Oomycetes Flashcards
What are the main characteristics of slime molds?
Eukaryotic
Found all over the world (cosmopolitan)
Protozoans = not true fungi
The vegetative body is an amoeba in the form of a plasmodium
Spores with a cell wall, formed in sporophores, sorocarps, in sporocarps or alone
Feed by phagocytosis
How do slime molds feed by phagocytosis?
Entrapment of a food particle
Formation of a food vacuole within the cell
Fusion of lysosomes with the food vacuole
Digestion of the food particle
What are the 3 main classes in Amoebozoa?
Myxogastria
Protostelea
Dictyostelia
What are the main characteristics of myxomycetes?
The largest of the 3 groups
Has 3 vegetative forms
-myxamoeba (haploid)
-swarmer cells (haploid)
-plasmodia (diploid) = wall-less protoplasms with 3 types
What can all vegetative forms produce?
Pseudopodia
What are the two types of pseudopodia?
Lobose or filose
What type of pseudopodia are found in Myxogastria?
Filose
What are the main characteristics of swarmer cells?
Flagellated
Have haploid gametes
Isogamous sex cells of any mating type, both gametes look alike
What is the main characteristic of plasmodia?
Wall-less (coenocytic) protoplasms that contain thousands of nuclei
What is the phaneroplasmodia plasmodial type?
Large, veined feeding structures with rhythmic streaming
When will a resting state or sclerotia form?
When the spore has to be resistant to extreme environmental conditions
What condition needs to be met for myxomycetes to form?
It has to be wet enough
What are the 3 common types of myxogastrial sporophores?
Sporangium
Aethalium
Plasmodiocarp
What does sporangium in myxomycetes contain?
Columella, capillitium, and spores
When does Aethalia occur?
When the entire plasmodium is converted into a cushion-like structure surrounded by one common peridium
How do plasmodiocarps occur?
Spores form in main veins of the plasmodium and are enclosed by peridium
What are the main characteristics of Dictylostelids?
The vegetative forms are amoeba, pseudoplasmodium, and slug
Fruiting bodies are usually sorocarps
Sorocarps contain haploid spores
“social amoebae”
What is the pseudoplasmodium of Dictylostelids made up of?
Many individual amoebae
How does sorocarp development occur?
Through chemotaxis
As the food supply drops, cAMP is secreted
What are the anterior (forward) cells in Dictylostelids converted into?
Stalk cells
Which cells in Dictylostelids get to reproduce?
Amoebae in the front of the slug become stalk cells
Cells positioned in the back are converted into spores
What are cheater line cells?
Cells that are known to avoid duty in the anterior part of the slug
What are the two types of cheater cell lines?
Those that perform tip duty if no others are available
Those that are unable to form a fruiting body in the absence of non-cheaters on whose backs they ride
What are the main characteristics of Protostelids?
Common on decaying matter, humus, dung, and in fresh water
Found everywhere, from the tundra to the tropics
Non-cellular
Filose pseudopodia
How are sorocarps formed?
The amoeba stops feeding
“Hat” stage
Steliogen begins to form
Extension and differentiation of apophysis and spore
Spore detaches
What are the main characteristics of Acrasids?
Common in decaying plant matter, soil, dung, and rotting mushrooms
Too small to be readily detected without a dissecting scope
Grown on nutrient-poor media and fed with yeasts
Chemical signal for aggregation is unknown, but it is not cAMP
Lonose pseudopodia
What is the similarity between Acrasids and Dictyostelids?
They are both cellular slime molds, but they are only distantly related
Where do Acrasids carry spores?
They carry spores in sorocarps that germinate and produce aggregating amoebae
Which major slime molds are plasmodial?
Mycetozoa
Protostelids
Which major slime molds are cellular?
Dictyostelids
Acrasids
Which major slime mold has a peridium?
Mycetozoa
Which major slime molds do not have a peridium?
Dictyostelids
Protostelids
Acrasids
Which major slime mold uses sporophores/sporangia?
Mycetozoa
Which major slime molds use sorocarps?
Dictyostelids
Acrasids
What major slime mold uses sporocarps?
Protostelids
Which major slime molds have filose morphology?
Mycetozoa
Dictyostelids
Protostelids
What major slime mold has lobose morphology?
Acrasids
Which major slime molds make use of plasmodium?
Mycetozoa
Protostelids
Which major slime molds make use of pseudoplasmodium?
Dictyostelids
Acrasids
What are oomycetes also known as?
Water moulds, downy mildews, seedlings blights, damping off, foliar blights
What is unique about oomycete flagella?
They are dissimilar and are indicative of spore type
What are the main characteristics of oomycetes?
“Egg fungus”
Saprotrophs or parasites in many terrestrial habitats
They form hyphae, and are assimilative heterotrophs like fungi
Hyphae are coenocytic
Vegetative cells are diploid
Zoospores are heterokontic
What is the major difference between heterokont and fungal mitochondria?
Heterokonts = mitochondria have an inner tubular network
Fungi = mitochondria have internal lamellae
What is the major difference between heterokont and fungal cell walls?
Heterokonts = cellulose
Fungi = chitin
What are some unique features of the life cycle in phytophthora (oomycete)
Delayed karyogamy
Penetration by fertilization tube
One meiotic event in each parent
What are the 3 layers in oomycete oospores?
Ooplast
Cytoplasm with lipid droplets
Endospore
Where do the zoospores in oomycetes discharge?
From the zoosporangium
How did oomycetes acquire pathogenicity?
From horizontal gene transfer with fungi
What are the main characteristics of plasmodiophorids?
Obligate parasites, mostly of plants
Propagate in part through zoospores
Zoospores possess two identical whiplash flagella
The vegetative state in an amoeba which can enlarge to become a plasmodium that feeds through phagocytosis
Lacks cellular differentiation
What do plasmodiophorids do?
They attack root hairs and inject their cytoplasm
How can we combat plasmodiophorid pests?
Liming
Mercury-based compounds used to be used, but are now banned
