BOT3015LSymbioses

Presentation created by Danielle SherdanAll photos from Raven et al. Biology of Plants except when otherwise noted

Symbiosis

Sym=together, bio=life

parasitism commensalism mutualism

A continuum:

A network of interactions among organisms on a continuum between beneficial and detrimental effects

A major driving force behind evolution

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

Vorticella (protozoan) under compound light microscope

One cell containing numerous autotrophic algal cells

Scanning electron microscope~5µm

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

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 bacteriaBacteria Example effect on plant physiology

Many are parasitic, but Rhizobium is mutualistic

RhizobiaSymbioses 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

RhizobiaSymbioses 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

Liposaccharides

Flavinoids

1. 2. 3.

4. 5.

Initiation of Rhizobium symbiosis at plant root

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

Bradyrhizobium on soybean (Glycine)Scanning electron micrograph

Infection thread with rhizobia

~1µm

Initiation of Rhizobium symbiosis at plant root

Bradyrhizobium on soybean (Glycine)Scanning electron micrograph

Groups of bacteroids surrounded by

membrane derived from infected root cell (uninfected cell in the above adjacent cell)

~2µm

Rhizobium symbiosis in dicot root nodule

Bradyrhizobium on soybean (Glycine)Compound light microscope

Cross section of mature root nodule. Rhizobia-

infected cells are stained dark.

Arrows indicate vascular bundles

~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

LichensSymbiosis between fungus and population of unicellular or

filamentous algal or cyanobacterial cells

Interactions between lichens and animals exemplify the network nature of symbioses.

Reindeer moss (Cladonia)(note the misnomer)

Caloplaca

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

Myco=fungus, rhiza=root

• Fungus gets carbohydrates from plant

• Plant gets better nutrient absorption• Both have protective effects on the

other

Exposure to mycorrhizal fungi

White pine (Pinus)

__ +

Endomycorrhizaeendo=within

Branched fungal hyphae (arbuscules) invaginate the plasma membrane of sugar maple (Acer) root cells

Scanning electron micrograph ~10µm

EndomycorrhizaePawpaw and Glomales, an order of promiscuous endomycorrhizal

fungi

Fungi (stained blue to visualize)

Plant cell wall

The fungus does not penetrate the symplast.

Modified from Outlaw’s lecture

hypha

arbuscules

Mycorrhizaedooryard observation

Pawpaw (Asimina triloba)

From Outlaw’s garden

Ectomycorrhizae

Lodgepole pine (Pinus)

Fungus surrounds roots and grows between intercellular regions

Cross section of pine root with ectomycorrhizae

Notice how much surface area is added by the fungus

~50µm

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.