Abstract
Lichens present a symbiotic association between two or more organisms. These
unique organisms produce many chemical compounds, known as secondary metabolites or lichen acids. Most of them are localized in the cortex and form specific
crystals on the surface of the fungal hyphae. Approximately 1000 secondary
metabolites were discovered so far and most of them are specific for lichens.
Lichen secondary metabolites showed many pharmaceutical activities, including
antimicrobial, antiproliferative, antioxidant, antiviral, anti-inflammatory, and further allelopathic, antiherbivore, photoprotective activities. Lichens are important
source of bioactive compounds, and despite a lot of studies dealing with activity of
lichen secondary metabolites, their production in lichens and their role is still very
enigmatic. In this chapter, we demonstrated all three main pathways of how
secondary compounds originate and chose most characteristic acids with their
proposed biological and ecological activities. This chapter gives a basic overview
of lichens, secondary metabolites, and their properties.
Keywords
Symbiosis · Lichens · Biosynthetic pathways · Secondary metabolites ·
Pharmaceutical activities
1
Introduction
Colonization of land by phototrophic organisms started in Silurian era around 450 million years ago [1]. The environment was not friendly for these organisms because they
needed to counter a low content of mineral nutrition, harmful UV-radiation from the
sun, high oscillation of temperature, as well as a lower content of water or even its
absence. All of these abiotic factors played important role in adaptations to the
terrestrial environment. Living forms, which would like to stand in these adaptations,
needed phosphorus to create nucleic acids and ATP (adenosine triphosphate). One
example of how to solve problem with phosphorus uptake was that first colonizing
organisms formed associations with mycorrhizal fungi [2, 3]. It needs to be mentioned
that early organisms were forced to establish a form of mutualism which means the
interaction between at least two different species of the individuals. Mutualism
provided various adaptations for terrestrial plants and played a crucial part for settling
on soil as well as in the evolution of land phototrophs [4].
Lichens (lichen-forming fungi) represent nearly one-fifth of all known fungal
species so far [5]. They are typical examples of mutualistic symbiosis, where both
partners need each other to benefit. The total number of lichens is still not known, but
around 18,500 species were already described around the world [6]. Lichens are the
dominant vegetation of approximately 8% of terrestrial ecosystems [7] and are
typically found in environments subjected to extremes such as temperature, desiccation, and nutrient status.
176
M. Goga et al.
Lichens present a symbiotic association between two or more organisms. These
unique organisms produce many chemical compounds, known as secondary metabolites or lichen acids. Most of them are localized in the cortex and form specific
crystals on the surface of the fungal hyphae. Approximately 1000 secondary
metabolites were discovered so far and most of them are specific for lichens.
Lichen secondary metabolites showed many pharmaceutical activities, including
antimicrobial, antiproliferative, antioxidant, antiviral, anti-inflammatory, and further allelopathic, antiherbivore, photoprotective activities. Lichens are important
source of bioactive compounds, and despite a lot of studies dealing with activity of
lichen secondary metabolites, their production in lichens and their role is still very
enigmatic. In this chapter, we demonstrated all three main pathways of how
secondary compounds originate and chose most characteristic acids with their
proposed biological and ecological activities. This chapter gives a basic overview
of lichens, secondary metabolites, and their properties.
Keywords
Symbiosis · Lichens · Biosynthetic pathways · Secondary metabolites ·
Pharmaceutical activities
1
Introduction
Colonization of land by phototrophic organisms started in Silurian era around 450 million years ago [1]. The environment was not friendly for these organisms because they
needed to counter a low content of mineral nutrition, harmful UV-radiation from the
sun, high oscillation of temperature, as well as a lower content of water or even its
absence. All of these abiotic factors played important role in adaptations to the
terrestrial environment. Living forms, which would like to stand in these adaptations,
needed phosphorus to create nucleic acids and ATP (adenosine triphosphate). One
example of how to solve problem with phosphorus uptake was that first colonizing
organisms formed associations with mycorrhizal fungi [2, 3]. It needs to be mentioned
that early organisms were forced to establish a form of mutualism which means the
interaction between at least two different species of the individuals. Mutualism
provided various adaptations for terrestrial plants and played a crucial part for settling
on soil as well as in the evolution of land phototrophs [4].
Lichens (lichen-forming fungi) represent nearly one-fifth of all known fungal
species so far [5]. They are typical examples of mutualistic symbiosis, where both
partners need each other to benefit. The total number of lichens is still not known, but
around 18,500 species were already described around the world [6]. Lichens are the
dominant vegetation of approximately 8% of terrestrial ecosystems [7] and are
typically found in environments subjected to extremes such as temperature, desiccation, and nutrient status.
176
M. Goga et al.