Chapter 31

Fungi

Characteristics• eukaryotic• mostly multicellular, yeasts unicellular• no locomotion• sexual & asexual reproduction in most• heterotrophic by absorption (digestion extracellular)• > 100,000 species• saprophytes (also parasites, mutualistic symbionts)• some pathogenic• decomposers• classified by sexual reproduction• cell walls of chitin (polysaccharide)

Structure• hyphae – rootlike structures for absorption

which collectively form a network, mycelium• cell walls:

– septate – with cross walls with large pores– aseptate(coenocytic)–no cross walls; multinucleate

• haustoria – nutrient-absorbing threads that penetrate tissues of host in some parasitic types • hyphae may grow as fast as 1km/day• mycelia have haploid nuclei, some dikaryons- 2 separate nuclei that are dissimilar

Fungal mycelia

Cell wall types

Figure 31.2x Septate hyphae (left) and nonseptate hyphae (right)

Haustoria

Reproduction• spores (usu. haploid), diploid in brief sexual

reproductive cycles, then meiosis

returns these to haploid

• syngamy – nuclear union in fertilization usu. involves some form of conjugation

• usu. asexually in optimal condtions, sexually in harsh conditions

Generalized life cycle

ClassificationDivision Zygomycota – conjugation fungi

-common molds, incl. Rhizopus stolonifer,

Pilobilus

~600 sp. mostly terrestrial in soil or on

decaying plants/animals

-coenocytic hyphae

-asexually produce sporangia

-sexually by zygosporangia formed during

conjugation (+ and – strains fuse)

Zygomycete life cycle

Conjugation

Rhizopus

Pilobilus

Division Ascomycota – sac fungi

~30,000 sp.

-yeasts (Saccharomyces, Candida), Peziza

(cup fungus), morels, Ceratocystis ulmi –

causes Dutch elm disease

-septate hyphae

-asexually by conidia on conidiophores

-sexually by haploid ascospores in asci

-most fungal symbionts in this group

Ascomycete life cycle

Peziza, truffle, morel

Yeast

Penicillium

apothecia

Division Basidiomycota – club fungi

~25,000 sp.

-mushrooms, puffballs, shelf fungi

-produce > 10 billion spores

-septate hyphae

-asexually none, or conidia in some

-sexually by basidiospores in basidium

Basidiomycete life cycle

basidiomycetes

Gills of a basidiomycete

Stinkhorn, Phallis impudicus

Amanita (death cap)

Fairy ring

Division Deuteromycota – imperfect fungi

~25,000 sp.

-ringworm, athlete’s foot fungus, Arthrobotrys –

prey on roundworms in soil

-asexually by conidia

-sexually none observed

Symbioses1) lichens – algae (filamentous green) –

Chlorophyta or blue green (cyanobacteria) &

fungus (ascomycete)

-may reproduce asexually either from

fragments or by dispersing tiny airborne

starters, soredia

Lichen structure

• each organism also reproduces either

sexually or asexually

• alga provides food for fungus, fungus

provides moisture, minerals, protection to

alga perhaps

• thought to be more of a controlled

parasitism, than mutualism

Lichens

• usu. given genus & specific name

• 3 types:

a) crustose – crusty

b) foliose – leafy

c) fruticose – shrubby

*air pollutant indicators

Crustose, fruticose, & folliose lichens

Symbioses

2) mycorrhizae – plant roots & fungus

-plant provides nutrients, fungus provides

more surface area to absorb water

-usu. basidiomycetes, may also be

ascomycetes or zygomycetes

*found in ~90% of tree species

Benefits of mycorrhizae

Mycorrhizae

Importance

Beneficial:

• decomposers

• food source

• source of antibiotics

• used in food and alcohol industries

Fungal production of an antibiotic

Importance

Harmful:

• decay products

• cause disease

• destroy crops

• spoil food

wheat rust, ergot on rye

pink ear disease of corn