StramenopilaStramenopila

Distinguishing CharacteristicsDistinguishing Characteristics

• Cell Walls have Cell Walls have CelluloseCellulose ( (-1,4 glucose linkage) vs. glucans.-1,4 glucose linkage) vs. glucans.

• Lysine biosynthesis is Lysine biosynthesis is DAPDAP (like plants), vs. (like plants), vs. AAAAAA like true fungi like true fungi

• Heterokont- biflagellate-- anterior tinsel and whiplash flagella (vs. lateral Heterokont- biflagellate-- anterior tinsel and whiplash flagella (vs. lateral whiplash).whiplash).

• Aquatic and soil fungi.Aquatic and soil fungi.

StramenopilaStramenopila

Other CharacteristicsOther 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 HyphochitryomycotaThe 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

Eg. Rhizidiomyces apophysatus

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

OomycotaOomycota

(5 orders, 65 genera, 500-800 species)—two we will discuss:

PeronosporalesPeronosporales

SaprolegnialesSaprolegniales

Saprolegnialeslong terminal sporangia with more than one egg per

oogonium ““Water molds” occur abundantly in clean water. Mostly saprobes Water molds” occur abundantly in clean water. Mostly saprobes

but a few parasites (but a few parasites (Saprolegnia parasiticaSaprolegnia parasitica) causes diseases of fish ) causes diseases of fish and fish eggs.and fish eggs.

Most are hermaphroditic and homothallic (self-fertile).Most are hermaphroditic and homothallic (self-fertile). May be mono- or dimorphic (two spore forms)May be mono- or dimorphic (two spore forms)

Eg. Saprolegnia

Sexual Reproduction in the Sexual Reproduction in the OomycotaOomycota

Eg. #2 Achlya bisexualis

Very similar asexual phaseUnique sexual phaseStudied 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 branchesB Male thallus w anther init. Induces formation of oogonial initialsC Oogonial initials Attracts anther branchesD Antheridia Oogonium & oospere differentiation

AchlyaAchlya

PeronsporalesPeronsporalesoval-lemon shaped zoosporangia with one oosphere oval-lemon shaped zoosporangia with one oosphere

per oogoniumper oogonium Well developed coenocytic myceliumWell developed coenocytic mycelium Most advanced and specialized order of the OomycotaMost advanced and specialized order of the Oomycota All members are monomorphic (one type of zoospore)All members are monomorphic (one type of zoospore) Three Families- distinguished by the structures that bear Three Families- distinguished by the structures that bear

sporangiasporangia

Families in the PeronosporaceaeFamilies 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”.

Ex. Pythium Debaryanum

PythiumPythium Asexual Asexual ZoosporangiaZoosporangia

Pythium Pythium Sexual ReproductionSexual Reproduction

Pythium Pythium OosporesOospores

‘‘Damping Off’ (Damping Off’ (Pythium)Pythium)

PhytophthoraPhytophthora

PhytophthoraPhytophthora- a devastating - a devastating facultative parasitefacultative parasite

Zoospore Release in Zoospore Release in Phytophthora sojaePhytophthora sojae

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

Peronosporaceae- the ‘Downy Peronosporaceae- the ‘Downy Mildews’Mildews’

Obligate parasitesObligate parasites Branched, determinate Branched, determinate

sporangiophoressporangiophores Sporangiophores protrude Sporangiophores protrude

through host stomatesthrough host stomates

Ex. Plasmopora viticola (Peronosporaceae)

Downy Mildew on GrapeDowny Mildew on Grape

Albuginaceae- the ‘White Albuginaceae- the ‘White Rusts’Rusts’

Obligate parasitesObligate parasites Club shaped sporangiophores (inside host leaf)Club shaped sporangiophores (inside host leaf) Sporangia rupture leaf epidermis and appear as a white Sporangia rupture leaf epidermis and appear as a white

crustcrust

Ex. Albugo cadida(Albuginaceae)