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Phylum Oomycota

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Mostly aquatic and parasitic on fungi, algae and marine crustacean larvae ... Achlya, Aphanomyces and Saprolegnia fish, crustaceans 'Water mold' applies to this group ... – PowerPoint PPT presentation

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Title: Phylum Oomycota


1
Phylum Oomycota
  • General Mycology
  • Pl P 42/1521
  • Lecture 21

2
Stramenopilous Fungi
  • Tinsel flagellum
  • Tubular mitochondrial cristae
  • Cellulose in cell walls
  • Lysine synthesis by diaminiopimelic acid pathway
    (DAP)

3
Phylum Oomycota
  • 1 class (Oomycetes), 8 orders, 92 genera and 800
    species
  • Orders to cover
  • Leptomitales
  • Filamentous thallus with cellulin plugs
  • Rhipidiales
  • Inflated, branched thallus with cellulin plugs
  • Saprolegniales
  • Holocarpic or eucarpic/filamentous
  • Lagenidiales
  • Holocarpic
  • Pythiales
  • Filamentous thallus
  • Peronosporales
  • Filamentous thallus

4
Characters
  • Predominantly diploid life cycle with gametangial
    meiosis
  • Oogamous sexual reproduction
  • Gametangia oogonia and antheridia
  • Thick-walled, resistant oospore formed inside
    oogonium from oosphere
  • Asexual reproduction by heterokont zoospores with
    tinsel whiplash flagella

5
(No Transcript)
6
Characters
  • Cell walls composed primarily of beta-glucans
    with small amounts of cellulose
  • Filamentous species generally produce coenocytic
    hyphae
  • Principle storage compounds are water-soluble
    mycolaminarins (beta-glucans)
  • Haustoria formed by plant parasitic species

7
Zoospores
  • Primary zoospores
  • First formed
  • Pip-shaped
  • Flagella emerging from anterior
  • Poor swimmers, encyst readily
  • Secondary zoospores
  • Reniform or bean-shaped
  • Flagella emerging from lateral groove

8
Zoospores
  • Dimorphic
  • Primary and secondary zoospores present in life
    cycle
  • Primary zoospores formed in zoosporangium
  • Secondary zoospores formed upon germination of
    primary zoospores
  • Monomorphic
  • Secondary-type of zoospores formed inside
    zoosporangium

9
Sexual Reproduction
  • Mostly heterogametic (morphologically
    differentiated gametangia)
  • Hyphal-like antheridia
  • Attracted to oogonium by hormones and develop
    fertilization tubes
  • Large, globose oogonia
  • One or more oospores in oogonium
  • Simultaneous meiotic divisions occur in
    antheridia and oogonia prior to fertilization
  • Karyogamy occurs in oosphere to form oospore that
    matures inside oogonium

10
Oospore from APSnet
11
Oogonia Oospores
  • Oospore wall consists of 3 parts
  • Exospore
  • Epispore
  • Endospore
  • Periplasm residual protoplasm
  • Plerotic periplasm present
  • Aplerotic lacking periplasm

12
Oogonium Antheridium
  • Hypogynous
  • Antheridium formed in oogonial stalk
  • Paragynous
  • Antheridium attaches laterally to oogonium
  • Monoclinousbranch off oogonial stalk
  • Diclinousbranch off separate hypha
  • Amphigynous
  • Oogonium grows through antheridium

13
Hypogynous
Paragynous/monoclinous
Paragynous/diclinous
Amphigynous
Oosphere
Oogonium
Fertilization tube
antheridium
14
Order Leptomitales
  • Mostly aquatic, saprotrophic
  • Filamentous thallus with regular constrictions
    plugged by chitinous material called cellulin
    granules
  • Asexual reproduction by elongated, hyphal-like
    zoosporangia
  • Some species form primary and secondary zoospores

15
Apodachlya
http//plantbio.berkeley.edu/taylor/pmb110/labpag
es/8leptopythi/index.htm
16
A, B. Leptomitus C-K. Apodachlya
From Sparrow, 1960. Aquatic Phycomycetes.
17
Order Rhipidiales
  • Strictly aquatic, saprotrophic, commonly in
    stagnant and polluted water
  • Thallus
  • Inflated and branched
  • Attached to substrate by rhizoids
  • Oogonia, antheridia and zoosporangia formed
    terminally
  • Branches and reproductive organs constricted at
    base and plugged with cellulin granules
  • Only secondary zoospores formed
  • Strong tendency towards fermentative metabolism

18
Zoosporangia
  • C. Sapromyces
  • Araiospora
  • Rhipidium
  • Mindeniella
  • Aqualinderella

Thalli
From Emerson and Weston, American Journal of
Botany 54 (1967)
19
Order Lagenidiales
  • Mostly aquatic and parasitic on fungi, algae and
    marine crustacean larvae
  • Endobiotic, mostly monocentric
  • Examples
  • Olpidiopsisobligate endoparasite of
    Saprolegniales
  • Lagenidiumendoparasites of algae and marine
    crustacean larvae

20
Lagenidium 1-4. Infection stages in
Spirogyra 5-10. Asexual reproduction 11-17.
Sexual reproduction
Karling, 1942. Simple Holocarpic Biflagellate
Phycomycetes.
21
Order Saprolegniales
  • Saprotrophs (fresh water and soil), or parasites
    (plants and animals)
  • Aphanomyces--sugar beets, peas, radishes,
    aquarium plants
  • Achlya, Aphanomyces and Saprolegniafish,
    crustaceans
  • Water mold applies to this group
  • Primary and secondary zoospores formed
  • Filamentous thallus, abundantly branched
  • Stout, coenocytic hyphae able to increase in
    diameter as they age
  • Gemmae modified segments of hyphae with dense
    cytoplasm

22
Saprolegnialessexual reproduction
  • Oogonia with multiple oospores
  • Oospores with prominent, granular, fluid ooplast
    (formed by coalescence of dense vesicles)
  • Extent of lipid coalescence used as taxonomic
    character
  • Centricsmall lipid drops uniformly surrounding
    ooplast
  • Eccentricooplast to one side of oospore, not
    completely surrounded by lipid globules

23
Sexual Reproduction
  • Most members are self-fertile
  • Sexual reproduction in both self-fertile and
    self-sterile forms involves pheromones
  • Diffusible substances produced by both partners
  • First demonstrated by John Raper (1940s)

24
Role of pheromones
  • Female produces and secretes antheridiol (hormone
    A sterol pheromone) which induces formation of
    antheridial branches in male strain
  • Male strain is stimulated to secrete oogonial
    (hormone B) which causes formation of oogonial
    initials in female
  • Antheridiol causes chemotropic growth of mail
    structures toward female

25
Asexual Reproduction
  • Primary zoospore stage formed in most species,
    but may be reduced
  • Achlya and Aphanomyces
  • Uninucleate protoplasts emerge from zoosporangium
    and encyst at opening or immediately after
    release
  • Dictyuchus
  • Cysts formed inside zoosporangium
  • Saprolegnia
  • Motile, primary zoospores released from
    zoosporangium

26
Saprolegnia
Proliferation of zoosporangium
Secondary zoospore
Primary zoospores
27
Achlya
Uninucleate protoplasts encyst in ball at mouth
of zoosporangium
Lateral proliferation of zoosporangium
Secondary zoospores emerge from cysts
From Webster, 1980
28
Dictyuchus
Primary cysts inside zoosporangium germinate to
release secondary zoospores
From Webster 1980
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