Fungi

Important words and concepts from Chapter 31, Campbell & Reece, 2002 (3/25/2005):

by Stephen T. Abedon (abedon.1@osu.edu) for Biology 113 at the Ohio State University

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(b) Unlike animals, "A fungus digests food outside its body by secreting powerful hydrolytic enzymes into the food. The enzymes decompose complex molecules to the simpler compounds that the fungus can adsorb and use."

(i) Saprobes (i.e., absorbing nutrients from no longer living organisms)

(ii) Parasites (i.e., absorbing nutrients of or derived from still living organisms, to the detriment of the organism being parasitized)

(iii) Mutuals (i.e., absorbing nutrients from still-living organisms, but providing something in return, such as protection or nutrients)

(d) Fungi are typically terrestrial (they probably, to a large extent, evolved on land)

(e) Fungi are key decomposers of plant material

(f) Most fungi derive their nutrition from plant material rather than from animals

(g) Fungi have cell walls made of chitin

(h) [fungi (Google Search)] [index]

FUNGAL ANATOMY

Some Fungal Anatomy: An Overview
Antheridia^*	Male-like donor of haploid nuclei (see Figure 31.8)
Asci	Sac-fungus sexually produced spore-containing structures
Ascocarp	Sac-fungus fruiting body (asci-containing structures)
Ascogonia^*	Sac-fungus female-like receiver of haploid nuclei from sac-fungi antheridia (Figure 31.8)
Ascospores	Sac-fungus haploid dispersal stage (spores)
To put the above in more familiar terms: Antheridia (boys) plus Ascogonia (girls) leads to the production of Ascocarp (~womb/mushroom equivalent) that contain Asci (~placenta/basidia equivalent) that contain Ascospores that are the sexually produced haploid dispersal stage of the sac fungi while the Conidia (defined below) are the asexually produced haploid dispersal stage of sac fungi (see Figure 31.8)
Basidia	Club-fungus asci equivalent (spore-containing structure)
Basidiocarp	Club-fungus basidia-containing structure
Coenocytic	A fungal hyphae that lacks septa
Conidia^*	Sac-fungus asexually produced spores (they don't come from asci)
Dikaryon	A fungus (cell, hyphae, or mycelia) that contains haploid nuclei sourced from different parents
Gametangia^*	Gametangia are the sexual organs of fungi and plants (note the common "gamet-" between gamete and gametangia); these are the supplies of haploid nuclei that ultimately will fuse (karyogamy) to form the diploid precursor to meiosis
Hyphae	Hyphae are the filamentous cells or linked-together cells that represent the bulk of the bodies of molds and macrofungi (e.g., mushrooms)
Mycelium	Mycelia are tangled masses of hyphae typically found growing within a fungal food source
Septa (septum)	These are crosswalls that separate (distinguish) the cells within hyphae; not all fungi possess crosswalls within all of their hyphae
^*Don't worry about knowing the above asterisk-denoted terms.

(3) Hyphae

(a) The dominant structural motif of fungi (except the yeasts ) is the hyphae

(b) Hyphae are long, multinucleated, typically multicelled, one-cell thick fungal tissue

(c) Hyphae are typically hidden from sight since fungi grow their hyphae into their food, releasing exoenzymes and absorbing nutrients

(d) In addition, hyphae serve as vascular channels along which nutrients are passed

(e) See Figure 31.2, Examples of fungal hyphae

(f) Hyphae (from aquatic fungus):

(g) [hyphae (Google Search)] [index]

(4) Mycelium

(a) An interwoven mat consisting of many intertwined hyphae is called a mycelium

(b) "A fungal mycelium grows rapidly, adding as much as a kilometer of hyphae each day as it branches within a food source. Such fast growth is possible because proteins and other materials synthesized by the entire mycelium are channeled by cytoplasmic streaming to the tips of the extending hyphae. The fungus concentrates its energy and resources on adding hyphal length rather than girth."

