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Microbial Ecology (BIOL 355) > Lecture 12: Plant-Microbes > Flashcards

Lecture 12: Plant-Microbes Flashcards

1
Q

How do microbes interact with plant roots?

A
  • Enter root cells and act symbiotically or pathogenically
  • Microbes are affected by plant root changes in the physical and chemical properties of the soil
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2
Q

What is the above ground portion of a plant called?

A

Phyllosphere

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3
Q

What is the rhizosphere?

A

The region of soil directly impacted by plant roots

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4
Q

Define endorhizosphere, rhizoplane, ectorhizosphere, and the rhizosphere effect.

A
  1. Endorhizosphere: epidermal and cortical cells
  2. Rhizoplane: colonization of the root surface
  3. Ectorhizosphere: soil surrounding the root surface
  4. Rhizosphere effect: 100x more microbes in that area
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5
Q

What is rhizodeposition?

A

Release of organics from roots

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6
Q

What is root exudate?

A

Organic compounds that improve growth

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7
Q

In what stage of plant development might bacterial colonization be established?

A

Bacteria will spread along the root as it growth downward and laterally before germination

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8
Q

What role does chemotaxis have in bacterial colonization of plant roots?

A
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9
Q

What are the the benefits for plants in microbe-root associations?

A
  1. Nutrient recycling
  2. Vitamins, amino acids
  3. Hormones
  4. Exclusion of pathogens
  5. Exclusion of other plants by allelopathic substances
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10
Q

The R/S ratio is an indicator of _____.

A

soil health

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11
Q

What can you say about species evenness?

A
  • Dry soils: able to host even distribution of species, including rare species
  • Why rare species? Dry environments are hard to survive in, so might foster growth of extremophiles, etc.
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12
Q

What gas makes water acidic?

A

CO2

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13
Q

Who respires in the rhizosphere?

A
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14
Q

What is ethylene?

A

A microbially produced plant growth regulator
- Low levels beneficial
- High concentrations inhibitory

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15
Q

What are precursors to ethylene?

A
  • Sugars
  • Alcohols
  • Organic acids
  • Amino acids
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16
Q

What is a phytotoxin? Give an example.

A

Compounds produced by plant pathogens to damage the plant cells
- Ex. cyanide

17
Q

What is the purpose of siderophores?

A

Used by bacteria to take up iron

18
Q

Where are hotspots of antibiotic resistance genes in soil microbes?

A

ARGs peaked in high-latitude, cold boreal forests
- Contained many ARGs of diverse types

19
Q

What is glomalin?

A

A soil stabilizer

20
Q

What is the end goal of the nitrogen fixation?

A

To release nitrate (NO3+) and ammonium (NH4+) for plants to use

21
Q

What is the term for nitrogen-fixing associations?

A

Diazotrophy

22
Q

What types of plants and bacteria form root-nodulating associations?

A
  • Plants: legumes
  • Bacterial genera: Rhizobium, Bradyrhizobium, Sinorhizobium, Mesorhizobium, Azorhizobium
23
Q

What genes control root-nodulating associations?

A

nod and nif genes

24
Q

Where on the plant are most nodules located?

25
What are the stages of nodulation?
1. Plant root hair releases amino acids and flavonoids 2. Rhizobium recognition chemotaxis and attachment 3. nod factors released by bacteria causes curling of root hair 4. Rhizobium enzymatically enter root hair cells, but not cytoplasm 5. Root cell membrane invaginates forming an infection thread to enter root 6. Root cortex cells form deformation layer called a nodule 7. Continued cell division leads to a bacteroid 8. Bacteroids produce nitrogenase for N2 fixation (can’t tolerate O2)
26
What are mycorrhizae?
Mutualistic plant fungi
27
What nutrients are exchanged in mycorrhizal associations?
- Carbon to fungi - Nitrogen and phosphorus to host
28
What are endomycorrhizae?
Layer of hyphae that penetrate cell wall but not plasma membrane - In about 85% of plant species - Aka arbuscular
29
What are ectomycorrhizae?
Layer of hyphae around roots (not in cells) - In about 10% of plant species (typically woody plants)
30
What types of organisms are the most common plant pathogens?
- Fungi - Viruses - Bacteria
31
What are often the vectors of plant pathogens?
insects
32
What are aggregates? Why are they important?
Soil particles held together to form a larger mass - Allow air to penetrate between the particles --> allows more stuff to colonize
33
Which of the following is true about nodulating symbioses? A. They are important for carbon fixation for the plant B. They involve physical transformations of the plant but not the bacteria C. They involve chemical communications between host and plant D. Both B & C E. All of the above

Microbial Ecology (BIOL 355) (17 decks)

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