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56 Cards in this Set
- Front
- Back
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Exudates |
- released by plant roots - contain sugars, organic acids, and amino acids - result in nutritionally enriched environment -> microbial growth |
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Diversity of microorganisms |
- from heavy colonization of plants |
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Biological processes involving soil microorganisms controbute to |
- maintenance of soil fertility in relation to N and P - reducing losses of nutrients |
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Microbes that colonize plants |
- epiphytes - plant surface - endophytes - plant interior |
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Epiphytes and endophytes are both |
- Bacteria - Fungi or oomycetes - Viruses - Protists - Algae - Nematodes |
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Types of plant-microbe interactions |
- Pathogenic - Symbiotic - Associative |
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Bidirectional interaction |
- Plants provide microbes with shelter - Microbes provide plants with nutrients - Microbial communities affect planr growth directly or indirectly |
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Interaction factors |
- decide which microbe interacts with a plant at any particular yime |
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Abiotic factors |
- Soil properties - Environmental factors |
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Soil properties |
- pH - soil type and structure - macronutrient distribution - organic material - moisture - salinity |
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Environmental factors |
- climate - light - water - UV radiation - geographical location |
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Biotic factors |
- plant factors - anthropogenic factors |
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Plant factors |
- immune system - plant compartment - metabolite secretions - plant age - plant-to-plant interactions - root morphology |
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Anthropogenic factors |
- agricultural practices (fertilizer, pesticide spray, cultivation practices) - pollution |
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Pathogenic/parasitic |
- plant is harmed, microbes benefit - occurs in apoplastic zone |
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Apoplastic zone |
- extracellular area between cell wall and plasma membrane |
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Pathogen types |
- biotroph - host alive - hemibiotroph - grows like biotroph but kills host - necrotroph - kills host and grows within it |
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Symbiotic/mutualistic |
- both benefit - endosymbionts - inside tissues of host - ectosymbionts - outside tissues of host - e.g. Rhizobium in root nodules, lichen terrestial plants and insects, pollination |
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In symbiotic/mutualistic relationships, microbes help in |
- nitrogen fixation - PGP hormones - recycling decaying material |
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In symbiotic/mutualistic relationships, beneficial compounds released by plant |
- carbohydrates - amino acids - organic acids - flavonoids - lipids |
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In symbiotic/mutualistic relationships, beneficial compounds released by microbes |
- N - PGP hormones and enzymes - minerals |
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Associative/commensalistic |
- one benefits, other unaffected - uncommon, but species may coexist without affecting one another - plant serves as habitat for microbial communities |
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Kinds of microbes |
- air - phyllosphere - plant surface areas - endophytic - within plant - rhizosphere - in/by root-soil - soil - in soil but not close to roots |
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Beneficial effects of microbiomes on flower |
- sexual health - reproductive success |
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Beneficial effects of microbiomes on leaf and stem |
- minimize stress from biotic and abiotic environment |
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Beneficial effects of microbiomes on roots |
- nutrient uptake - resists pathogen establishment - regulate host immunity |
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Significance of studying plant-microbe interactions |
- understand plant health in presence/absence of microbes - reduce chemical pesticides and fertilizer use - understand how PGP microorganisms exert beneficial effects - understand how plant pathogens can cause disease - optimize plant cultivation to provide food for growing population |
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Rhizosphere |
- immediate area around soil inhabited by unique population of microorganisms |
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Why plants need microbes in rhizosphere |
- lack mobility and have large size - allows nutrients to be obtained efficiently |
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Effect of exudates on bacteria and fungi |
- bacteria: sugar and carbon -> colonies grow - fungi: form huge underground netrworks -> large SA, more nutrients extracted |
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Effect of modern farming practices on soil food web |
- detrimental |
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Importance of legume-rhizobium interaction |
