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