Transcript symbiosis in fungi

Fungal Symbiosis
(Lichens and Mycorrhizae)
By : Thabat Khatib
Presented for: Dr. Ghadeer Omar
What is Symbiosis ?
• Symbioses are intimate associations involving
two or more species (often long-term
interaction).
• In the natural world no organism exists in
absolute isolation, and thus every organism
must interact with the environment and other
organisms.
Classification of Symbiosis
Symbiosis can be classified into different
categories:
•
•
•
•
Dependent on each other for survival.
Physical attachment of the organisms.
Physical interaction.
Biological interaction.
Dependent on each other for survival
Symbiosis
Obligate
Both symbionts
entirely depend on
each other for
survival
Facultative
They can, but do
not have to live
with the other
organism
Physical attachment of the organisms
Symbiosis
conjunctive
symbiosis
disjunctive
symbiosis
The organisms
have bodily
union
The
organisms are
not in union
Physical interaction
Symbiosis
Endosymbiosis
Exosymbiosis
One symbiont lives
within the tissues of
the other, either
within the cells or
extracellularly
The symbiont lives on
the body surface of the
host, including the
inner surface of the
digestive tract
Biological interaction
Symbiosis
Mutualism
Parasitism
Both
One of the
Commensalism
organisms
organisms
benefit in a
benefits,
One of the organisms
symbiotic
where the
relationship benefits, where the other is other one is
unaffected
harmed
Fungal Symbiosis
Many fungi have important symbiotic
relationships with organisms from most if not all
Kingdoms.
Fungi Symbiosis
With insects
With plants
With algae and cyanobacteria
Importance of Fungal Symbiosis
1. The main physiological basis for this symbiosis
is bidirectional nutrient transfer.
1. The ability of symbiotic partners to tolerate
environmental
stress
and
inhabit
environments that they could not live in
individually.
Fungi-Plant Symbiosis
(Mycorrhiza)
• A mycorrhiza is defined as a
symbiotic
relationship
between the roots of plants
and fungi.
• Includes plants that do not
have
roots,
such
as
bryophytes (mosses and
liverworts).
Fungi
Plant
Characteristics of Mycorrhizae
• Enhances mineral transport to plants, especially
phosphorous.
• Infection occurs only at root tips.
• Relationships obligate and facultative.
• Plants with mycorrhizae more drought resistant.
• Plants with mycorrhizae more resistant to plant
pathogens.
What happens in Mycorrhizae ?
• Fungi: invades tree roots and
nourishment by tapping into the
vascular system.
obtains
plant’s
• Plant: increasing the plant’s access to water and
relatively immobile nutrients (greater uptake of
mineral ions such as nitrogen, potassium and
particularly phosphorus) and protection of its
roots against pathogens.
Categories of Mycorrhizae
Two Major
Categories:
Endomycorrhizae
Ectomycorrhizae
Mycelium does not
form sheath and
does penetrate
root cells
Mycelium forms an
external sheath
around root tip. Does
not penetrate cells of
root.
Ectomycorrhizae
• Fungus groups involved are mostly
mushrooms and related groups with large
fruiting bodies, e.g. mushrooms, truffles and
puffballs.
• Fungus receives carbohydrate from plant and
plant has enhanced mineral uptake.
Ectomycorrhizae
• Mycelium forms only around the root tips,
forming an external sheath around root.
• Fungus penetrates epidermis and grows
between root cells in cortex.
• Fungus does not penetrate cells of root.
Normal Uninfected Root
Root
Cortex
Epidermis
Infected Ectomycorrhizal Root
Mycelial Sheath
Intracellular
mycelial
Growth
The infected roots are very distinctive, forming
short, paired, branches (induces root tips to
branch, dichotomously).
Endomycorrhizae
•
•
•
•
Most mycorrhizal fungi in this group.
The sheath is reduced or absent.
Occurs in almost all groups of plants.
Endomycorrhizae inconspicuous due to lack of
large fruiting body
How does it Occur ?
• For a hypha to enter into a root, it adheres by the
formation of a swollen structure called appressorium.
• This appears to be formed as a result of topographical or
biochemical signals.
• Following adhesion, the colonization of the root cortex
occurs.
Categories of Endomycorrhizae
Arbuscular
mycorrhizae
Ericaceous
Endomycorrhizae
Orchid
Endomycorrhizae
1) Arbuscular mycorrhizae
• Vesicular-Arbuscular Mycorrhizae (VAM). Now
Arbuscular mycorrhizae .