- supply of biologically fixed nitrogen during cropping |
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Partnership between plant roots and bacterial cells |
- initiated by communication by plant roots and free-living stage - root nodules -> where bacteria normally lodge and multiply |
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Rhizobacteria |
- found in root nodules - inert atmospheric nitrogen gas -> ammonia and amino acids -> available for plant absprption and metabolism - energy supplied by plants |
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Color of rhizobacteria |
- viable and active - red - dead or inactive - grayish green |
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Process of legume-rhizobium interaction (1-4) |
1) Rhizobia live normally in soil 2) FLAVONOIDS: limited soil nitrogen -> legumes release flavonoids -> signal to rhizobia that plant is seeking symbiotic bacteria 3) NOD FACTORS: rhizobia exposed to flavonoids -> attach to root hair -> release nodulation factors -> plant creates deformed root hairs 4) INFECTION THREAD: rhizobia form infection thread -> can enter plant through root hairs |
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Process of legume-rhizobium interaction (5-7) |
5) NODULE: rhizobia are inside -> root cells divide rapidly, forming nodule 6) PLANT GAINS: plant gains ammonia, created by rhizobia from N in air -> creates amino acids and nucleotides 7) RHIZOBIUM GAINS: sugar! |
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Isolating rhizobium from root nodules (1-4) |
1) Sterilize materials (15 min) with ethanol in laminar flow cabinet 2) Wash legume root to detach nodule 3) 96% ethanol (5s): sterilizes surface of nodule 4) Sodium hypochlorite (3 min): cuts up DNA |
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Why nodule is handled with root fragment |
- to not touch nodule itself - if nodule punctured, sterile water contaminated |
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Isolating rhizobium from root nodules (5-8) |
5) Five washes of sterile water: to remove bleach and alcohol 6) Crush nodule with scalpel on clean petri lid: to confirm success of surface disinfection process 7) Streak liquid with sterile loop over Yeast Mannitol Agar 8) Incubate plate at 25⁰C for 3-10 days |
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Creating clean rhizobia culture |
1) rhizobia: white gooey stuff 2) dip sterile loop into clean part of plate 3) streak in three rotations 4) incubate at 25⁰ in dark 5) purer culture! |
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Atmospheric nitrogen to plants |
- 78% - cannot be utilized by humans so we obtain from food - falls to earth by precipitation - finds its way to bacteria in roots of plants |
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Nitrogen fixation |
- in roots of plants - N + H -> NH4 |
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Nitrification |
- ammonia combines with O2 to form nitrites (NO2) |
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Nitrifying bacteria |
- converts nitrite to nitrate (NO3) |
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Assimilation |
- plants can absorb nitrogen in the form of nitrate |
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Denitrifying bacteria |
- allow nitrates not yet absorbed back into atmosphere (NO3 -> N2) |
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Ammonification |
- nitrogen in animal either excreted or returned to soil when animal dies - allows nitrogen to enter cycle again - by decomposers and some bacteria (NO3 -> NH4) |
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Eutrophication |
- increased richness of nutrients in body of water - caused by increased nitrogen or phosphorus |
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Result of eutrophication |
- excessive plant and algal growth (dense blooms) - death of animal life due to hypoxia - reduce water clarity - harm water quality |
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Why chemical fertilizers are not the answer |
- high cost - pollution - estimated 90% never reach roots, contaminate groundwater |
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Possible causes of eutrophication |
- fertilizer runoff - concentrated animal feeding operations - direct discharge of sewage and industrial waste into water bodies - aquaculture - growing of fish, shellfish, and plants in water with dissolved nutrients - natural events - floods, currents |
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Eutrophication effects on people |
- toxic cyanobacteria -> increases chances of food poisoning and diseases - threatens potable drinking sources, fisheries, recreational water bodies - can harm livelihood |
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Eutrophication effects of animals |
- high photosynthesis rates -> deplete dissolved inorganic carbon -> raise pH to extreme levels - impair chemosensory abilities of some organisms - hypoxic environments and accumulation of toxins - kill fishes and other aquatic life -> harms biodiversity |
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Eutrophication effect on plants |
- more nutrients -> promotes growth - reduced growth in littoral (nearshore) zones -> algal blooms limit light penetration |
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Strategies to avoid eutrophication |
- regulate fertiler usage and optimize nutrient use - alternative biofertilizers - proper soil management to prevent washout and fertilizer runoff -> reduced tillage, covered crops, contour farming - improve sewage systems and wastewater management - wetlands could be used as nutrient sinks |
