Summer Bio153S: lecture 10
biology of fungi (II)
Reproduction in Fungi:
• budding, fission
• breakage of mycelium
(fragmentation)
• sporulation (sexual and
asexual)
asexual sporulation in different
phyla:
• Chytridiomycota:
motile zoospores
• Zygomycota: sporangia
asexual sporulation:
• common in most fungi (except
Basidiomycota)
• spore-forming structure separated
from rest of hypha by a wall
sporulation:
• production of spores key to fungal
success
• light (travel far; windborne)
• resistant to dessication, etc.
• can remain dormant
• Ascomycota: conidia
• produced in huge numbers
• onset of sporulation:
seasonal, nutrient levels, light,
CO2…
sexual reproduction in fungi:
dikaryon: found only in fungi
1
Heterokaryon (dikaryon): cell
containing nuclei from 2 individuals
how is it formed?
plasmogamy: fusion of cytoplasm
from haploid cells of complementary
mating types
followed by:
karyogamy: fusion of nuclei (2n)
dikaryon :
• may be a short stage
• may last years!
• both nuclei transcriptionally active
mitosis of dikaryotic
hyphal cell
plasmogamy ⇒ karyogamy ⇒ meiosis
n+n
n
2n
sexual reproduction in this clade:
1.
2.
3.
4.
no gamete cells; only gametic nuclei
no sexes, but mating types (+ & -)
formation of dikaryon
no true diploid tissue (meiosis
without mitosis)
dikaryon:
synapomorphy
lineages differ in production of
sexual spores
Chytridiomycota motile zoospores
Zygomycota
thick-walled zygospore
Ascomycota
spores borne internally in
ascus
Basidiomycota
spores borne externally on
basidium
2
Chytridiomycota:
• motile gametes formed
in gametangia
• diploid organism ⇒ 2n
zoospores (disperse)
• sporangia (resting
phase); meiosis ⇒
haploid zoospore
Chytridiomycota:
• true alternation of generations
(persistent diploid structure)
• only fungi with motile cells
• no dikaryon stage
Zygomycota
• tips of hyphae form
gametangia
• zygosporangium (n + n)⇒
2n zygote ⇒ meiosis
Ascomycota
• haploid hyphae fuse; make
dikaryon
• meiosis + mitosis = 8
ascospores
3
Basidiomycota
• basidium = swollen tip of
hypha (site of nuclear fusion)
• equivalent to ascus
• dikaryotic stage usually long
mushroom = basidiocarp
• fruiting structure
mycorrhizae:
•
•
• gills, teeth, pores:
site of enormous
#’s of basidia
1. Endomycorrhizae:
• more common
• fungus (Zygomycota
(Glomeromycetes)) penetrates root
cortex cells
• grasses, herbaceous plants, a few
trees
•
plant gets: increased SA for
nutrient absorption
fungus gets: sugar (stores as
glycogen)
2 types:
2. Ectomycorrhizae:
• fungus (Basidiomycota) forms a
sheath around root
• may penetrate between cortical
cells
• spruce, pine, oak, beech, birch…
4