Announcements

• Next week – no lab Wednesday evening– Lab closes 5pm for Biol 203 exam– Lab will be open Tuesday 5-10 pm

• Biol 204 notes– www.usask.ca– Biology– Class notes -- Biol 204 – kaminskyj– 2004 lectures

Cytoplasmic migration in tip growth

Fungal cell walls

• Thin• Fiber reinforced

– Taxonomically relevant

• Plastic/extensible at tip

• Elastic/inextensible at maturity

Wall vesicle exocytosis at Saprolegnia hyphal tip

Hydrophobins

• Without hydrophobins, hyphae cannot break through the surface tension of water

• Hydrophobins are essential for mold sporulation and mushroom formation

Hydrophobin rodlets

Diverse features of Protista (P), Chromista (C), Eumycota (F)

• Walls in vegetative phase– Lacking (P)– Having (C, F)

Diverse features of Protista (P), Chromista (C), Eumycota (F)

• Walls in vegetative phase

• Mode of nutrition (always heterotrophic)– Ingestive (P)– Absorptive (C, F)

Protistan fungi – three taxa

• Myxomycota – “acellular” slime molds

Dictyosteliomycota – cellular slime molds

Plasmodiophoromycota – endoparasitic slime molds

Common features of Protistan fungi

• Nutrition by ingestion– Possible because vegetative stages do not

have walls

Common features of Protistan fungi

• Nutrition by ingestion

• Lifestyle – Individual cells or colonies– Dictyosteliomycota -> Alternating individual

and colonial stges

Common features of Protistan fungi

• Nutrition by ingestion• Lifestyle

– Individual cells or colonies

– Alternating individual and colonial stges (Dictyosteliomycota)

• Sexual reproduction by spore formation– Only walled stage– Fibrils of peptidoglycan, cellulose, chitin

Myxomycete plasmodia

Physarum – nuclear behaviour

Myxomycete plasmodia can distinguish nonself and self

Physarum on heterogeneous substrate – food preference

Myxomycete spores in sporangia

Physarum Stemonitis

Myxomycete spore walls contain peptidoglycan

Dictyosteliomycota – “cellular” slime molds

Dictyostelium

Aggregation of amoebae uses chemical signals

Dictyostelium cell differentiation model system

www2.mrc-lmb.cam.ac.uk

Dictyostelium spore walls contain cellulose

niko.unl.edu

Plasmodiophoromycota – endoparasitic slime molds

Plasmodiophora in cabbage root hair

Plasmodiophora resting spores

Chromistan fungi – Oomycetes

• Saprobes, parasites/pathogens

Chromistan fungi – Oomycetes

• Saprobes, parasites/pathogens

• Obligate parasites – must have a living host to complete life cycle – aggressive

• Facultative parasites – parasitism is optional – less aggressive

Saprophytes and facultative parasites

Asexual zoospores ofAchlya biusexualis

Attachment, infection, colonization

• In nature, infective stage is motile flagellated zoospores – primary and secondary

• Heterokont flagella• Zoospores find a food

source by chemotaxis

Attachment, infection, colonization

• In nature, infective stage is motile flagellated zoospores – primary and secondary

• Heterokont flagella

• Zoospores locate a food source by chemotaxis

Attachment, infection, colonization

• In nature, infective stage is motile flagellated zoospores – primary and secondary

• Zoospores find food a source by chemotaxis

• Attachment is followed by shedding flagella

• Infection requires growth of a penetrating hypha

Saprophyte attachment and germination

1° zoospore

1° cyst

2° zoospore

2° cyst

germinationandinfection

Morphology and parasitic aggressiveness

Parasitism

The joy of slime

Oomycetes as plant pathogens Phytophthora infestans

www.scisoc.org/feature/lateblit/chapter1/epidemic.htm

Understanding late blight

• disease attributed to – excess water in the plants, – effects of the newly

introduced steam locomotives

• Reverend M.J. Berkeley– Early 1850’s– Fungal pathogen

Phytophthora sporangia and zoospores

www.scisoc.org/feature/lateblit/chapter1/epidemic.htm

Drier soils -> direct germination

Wet soils -> zoospores

Social consequences of Phytophthora infestans riots, eviction, emigration

Sexual spores of oomycetes

Major significance in genetic recombination -> development of new pathotypes

Next time:it’s not easy being green