Bio153S: Lecture 12
The Fungi
one of the 3
major
lineages of
multicellular
terrestrial
eukaryotes
fungi are heterotrophs
• “osmotrophs”: digest, then ingest
• hydrolytic exoenzymes
• can break down lignin, cellulose
(also petroleum, waxes,
photographic film…)
• saprobes, parasites, predators,
mutualistic symbionts…
many fungi are saprobes:
• break down dead organic material
• important in cycling C, N etc.
• coal & peat deposits
formed in Carboniferous
period due to lack of fungal
activity (too acidic)
fungal morphology
•
cell walls contain
chitin (N–rich
polysaccharide)
1. exist as single cells
(yeasts)
2. most multicellular
• body = mass of
hyphae (mycelium)
1
filaments in mycelium are called
hyphae:
2 types:
1. septate (cross-walls separate
compartments with a nucleus)
2. coenocytic ( cytoplasm with many nuclei)
mycelia can be huge!!
Armillaria ostoyae
• a honey fungus in
Oregon: 860 ha; 2,600
years old!
• 1 cm3 of soil : 1 km of
hyphae; surface area >
300 cm2
• mycelia are non-motile;
grow rapidly
• ↑ hyphal length rather
girth; maximize SA: vol
mycorrhizae:
•
•
•
symbiotic relationship between plants
and fungi (~90% of plant species!)
plant gets: increased SA for nutrient
absorption
fungus gets: carbohydrates
• “fairy ring”: outward growth of
mycelium; appearance of fruiting
bodies
• mycorrhizae critical to
plant success;
productivity
• animals are important
in dispersing fungal
spores in many forest
ecosystems
• 2 types of
mycorrhizae:
2
1.
•
•
•
Endomycorrhizae:
arbuscular mycorrhizal fungi (AMF)
fungus penetrates root cortex cells
haustorium: modified hypha for
penetration
AMF:
2. Ectomycorrhizae:
•
•
EMF
fungus
forms a
sheath
around
root
fungal symbiosis: lichen
• fungus + cyanobacteria or alga
• probably evolved from parasitism
EMF:
• important
in Arctic
ecosystems
FungusFungus-garden ants:
• ants feed and tend
fungus
in special chambers
• fungal hyphae are
sole food of larvae
3
predacious fungi:
parasitic fungi:
• virtually all animals &
plants are susceptible
• plant pathogens; blights,
mildews, smuts, rusts
• e.g. Cordyceps: parasite affects host
behaviour and physiology
• chemicals affect nervous system
Claviceps purpurea
• ergotism: muscle spasms, delusions and
hallucinations, gangrene
• original source of LSD
• outbreaks of ergotism: St. Anthony's
Fire
benefits to humans:
• Salem Witch Trials
(1692)
• source of antibacterial agents e.g.
cyclosporin
• caused by outbreak
of ergotism
• source of many foodstuffs:
4
origin of fungi:
4 distinct reproductive structures:
• evolved from unicellular,
aquatic, flagellated
ancestor
• member of clade
Opisthokonta (includes
animals & some protists)
~ 460 m.y.
old fossil
• adaptive radiation:
colonized land
traditional phylogeny
based on mode of
reproduction
Chytridiomycota:
• basal fungi?
• only fungi with alternation of
generations (multicellular 1n and
2n stages)
• motile gametes & spores
• mostly freshwater
• some are commensals
in guts of mammals
• parasitic species
implicated in loss of
amphibian biodiversity
5
Glomeromycota:
Zygomycota
• paraphyletic group
• zygote formed where hyphae of
different mating types contact
• all form arbuscular mycorrhizae
• appear late in fungal evolution
bread
mold
Basidiomycota
Amanita
• “mushrooms” and bracket fungi
Auricularia
Phallus
Geastrum
Ascomycota
• some secondarily unicellular
(derived) e.g. Saccharomyces
• reproductive structure = ascus
• many form lichen
next:
• life cycles of fungi
cup fungus
6