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.
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.
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
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
Oomycota (5 orders, 65 genera, 500-800 species)—two we will discuss: Peronosporales Saprolegniales
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)
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
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
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”.
Peronosporaceae- the ‘Downy Mildews’ • Obligate parasites • Branched, determinate sporangiophores • Sporangiophores protrude through host stomates
Albuginaceae- the ‘White Rusts’ • Obligate parasites • Club shaped sporangiophores (inside host leaf) • Sporangia rupture leaf epidermis and appear as a white crust