Lecture 4: Fungi
I.
Background
A.
1.
2.
Characteristics
Eukaryotic, multicellular (except yeasts)
Acquire nutrition through absorption
a.
Secrete hydrolytic enzymes to decompose complex molecules in the environment
Specialized vegetative body—mycelium
3.
a.
4.
5.
Comprised of hyphae
i.
Tubular walls that include chitin
ii.
Usually haploid
b.
Organized into intertwined mats
c.
Grows rapidly
i. I
ncreases surface area for absorption
ii.
Cytoplasmic streaming moves absorbed nutrients to the growing hyphal tips
iii.
Growth brings organism into contact with new sources of food
Types of hyphae
a.
Aseptate
i.
Lack cross-walls and are coencytic
ii.
Formed by repeated mitotic divisions without cytokinesis
b.
Septate
i. Divided into cells by crosswalls called septa
No flagellated stages
B. Reproduction
1.
2.
3.
4.
5.
Release of haploid spores
a.
Either sexual or asexual process
In favorable conditions enormous numbers of spores are produced asexually
a.
Mitosis
Sexual production of spores generally only occurs in limiting conditions for many types of
fungi
Spores are spread by wind or water
Syngamy
a.
Sexual union of haploid cells from two individuals
b.
Occurs in two stages
7.
i.
Plasmogamy—fusion of cytoplasm
ii.
Karyogamy—fusion of nuclei
Plasmogamy occurs that produces a dikaryon
a.
Nuclei stay unfused
b.
Divide synchronously for extended periods of time
When karyogamy occurs, diploid cell immediately undergoes meiosis to reform haploid state
II.
Phylogenetic Organization of Fungi
A.
Four divisions
1.
2.
3.
4.
Chytridiomycota
Zygomycota
Ascomycota
Basidiomycota
6.
B.
1.
2.
3.
Differences among divisions
Structures involved in plasmogamy
Time spent as a dikaryon
Sexual structures in which karyogamy occurs
III.
Division Chytridiomycota
A.
Originally placed in Kingdom Protista
1.
B.
1.
2.
3.
4.
Presence of flagellated zoospores and gametes
a.
Protistan characteristics
Have many other characteristics shared with fungi
Absorptive mode of nutrition
Cell walls of chitin
Hyphae
Common metabolic pathways
IV.
Division Zygomycota
A.
Characteristics
1.
2.
Dikaryotic zygosporangia
Mostly terrestrial
a.
Live in soil or decaying organic material
Some form mycorrhizae
a.
Mutualistic association with plant roots
Coencytic hyphae
Septa present only in reproductive cells
3.
4.
5.
6.
Reproduction
a.
Asexual
i.
Favorable conditions
ii.
Mitosis produces air dispersed haploid spores
iii.
When introduced to favorable environmental conditions, spores germinate into
new mycelia
b. Sexual
i.
ii.
iii.
iv.
v.
vi.
V.
Unfavorable conditions
Mycelia of opposite mating types produce gametangia containing haploid nuclei
Plasmogamy of gametangia of the opposite mating types produces a dikaryotic
zygosporangium
Zygosporangium is resistant to desiccation and freezing
When conditions become favorable, karyogamy occurs followed by meiosis that
produces haploid spores
Spores germinate to form new mycelia
Division Ascomycota
A. Characteristics
1.
Hyphae are septate
2.
Named for reproductive structure formed during sexual reproduction
a.
b.
Ascocarps
i.
Fruiting structure consisting of many asci
Asci
i.
Sac of sexually produced spores
VI.
Division Basidiomycota (Club fungi)
A.
1.
Characteristics
Named for diploid stage—basidium
a.
Club-shaped spore producing structure
b.
Short lived structure
Most of their life cycle is spent in the dikaryotic mycelia form
Decomposers of wood and other plant material
a.
Include mushroom forming fungi
i.
Predominantly saprobic and mycorrhizae
2.
3.
VII.
A.
1.
2.
3.
4.
Unique Fungal Lifestyles
Four forms
Molds
Yeasts
Lichens
Mycorrhizae
B.
1.
2.
3.
4.
Molds
Fast growing, asexually producing fungus
Saprobes or parasites
May be zygomycetes, ascomycetes, basidiomycetes
a.
Classification based on sexual stages
Deuteromycota
a.
Molds with no known sexual stages
C.
1.
2.
Yeasts
Unicellular fungi
Reproduction
a.
Asexually by simple cell division
b.
Sexually by producing asci or basidia
D.
Lichens
1.
Highly integrated symbiotic association between algae and fungal hyphae
a.
Fungus grows on a lawn of algae
E.
1.
Mycorrhizae
Mutualistic association between plant roots and fungi
a.
Fungus increase root surface area and exchanges soil minerals