toadstools. An example of the stalkless (sessile) type that nevertheless has distinct capsules (sporangia) is
shown below. The stalkless types are often larger than the stalked sporangia, with each capsule often several
centimetres across in some species.
usually mistake them for foam that some one has sprayed! This is the type of structure formed by the large
Physarum polycephalum species. Actually, many species do not form these structures, but instead form one or
more rounded nodules or clusters of tiny stalked sporangia, very similar to those produced by cellular slime moulds
but usually occurring in groups rather than singly. These stalked structures are easily seen on rotting logs, but are
missed by most people because of their small size - they are slimy and usually brightly coloured and much smaller
than toadstools. An example of the stalkless (sessile) type that nevertheless has distinct capsules (sporangia) is
shown below. The stalkless types are often larger than the stalked sporangia, with each capsule often several
centimetres across in some species.
A cluster of stalkless slime mould
sporangia.
sporangia.
Eventually, these structures, either the foam-like mass or discrete sporangia capsules, will harden and turn darker
and eventually the whole organism turns into a mass of dark powder enclosed by a dry skin. This 'skin' cracks and
the spores escape, to be carried away by wind or rain. This powder is a mass of spores have a characteristic minty
odour (never sniff spores of any slime mould or fungus if you are asthmatic!). If they find a suitable place in rich
soil, then the spores will germinate, releasing a single microscopic amoeboid cell, to continue the cycle over again.
The advantage of this complex life-cycle is that it better enables the creature to find food when food is scarce,
since the large plasmodium can cover more ground than a microscopic amoeba, and it also enable the creatures
to crawl high up tree trunks and the such, to better disperse their spore over long distances.
Is it any wonder that for a long time biologists could not decide what to classify plasmodial slime-moulds as -
sometimes they were included with the fungi, sometimes with animals and finally (or not?) with the protoctistans -
which includes all sorts of creatures that do not neatly fit anywhere else!
Plasmodia are food for some creatures - certain insects, like some fly species, make a living out of laying eggs in
plasmodia, the maggots then eat part or all of the plasmodium before pupating. I once saw a batch of maggots eat
part of a large plasmodium that had settled down to spore (the same one on the oak tree mentioned above) before
pupating as strange spiny pupae which emerged into what I never saw. They did not destroy the whole slime
mould, however, which went on to produce millions of spores! I believe that a certain species is eaten in Mexico as
a delicacy (?) but they are generally not edible. Years in which slime moulds grow especially well have been known
to create public scares as people report seeing strange pulsating blobs, mistaken for aliens from outer space!!
and eventually the whole organism turns into a mass of dark powder enclosed by a dry skin. This 'skin' cracks and
the spores escape, to be carried away by wind or rain. This powder is a mass of spores have a characteristic minty
odour (never sniff spores of any slime mould or fungus if you are asthmatic!). If they find a suitable place in rich
soil, then the spores will germinate, releasing a single microscopic amoeboid cell, to continue the cycle over again.
The advantage of this complex life-cycle is that it better enables the creature to find food when food is scarce,
since the large plasmodium can cover more ground than a microscopic amoeba, and it also enable the creatures
to crawl high up tree trunks and the such, to better disperse their spore over long distances.
Is it any wonder that for a long time biologists could not decide what to classify plasmodial slime-moulds as -
sometimes they were included with the fungi, sometimes with animals and finally (or not?) with the protoctistans -
which includes all sorts of creatures that do not neatly fit anywhere else!
Plasmodia are food for some creatures - certain insects, like some fly species, make a living out of laying eggs in
plasmodia, the maggots then eat part or all of the plasmodium before pupating. I once saw a batch of maggots eat
part of a large plasmodium that had settled down to spore (the same one on the oak tree mentioned above) before
pupating as strange spiny pupae which emerged into what I never saw. They did not destroy the whole slime
mould, however, which went on to produce millions of spores! I believe that a certain species is eaten in Mexico as
a delicacy (?) but they are generally not edible. Years in which slime moulds grow especially well have been known
to create public scares as people report seeing strange pulsating blobs, mistaken for aliens from outer space!!
