Fungi

Shared Characteristics• Distinctive fungal features

– Fungi are heterotrophs.– Fungi have several cell types.– Some fungi have a dikaryon stage.

Two haploid cells coexisting in a single cell (dikaryon) before fusion to form nucleus (diploid)

– Fungi have cell walls that include chitin.– Fungi undergo nuclear mitosis.

In mitosis, nuclear membrane does not breakdown, mitosis occurs in the nucleus

The Body of a Fungus

• Fungi exist mainly in the form of slender filaments (hyphae).

– long chains of cells joined end-to-end divided by cross-walls (septa)

rarely form complete barrier

cytoplasm freely streams in hyphae

– mycelium - mass of connected hyphae

grows through and penetrates substrate

The Body of a Fungus

• Fungi cell walls are formed of polysaccharides and chitin.

– not cellulose like those of plants• Mitosis is unique.

– nuclear envelope does not break down and re-form

spindle apparatus formed within spindle plaques take place of centrioles

How Fungi Reproduce

• Differ from most animals and plants in that each compartment of hypha can contain one, two or more nuclei

– monokaryotic - each compartment has a single nucleus

– dikaryotic - two distinct nuclei within each hyphae compartment

How Fungi Reproduce• Fungi are capable of both sexual and asexual

reproduction.– Fungi reproduce sexually after two hyphae

of opposite mating type fuse. in some fungi fusion two haploid cells

immediately results in diploid cell (2n) basidiomycetes and ascomycetes have

dikaryotic stage (1n + 1n) before parental nuclei fuse to form diploid nucleus

Hyphal growth from spore

mycelium

germinatingspore

Mycelia have a huge surface area

Four Major Groups of Fungi

• Four major groups– Chytridiomycota– Zygomycota– Basidiomycota– Ascomycota

Chytridiomycota

• aquatic, flagellated fungi– most closely related to ancestral fungi

Zygomycota

• includes common bread molds• produces temporarily dormant zygosporangia• sexual reproduction occurs by fusion of

gametangia• asexual reproduction most common

– hyphae produce clumps of erect stalks - sporangiophores

form sporangia

The life cycle of the zygomycete Rhizopus (black bread mold)

Zygomycota

Ascomycota

• Very large group including yeasts, common molds, and morels

• Named for reproductive structure ascus– haploid zygotic nucleus formed within– asci differentiated with ascocarp

• Asexual reproduction takes place in conidia spores at the end of conidiophores.

A moldy orange (left), Penicillium (right)

PenecilliumConidiophores carrying Conidia

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Ascomycota

Sac Fungi: Ascomycetes - Life cycle

Ascomycota

• Yeasts– unicellular - most reproduction is asexual

and takes place by cell fission or budding ferment carbohydrates play a leading role in genetic research

Basidiomycota

• Most familiar fungi (mushrooms, toadstools, puffballs, rusts, and smuts)

– named for characteristic sexual reproductive structure, basidium

• Four haploid products of meiosis incorporated into basidiospores

• Mycelium made up of monokaryotic hyphae is called primary mycelium.

– fusion of different mating types forms dikaryotic, secondary mycelium.

Gills (reproduction)

Basidiomycota

The life cycle of a mushroom-forming basidiomycete

Ecology of Fungi

• Mutualistic associations– lichens - fungi and green algae– mycorrhizae - fungi and plant roots

Lichens

• Lichens are symbiotic associations between a fungus and a photosynthetic partner.

– usually ascomycetes Specialized fungal hyphae penetrate

photosynthetic cells and transfer nutrients to fungal partner.

Durable fungus, combined with photosynthetic properties, has enabled lichens to invade harsh climates.

– extremely sensitive to pollutants

Mycorrhizae

• Roots of about 90% of all kinds of vascular plants are involved in mutualistic symbiotic relationships (mycorrhizae).

– arbuscular mycorrhizae - fungal hyphae penetrate outer cells of plant root

most common– ectomycorrhizae - hyphae surround, but

do not penetrate, cell walls of roots

Mycorrhizae