L9- Microbial associations with plants Flashcards
What’s in a nitrogenase complex?
- Dinitrogenase- Fe and Mo cofactors
- Dinitrogenase reductase- Fe cofactor
Where do nitrogenase complexes occur?
Free living aerobes
Free living anaerobes
Symbiotic microbes with plants
What do legumes have on their roots?
Specialised organs called nodules, containing bacteria called rhizobia
Where do Rhizobia invade the roots?
Either within the nodule or in the soil, but only fix N2 inside the nodule
How do Rhizobia invade the roots?
- Recognition and attachment at root hair
- Excretion of nod factors cause root hair curling
- Rhizobia penetrate root hair and multiply within an infection thread
- Bacteria in infection thread grow towards root cell
- Formation of bacterioid state within the plant cell
- Continued plant and bacterial cell division
What do Rhizobia in the plant cells differentiate into?
N2- fixing cells called bacteroids
In a mutualistic relationship, what does the plant gain? What does the bacteria gain?
Plant- nitrogen
Bacteria- anaerobic environment for N2 fixation and carbon for energy
What are Mycorrhizal associations?
Fungal associations with plant roots
Where does it occur?
In 95% of all vascular plants
What are the 2 main types of Mycorrhizal associations?
- Ectomycorrhiza- mainly basidiomycetes/trees
2. Endomycorrhiza- mainly zygomycetes/grasses
In ectomycorrhiza, what effect does it have?
No plant cell invasion
Greatly increases effective root surface area
What does the Mycorrhizal fungus do?
Uptake of inorganic nutrients, particularly phosphate
What does the tree provide for mycorrhizal fungus?
Sugars from photosynthesis
What is AM?
Arbuscular mycorrhiza fungus-> where the fungus penetrates the corticol cells of the roots of a vascular plant.
Which group is AM in?
Endomycorrhiza
What happens in the plant when AM invade?
Hyphae penetrate cells- arbuscles. Form branched clusters of hyphae, nutrient exchange, large surface area.
Why do orchids rely on mycorrhiza?
They initially lack chlorophyll and some even lack it as adults
What do AM fungi produce within the roots?
Vesicles containing lipids, used for storage
What happens when orchid cells are invaded?
Hyphae form coils called pelotons. Pelotons incrase surface area between orchid and fungi. Each peloton has a short life span and then is digested by the orchid cell.
Relationships between orchids and mycorrhiza are unstable. What are the 3 potential infection outcomes?
- Germination and mycorrhiza formation
- Parasitisation, orchid dies
- Orchid rejects infection, orchid dies
What are lichens?
Organism made of cyanobacteria or algae (or both) living among filaments of a fungus in a mutually beneficial relationship.
What are the layers of lichen?
Cortex (top)
Algal layer
Medilla (bottom)
What do alga provide? WHat does the fungus provide?
Alga- provides sugars
Fungus- protects alga from desiccation
Why can lichens be used as indicators?
They’re very sensitive to air pollution
