Weber State University Department of Botany |
BOTANY LS1203 - PLANT BIOLOGY
FUNGI
General Characteristics of the Fungi
eukaryotes
nuclear envelope does not breakdown during mitosis and
meiosis
heterotrophic – external digestion followed by absorption
glycogen is primary storage carbohydrate
chitin in cell walls
mostly grow in filaments called hyphae
(some are unicellular, like yeast)
(lots of hyphae = mycelium)
some make distinctive fruiting bodies during sexual reproduction
(used to ID the fungi that make them)
all phyla can make spores asexually
form a variety of symbiotic
relationships with plants
PHYLA
chytrids:
considered protists by some, due to the presence of
flagellated cells
plant diseases:
brown spot of corn, black wart of potato
zygomycetes:
black bread mold
endomycorrhizae
plant diseases:
soft rots of squashes, some fleshy fruits, and bulbs
ascomycetes (sac fungi):
morels, truffles
yeast
most (~98%) lichens
ectomycorrhizae
endophytes:
Claviceps
plant
diseases: Dutch elm disease, chestnut blight
basidiomycetes (club fungi):
mushrooms, puffballs, stinkhorns,
earth stars, bird’s nest fungus, bracket
(shelf) fungi
fairy
rings
ectomycorrhizae; endomycorrhizae of
orchids
plant
diseases: rusts and smuts
deuteromycetes (imperfect fungi):
Penicillium, Aspergillus
an artificial grouping
due to no known sexual reproductive
cycle
most are related to known ascomycetes; remainder are zygomycetes or
basidiomycetes
PLANT DISEASES
fungi cause ~70% of known plant diseases
fungi
invade by secreting enzymes that degrade the cells walls of plants
plants can respond by making phytoalexins
control of fungal diseases: Cu, S, Bordeaux mixture, synthetic chemicals,
resistant plant varieties
MYCORRHIZAE
generally viewed as a mutualistic relationship
very common, could be present in as high as 90% of all plants: natural
and agricultural conditions; seed plants, seedless vascular plants, and non-vascular
plants
Endomycorrhizae: grown inside the cells of the root. Orchids,
VAM
(Vesicular Arbuscular Mycorrhizae)
Ectomycorrhizae: grow on the outside of the root and between the
cells of the cortex.
ENDOPHYTES
fungi that grow within the stems or leaves of a plant
generally viewed as not causing disease of the plant
protect plants by making molecules that decrease herbivory
also increase growth, drought tolerance
tall fescue (Festuca arundinaceae) + Sphacelia typhina (an ascomycete)
Cattle will graze on uninfected tall fescue; avoid the infected plants.
(infected plants are also avoided by insects)
If only infected grass is available, cattle will graze on it, thereby ingesting
the alkaloids produced by Sphacelia typhina. The cattle become lethargic,
stop grazing, pant, drool (better move them to other forage), become feverish,
gain weight slowly, decrease milk production, develop gangrene, have difficulty
conceiving, . . . die.
Claviceps purpurea (ergot)
infects grains (rye, wheat); forms black spots on the
grains. Makes alkaloids. When people eat the grain, they display
symptoms of ergotism (St. Anthony’s Fire): gangrene in extremities
(extremities feel like they are on fire), nervous spasms, convulsions, delusions,
death.
994: ~ 40,000 people in southern France died of ergot poisoning
Some of the Claviceps alkaloids have been used to hasten uterine contractions
during childbirth; others have been used to treat severe migraines.
FAIRY RINGS
basidiomycetes
diameter expands over time
grown into new thatch zones, release N, and the grass greens up behind the
advancing rings
for some, the youngest hyphae make the soil water repellent, resulting
in a dead zone of grass
can be formed by mycorrhizal fungi
WOOD DECAY FUNGI
some are important tree pathogens;
most are saprobes with a key role in nutrient cycling
include some
bioluminescent fungi (foxfire)
commercial interest in them because of their ability to breakdown cellulose,
lignin
PREDACEOUS FUNGI
have various mechanisms for capturing small animals like nematodes
Oyster mushrooms: grow on decaying wood, a poor source of N.
Therefore, get N by catching nematodes. The fungus secretes an
anesthetic, then its hyphae grow into the nematode.
> 50 imperfect fungi make loops in their hyphae to catch nematodes
FLOWER MIMIC
Puccinia species:
cause rusts
Puccinia monoica - infects rockcress in the Rocky Mts and causes the leaves
to form flower mimics. A fragrant nectar attracts insects to the false
flowers, and the insects end up dispersing fungal spores instead of flower
pollen.
LICHENS
a symbiotic association of a fungus (usually an ascomycete) with a green alga or cyanobacterium
will return to lichens after we cover algae
WHAT IS THE LARGEST ORGANISM?
non-clonal
clonal
~ 106 acres (6,000 tons)
~ 38 acres in Michigan (est. 100 tons)
~ 1,500 acres in Washington
~ 2,200 acres in OregonREVIEW
What characteristics are found in all fungi?
What are the five phlya of the Fungi Kingdom? Why are the ascomycetes known as sac fungi? Why are the basidiomycetes known as
club fungi?
In order for plant disease fungi to invade a plant, they need to break down
cell walls. The wall fragments trigger plants to defend themselves
by making phytoalexins. What are phytoalexins?
What is Bordeaux mixture?
What are fairy rings? How large can they get? Why do they sometimes
cause problems in lawns?
Why is lignin a problem in wood pulp used
for paper? How could the problem be solved with wood decay fungi?
Endophytes
Benefits to the plants. Ergot.
Predaceous fungi: what is the main thing obtained from the prey that
is missing from materials that these fungi decompose?
Suggested Online Reading
The Microbial World: Basidiomycota: activities and lifestyle (by Jim Deacon at the University of Edinburgh)
The Amazing Kingdom of Fungi (by W. P. Armstrong at Palomar College; author of Wayne's Word, an Online Textbook of NAtural History)
Kingdom Fungi (by Steven Wolf at California State University Stanislaus)
Fungal Diversity, Spore Dispersal in Fungi, and Symbiosis: Mycorrhizae and Lichens (by George Wong at the University of Hawai`i at Manoa)
Tom Volk's Fungi (by Tom Volk at the University of Wisconsin - LaCrosse)
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Revised 5 November 2009. Links checked 5 November 2009.