This symbiotic partnership consists of fungal partner (called also mycobiont) and
one or more photoautotrophic partners (called photobiont or phycobiont) [8]. For
almost 150 years, lichens had been the model organisms of symbiosis on the lands
until the researchers uncovered an unexpected third partner in the lichen cortex –
yeast [9].
Lichens as fossils are scarce. Fossil evidence for the interactions of fungi with
other organisms, including phototrophs, has been found originating from an era
approximately 400 million years ago, in the area of Rhynie chert in Scotland.
However, the discovery of lichen-like fossils preserved in marine phosphorite of
the Doushantuo Formation (approximately 600 million years old) at Weng’an in
southern China indicates that lichenization could have arisen even before the
evolution of vascular plants [10]. In addition, recent molecular data suggest that
lichen symbioses arose repeatedly during the evolution of fungi [11] and had a very
important role in the evolution of Ascomycota [12].
2
Lichen Symbiotic Partners
Based on the most definitions, the lichen is the organism that represents the
symbiotic association between the fungus (mycobiont) and the photosynthetic
partner (photobiont). Photobiont coexistence with the lichen mycobiont brings
many benefits that none of the organisms itself cannot achieve [13]. Although the
dual nature of most lichens is now widely established, it is less commonly known
that some lichens are symbioses involving three or more partners [8]. It has been
suggested that they are mainly bacteria involved in the formation of complete lichen
thalli [14].
2.1
Mycobiont
Most of the fungal partners belong to Ascomycota [15, 16], but we can also find
species belonging to the Basidiomycota and anamorphic fungi. Mycobiont (Fig. 1a)
is the dominant component of the lichen thallus. Separated “biont” cells in most
cases are in direct contact, where fungal hyphae try to penetrate to cells of photobiont. There are known some cases where mycobiont is in contact not only with one
type of photobiont but with two or even more. This leads to the creation of specific
structure, cephalodium (e.g., Peltigera aphthosa). Because mycobiont is unable to
produce the organic substances necessary for its growth, hence it must acquire them
from a symbiosis. Heterotrophic mycobiont acquires fixed carbon in symbiosis from
an autotrophic green algae or cyanobacteria. These are photosynthesis products
(ribitol, sorbitol, glucose). In the lichen symbiosis, mycobiont ensures the intake
of water and minerals for lichen thallus. It creates morphology and structures that are
involved in both sexual and nonsexual reproduction. One of the most important roles
9 Lichen Metabolites: An Overview of Some Secondary Metabolites and Their. . .
177
one or more photoautotrophic partners (called photobiont or phycobiont) [8]. For
almost 150 years, lichens had been the model organisms of symbiosis on the lands
until the researchers uncovered an unexpected third partner in the lichen cortex –
yeast [9].
Lichens as fossils are scarce. Fossil evidence for the interactions of fungi with
other organisms, including phototrophs, has been found originating from an era
approximately 400 million years ago, in the area of Rhynie chert in Scotland.
However, the discovery of lichen-like fossils preserved in marine phosphorite of
the Doushantuo Formation (approximately 600 million years old) at Weng’an in
southern China indicates that lichenization could have arisen even before the
evolution of vascular plants [10]. In addition, recent molecular data suggest that
lichen symbioses arose repeatedly during the evolution of fungi [11] and had a very
important role in the evolution of Ascomycota [12].
2
Lichen Symbiotic Partners
Based on the most definitions, the lichen is the organism that represents the
symbiotic association between the fungus (mycobiont) and the photosynthetic
partner (photobiont). Photobiont coexistence with the lichen mycobiont brings
many benefits that none of the organisms itself cannot achieve [13]. Although the
dual nature of most lichens is now widely established, it is less commonly known
that some lichens are symbioses involving three or more partners [8]. It has been
suggested that they are mainly bacteria involved in the formation of complete lichen
thalli [14].
2.1
Mycobiont
Most of the fungal partners belong to Ascomycota [15, 16], but we can also find
species belonging to the Basidiomycota and anamorphic fungi. Mycobiont (Fig. 1a)
is the dominant component of the lichen thallus. Separated “biont” cells in most
cases are in direct contact, where fungal hyphae try to penetrate to cells of photobiont. There are known some cases where mycobiont is in contact not only with one
type of photobiont but with two or even more. This leads to the creation of specific
structure, cephalodium (e.g., Peltigera aphthosa). Because mycobiont is unable to
produce the organic substances necessary for its growth, hence it must acquire them
from a symbiosis. Heterotrophic mycobiont acquires fixed carbon in symbiosis from
an autotrophic green algae or cyanobacteria. These are photosynthesis products
(ribitol, sorbitol, glucose). In the lichen symbiosis, mycobiont ensures the intake
of water and minerals for lichen thallus. It creates morphology and structures that are
involved in both sexual and nonsexual reproduction. One of the most important roles
9 Lichen Metabolites: An Overview of Some Secondary Metabolites and Their. . .
177