Transcript Chapter 3 BOT3015L Biology of Flowering Plants

Chapter 9
BOT3015L
Symbioses
Presentation created by Danielle Sherdan
All photos from Raven et al. Biology of Plants except when otherwise noted
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
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
Example of endosymbiosis
One cell
containing
numerous
autotrophic
algal cells
Vorticella (protozoan) under
compound light microscope
~5µm
Scanning electron microscope
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
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)
Symbioses between plants and bacteria
Bacteria
Example effect on plant physiology
Many are parasitic, but
Rhizobium is mutualistic
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
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
Initiation of Rhizobium
symbiosis at plant root
Flavinoids
Liposaccharides
1.
4.
2.
5.
3.
Modified from Outlaw lecture
Initiation of Rhizobium
symbiosis at plant root
Rhizobia (arrows)
attached to young root
hair
Bradyrhizobium on soybean (Glycine)
Scanning electron micrograph
~5µm
Initiation of Rhizobium
symbiosis at plant root
Root hair containing
multiple infection
threads (arrows)
Bradyrhizobium on soybean (Glycine)
Differential-interference contrast photomicrograph
~20µm
Initiation of Rhizobium
symbiosis at plant root
Infection thread with
rhizobia
Bradyrhizobium on soybean (Glycine)
Scanning electron micrograph
~1µm
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
Rhizobium symbiosis in dicot root
nodule
Cross section of mature
root nodule. Rhizobiainfected cells are
stained dark.
Arrows indicate
vascular bundles
Bradyrhizobium on soybean (Glycine)
Compound light microscope
~500µm
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
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.
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
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)
Endomycorrhizae
endo=within
Branched fungal hyphae (arbuscules) invaginate the plasma
membrane of sugar maple (Acer) root cells
Scanning electron micrograph
~10µm
Endomycorrhizae
Pawpaw and Glomales, an order of promiscuous endomycorrhizal
fungi
Fungi (stained blue to visualize)
hypha
arbuscules
Plant cell
wall
Modified from Outlaw’s lecture
The fungus does not
penetrate the symplast.
Mycorrhizae
dooryard observation
Pawpaw (Asimina triloba)
From Outlaw’s garden
Ectomycorrhizae
Fungus surrounds roots
and grows between
intercellular regions
~50µm
Cross section of pine root
with ectomycorrhizae
Lodgepole pine (Pinus)
Notice how much surface
area is added by the fungus
Today
Investigating two questions:
1. 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?
2. 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?