10.1 – FUNGI (The Fifth Kingdom)

1. 10.1 – FUNGI (The Fifth Kingdom) • fungi are very diverse  species range from simple, single-celled organisms to very complex, multicellular organisms • the scientific classification of living organisms began in the 18th century • then only two Kingdoms were recognised—the Plant Kingdom and the Animal Kingdom  anything that didn't move was put in the Plant Kingdom, so that's where fungi were classified • however, fungi are very strange 'plants‘ •  they cannot make their own food as 'ordinary' plants do through the process of photosynthesis, and their chitinous cell walls make them more like insects! • there are many characteristics that distinguish fungi from plants: • they often have many nuclei per cell; are heterotrophic; have few or no storage molecules; have no roots; often have chitin in their cell walls; none reproduce by seed • the structure of fungi has been adapted to two main functions: absorption of nutrients and reproduction • most fungi are saprophytes, feeding on dead or decaying matter • digestion is extracellular - enzymes are secreted onto a substrate to digest it and then the nutrients are absorbed (which is why fungi are often termed “absorbotrophic”).

2. “true” fungi grow vegetatively in a substrate as microscopically branching filaments (fine threads called hyphae) which mesh into a visible mycelium •  often the only visible parts of a fungus are its reproductive structures (fruiting bodies like mushrooms, morels, and jelly fungi), discussed in more detail as Ascomycetes and Basidiomycetes

3. Lower Fungi (Chytrids and Water Moulds) • all have cellulose cell walls • can be unicellular, or multicellular and filamentous • water moulds have spores have two flagella, a posterior whiplash flagellum and an anterior tinsel flagellum • Chytrids have zoospores with just one anterior tinsel flagellum.

4. Kingdom Eumycota (True Fungi) • the Eumycota are united in having cell walls consisting of chitin (the same substance that makes up insect exoskeletons) •  this Kingdom contains three Divisions, all of which are made up of hyphae (which are microscopically thin filaments) and none produce zoospores. • The Zygomycetes • Zygomycetes are widespread in many habitats and there are saprotrophic, parasitic and mutualistic species •  most people are very familiar with one widespread Zygomycete, the common bread mould Rhizopus stolonifer. • sexual reproduction in Rhizopus stolonifera, as in other zygomycetes, occurs when haploid hyphae of different mating types are in close proximity to each other • growth of the gametangia commences after hyphae come in contact, and fusion of the cytoplasm and nuclei produce zygosporangia containing diploid zoospores • Zygosporangia are typically thick-walled, highly resilient to environmental hardships, and metabolically inert

5. many of the Zygomycota are parasites of invertebrates such as amoebae, nematodes and insects •  many people will have seen dead houseflies, covered or surrounded by a white 'powder‘  in fact, the fly will have been killed by a member of the Zygomycota called Copyceps, and the powdery granules are asexual spores of the fungus, ready to infect any other fly that walks across that powdery layer  the infected flies often crawl to exposed areas, such as window panes, before dying • Glomusi are both ecologically and economically important, for they form mutualistic associations (called mycorrhizae) with numerous plant families.

6. The fungi in the final two Divisions produce sexual spores, using genetic material from two parents, and are distinguished by the method of production of those spores. • The Ascomycetes • sexual spores are produced within microscopic sacs called asci •  a spore-filled ascus is commonly (but not always) cylindrical in shape and each holds eightascospores • the most commonly seen ascomycetes are the simple cup fungi, such as this Aleuria aurantia •  if you cross-section one of these cup- or disk-shaped fruiting bodies (called an apothecium) you'd find that the internal structure was of the following form: • the spore-filled asci would be present in the area marked in black  if you took a small section of the black area and magnified it you'd see something like the second diagram  there are numerous asci containing ascospores

7. a fungus such as Morchella (a morel) has a more complicated fruiting body, consisting of depressions and ridges • in effect, each depression is like an individual apothecium so that, superficially, it looks as if a number of separate apothecia (sometimes distorted in shape) have been glued together onto a stalk • while many species of the Division Ascomycota produce easily visible fruiting bodies, there are also many microscopic ascomycetes, many of which are economically important • many yeasts are ascomycetes, for example those used in the manufacture of bread and wine • this picture shows the yeast Schizosaccaromyces octosporus.

8. The Basidiomycetes • in the Division Basidiomycota the sexual spores are produced on microscopic organs called basidia • a basidium is often somewhat club-shaped, generally with several terminal prongs and commonly each basidium has four prongs and four spores • in most basidiomycetes the basidia have no dividing walls (or septa) • all mushrooms are basidiomycetes and the gills of a mushroom are lined with basidia •  if you take a thin slice, across several gills and magnify it about a hundred times you'd see the basidia sticking out from the gills, as shown in the diagram to the right.

9. if you took a small section from a gill (such as the area contained in the small rectangle in the above diagram) and looked at it under the microscope at a magnification of several hundred times, you'd see something resembling the diagram to the right •  you can now see the basidia much more clearly and also see the hyphae that make up the gill tissue, and you can also see the septa that divide the filamentous hyphae into separate compartments • other commonly seen basidiomycetes are the boletes, polypores, coral fungi, jelly fungi, stinkhorns, birds-nest fungi and puffballs.