beneficial plant-microbe interactions Flashcards
define rhizosphere
- the zone of soil around plant roots which has its properties influenced by root activities such as secretions and microbial activity
- changing the properties of the rhizosphere influences plant growth and disease
- evolution and selection have neant plants are very selective if which microbes are present in the rhizosphere
what did Van Luijk discover
when germinating seeds, a higher percentage of seeds germinate in non-sterile soils compared to sterile soils; microorganisms are needed to promote plant growth
name the three groups of beneficial plant microbes
1) Plant growth promoting bacteria
- a) Biofertilising PGPB
- b) Biocontrol PGPB
2) Plant growth promoting fungi
- a) ectomycorrhiza
- b) endomycorrhiza
3)beneficial saprophtic fungi
what % of rhizosphere promote plant growth
1%
define PGPB; 2
what are the 5 functions of biofertilising PGPB
- the 1% of the rhizosphere which actually promote plant growth by wither colonising the rhizosphere, the root surface or within the root.
- mainly gram negative
to in crease the availability of plant nutrients
i)lower ethylene level in plants by breaking down the ethylene precursor ACC using ACC deaminase. lower amounts of ethylene means less inhibitory effects allowing for root and shoot length increase despite environmental stress
ii) solubilise phosphate from insoluble sources by releasing acidic metabolites which lower pH and liberate phosphate.
- phosphate is not a limiting factor and no phosphate needs to be applied
iii) increase iron availability by releasing sidephores which have a high affinity for iron. plants take up sidophores via a receptor
iv) fix nitrogen; rhizobia and frankia form nodules in plants and fix N2 into ammonia.
v) produce volatiles and phytohormones; tyrosine diffuses into bacteria which convert it to IAA (an auxin). IAA diffuses back into the plan and causes effects such as cell elongation and division
discuss what role biocontrol-PGPB have (1) and how
that have indirect effects which cause supression of disease
i) competition for nutrients and sidophore production stops pathogen proliferation
ii) antibiotic and fungicide production damages pests
iii) niche exclusion; colonising roots means pathogens cant colonise roots
- -some bacteria leave spores assosiated with crystals on platn surface; insects eat the plant and ingest spore-crytals which dissolve and activate toxins which damage the insect
iiii) induced systemic resistance; microbial inoculation activates the plants immune system so future microbes wont damage the plant
what % of plants have PGPF;1
discuss how PGPF work; 1
what are the two types of PGPF
- 80% of terrestrial plants have mycorrhizae (sym iotic fungi in roots)
- fungi imrove nitrogen and phosphorus availability
i) ectomycorrhizae; hartig net on tip outside of the root
ii) endomycorrhizae; intracellular projections
- –Arbuscalar mycorrhizal fungi (AMF) penetrates cortical cells
the mode of action of beneficial saprophytic fungi is not fully understood, discuss what these fungi do
- they get their energy from decaying matter
- perform fungicide production, compete for nutrients against pathogens, do niche exclusion, perform phosphate solubleisation etc
describe the process of creating an inoculant
1) isolate bacteria/fungi from soil and do a dilution
2) perform a spread plate
3) characterise microbe via SSU sequencing
4) perform experiments to check the microbe does what its sopposed to (first lab then field)
5) form inoculant/co-inoculant (use bacteria and fungi)
which is the model plant for experimental investigations involving inoculants, and why
vigna radiata
sensitive to hormone concentration change so its easy to see the effects of the inoculant
what are the advantages of inoculants
less environmental effects than fertiliser
less costly than fertiliser in LEDC’s
the use of inoculants is well established and has been done for centuries
what are the characteristics of a good PGPB?F; 9
enhances plant growth
ability to survive and multiply in targte rhizosphere
ability to colonise root while in competition with others
easily scaleable in lab
broad spectrum
easily monitorable
environmentally safe
compatible with other PGPB/F
tolerant to environemtal extremes like heat, water
what are the 4 different types of inoculant
- cells suspended in liquid with substances to improve stickiness and dispersal ability; very effective
- an organic carrier material like peat or cork is used; destruction of peat bogs
- soil from bacterias habitat are used
- synthetic polymer carriers like alginate, agar and pectin are used (trap bacteria inside the polymer)
what are the 5 inoculation techniques
apply to seeds inoculate soil dip cuttings in innoculant spray plant spray bees
how can we confirm microbial colonisation
microbiology; selective medium with antibiotics etc
direct methods; GFP engineered into microbe
molecular methods; DNA probes/PCR
