1. Chapter 9 BOT3015L Symbioses
Presentation created by Danielle Sherdan
All photos from Raven et al. Biology of Plants except when otherwise noted

2. Sym=together, bio=life
Symbiosis
Sym=together, bio=life
A network of interactions among organisms on a continuum between beneficial and detrimental effects
A major driving force behind evolution
A continuum:
parasitism
commensalism
mutualism

3. 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

4. Example of endosymbiosis
One cell containing numerous autotrophic algal cells
Vorticella (protozoan) under compound light microscope
~5µm
Scanning electron microscope

5. Basic Outline of (Primary) Endosymbiosis using the plastid as an example
Some debate about origin of outer membranes of plastids
The bulk of evidence (more later) indicates that all chloroplasts resulted from a single primary endosymbiotic event (=monophyletic origin of plastids) involving cyanobacteria.
Modified from Outlaw lecture

6. 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)

7. Symbioses between plants and bacteria
Example effect on plant physiology
Many are parasitic, but Rhizobium is mutualistic

8. Rhizobia Symbioses between plants and bacteria Nitrogen Fixation
Legumes (and a few other plants) form a symbiosis with a nitrogen-fixing bacterium.
The bacterium enters the root and a nodule—part plant, part bacterium—is formed as a growth on the root.
From Outlaw lecture

9. Rhizobia Symbioses between plants and bacteria Nitrogen 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

10. Initiation of Rhizobium symbiosis at plant root
Flavinoids
Liposaccharides 1. 2. 3. 4. 5.
Modified from Outlaw lecture

11. Rhizobia (arrows) attached to young root hair
Initiation of Rhizobium symbiosis at plant root
Rhizobia (arrows) attached to young root hair
Bradyrhizobium on soybean (Glycine)
Scanning electron micrograph
~5µm

12. Root hair containing multiple infection threads (arrows)
Initiation of Rhizobium symbiosis at plant root
Root hair containing multiple infection threads (arrows)
Bradyrhizobium on soybean (Glycine)
Differential-interference contrast photomicrograph
~20µm

13. Infection thread with rhizobia
Initiation of Rhizobium symbiosis at plant root
Infection thread with rhizobia
Bradyrhizobium on soybean (Glycine)
Scanning electron micrograph
~1µm

14. Initiation of Rhizobium symbiosis at plant root
Groups of bacteroids surrounded by membrane derived from infected root cell (uninfected cell in the above adjacent cell)
Bradyrhizobium on soybean (Glycine)
Scanning electron micrograph
~2µm

15. Rhizobium symbiosis in dicot root nodule
Cross section of mature root nodule. Rhizobia-infected cells are stained dark. Arrows indicate vascular bundles
Bradyrhizobium on soybean (Glycine)
Compound light microscope
~500µm

16. 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

17. Lichens
Symbiosis between fungus and population of unicellular or filamentous algal or cyanobacterial cells
Reindeer moss (Cladonia)
(note the misnomer)
Caloplaca
Interactions between lichens and animals exemplify the network nature of symbioses.

18. 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

19. Myco=fungus, rhiza=root
Mycorrhizae
Exposure to mycorrhizal fungi __ +
Myco=fungus, rhiza=root
Fungus gets carbohydrates from plant
Plant gets better nutrient absorption
Both have protective effects on the other
White pine (Pinus)

20. Endomycorrhizae endo=within
Branched fungal hyphae (arbuscules) invaginate the plasma membrane of sugar maple (Acer) root cells
Scanning electron micrograph
~10µm

21. Endomycorrhizae Pawpaw 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 Outlaw’s lecture

22. Mycorrhizae dooryard observation
Pawpaw (Asimina triloba)
From Outlaw’s garden

23. Ectomycorrhizae Notice how much surface area is added by the fungus
Fungus surrounds roots and grows between intercellular regions
~50µm
Cross section of pine root with ectomycorrhizae
Lodgepole pine (Pinus)

24. Today Investigating two questions:
What are the effects of fertilizer on Vicia faba?
Based on this discussion, what do you expect?
What should be measured to answer this question?
How should these be measured?
Which local plants have mycorrhizal associations? And, which type (endo- or ecto-) do they have?
How should data be collected?
In your discussion: Why is it important that we investigate these questions on organism and ecological levels?