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                                                    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

General Sherman, a giant sequoia (Sequoiadendron giganteum) weighing in at an estimated 1200 tons
largest tree by volume
275 ft. tall
California or coastal redwood (Sequoia sempervirens)
tallest trees known
Hyperion, 379.1 ft.


clonal

quaking aspen in the Rocky Mts.

  ~ 106 acres (6,000 tons)

Armillaria bulbosa

  ~ 38 acres in Michigan (est. 100 tons)

Armillaria ostoyae

  ~ 1,500 acres in Washington

              ~ 2,200  acres in Oregon

REVIEW

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 DiversitySpore 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.