• The name comes from the distinct structures
that can be seen inside the cells of the
infected roots, the rounded vesicles and the
branched tree-like arbuscules.
Vesicles and Arbuscules of VAM
Fungus
Vesicles
Arbuscules
AM Endomycorrhizae
• Vesicles and arbuscules within cells are lysed
by host-root cells where the stored minerals
needed by plant is stored.
• Identified by the large spores that are
produced in the soil.
• Spores are just visible to the naked eye.
Spores of VAM Fungus
Round, yellow-orange structures are VAM
spores
VAM Spores Under Microscope
Relevance of VAM
Many native Hawaiian
plants’ seeds cannot be
germinated
and
if
germinated do not readily
grow.
2) Orchid Endomycorrhizae
• Orchid, if not photosynthetic, derives
carbohydrate from fungus, until it is able to
produce its own food.
• Even then, it is still dependent upon fungus for
minerals.
3) Ericaceous Endomycorrhizae
Classified into two main
groups
Ericoid
Mycorrhizae
Monotropoid
Mycorrhizae
Found with plants in
stress environment
and requires fungus
to grow normally
Found with nonchlorophylls parts of
some plants.
Lichens
Lichen is an intimate,
symbiotic association
of a tangled mass of
fungal hyphae that
holds a photosynthetic
green or a blue-green
partner a stable thallus
of specific structure
Mycobiont
Photobiont
Algae
Symbiotic
Relationship
Fungi
Cyanobacteria
Importance of Lichens
• Lichens can survive in the most extreme and severe
environments where neither plants nor fungi can exist alone.
• Lichens can also tolerate heat that would desiccate and kill
most plants.
• Antibiotics have been extracted from lichens.
• Some lichens used as a source of food.
• Most species of lichens are extremely sensitive to sulfur
dioxide in the air and are therefore indicators of air
pollution.
Do lichens represent a true mutualistic
type of symbiosis?
One of the most basic questions, that has been
asked since the discovery of the lichen
symbiosis, concerns whether lichens represent a
true mutualistic symbiosis or nothing more than
a variation of a host-parasite relationship.
A thallus, which is
leaf-like, and
attached to the
substrate at various
points
Crustose
A thallus, which is
flattened against
the substrate and
its lower surface
entirely attached
Foliose
The
Lichen
Thallus
Squamulose
A thallus, which is
made up of
pendulous
branches. Attached
at a single point
Fruticose
A thallus, which
starts off like a
foliose lichen, then
develops branches
called podetia
Foliose Lichen
Section of Foliose Thallus
• Upper Cortex: Tightly woven
mycelial layer.
• Algal Layer: Algal Cells and
mycelium.
• Medullary Layer: Loosely
interwoven mycelium.
• Lower Cortex: Tightly woven
mycelial layer.
• Rhizines: Outgrowth of lower
cortex that attaches to
substrate .
Section of Foliose Thallus
Crustose thallus
Crustose thallus: Flattened against substrate,
attached by medulla. Often looks like a painted
surface.
Section of Crustose Lichen
Fruticose Lichen
Fruticose thallus: Often stringy in
appearance and attached at a single point.
Commonly found hanging on trees.
Section of Fruticose Lichen
Squamulose lichens
Lichen
Podetia
Section of Squamulose lichens
Some lichens have a portion of their
thallus lifted off the substrate to form
'squamules
Leprose Lichens (Rare form)
Leprose lichens are an odd
group of lichens
Reproduction of Lichens
• Soredia: fragments of algal layer that is
dispersed through a rupture in upper cortex.
Each soredium can give rise to a lichen.
Fungal Symbiosis With Insects
• The fungus grows a tough cover over the
colony of scale insects or arthropods.
• The fungus also penetrates insects through
natural openings forming haustoria . Insects
continue to feed, providing a flow of nutrients
to the fungus directly from the plant
Haustorium
The appendage or portion of a parasitic fungus (the hyphal tip) or of
the root of a parasitic plant that penetrates the host's tissue and
draws nutrients from it
Many insects have a symbiotic relationship with certain
types of fungi:
1. Termites: When termites have eaten a big meal of
wood or leaves, they also eat some fungi from their
gardens. The fungi help them digest the wood or leaves.
2. Leafcutter ants: grow fungi on beds of leaves in their
nests. The fungi get a protected place to live. The ants
feed the fungi to their larvae.
3. Ambrosia beetles: live in the bark of trees. Like ants
and termites, they grow fungi inside the bark of trees
and use it to help digest their food.
Thank
You