BOT3015L Symbioses

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BOT3015LSymbioses
Presentation created by Danielle Sherdan All
photos from Raven et al. Biology of Plants except
when otherwise noted
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Symbiosis
Symtogether, biolife
A network of interactions among organisms on a
continuum between beneficial and detrimental
effects
A major driving force behind evolution
parasitism
commensalism
mutualism
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A few examples

• Flowering plants and pollinating animals
• Humans and domesticated plants and animals
• Humans and bacteria in their digestive system
• Endosymbionts
• Origination of mitochondria and chloroplasts

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Example of endosymbiosis
One cell containing numerous autotrophic algal
cells
Vorticella (protozoan) under compound light
microscope
5µm
Scanning electron microscope
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Basic Outline of (Primary) Endosymbiosisusing
the plastid as an example
Some debate about origin of outer membranes of
plastids
The bulk of evidence indicates that all
chloroplasts resulted from a single primary
endosymbiotic event (monophyletic origin of
plastids) involving cyanobacteria.
Modified from Outlaw lecture
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A few examples

• Flowering plants and pollinating animals
• Humans and domesticated plants and animals
• Humans and bacteria in their digestive system
• Endosymbionts
• Origination of mitochondria and chloroplasts
• Plants and bacteria
• Rhizobia (also an example of endosymbiosis)

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Symbioses between plants and bacteria
Bacteria
Example effect on plant physiology
Many are parasitic, but Rhizobium is mutualistic
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RhizobiaSymbioses between plants and
bacteriaNitrogen Fixation
Legumes (and a few other plants) form a symbiosis
with a nitrogen-fixing bacterium.
From Outlaw lecture
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RhizobiaSymbioses between plants and
bacteriaNitrogen Fixation
Benefit to the plant Source of usable nitrogen,
which is limiting to growth.
Benefit to the bacterium Low O2 environment (O2
denatures nitrogenase) and source of reduced
carbon.
From Outlaw lecture
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Initiation of Rhizobium symbiosis at plant root
1.
3.
2.
4.
5.
Modified from Outlaw lecture
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Rhizobia (arrows) attached to young root hair
Initiation of Rhizobium symbiosis at plant root
Bradyrhizobium on soybean (Glycine) Scanning
electron micrograph
5µm
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Root hair containing multiple infection threads
(arrows)
Initiation of Rhizobium symbiosis at plant root
Bradyrhizobium on soybean (Glycine) Differential-i
nterference contrast photomicrograph
20µm
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Infection thread with rhizobia
Initiation of Rhizobium symbiosis at plant root
Bradyrhizobium on soybean (Glycine) Scanning
electron micrograph
1µm
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Groups of bacteroids surrounded by membrane
derived from infected root cell (uninfected cell
in the above adjacent cell)
Initiation of Rhizobium symbiosis at plant root
Bradyrhizobium on soybean (Glycine) Scanning
electron micrograph
2µm
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Cross section of mature root nodule.
Rhizobia-infected cells are stained dark.Arrows
indicate vascular bundles
Rhizobium symbiosis in dicot root nodule
Bradyrhizobium on soybean (Glycine) Compound
light microscope
500µm
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A few examples

• Flowering plants and pollinating animals
• Humans and domesticated plants and animals
• Humans and bacteria in their digestive system
• Endosymbionts
• Origination of mitochondria and chloroplasts
• Plants and bacteria
• Rhizobia (also an example of endosymbiosis)
• Humans and fungi
• Leafcutter ants and fungi
• Lichens

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Lichens

• Symbiosis between fungus and population of
  unicellular or filamentous algal or
  cyanobacterial cells

Caloplaca
Reindeer moss (Cladonia) (note the misnomer)
Interactions between lichens and animals
exemplify the network nature of symbioses.
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A few examples

• Flowering plants and pollinating animals
• Humans and domesticated plants and animals
• Humans and bacteria in their digestive system
• Endosymbionts
• Origination of mitochondria and chloroplasts
• Plants and bacteria
• Rhizobia (also an example of endosymbiosis)
• Humans and fungi
• Leafcutter ants and fungi
• Lichens
• Plants and fungi
• Mycorrhizae

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Mycorrhizae
Exposure to mycorrhizal fungi
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• Mycofungus, rhizaroot

• Fungus gets carbohydrates from plant
• Plant gets better nutrient absorption
• Both have protective effects on the other

White pine (Pinus)
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Endomycorrhizae endowithin
Branched fungal hyphae (arbuscules) invaginate
the plasma membrane of sugar maple (Acer) root
cells
Scanning electron micrograph
10µm
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EndomycorrhizaePawpaw and Glomales, an order of
promiscuous endomycorrhizal fungi
Fungi (stained blue to visualize)
hypha
arbuscules
Plant cell wall
The fungus does not penetrate the symplast.
Modified from Outlaws lecture
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Mycorrhizaedooryard observation
Pawpaw (Asimina triloba)
From Outlaws garden
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Notice how much surface area is added by the
fungus
Ectomycorrhizae
Fungus surrounds roots and grows between
intercellular regions
50µm
Cross section of pine root with ectomycorrhizae
Lodgepole pine (Pinus)
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TodayInvestigating mycorrhizae
Comparative study of mycorrhizae in local
plants Work in groups of 2-3 to stain, observe,
draw, and describe mycorrhizae in at least 3
different plant species Draw and describe lichen
and nodules without magnification, then section
them, then draw them as they appear under the
dissecting scope at a high magnification.