selection pressure on plants. Plant genes involved in defense and virulence genes of
the pathogens are polymorphic in their genome and hence change rapidly with
selection pressure. This can be termed as gene-to-gene interaction in which genes
of both sides evolved (modify) to counteract each other [19]. Such variations play
important role in creating the ecological niche differentiation among individual
plants. Such intravariations reduce competition and support coexistence
[20]. Glucosinolates in cabbage are an excellent example of variation in secondary
metabolites in host and protection from herbivores. Glucosinolates are an important
group of secondary metabolites mainly present in cabbage and mustard family
(Brassicaceae). A recent study on wild cabbage showed that increased variation in
glucosinolates among neighboring plants correlated positively with associated insect
community and negatively with plant damage [21]. In another study, the dynamics of
glucosinolates in the perennial wild cabbage, in response to herbivory by Pieris
rapae caterpillars, was studied, and it was recorded that herbivore-induced changes
in the concentrations of aliphatic glucosinolates were population-specific and their
concentrations were found to increase in primarily one population only [22].
Adaptation of plants to land was a major breakthrough toward the requirement to
synthesize and diversify secondary metabolites. Colonization of land by phototrophic organisms is confronted with a hostile environment for these organisms as
land has low content of mineral nutrition, harmful UV radiation from the sun, high
variation in day and night temperature, as well as frequent drought. All of these
abiotic factors played important role in adaptations to the terrestrial environment.
Mutualism was one of the major strategies to share fight against all odds, and lichens
are an example to colonize new habitats (see ▶ Chap. 9, “Lichen Metabolites: An
Overview of Some Secondary Metabolites and Their Biological Potential” in this
book). Fossil records show that lichens might have originated even before evolution
of vascular plants. On land, plants were exposed to different stress conditions, and in
order to survive, they began to synthesize an array of secondary metabolites. These
secondary metabolites helped them in attracting pollinators and defending predators
and hence adapting to grow successfully in their ecological niche. Probably today’s
secondary metabolites are the outcome of pre-existing molecules from primary
metabolism in algae and bryophytes [23, 24]. Some of the precursors are detected
in Charophycean algae, mosses, and hornworts [25–28]. It was concluded from these
works that land plants (Bryophytes and vascular plants) are descended from green
algae-like ancestors. Present-day green algae and vascular plants might have a
common ancestor, bifurcating at initial evolutionary stage (Fig. 2). This conclusion
is based on phylogenetic analysis using DNA sequence data of a large number of
algal and vascular plants. As a part of evolution, plant lineage continues to synthesize new compounds and limit the synthesis of others. Sometimes plant lineage
synthesizes secondary metabolites which are already present in different pedigree to
fulfill same type of functions [29].
Plants also started to develop secretory structures like resin ducts and laticifers.
These are thought to be first apparent as intracellular oil bodies in liverworts. These
secretory structures were also a significant adaptation, as they are being able to
sequester secondary metabolites and defense proteins [30]. Further, an important
development was biosynthesis of lignin and the origin of lateral meristems, which
1 Co-evolution of Secondary Metabolites During Biological Competition for. . .
7
the pathogens are polymorphic in their genome and hence change rapidly with
selection pressure. This can be termed as gene-to-gene interaction in which genes
of both sides evolved (modify) to counteract each other [19]. Such variations play
important role in creating the ecological niche differentiation among individual
plants. Such intravariations reduce competition and support coexistence
[20]. Glucosinolates in cabbage are an excellent example of variation in secondary
metabolites in host and protection from herbivores. Glucosinolates are an important
group of secondary metabolites mainly present in cabbage and mustard family
(Brassicaceae). A recent study on wild cabbage showed that increased variation in
glucosinolates among neighboring plants correlated positively with associated insect
community and negatively with plant damage [21]. In another study, the dynamics of
glucosinolates in the perennial wild cabbage, in response to herbivory by Pieris
rapae caterpillars, was studied, and it was recorded that herbivore-induced changes
in the concentrations of aliphatic glucosinolates were population-specific and their
concentrations were found to increase in primarily one population only [22].
Adaptation of plants to land was a major breakthrough toward the requirement to
synthesize and diversify secondary metabolites. Colonization of land by phototrophic organisms is confronted with a hostile environment for these organisms as
land has low content of mineral nutrition, harmful UV radiation from the sun, high
variation in day and night temperature, as well as frequent drought. All of these
abiotic factors played important role in adaptations to the terrestrial environment.
Mutualism was one of the major strategies to share fight against all odds, and lichens
are an example to colonize new habitats (see ▶ Chap. 9, “Lichen Metabolites: An
Overview of Some Secondary Metabolites and Their Biological Potential” in this
book). Fossil records show that lichens might have originated even before evolution
of vascular plants. On land, plants were exposed to different stress conditions, and in
order to survive, they began to synthesize an array of secondary metabolites. These
secondary metabolites helped them in attracting pollinators and defending predators
and hence adapting to grow successfully in their ecological niche. Probably today’s
secondary metabolites are the outcome of pre-existing molecules from primary
metabolism in algae and bryophytes [23, 24]. Some of the precursors are detected
in Charophycean algae, mosses, and hornworts [25–28]. It was concluded from these
works that land plants (Bryophytes and vascular plants) are descended from green
algae-like ancestors. Present-day green algae and vascular plants might have a
common ancestor, bifurcating at initial evolutionary stage (Fig. 2). This conclusion
is based on phylogenetic analysis using DNA sequence data of a large number of
algal and vascular plants. As a part of evolution, plant lineage continues to synthesize new compounds and limit the synthesis of others. Sometimes plant lineage
synthesizes secondary metabolites which are already present in different pedigree to
fulfill same type of functions [29].
Plants also started to develop secretory structures like resin ducts and laticifers.
These are thought to be first apparent as intracellular oil bodies in liverworts. These
secretory structures were also a significant adaptation, as they are being able to
sequester secondary metabolites and defense proteins [30]. Further, an important
development was biosynthesis of lignin and the origin of lateral meristems, which
1 Co-evolution of Secondary Metabolites During Biological Competition for. . .
7