(c) See Figure 31.1, Fungal mycelia

(d) A tangled mass of hyphae:

(e) [mycelium (Google Search)] [index]

(5) Septa

(a) The crosswalls that delineates individual fungi cells, within hyphae, are called septa (sing. = septum)

(b) Septa typically possess pores through which cytoplasm can flow

(d) See Figure 31.2, Examples of fungal hyphae

(e) Septa within hyphae:

(f) [fungus septa (Google Search)] [fungus septa (Google Search)] [index]

(6) Coenocytic

(a) The absence of septa within hyphae is called coenocytic

(b) We see this word again when discussing plasmodial slime molds which possess multiple nuclei within a single (very large) cytoplasm

(c) See Figure 31.2, Examples of fungal hyphae

(d) [coenocytic (Google Search)] [index]

FUNGAL REPRODUCTION

(7) Reproduction (generalized fungal life cycle)

(a) All fungi reproduce by mitosis

(b) Most fungi additionally reproduce by meiosis

(d) Mating is accomplished via the growing together of hyphae sourced from different parents

(e) Hyphae fusing together (fungi mating = plasmogomy); numbers are in minutes:

(f) We can summarize a generalized fungal life cycle as follows (ploidy is in parentheses):

(i) Sexual reproduction (note: order of terms is relevant):

· mitosis

· Hyphae (ploidy = n)

· mitosis

· Mycelium (ploidy = n)

· Plasmogamy (a process) (= fusion of cytoplasm)

· Dikaryotic stage (ploidy = n + n) (occurs within zygosporangia for Zygomycete, ascogonia for Ascomycete, or hyphae for Basidiomycete)

· mitosis

· Karyogamy (a process) (= fusion of haploid nuclei)

· Diploidy (ploidy = 2n) (occurs within zygosporangia for Zygomycete, ascocarps for Ascomycete, or basidiocarps for Basidiomycete)

· Meiosis (a process)

· Spore-producing structures (ploidy = n) (= sporangium for Zygomycete, asci for Ascomycete, or basidia for Basidiomycete)

· Spores (ploidy = n) (= spores for Zygomycete, ascospores for Ascomycete, or basidiospores for Basciomycete)

· Germination (a process)

· mitosis

· Hyphae (ploidy = n)

· mitosis

· Mycelium (ploidy = n)

Overview of Fungi Asexual Reproduction

mitosis (m) à Hyphae à (m) à Mycelium à (m) à

[ Spore-producing structures à (m) à Spores à ]

Germination à (m) à Hyphae à and so on

Overview of Fungi Sexual Reproduction

mitosis (m) à Hyphae à (m) à Mycelium à

[ Plasmogamy à Dikaryon à (m) à Karyogamy à Diploidy à Meiosis à Spores à ]

Germination à (m) à Hyphae à and so on

(ii) Asexual reproduction (note: order of terms is relevant):

· mitosis

· Hyphae (ploidy = n)

· mitosis

· Mycelium (ploidy = n)

· mitosis

· Spore-producing structures (ploidy = n)

· mitosis

· Spores (ploidy = n) (= conidia for sac fungi)

· Germination (a process)

· mitosis

· Hyphae (ploidy = n)

· mitosis

· Mycelium (ploidy = n)

(g) See Figure 31.3, Generalized life cycle of fungi

(h) Shown is sexual portion of life cycle:

(i) [fungus reproduction (Google Search)] [index]

(8) Ploidy

(a) Fungi typically possess haploid nuclei, except just prior to meiosis

(b) Only following nuclear fusion (karyogamy) are fungi diploid, and mitosis in fungi does not occur in the diploid state

(c) However, many fungi routinely achieve a diploid-like state following cytoplasmic fusion (plasmogamy) that is called a dikaryon state or stage; note that dikaryon is not synonymous with diploid since nuclei remain haploid even if found in same cytoplasm

(9) Plasmogamy

(a) Though fungi nuclei are typically haploid, that doesn't stop haploid nuclei from different fungal parents (e.g., mom and dad equivalents) from being present in the same cytoplasm

(b) The process by which the cytoplasms of two parental fungi fuse is called plasmogamy

(c) Note that plasmogamy may be followed by nuclei fusing, though this does not necessarily occur immediately, and for some fungi the time until nuclear fusion occurs can be greatly extended (days, months, years)

(d) [plasmogamy (Google Search)] [index]

(10) Dikaryon state or stage

(a) The post-plasmogamy condition in which two different haploid nuclei occupy the same cytoplasm is a dikaryon state or stage

(b) Being a dikaryon, since cytoplasms are shared, provides the masking of deleterious alleles of diploidy without the possession of diploid nuclei

(11) Karyogamy

(a) The fusion of haploid nuclei found in dikaryonic fungal cells is called karyogamy

(b) Karyogamy is necessary for the occurrence of meiosis (since haploid nuclei cannot undergo meiosis)

(d) [karyogamy (Google Search)] [index]

FUNGAL PHYLOGENETIC DIVERSITY

(12) Fungi divisions

(a) Like plants, fungi are grouped into taxonomic categories called divisions which are equivalent to the phyla possessed by protists and animals

(b) Your text classifies fungi into four divisions, differentiated molecularly as well as more traditionally in terms of sexual structures

(i) Division Chytridiomycota (chytrids) (no need to learn)

(ii) Division Zygomycota (zygote fungi )

(iii) Division Ascomycota (sac fungi )

(iv) Division Basidiomycota (club fungi )

(i) The yeasts

(ii) The molds

(iii) The imperfect fungi

(d) [fungus classification (Google Search)] [index]

(13) Division Zygomycota (zygote fungi)

(a) These are the zygote fungi

(b) In their sexual cycle these fungi form gametangia that are multinucleated cells walled off from parental cells by septa

(c) Gametangia from two different parental fungi fuse (undergo plasmogamy) to form dikaryonic zygosporangia that are capable of toughening to form a dormant stage

(d) Zygosporangia give rise to sporangia following germination, karyogamy , and meiosis

(e) The black areas in the center of the first photo are gametangia (post-plasmogamy structure, a.k.a., young zygosporangium, a.k.a., dikaryotic structure):

(f)

(g) Sporangia may also be formed from haploid tissue in asexual reproduction by mitosis

(h) See Figure 31.7, Zygomycota (zygote fungi): the life cycle of the zygomycete Rhizopus (black bread mold)

(i) Bread mold fruiting structure (a.k.a., sporangium):

(j) [Zygomycota (Google Search)] [zygote fungi (Google Search)] [index]

(14) Division Ascomycota (sac fungi)

(a) These are the sac fungi

(b) They are named after the asci which are sac-like housings of the sexually-produced haploid spores found grouped in structures called ascocarps

(c) See Figure 31.9, Ascomycota (sac fungi)

(d) See Figure 31.10, The life cycle of an ascomycete

(e) [Ascomycota (Google Search)] [sac fungi (Google Search)] [index]

(15) Ascomycota gametangia^* (antheridia^*, ascogonia^*)

(a) Gametangia are sexual organs of plants, and they are the name given to the sexual organs of fungi as well

(b) In sac fungi, gametangia are divided into essentially two genders: ascogonia and antheridia

(d) [ascomycota gametangia (Google Search)] [index]

(16) Ascomycota fruiting bodies (asci, ascocarp, ascospores)

(a) The resulting dikaryotic ascogonium gives rise to the ascocarp, the sac fungi fruiting body, in which numerous asci are arrayed

(b) To effect dispersal, asci forcibly expel their ascospores into the air

(c) See Figure 31.10, The life cycle of an ascomycete

(d) Note these various stages in the figure

(e) These are ascocarps of morels (plus poisonous false morels):

(f) [ascomycota fruiting bodies (Google Search)] [ascocarp (Google Search)] [asci and fungus (Google Search)] [ascospore (Google Search)] [index]

(17) Conidia^*

(a) Conidia are asexually produced spores generated by sac fungi (division Ascomycota)

(b) [conidia (Google Search)] [index]

(18) Division Basidiomycota (club fungi, mushrooms)

(a) Members of Division Basidiomycota are also called the club fungi and include the mushrooms

(b) Mushrooms are fruiting bodies of underground mycelia

(d) See Figure 31.11, Basidiomycota (club fungi)

(e) See Figure 31.12, The life cycle of a mushroom-forming basidiomycete

(f) [Basidiomycota (Google Search)] [club fungi (Google Search)] [index]

(19) Basidiocarp (basidia)

(a) Basidiocarp is the general name for the fruiting body of a club fungi

(b) For example, a mushroom is a basidiocarp of a mushroom-producing mycelium

(c) Note that mushrooms are members of the basidiomycota, though not all mushroom-like fungal fruiting bodies are mushrooms (they aren't if they aren't club fungi and, for that matter, not all club fungi fruiting bodies are mushrooms, either, e.g., puffballs and shelf fungi-see Figure 31.9 from your text)

(d) Spores are released from structures called basidia which, in turn, are displayed, for example, on the surface of a mushroom's gills

(e) See Figure 31.12, The life cycle of a mushroom-forming basidiomycete

(f) Note that the basidia look like little clubs (i.e., as in club fungi)

(g) These are the basidia (note containing four spores each) found within the gill of a mushroom:

(h) [basidiocarp (Google Search)] [basidia (Google Search)] [index]

SOME FUNGAL ANATOMICAL DIVERSITY

(20) Molds

(a) Molds are microscopic, multicelled, asexually reproducing, hyphae-producing fungi

(b) Molds are polyphyletic, rising independently from many fungi lineages

(c) While molds are capable of sexual reproduction, the mycelia produced by a mold is the product of asexual (i.e., mitotic) division rather than sexual reproduction; thus, a mold can represent only a single individual and will not display a conspicuous fruiting body

(d) This is true of mycelia in general and a single mycelium can be huge, on the order of many meters on up to kilometers in diameter

(e) See Figure 31.6, The common mold Rhizopus decomposing strawberries

(f) See Figure 31.14, A moldy organge

(g) [mold (Google Search)] [index]

(21) Yeasts

(a) Yeasts are unicellular fungi

(b) Yeasts are polyphyletic, rising independently from many fungi lineages

(d) See Figure 31.15, Budding yeast

(e) [yeast, Saccharomyces cerevisiae, Candida albicans (Google Search)] [index]

(22) Imperfect fungi

(a) Imperfect fungi fail to reproduce sexually, consequently fail to produce the sexual structures by which other fungi are classified (at least traditionally), so are not well phylogenetically classified, at least using classical methods

(b) [imperfect fungi (Google Search)] [fungi imperfecti (Google Search)] [index]

SOME FUNGAL ECOLOGICAL DIVERSITY

(23) Lichens

(a) Lichens are a polyphyletic grouping of fungi that possess algae (eukaryotic or blue-green) symbionts

(b) "The fungus usually gives the lichen its overall shape and structure, and tissues formed by hyphae account for most of the lichen's mass… The alga always provides the fungus with food. Cyanobacteria in lichens fix nitrogen and provide organic nitrogen. The fungus provides the alga with a suitable physical environment for growth. Lichens absorb most of the minerals they need either from air or in the form of dust… Fungal pigment shades the algae from intense sunlight. Some fungal compounds are toxic and prevent lichens from being eaten by consumers."

(c) "Lichens are important pioneers on newly cleared rock and soil surfaces, such as burned forests and volcanic flows. Physical penetration of the outer crystals of rocks and chemical attack of rock by lichen acids help break down the rock and establish soil-trapping lichens. This process makes it possible for a succession of plants to grow. Nitrogen-fixing lichens also add organic nitrogen to some ecosystems."

(d) See Figure 31.16, Lichens

(e) See Figure 31.17, Anatomy of a lichen

(f) [lichens (Google Search)] [index]

(24) Mycorrhizae

(a) Mycorrhizae fungi are plant mutualists with the fungal hyphae serving to increase the absorptive area and potential of plant roots

(b) In return the plant supplies the fungus with carbon and energy

(c) Note the similarity between the mycorrhizae symbiosis and that symbiosis between fungi and algae found within lichens

(d) See Figure 31.18, Mycorrhizae

(e) See Figure 31.19, An experimental test of the benefits of mycorrhizae

(f) [mycorrhizae (Google Search)] [index]