Lecture 10: Growth & sexual reproduction Flashcards
spore:
small, reproductive structures.
DORMANT
hyphae:
long, branching filamentous structure. Main mode of vegetative growth
Mycelium:
collective name for mass of hyphae
Mycelium are great of ___, bad for ____
great for ABSORPTION
bad for WATER LOSS
fungal diversity is highest in
tropics
Germination (Spore –> hyphae) only occurs when conditions are right
moisture & nutrients
Hyphae structure:
chain of cells:
CONTAINING: golgi, vacuole, lipid body, nucleus, mitochondrion, cell wall, plasma membrane.
CELLS SEPARATED BY SEPTUM
cells in hyphae are surrounded by a
tubular cell wall
the major structural polymer in fungal cell walls is typically
CHITIN - long chain polymer, v tough
glucans –>
really long glucose polymers, crosslink the chitin
4 layers to the fungi cell wall: (INNER TO OUTER)
- Chitin microfibrils & protein
- Mainly protein
- The reticulum - glucans and protein
- outer mixed glucans
FUNCTIONS of the fungi cell wall
- maintain cell shape
- Barrier to external world (e.g. prevents osmotic lysis)
- molecular sieve
- cellular protection (melanised for UV protection)
- physiology (binding site for enzymes)
- antigenic properties (regulates interactions with other organisms)
septa are?? (septum)
- divide some fungal cell by internal cross-walls
- usually perforated by large pores (large enough for organelles to flow between cells) -> movement/ communication between cells
hyphae grow from the
TIP
branching:
outgrowth a little way behind the tip
hyphae deposition of organelles:
at growing tip:
- mitochondrion more abundant (ENERGY)
- vesicles adding new section to the cel wall
- denser cytoplasm in younger plants
further in from tip:
- storage granule(for lipids, glycogen etc)
- less dense cytoplasm in older parts
- vacuole
fungi are heterophiboc/ homophobic?
heterotrophic: most acquire external sources of food (like animals)
whats ‘food’ to fungi ?
simple sugars, polypeptides and more complex carbohydates.
how do fungi get there food?
EXTRACELLULAR DIGESTION
2 types of substances carried in vesicles
- carrying digestive enzymes
- cell-wall components
Extracellular digestion:
- golgi apparatus packages proteins into membrane-bound organelles
- vesicles carrying precursors are transported to the tip along microtubules & actin filaments
- vesicles fuse and released digestive enzymes (e.g. amylases, lipase, proteases)
- resulting organic molecules are taken via plasma membrane proteins
fungal colony structure:
- extension zone
- productive zone
- fruiting zone
- aged zone
extension zone:
hyphae are extending into the unexploited medium, seeking out fresh nutrients
productive zone:
hyphae linked by anastomososis into a network. Net increase in biomass
Anastomosis:
fusion between hyphae. Means of communication with itself
fruiting zone:
Initiation of fruit bodies. Turnover of storage reserves
aged zone:
Decline phase. Hyphae become vacuolated and empty of protoplasmic contents. Autolysis (self-digestion) occurs
indeterminate growth:
- Each ring is a single genototype of Armillaria bulbosa
- Largest colony found is over 600m in diameter -Growth rate consistently ~ 0.2m per year
- Age ~ 1500 y
- Estimate that the fresh weight is at least 10,000kg
- Communication over large distance maintained by anastomosis
a spore germinated to form a
hyphae
collection of hyphae is called a
mycelium (huge SA)
hyphae grow at the __ and branch __
Hyphae grow at the tip, branch just behind
Fungi mating types:
are +/- NOT sexes (m/f)
do all fungi reproduce sexually?
Notallfungireproducesexuallyand many that do are isogamous; thus, the terms “male” and “female” do not apply.
isogamy:
gametes similar size & structure
homothallic species:
able to mate with themselves (mate type switching)
heterothallic species:
only isolates of opposite mating types can mate.
