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Stramenopila

Stramenopila

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Stramenopila

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  1. Stramenopila Distinguishing Characteristics Cell Walls have Cellulose (-1,4 glucose linkage) vs. glucans. Lysine biosynthesis is DAP (like plants), vs. AAA like true fungi Heterokont- biflagellate-- anterior tinsel and whiplash flagella (vs. lateral whiplash). Aquatic and soil fungi.

  2. Stramenopila • Other Characteristics • Motile spores formed in a sporangium • Sexual reproduction by gametangial contact • Diploid through most of the life cycle • Somatic structures are unicellular and holocarpic, or rhizoidal, or coenocytic.

  3. The Hyphochitryomycota • Anterior tinsel flagellum • Aquatic habitat • Some parasites (on algae and fungi), others saprobes • Thallus is holocarpic or eucarpic • Holocarpic species are endobiotic • Eucarpic species may be mono- or polycentric • Zoosporangia are inoperculate, zoospore release is through a discharge tube

  4. Eg. Rhizidiomyces apophysatus

  5. The Oomycota • Zoospore biflagellate, heterokont—posterior facing whiplash, anterior facing tinsel (emerge adjacent) • Sexual Reproduction by gametangial contact • Oogamous—two different types of gametangia, contact, contents of one flow into the other • Oospore is the sexual spore--thick walled resting spore • Meiosis occurs in gametangium • Haplobiontic (only diploid thallus, no haploid thallus) • Some are holocarpic, no mycelium • Some are eucarpic, but monocentric with rhizoids • Some produce extensive mycelia with coenocytic hyphae

  6. Oomycota (5 orders, 65 genera, 500-800 species)—two we will discuss: Peronosporales Saprolegniales

  7. Saprolegnialeslong terminal sporangia with more than one egg per oogonium • “Water molds” occur abundantly in clean water. Mostly saprobes but a few parasites (Saprolegnia parasitica) causes diseases of fish and fish eggs. • Most are hermaphroditic and homothallic (self-fertile). • May be mono- or dimorphic (two spore forms)

  8. Eg. Saprolegnia

  9. Sexual Reproduction in the Oomycota

  10. Eg. #2 Achlya bisexualis • Very similar asexual phase • Unique sexual phase • Studied by John Raper in the 40’s and 50’s demonstrating a complex hormone system involved in sexual development • Hormone Source Function • A Female somatic thallus Induces antheridial branches • B Male thallus w anther init. Induces formation of oogonial initials • C Oogonial initials Attracts anther branches • D Antheridia Oogonium & oospere differentiation

  11. Achlya

  12. Peronsporalesoval-lemon shaped zoosporangia with one oosphere per oogonium • Well developed coenocytic mycelium • Most advanced and specialized order of the Oomycota • All members are monomorphic (one type of zoospore) • Three Families- distinguished by the structures that bear sporangia

  13. Families in the Peronosporaceae • Pythiaceae- sporangia directly borne on vegetative hyphae. These fungi are saprophytes or facultative parasites (very destructive) • Peronsoporaceae- sporangia borne on branched, determinate sporangiophores (protrude through stomates). Obligate parasites called the “Downy Mildews” • Albuginaceae- chains of sporangia on club shaped sporangiophores that rupture host epidermis to form a white crust on leaf surface. Obligate parasites called “White Rusts”.

  14. Ex. Pythium Debaryanum

  15. Pythium Asexual Zoosporangia

  16. Pythium Sexual Reproduction

  17. Pythium Oospores

  18. ‘Damping Off’ (Pythium)

  19. Phytophthora

  20. Phytophthora- a devastating facultative parasite

  21. Zoospore Release in Phytophthora sojae

  22. Peronosporaceae- the ‘Downy Mildews’ • Obligate parasites • Branched, determinate sporangiophores • Sporangiophores protrude through host stomates

  23. Ex. Plasmopora viticola(Peronosporaceae)

  24. Downy Mildew on Grape

  25. Albuginaceae- the ‘White Rusts’ • Obligate parasites • Club shaped sporangiophores (inside host leaf) • Sporangia rupture leaf epidermis and appear as a white crust

  26. Ex. Albugo cadida(Albuginaceae)