Fungi Flashcards
classification
eukaryotes - opisthokonta ‘cells propelled by a single posterior flagella’ although it’s been lost in fungi
name 2 things only recently eliminated from fungi
the slime moulds and oomycetes, traditionally placed in the fungi, are in completely different groups and have only recently (2010!) been eliminated from fungi. Still v controversial among mycologists
fungal phyla
basidiomycota ascomycota glomeromycota zygomycota chytridomycota
IN THAT ORDER
which phyla haven’t moved about
basidiomycota
ascomycota
what are fungi?
• Eukaryotic
• Typically haploid nuclei
▪ They are true diploids but spend most of their time in haploid state
• Reproduce mainly with sexual and asexual spores
• Rigid cell walls with chitin
• Mostly filamentous (hyphal) growth form
• Heterotrophic
▪ All require preformed organic material
▪ There are no known photosynthetic fungi!!!!!
fungal cell wall
mannoproteins B-1,6-glucans and B-1,3-glucans CHITIN (makes it rigid) phospholipid bilyaer of cell membrane
function of fungal cell wall
Functions: • Determines shape • Provides protection • Site of nutrient exchange • Allows system to be pressurised via turgor (osmotic pressure)
what are fungal hyphae?
- Hollow tube containing cytoplasm
- Has a rigid wall
- Lots of CYTOPLASMIC STREAMING which move at quite high rates (allow mixing and transport of contents)
- May be compartmentalised with SEPTA, which roughly divide the tube into different sections
- Growth occurs at the tip and branch points (vesicles!)
- Typical eukaryote with nucleus in membrane, ER, mitochondria, golgi etc.
Model of apical hyphal growth
Model of apical hyphal growth
• Vesicles containing lytic enzymes fuse with the membrane about 10μm from the tip
• Enzymes break down some of the wall polymers – local weakening
→ There is a constant balancing act between stability and chaos
→ The enzymes want to dissolve the wall enough to weaken it without deforming too much so that it fails
• High turgor pressure in the hyphae causes weakened viscoelastic wall to stretch
• Vesicles containing new wall precursors fuse and new material is synthesised
→ The cytoplasmic stream is essential to transport material for forming a new cell wall from far away
• Hyphae re-hardens and tip has moved forwards
Complex 3D hyphal networks
- form by
- gives rise to
These form by…
• apical tip growth and branching
- The extent of branching dep. on the species and the nutritional status of the environment
• hyphal fusion (anastomosis)
- Fusion allows remodulation of transport system. Can do so in optimal fashion
This gives rise to…
• Radially symmetrical colonies on rich media
- Hyphal fusion can remodel these radial colonies
Function of septa
Provides mechanical strength
Mechanism for isolating damaged or ageing hyphal lengths
Allows differentiation e.g. during sporulation
Not all fungi have them!
- zygomycetes don’t, asco and basidio do
hyphae colonies
- diff between inner and outer regions
- regulation of whole colony growth under diff environmental conditions
Inner region = denser, fused hyphae
- Positive autotrophy and anastomosis give good connectivity for transport
Outer region = sparser, unbranched hyphae
- Exploratory hyphae
- Negative autotropy giving good space-filling
• Branching frequency is sensitive to environmental conditions.
- Under nutrient excess, there are more exploratory hyphae (fungal foraging) and there are more dense colonies
Autotropism –
sensing of neighbouring hyphae via O2 or CO2 concentrations followed by growth towards (+ve) or away (-ve) from neighbours
Do zygomytes have septa?
- Normally aseptate, allowing unrestricted cytoplasmic streaming.
- But sometimes form septate to allow isolation
Do Ascomycetes have septa?
Ascomycetes – Woronin body
- Woronin bodies clog septal pores
- Open form allows cytoplasmic streaming and nuclear and major organelle movement
- Closed form provides isolation if compartment damaged