4 types of fungi (phylogeny)
- zygomycota (zygomycetes)
- imperfect fungi
- Ascomycota (ascomycetes)
- Basidiomycota (basidiomycetes)
2 “higher fungi” (subkingdom Dikarya)
- Ascomycota (ascomycetes)
- Basidiomycota (basidiomycetes)
how are the major phyla classified
- mainly on the basis of their sexual reproductive structures
- also hyphae structure
imperfect fungi explanation
- no sexual stage known
- polyphyletic group of species not yet placed in any existing group. 25,000 species
non-septate hyphae
(aka coenocytic)
- ZYGOMYCOTA
- more primitive
- one cell with many nuclei
septate hyphae
- Ascomycota (ascomycetes)
- Basidiomycota (basidiomycetes)
- more advanced
- dividers (septa) between the cells
Basidiobycota
-a.k.a Club fungi
-Includes these groups: Mushrooms, puffballs, stinkhorns, bracket fungi, jelly fungi ,boletes, chanterelles, earth stars, smuts, bunts, rusts
~31,500 series described
Basidium (pl. basidia) are
microscopic, spore-producing structure. The presence of basidia is one of the main characteristics of the Basidiomycota
each basidium usually bears
4 sexual spores (basidiospores)
Basidiomycota: Sexual reproduction
1.Spores land and germinate. =HAPLOID (n)
2. Hyphal union. Hyphae fuse and PLASMOGAMY occurs =Dikaryotic (n+n)
3. Fruiting body (BASIDIOCARP) develops aboveground. Gills are lined with HYMENIUM (the tissue layer where the cells develop into basidia)
4. KARYOGAMY occurs (fusion of haploid nuclei) in the basidium
= DIPLOID (2n)
5. Meiosis occurs. Basidiospores are formed and released =HAPLOID (n)
bioluminescence aids???
spore dispersal??
- prosthetic LED-illuminated acrylic mushrooms can be used to study insect behaviour
- insects that can disperse fungal spores are attracted to light at night
- Bioluminesecence peaks at night when it is most visible and thus saves energy
- Why in tropical forests? Little wind flow
plasmogamy:
cytoplasm of two parent cells fuses together without the fusion of nuclei
Dikaryotic:
the two nuclei of two cells pair off and cohabit without fusing (neither truly diploid or haploid) *CONDITION UNIQUE TO THE FUNGI *
karyogamy:
final step in the process of fusing together two haploid eukaryotic cells, and refers specifically to the fusion of the two nuclei
Ascomycota a.k.a Sac fungi. includes:
- yeasts, truffles, morrels and Penicillium, also many animal & plant pathogens
- Largest phylum of fungi (>64000 sp)
Ascus (pl. Asci)
microscopic, sac-like, sexual structure i which spores are formed; defining feature of the Ascomycota
typically how many spores per ascus
8
Ascomycota: sexual reproduction
- ascospores (n) release (active or passive)
- formation of GAMETANGIA
- nuclei migration
- dikaryotic mycelium (n+n)
- fruiting body (ascocarp) forms, including HYMENIUM
- karyogamy occurs (2n)
- meiosis
- mitosis (n)
Ascomycota: specific mating structure interaction
-A very fine hyphae (trichogyne) emerges from one gametangium (ascogonium)
• It merges with a gametangium (antheridium) of the other fungal isolate.
• The nuclei in the antheridium then migrate into the ascogonium
HYMENIUM:
the tissue layer where the cells develop into asci in the bottom of the cup
Zygoymcota a.k.a conjugating fungi.
includes:
- molds, plant symbionts, pathogens to plants and animals (e.g Fly death fungus)
- Small phylum of fungi (>1050 sp) and most primitive
Zygomycota: sexual reproduction
- hypha of two different mating types (+/-) come together
- Gametangia formed (n)
- Plasmogamy occurs gives zycosporangium
- fertilisation (karyogamy)
- DIPLOID (2n) multinucleate zygospore are within zygosporangium
- meiosis occurs
- sporangium forms on top of sporangiophore
- releases spores AND REPEAT
when does dikaryotic stage occur in all fungi
between plasmogamy and karyogamy (fertilisation)
