Fungi Shared Characteristics Distinctive fungal features

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

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)

Ascomycota

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