Download BIO605 Lecture # 10 File

School of Sciences, Lautoka Campus
BIO509 Botany Lecture 10: Symbiotic
relationships between fungi and other
organisms.
Learning objectives
• Know the kinds of symbiotic relationships
that exist between fungi and other
organisms.
• Understand and appreciate their importance.
Symbiosis
Comes from a Greek word meaning “living
together”
It is a permanent or long-lasting association
between two or more different species.
Occur when two or more different species depend
on each other for food, shelter, or protection.
There are a wide array of symbioses.
• In symbiosis, at least one member of
the pair benefits from the relationship.
•
The other member may be
- injured or harmed
parasitism
- relatively unaffected commensalism
-
may also benefit
mutualism
Mycorrhizae
• Are modified roots consisting of
symbiotic associations of fungi and
roots.
• Almost all plant species have
mycorrhizae.
• Fossilized roots from some early
plants include mycorrhizae - one of
the evolutionary adaptations that
made it possible for plants to
colonize the lands.
Mutualistic relationship between fungus and roots
• Both fungus and roots
benefit.
• Fungus absorbs and
concentrates phosphorous.
• Fungus forms a mantle of
million thread like stands
that facilitate absorption of
water and nutrients.
Essential to normal
growth and development
of many plants.
Fungus provides
protection from
pathogenic fungi and
nematodes.
Host plant provides
carbohydrates and
vitamins for fungal
growth.
Two types of mycorrhizae
Ectomycorrhizae
– Mycelium forms a dense sheath
or mantle over the root surface.
– Hyphae extend over the root
surface increasing the surface
area for water and mineral
absorption.
– Root cells are not penetrated by
the hyphae
– Common in woody plants such
as pine, spruce, oak, walnut,
birch, willow and eucalyptus
families.
Endomycorrhizae
– Do not form a mantle.
– May and may not penetrate
the root cells
– Forms dense knotlike
structures called arbuscules.
– Much more common than
ectomycorrhizae
– Occurs in over 90% plant
species including important
crop plants.
Human and ecological significance of mycorrhizae
• Help in plant establishment on nutrient poor
soils.
• Increase plant growth in short time period
(forestry).
• Reduce fertilizer requirements.
• Cut down production costs.
• Decrease fertilizer contamination of the
environment
Lichens
• A lichen is a mutualistic
relationship between a fungus
(mycobiont) and an alga and/or a
cyanobacterium (photobiont).
• In the case of lichens the
symbiosis results in an organism
that looks completely different to
either the fungal or photosynthetic
partner.
• The combination of
photosynthetic and fungal cell
creates something new.
• The fungal component is most commonly an
ascomycete. Basidiomycete lichen are also known
to occur.
• Fungus gives the lichen its overall shape and
structure.
• Fungus provides alga with suitable physical
environment for growth.
• Alga provides fungus with food.
• There major growth forms of lichens – crustose,
fruticose, foliose.
Fruticose (shrubby) lichens
Crustose lichens
Foliose (leafy) lichens
• Lichens absorb most of the minerals needed from
the air or from the rain water.
• Physical arrangement of hyphae retains water and
minerals, allows gas exchange and protect the algae.
• Fungal pigments shade the algae from intense
sunlight.
Ascocarp of fungus
Soredia
Fungal hyphae
Algal layer
Algal cell
Fungal hyphae
Reproduction of lichen
• Fungus of lichen reproduces
sexually by producing ascocarp
or basidiocarp.
• Algae reproduce by asexual
cell division.
• Lichen as dual organism
reproduce through asexual
reproduction by production of
symbiotic units called soredia.
Human and Ecological relevance if
Lichens
• Lichens are extremely sensitive to
sulphur dioxide. The amount of sulphur
in the air can be determined by the
appearance and disappearance of
lichens. Lichens do not exist in industrial
environment with SO2 emissions.
• Lichens are also very sensitive to
nuclear radiation.
• Acids produced by lichens destroy historical
ruins and exposed rocks.
• Lichens provide food for some animals.
(reindeer, North African sheep)
• Many have been investigated for antibiotic
properties.
• Extracts are used in soap and perfumes.
Questions??