reading 10 (plp 148)

morphological features of zygomycetes

• zygospore

• most species are hyphal

• asexual spores are typically formed in a sporangia

morphological features of glomeromycotina

least variation in ecology across the phylum (except for microsporidia)

arbuscule mycorrhiza

mycelia are characteristically nonseptate

• septa do form, but onlyl to delimit spores or to seal of old hyphae

spores typically form at the apex of hyphae

• develop thick walls to survive harsh environmental conditions

• germinate, infect into roots and set up new mycorrhizal association

• large spores usually develop very thick walls

  • contain lipids, cytoplasm, and numerous nuclei

• aggregated into groups called sporocarps

sexual reproduction in zygomycetes

1. progametangia come into contact

2. gametangia form as the tips of the progametangia are separated by formation of septa

3. the gametangia then fuse together at the point of contact, accomplishing plasmogamy

   1. karyogamy follows quickly afterward to form a diploid zygote

4. thick cell wall forms around the mature zygospore to protect the zygote from the elements

5. meiosis occurs just before germination, with only 1 haploid nucleus surviving to develop a haploid thallus

asexual reproduction in zygomycetes

1. zygospores germinate (?) into a sporangiophore which contains a sporangium

2. sporangium produce spores (1n)

3. hyphae of different mating types interact and lead to gametangia production

4. as gametangia are being produced, plasmogamy occurs, and karyogamy right after

5. resulting in multinucleate zygospore that undergoes meiosis to produce 1 haploid nucleus

rhizoids

in Rhizopus

anchor the fungus to its substrate, and serve in nutrient uptake

zygospore

unicellular sexual spore that characterizes zygomycetes

sexual reproduction in the zygomycetes results in the formation of a multi-nucleate zygospore and thick-walled, resistant, or resting spore

sporangiophore

a specialized stalk or hypha that bears one or more structures called sporangia, which contain spores used for asexual reproduction

columellum

a sterile, column-like structure that protrudes into the sporangium to provide support and aid in the release of spores

arbuscule

tree-like structures are points of nutrient exchange between fungus and plant within plant root cells

found within individual plant cells between the cell wall and the cell membrane

vesicle

subsporangial vesicle

• swollen area in the sporangiophore just below the sporangium

• detects light at its base, causes sporangiophore to grow toward the light

• at maturity, sporangiophores are all pointed toward the light

• turgor pressure builds up until wall ruptures, sporangium is “squirted” up to a meter

Glomeromycota

• form vesicles in roots

• hyphal swellings in the root cortex that contain lipids and cytoplasm

• storage organs

sporocarp

glomeromycota

• some species, spores are aggregate into groups called sporocarps

  • may be encased in an outer layer (peridium)

ecological features of zygomycetes

majority are saprobes, growing on damaged fruit and also on mammal dung

Rhizopus and Pilobolus

• grow as hyphae, or as yeasts where oxygen is scarce and carbon dioxide is abundant

• septa in hyphae are rare, most septa that are formed separate hyphae from reproductive structures

• mitotic spores are formed in sporangia in process similar to zoospore formation within chytrid sporangia , but w/o flagella and WITH cell walls

Rhizopus

• forms stolons rapidly to colonize a substrate, cobwebby appearance of cultures is due to the presence of the stolons

• rhizoids anchor the fungus to its substrate, 

Pilobolus

• dung-fungus

• spores attach to grass and eaten by cows

• pass through cows gut, which breaks down the resistant spore wall, grows on organic matter,

• as patties decompose, fungus is exposed to light, which stimulates formation of the next generation of spores

entomophthora

zygomycetes

insect host

sporangia are actually conidia, forming via blastic process similar to Ascomycota and diff than what is typically seen in zygomycetes

• spores actively discharged

• shot away from dead insect

ecological features of glomeromycotina

biotrophic symbionts

least variation in ecology across the phylum (with possible exception of the microsporidia)

all but 1 species are obligately symbiotic with plant roots

arbuscular mycorrhiza with plants