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Mushrooms follow an almost embryo-like developmental pathway. These are
microscope images of sections cut right through the centres of developing
fruit body 'initials' of the field mushroom Coprinus cinereus; the
youngest is on the left of the panel.
You can see that a 'young mushroom' is clearly established well before the initial reaches one millimetre high. The mature mushroom will be 100 mm tall, so this is a tiny embryo by comparison. |
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| Homologues and
analogues of all of the developmental mechanisms known in animals and plants
can be found in fungi
But there are differences. For example, hyphal cells require continuous reinforcement of their differentiation 'instructions'. This reinforcement is part of the context within which they normally develop and if they are removed from it then most differentiated fungal cells can revert to being undifferentiated hyphae. |
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Fungi are modular organisms |
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| Remember that
mushrooms not individual organisms. Mushrooms are appendages (literally
'fruits') of their
mycelium. In fact, fungi are 'modular organisms', like clonal corals and
vegetatively-propagated plants. The nature of modular organisms is discussed in these two references:
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Developmental subroutines |
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| Fungal morphogenesis
is organized into a collection of distinct developmental processes, called
'subroutines'. These are recognizable at all levels, and are genetically and physiologically distinct. Developmental subroutines may run in parallel or in sequence. Normal morphogenesis is made up of a range of developmental subroutines:
When played out in their correct arrangement, ‘normal’ morphology is obtained. Subroutines may be disabled genetically or through physiological stress. If some subroutines are disabled, an abnormal morphology results. |
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| Twin fruit bodies of Clitocybe nebularis | Triple fruit bodies of Melanoleuca melaleuca | Twin fruit bodies of Clitocybe nebularis | |||||||||||
| Photos by H. van der Aa, from Mycologist, volume 11, part 2 (May 1997), p. 81 | |||||||||||||
| This close up shows how one fruit body of Clitocybe nebularis has burst out of the internal tissues of its twin. For some reason, the upper fruit body formed in a completely inappropriate position - within the cap of a pre-existing fruit body. In these examples, the subroutines for fruit body initiation and development were put into effect in the wrong place and at the wrong time, but they otherwise gave rise to an essentially normal morphology. |
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| Other examples show
that 'fruit bodies' very different from the normal morphology can be
produced.
This is what the fruit bodies of Volvariella bombycina normally look like ... and the pictures below show some abnormal ones; from left - a Morchella-like fruit, an inverted cap and a club-shaped fruit body. |
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| Developmental errors are not limited to fungi. 10 to 15% of human embryos suffer major malformations (defined as primary errors of development) soon after conception - the majority are aborted. About 0.7% of newborns have multiple major malformations, about 3% have one major malformation and 14% have a single minor malformation. The difference with fungi, is that most of the abnormal fungal fruit bodies still produce spores. That is, they are still functional. It seems that fruit body abnormalities in fungi demonstrate their flexibility in expression of their developmental subroutines in ways that allow the fruit body to react to adverse conditions and still produce a crop of spores. I call this tolerance of imprecision. Fungal fruit bodies can tolerate imprecision of their development, and this ability to tolerate uncertainty in development is what makes the fungi so successful. |
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For the full story ...
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