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Summer Research Fellowship Programme of India's Science Academies

CHEMOTAXONOMY IN LICHENS

Jisnet George

BSc, Nirmalagiri College, Kuthuparamba, Kannur, Kerala 670 701

Dr. Dalip Kumar Upreti

CSIR-Emeritus Scientist, Lichenology Laboratorty, CSIR-National Botanical Research Institute, Lucknow 226 001. Uttar Pradesh

Abstract

Lichens are organisms that control the parasitic or symbiotic association between algae and fungi. The fungal component is known as mycobiont and the algal component is called photobiont. The photobiont can be green algae or blue green algae while mycobiont may be ascomycetes, basidiomycetes or deuteromycetes fungi. Based on thallus morphology, lichens are classified as crustose, squamulose, foliose and fruticose. Lichens are good biomonitors, bioindicators and bioaccumulators, thus are excellent organisms for environmetal pollution monitoring and climatic change in an area. So far more than 20,000 species of lichens are known from the world of which, India is repersented by more than 2700 species. The lichens known produce more than 1000 types of lichen chemicals.

Lichens produce two types of lichen compounds, primary metabolites and secondary metabolites. Primary metabolites are produced either by fungal component or by algal component and are meant for the growth and development of the lichen thallus, which are soluble in water. Secondary metabolites are produced by mycobiont and are meant for protection and defence mechanism of lichens and are found on the surface of fungal hyphae in lichens. Each lichen have their own characteristic chemicals which play a significant role in protection against UV radiations, water potential changes and protection against pesticides and herbivores. Mostly the secondary metabolites are insoluble in water and different layers of lichens have different types of secondary metabolites. Apart from various physiological activities, chemicals also play a prominent role in the taxonomy of lichens, that is in the segregation of different taxa. When lichen taxa are similar in morphology, or species are difficult to segregate on the basis of their morphological characters, the chemistry of lichen becomes important in the systematics. This can be attained by comparing the lichen thallus morphological characters and then by comparing its chemistry. The chemicals of lichen can be identified on the basis of colour tests with different reagents, microcrystallography, and thin layer chromatography. Thus it helps to establish the role of lichen chemistry in its taxonomy.

Keywords: Lichen, secondary metabolites, lichen chemistry, lichen substances, chemotaxonomy

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