Presented By K . SailajaTAM/14/21
Lichens
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
Where they are?
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
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
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 Deuteromycota20% of all fungi & 40% of ascomycotina are
lichenised( Krik et al.,2008).
In culture what happens ?
Photobiont : Trebouxia : produces zoospores produce gelatinous
sheath
Nostoc : produce gelatinous sheath
Mycobiont :Develops into an undifferentiated
mass of hyphae. (Bordo et al.,2001 )
Optional lichenization
As ecological adaptation (sedin et al ., 2004 )
Conotrema (lichenizing fungi )Strictis ( non –lichenizing )Both belongs Leucanoromycetes
(Pezizomycotina ).
Thallus morphology
4 basic typesCrustose – flattened,
scalelike, No lower surface,
tightly bound to substratum
Thallus morphologyFruticose – branched, strap shaped or
threadlike thallus, upright or hanging
Thallus morphology
Foliose – flattened branching lobes loosely attached to the substratum, leaflike
Have upper and lower surfaces
Anatomically similar to angiosperm leaf.
Thallus morphology Squamulose – intermediate
between foliose and crustoseScales, lobes smaller than in
foliose
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 growthLight – variable – some prefer low
light intensities, others highTemperature – variableMoisture – appears to be an
important variable, do not have water absorbing organs, depend on moisture in air
MoistureWhen 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
Asexual reproduction
Fragmentation Soredia - algal
cells enveloped by hyphae, no cortex, form powdery masses on surface of thallus, detach from thallus
Isidia – column like structures with cortex
SEM of Bulbothrix with isidia
Sexual reproductioncharacteristic of fungal symbiontAscospores are discharged, algal
cells are not discharged with them
Thought that after ascospores germinate, they make contact with algal cells
Internal structure
Hypogymnia
Haematomma
Perithecia in crustose lichen Pyrenula
Pseudothecia of Niebla
Pseudothecia of Melanotheca
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
400 lichenic acids reported 230 found only in lichens
Role of lichen acidsUsnic 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.
Lichen acidsAs defense chemicals against
attacks by slugs & other minute animals
Have good chelating properties (metal binding )
Tranlocate substances between partners
Increase permiability of algal cellsStabilize the amount of light
reaching the photobiont layer
uses
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).
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
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 propertiesPeltigera canina - hydrophobiaParmelia saxatilis - epilepsyLobaria pulmonaria - lung infections
Perfumes & dyesThe 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)
lichenometry1st employed by Faegri 1950Most accurate when rocks are
lessthan 1000 yrs10,000 yrs maximum age limit (10 % error ) Mostly used are ascomycetous
genera Rhizocarpon & Xanthoria elegans
Lichens are advantage over vascular plantsAs a bioindicator of air pollution: because theyhave no wax & cuticle to protect cells (inner structure)
Cortex:Fungal layer
Algal layer
Medulla
Fruticose : The most sensitive
Lichens are differently sensitivity to air pollution
Foliose : The second
Crustose :The most resistance
Lichen are efficient indicator of air pollution & acid deposition.
They are less cost comparing with expensive equipments.
Appropriate technique should be developed especially in developing countries to use lichens as bio-monitoring of airPollution.
Lichens provide warning signal before severe damages occur on ecosystem & health.
Fungal
gardens
Thank you