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