Above: a plasmodium about one foot in length has formed a foam-like streak on the bark of this old oak tree
(the tree is estimated to be about 400 years in age) - much of its is covered by the ivy. This plasmodium is
stationary, having left the fan-like crawling stage (the plasmodium proper) and begun to transform into a
sporing stage. Over the next few days the mass dried, and beneath the hardened crust was a mass of powder
with a minty odour (do not sniff spores if you suffer from asthma!). Some plasmodia can dry reversibly into a
dormant stage (sclerotium) that comes back to life on application of water, but I think this one was in the
terminal fruiting stage. Slime moulds have specialised predators, and some sort of fly laid its eggs in this one,
the hatchling maggots devoured part of the slime before pupating, several days later, as spiny pupal cases
from which adult flies emerged (I never got to see the adults). However, most of the slime mass remained, so
this creature did its job in producing plenty of spores. They are very hard to destroy by mechanical means -
no matter in to how many parts they are cut, broken or crushed, the parts go on living and can rejoin if the
plasmodium is still in its motile stage!
(the tree is estimated to be about 400 years in age) - much of its is covered by the ivy. This plasmodium is
stationary, having left the fan-like crawling stage (the plasmodium proper) and begun to transform into a
sporing stage. Over the next few days the mass dried, and beneath the hardened crust was a mass of powder
with a minty odour (do not sniff spores if you suffer from asthma!). Some plasmodia can dry reversibly into a
dormant stage (sclerotium) that comes back to life on application of water, but I think this one was in the
terminal fruiting stage. Slime moulds have specialised predators, and some sort of fly laid its eggs in this one,
the hatchling maggots devoured part of the slime before pupating, several days later, as spiny pupal cases
from which adult flies emerged (I never got to see the adults). However, most of the slime mass remained, so
this creature did its job in producing plenty of spores. They are very hard to destroy by mechanical means -
no matter in to how many parts they are cut, broken or crushed, the parts go on living and can rejoin if the
plasmodium is still in its motile stage!
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Above: a cross-section through a plasmodial strand
(vein). Bundles of actin filaments in the outer
(gelatinous) attached to the plasma membrane at
membrane invaginations (clefts) contract (probably with
the aid of mysosin) ectoplasm contract, narrowing the
vein and squeezing the endoplasm along it. Endoplasm
may move at speeds of 1 mm/s in this fashion. Actin
and myosin form bundles called microfilaments or
microfibrils. In animal muscle these bundles (called
myofilaments) bring about contraction of the muscle.
(vein). Bundles of actin filaments in the outer
(gelatinous) attached to the plasma membrane at
membrane invaginations (clefts) contract (probably with
the aid of mysosin) ectoplasm contract, narrowing the
vein and squeezing the endoplasm along it. Endoplasm
may move at speeds of 1 mm/s in this fashion. Actin
and myosin form bundles called microfilaments or
microfibrils. In animal muscle these bundles (called
myofilaments) bring about contraction of the muscle.
This mass of spores is all that remains of a sporing mass probably
belonging to Reticularia lycoperdon. A few days earlier, the
plasmosdium had turned into a white hemi-spherical mass (about
the size of a fist in this case) attached to this fallen log. This browns
as it ripens and turns into a mass of spores. Unfortunately, when I
returned a few days later the impressive sporing body had already
disintegrated! The slightest tap to the log would send a cloud of
spores shooting into the air. The moral of the tale is - when walking
in the countryside always carry a camera, because you never know
what you may find!
belonging to Reticularia lycoperdon. A few days earlier, the
plasmosdium had turned into a white hemi-spherical mass (about
the size of a fist in this case) attached to this fallen log. This browns
as it ripens and turns into a mass of spores. Unfortunately, when I
returned a few days later the impressive sporing body had already
disintegrated! The slightest tap to the log would send a cloud of
spores shooting into the air. The moral of the tale is - when walking
in the countryside always carry a camera, because you never know
what you may find!
This is probably Trichia deciphens. In many slime moulds, such as
this, the plasmodium transforms into a mass of small sporangia,
which are often born on short stalks (as in this case). The whole
mass (of which half is visible here) covered about two hand-spans
of this rotting ash log. The sporangia at first appear pink on short
white stalks (can you see one that is still pink?) but by the next day
they mature to black. This entire mass could be from a single
plasmodium.
this, the plasmodium transforms into a mass of small sporangia,
which are often born on short stalks (as in this case). The whole
mass (of which half is visible here) covered about two hand-spans
of this rotting ash log. The sporangia at first appear pink on short
white stalks (can you see one that is still pink?) but by the next day
they mature to black. This entire mass could be from a single
plasmodium.
More field observations:
