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Fungi. Chapter 31. Fungi Characteristics. Despite their diversity f ungi share some key traits: Fungi are heterotrophs but do not ingest their food Fungi secrete exoenzymes into their surroundings which break down molecules and then the fungi absorbs the remaining smaller compounds

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fungi

Fungi

Chapter 31

fungi characteristics
Fungi Characteristics
  • Despite their diversity fungi share some key traits:
  • Fungi are heterotrophs but do not ingest their food
    • Fungi secrete exoenzymes into their surroundings which break down molecules and then the fungi absorbs the remaining smaller compounds
    • This mode of nutrition is related to the diverse lifestyles exhibited by fungi:
    • Decomposers, Parasites, Mutualistic symbionts
body structure

Reproductive structure.The mushroom produces tiny cells called spores.

Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae.

Spore-producing structures

20 m

Mycelium

Body Structure
specialized hyphae

Nematode

Hyphae

25 m

(a) Hyphae adapted for trapping and killing prey

Plant cell wall

Fungal hypha

Plant cell

Plant cell plasma membrane

Haustorium

(b) Haustoria

Specialized Hyphae
  • Some unique fungi have specialized hyphae that allow them to penetrate the tissues of their host
  • Mycorrhizae are mutually beneficial relationships between fungi and plant roots
reproduction in fungi
Reproduction in Fungi
  • Fungi propagate themselves
    • By producing vast numbers of spores, either sexually or asexually
  • Spores can be carried long distances
  • Only if they land in an acceptable area will they germinate and produce new mycelia
life cycle of fungi

Key

Heterokaryotic

stage

Haploid (n)

Heterokaryotic

(unfused nuclei from

different parents)

PLASMOGAMY

(fusion of cytoplasm)

Diploid (2n)

KARYOGAMY

(fusion of nuclei)

Spore-producing

structures

Zygote

SEXUAL

REPRODUCTION

Spores

ASEXUAL

REPRODUCTION

Mycelium

MEIOSIS

GERMINATION

GERMINATION

Spore-producing

structures

Spores

Life Cycle of Fungi
sexual reproduction
Sexual Reproduction
  • The sexual life cycle involves
    • Cell fusion, plasmogamy
    • Nuclear fusion, karyogamy
  • An intervening heterokaryotic stage
    • Occurs between plasmogamy and karyogamy in which cells have haploid nuclei from two parents
    • Sometimes can be dikaryotic and have two different, separate nuclei
  • The diploid phase following karyogamy
    • Is short-lived and undergoes meiosis, producing haploid spores
sexual reproduction9

3

2

Diploid nuclei

Sporesreleased

1

Fruiting body(mushroom)

Meiosis

Fusion of haploid nuclei

Haploidnucleus

DIPLOID

Spore

HAPLOID

DIKARYOTIC

4

Germination of sporesand growth of mycelia

6

Growth ofdikaryotic mycelium

5

Fusion of two hyphaeof compatible mating types

Sexual Reproduction
asexual reproduction

Parent cell

Bud

Asexual Reproduction
  • Many fungi that can reproduce asexually
    • Grow as mold, sometimes on fruit, bread, and other foods
    • Clones are produced by mitotic production of spores
  • Other asexual fungi are yeasts
    • Which produce by simple cell division
the phylogeny of fungi

Arbuscular mycorrhizal fungi

Club fungi

Zygote fungi

Sac fungi

Chytrids

Zygomycota

Ascomycota

Basidiomycota

Glomeromycota

Chytridiomycota

The Phylogeny of Fungi
  • Fungi can be placed into five major phyla based on morphological and molecular findings
chytrids

Hyphae

Chytrids
  • Phylum Chytridiomycota
    • Are found in freshwater and terrestrial habitats
    • Can be saprobic or parasitic
    • Unique to other fungi in having flagellated spores called zoospores
zygomycetes
Zygomycetes
  • Considerable diversity of life histories
  • Include fast-growing molds, parasites, and commensal symbionts
  • Are named for their sexually produced zygosporangia
    • Where karyogamy and meiosis occur
zygomycetes15
Zygomycetes
  • Some zygomycetes, such as Pilobolus
    • Can actually “aim” their sporangia toward conditions with good food sources
  • Zygosporangia are resistant to freezing and drying
    • Are capable of persisting through unfavorable conditions
    • Can undergo meiosis when conditions improve
ascomycetes
Ascomycetes
  • Found in marine, freshwater, and terrestrial habitats
  • Defined by the production of sexual spores in saclike asci, which are contained in fruiting bodies called ascocarps
    • Commonly called sac fungi
  • Vary in size and complexity
ascomycetes17

(a)The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia give this species its common name: orange peel fungus.

(b) The edible ascocarp of Morchella esculenta, the succulent morel, is often found under trees in orchards.

10 m

(c)Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open.

(d)Neurospora crassa feeds asa mold on bread and other food (SEM).

Ascomycetes
slide18

Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae.

Ascomycete mycelia can also reproduce asexually by producing haploid conidia.

Key

Conidia;mating type ()

1

7

Haploid (n)

Dikaryotic (n n)

Diploid (2n)

Dispersal

Germination

Matingtype ()

ASEXUALREPRODUCTION

Mycelium

PLASMOGAMY

A dikaryotic ascus develops.

2

Ascus(dikaryotic)

Ascogonium

Mycelia

Conidiophore

Dikaryotichyphae

SEXUALREPRODUCTION

KARYOGAMY

Germination

Karyogamy occurs within theascus, producing adiploid nucleus.

Dispersal

Diploid nucleus(zygote)

3

Eightascospores

Asci

Fourhaploidnuclei

MEIOSIS

Ascocarp

The diploid nucleusdivides by meiosis, yieldingfour haploid nuclei.

Each haploid nucleus dividesonce by mitosis, yielding eightnuclei. Cell walls develop aroundthe nuclei, forming ascospores (LM).

4

5

  • Ascomycetes reproduce
    • Asexually by producing asexual spores called conidia
basidiomycetes
Basidiomycetes
  • Mushrooms, shelf fungi, and

some mycorrhizae and molds

    • Some nasty plant parasites, rusts and smuts
  • Are defined by a clublike structure called a basidium, a transient diploid stage in the life cycle
    • Club fungus
  • Important decomposers of
  • wood and other plant material
basidiomycetes20

(b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat

(a) Fly agaric (Amanita muscaria), acommon species in conifer forests in the northern hemisphere

(d) Puffballs emitting spores

(c) Shelf fungi, important decomposers of wood

Basidiomycetes
basidiomycetes21

A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia.

2

Two haploid mycelia of different mating typesundergo plasmogamy.

1

Environmental cues such as rain ortemperature changes induce the dikaryoticmycelium to formcompact masses thatdevelop intobasidiocarps(mushrooms, in thiscase).

Dikaryoticmycelium

3

PLASMOGAMY

In a suitableenvironment, thebasidiospores germinate andgrow intoshort-livedhaploid mycelia.

Matingtype ()

8

Matingtype ()

Haploidmycelia

Gills linedwith basidia

SEXUALREPRODUCTION

Basidiocarp(dikaryotic)

Dispersalandgermination

When mature,the basidiosporesare ejected, fallfrom the cap, andare dispersed bythe wind.

7

Basidiospores

Basidia(dikaryotic)

Basidium withfour appendages

Basidium containingfour haploid nuclei

Basidium

The basidiocarpgills are lined withterminal dikaryoticcells called basidia.

4

KARYOGAMY

MEIOSIS

Each diploid nucleus yields four haploid nuclei. Each basidiumgrows four appendages, and one haploid nucleusenters each appendage and develops into a basidiospore (SEM).

6

Key

Diploidnuclei

Karyogamy in the basidia produces diploidnuclei, which thenundergo meiosis.

Haploid (n)

5

Basidiospore

Dikaryotic (n n)

1 m

Diploid (2n)

Basidiomycetes
lichens

Ascocarp of fungus

Soredia

Fungal

hyphae

Algal

layer

Algal cell

Fungal hyphae

Lichens
  • The ultimate symbiosis
    • Algae and fungus
  • The fungal component of a lichen
    • Is most often an ascomycete
  • Algae or cyanobacteria
    • Occupy an inner layer below the lichen surface