Fungi: Amazingly diverse, but neither plant nor animal
Looking at one’s old school books, university notes or lab work not only allows you to reflect on past events in your life, it can also raise questions. Why, for example, did I have to examine mushrooms in the Botany practical? Why are fungi dealt with in Botany classes or featured in botany textbooks? They aren’t plants after all. But they aren’t animals either. So, what are they? Let me tell you: they are the most interesting of all life forms!
From microscopically small parasitic or free-living species, present on land in soils or above ground, in the water, on or in plants and animals, being providers of antibiotics (but also the causers of diseases and producers of deadly poisons), helping us make bread and produce alcoholic drinks, rendering some meals more palatable, but also ‘recycling’ wastes… fungi are everywhere. Although they are neither plant nor animal but represent a kingdom of their own, they are traditionally ‘handled’ even now mostly by Botany departments (despite having really more in common with animals than plants).
First of all, like animals they ‘feed’ on organic food stuff; they are said to be ‘heterotrophs’ and cannot photosynthesize like the ‘autotrophic’ plants as fungi lack the green chlorophyll. Fungi, instead, often possess melanin pigments, common in animals, but rare in plants. Moreover, fungal cell walls never contain cellulose, the typical polysaccharide of all plants. Fungal cell walls are made of chitin, a carbohydrate that is prevalent in the cuticles of insects, crustaceans and other arthropods. Perhaps an even more surprising similarity to animals is the ability of fungi to break down collagen (a type of protein associated with muscle tissue, bones and the skin). For that task, many fungal species possess the enzyme collagenase, a chemical that never occurs in plants.
Most amazing (I think) is the dikaryotic condition of many fungi, especially those we tend to consume, i.e. species belonging to the Basidiomycetes and Ascomycetes. In plant as well as animal cells the nuclei of male and female individuals, when brought together during fertilisation, fuse and form a zygote, but in the fungi over most of their life span, the two nuclei exist side-by-side in cells, that divide and multiply – always with the two separate nuclei in them. Only shortly before the formation of spores (fungi do not produce seeds and never have ‘flowers’), the two nuclei fuse. The uniqueness of fungi doesn’t end here: I once observed microscopic fungi that were catching and ‘consuming’ animals; mind you, very small animals: tiny nematode worms. And then there are fungi that produce bright greenish lights like fireflies or glowworms. Such fungi are bioluminescent. However, this fungal light production, whose chemical origins have recently been unravelled by Ilia Yampolsky and co-workers in Moscow, is not related to yet another amazing feature of some fungi: certain species are radiotrophic. Having been discovered in and on the remains of Chernobyl’s radiating reactors, these black, melanin containing fungi were subsequently grown under controlled conditions and it could be shown that they thrive on ionizing radiation and even grow on Russia’s MIR space station!
My own interest in fungi (apart from collecting and eating them) has three reasons: I wonder how fungi called ink-heads, which I love, year after year know exactly when to appear above ground for about 10 days. What tells them it’s the right time to produce their fruiting body, the “mushroom”? Do the fungal hyphae underground have temperature or humidity sensors, or do they rely on an inbuilt circannual rhythm? It’s a mystery. The second reason are Flat-footed flies of the genus Agathomyia: in plants, galls are common and can be found on almost any species. But the only known galls on mushrooms appear to be caused by those Flat-footed flies: thus, galls on mushrooms compared with those on plants are very rare. And the third reason? Laboulbeniales, named after Monsieur le docteur J. Alexandre Laboulbène! These tiny, harmless fungi grow on the surface of living insects (not inside them like -to insects- the deadly Cordyceps fungus) and resemble cuticular hairs. If you’ve been fooled by them once, you’ll never forget them (and of course also not their beautiful name: Laboulbeniales).
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2019.
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