Lichens are a symbiotic relationship between fungi and algae or cyanobacteria. The algae or cyanobacteria conduct photosynthesis to produce food, while the fungal partner provides structure and absorbs water and minerals. Lichens grow slowly and can be crustose, foliose, fruticose, or squamulose in morphology. They reproduce asexually through soredia, isidia, or fragmentation, and sexually through ascospores. Lichens produce protective lichen acids and have various uses as food, fodder, dyes, perfumes, and indicators of air pollution due to their sensitivity. They are also useful for dating surfaces in the field of lichenometry.
2. Lichen is derived from the Greek word
‘Leprous’ and refers to medicine used
for treatment of skin diseases
because of their appearance as
peeling skin
Schwendener –dual nature
5. Relationship between
algae and fungus
- Mutualism - both gain benefits
-Algae produce carbohydrates as
food supply
-Fungus with hyphae holds the
structure firmly on substrates and
absorb mineral salts
-Controlled parasitism
6. Photobiont
Green algae – Trebouxia is a common
genus, found in 75% of lichens in
temperate zone
Cyanobacteria – Nostoc is a common
genus
25 genera of algae and 15 of
cyanobacteria found in lichens, 90% of
lichens contain Trebouxia, & 8 %
Nostoc or one other genus
7. Mycobiont
Most lichenized fungi are Ascomycotina – most
form apothecia, some form perithecia and
pseudothecia.
12 orders include mostly lichenized members
(Arthoniomycetes , Eurotiomycetes ,
Leucanomycetes , Lichenomycetes )
Some are Basidiomycotina – Aphyllophorales,
few Agaricales .
Some are Deuteromycota
20% of all fungi & 40% of ascomycotina are
lichenised( Krik et al.,2008).
8. In culture what happens ?
Photobiont :
Trebouxia : produces zoospores
produce gelatinous sheath
: produce gelatinous Nostoc
sheath
Mycobiont :
Develops into an undifferentiated mass
9. Optional lichenization
As ecological adaptation (sedin et al .,
2004 )
Conotrema (lichenizing fungi )
Strictis ( non –lichenizing )
Both belongs Leucanoromycetes
(Pezizomycotina ).
10. Thallus morphology
4 basic types
Crustose – flattened,
scalelike,
No lower surface, tightly
bound to substratum
12. Thallus morphology
Foliose – flattened
branching lobes
loosely attached to
the substratum,
leaflike
Have upper and
lower surfaces
Anatomically
similar to
angiosperm leaf.
14. Growth
Exhibit low growth rates (crustose) –
many grow at rates of 1-4 mm/yr, up to 9
cm/yr (foliose)
Makes studies difficult
Factors affecting growth
Light – variable – some prefer low light
intensities, others high
Temperature – variable
Moisture – appears to be an important
variable, do not have water absorbing
organs, depend on moisture in air
15. Moisture
When lichen thallus is wetted, absorbs
water quickly by gelatinous matrix in the
cortex Starts growth process
As thallus dries, growth process slows
and stops
Dew and humidity are important sources
of moisture
Thalli are inactive when dry – only grow
when wetted
Most of them require low light intensity,
cool temperature & moisture.
may be responsible for slow growth rate
20. Sexual reproduction
characteristic of fungal symbiont
Ascospores are discharged, algal cells
are not discharged with them
Thought that after ascospores
germinate, they make contact with
algal cells
24. Lichen acids
The metabolites (mainly secondary) are
antimycobacterial, antiproliferative,
antiviral, antibiotic, anti-inflammatory,
cytotoxic, analgesic and antipyretic
effects.
belongs to depsides & depsidones
(which are condensation products of 2-or
3 phenyl carboxilic acids mainly orsellinic
or ß- orsellinic acid held together by ester
linkage
25. Role of lichen acids
Usnic acid – wide spectrum antibiotic
activity (Shibamoto and Wei, 1984,
Rowe et al., 1991).
Vulpinic acid exhibited mild antibiotic
activity (Lauterwein et al.,1995).
These acids inhibited the growth of
Bacillus subtilis, Staphylococcus aureus
and Bacillus magaterium.
26. Lichen acids
As defense chemicals against attacks by
slugs & other minute animals
Have good chelating properties (metal
binding )
Tranlocate substances between partners
Increase permiability of algal cells
Stabilize the amount of light reaching the
photobiont layer
28. As source of food
Cetraria islandica was used as food in
Northern Europe and was cooked as
porridge, soup, bread, salad and pudding.
Bryoria fremoontii were mostly used as
food in times of famine in North America
so they were called famine food.
In China, lichens are used as food
(Lobaria isidiophra, L.yoshimurae) and
also as health promoting tea (Thamnolia
subuliformis, Lethariella cashmeriana).
29. As fodder
Cladonia rangiferina in
taundra,
Cetraria islandica in iceland
Sps of Lecanora
Nutritive value is due to lichenin
As initiators of vegetation on rocks
Crustose lichens are primary colonizers
30. Some lichens known as Earth Flowers
have a strong and distinct odour so they
are smoked along with tobacco used in
summer dances (Curtin, LSM. 1984).
Medicinal properties
Peltigera canina - hydrophobia
Parmelia saxatilis - epilepsy
Lobaria pulmonaria -
lung infections
31. Perfumes & dyes
The extracts are used to dye wool .
They are also used in the
manufacture of ‘moss’ and ‘leather’ &
fragrances in perfumes and some
type of soaps (Richardson, D. H. S.
1974)
32. lichenometry
1st employed by Faegri 1950
Most accurate when rocks are
lessthan 1000 yrs
10,000 yrs maximum age
limit (10 % error )
Mostly used are ascomycetous genera
Rhizocarpon & Xanthoria elegans
33. Lichens are advantage
over vascular plants
As a bioindicator of air
pollution: because they
have no wax &cuticle
to protect cells (inner
structure)
Cortex:
Fungal layer
Algal layer
Medulla
34.
35. Fruticose : The most sensitive
Lichens are differently sensitivity to air pollution
38. Lichen are efficient indicator of
air pollution &aciddeposition.
They are less cost comparing
with expensive equipments.
Appropriate technique should
be developed especially in
developing countries to use
lichens as bio-monitoring of air
Pollution.
Lichens provide warning signal
before severe damages occur
on ecosystem & health.
