levels of red coloring are sought in varieties intended for fresh consumption. By
contrast, the reduction of pigment content in any part of the fruit is the goal of most
canning programs for the canning industry [5].
Plants have developed the ability to synthesize and store secondary metabolites as
a means of protecting against herbivores, bacteria, fungi, and viruses, as well as other
competing plants. Plants typically produce complex mixtures of SMs that can work
in an additive or even synergistic ways. The mechanism of the protective action of
secondary metabolites is not fully elucidated. Some protecting compounds are
directed to a particular target, e.g., the neurotransmitter receptor or the ion channel
of the animal pest; others have a broad spectrum of activity and show pleiotropic
activity for several purposes. In addition to protective function, secondary metabolites also serve as signal compounds attracting pollinators and seeds spreading
animals [6]. A characteristic feature of secondary metabolites is that their metabolism, especially synthesis and accumulation, strongly depends and is regulated by
the conditions of the environment. The use of biostimulants can also have a positive
effect on the biosynthesis of secondary metabolites, which increases the resistance of
plants to various stress factors.
2
Secondary Metabolites: Classification and Function
Plants are a rich source of thousands of secondary metabolites. They consist of low
molecular weight compounds that are considered crucial to the survival of the
organism that produces them. These compounds are often accumulated by plants
in smaller quantities than the major metabolites [7]. Secondary metabolites are
produced by plants and play an important role as protective chemicals and signaling
molecules. Alkaloids, flavonoids, essential oils, phenols, terpenes, etc. are included
in this class of compounds [3, 8]. Signaling messages that regulate plant behavior are
delivered from a wide range of chemical compounds. In some cases, they can
facilitate communication between members of a species (e.g., pheromones) or
between members of different species (e.g., allopathic substances) [9, 10]. These
interactions have a largely negative effect on the germination, growth, development,
propagation, and behavior of other organisms [7, 11, 12].
There are different classifications of secondary metabolites based on the content
or absence of nitrogen in the molecules as well as their biosynthetic pathway or
precursor. The most common classifications divide the secondary metabolites into
two main groups: nitrogen-containing and non-nitrogenous compounds, each of
which is subdivided into subgroups (Table 1).
Depending on the biosynthetic pathway, the secondary metabolites are divided
into three main groups: (1) Terpenoids; (2) Flavonoids and concomitant phenolic
and polyphenolic compounds; (3) Nitrogen-containing alkaloids and sulfurcontaining compounds [14] (Fig. 1).
Terpenoids are the largest and most diverse family of natural products, ranging
from linear to polycyclic molecule structures, and ranging in size from five-carbon
(C5) hemiterpenes to natural rubber containing thousands of isoprene units (C5). All
16 Deranged Physiology of Peach
379
contrast, the reduction of pigment content in any part of the fruit is the goal of most
canning programs for the canning industry [5].
Plants have developed the ability to synthesize and store secondary metabolites as
a means of protecting against herbivores, bacteria, fungi, and viruses, as well as other
competing plants. Plants typically produce complex mixtures of SMs that can work
in an additive or even synergistic ways. The mechanism of the protective action of
secondary metabolites is not fully elucidated. Some protecting compounds are
directed to a particular target, e.g., the neurotransmitter receptor or the ion channel
of the animal pest; others have a broad spectrum of activity and show pleiotropic
activity for several purposes. In addition to protective function, secondary metabolites also serve as signal compounds attracting pollinators and seeds spreading
animals [6]. A characteristic feature of secondary metabolites is that their metabolism, especially synthesis and accumulation, strongly depends and is regulated by
the conditions of the environment. The use of biostimulants can also have a positive
effect on the biosynthesis of secondary metabolites, which increases the resistance of
plants to various stress factors.
2
Secondary Metabolites: Classification and Function
Plants are a rich source of thousands of secondary metabolites. They consist of low
molecular weight compounds that are considered crucial to the survival of the
organism that produces them. These compounds are often accumulated by plants
in smaller quantities than the major metabolites [7]. Secondary metabolites are
produced by plants and play an important role as protective chemicals and signaling
molecules. Alkaloids, flavonoids, essential oils, phenols, terpenes, etc. are included
in this class of compounds [3, 8]. Signaling messages that regulate plant behavior are
delivered from a wide range of chemical compounds. In some cases, they can
facilitate communication between members of a species (e.g., pheromones) or
between members of different species (e.g., allopathic substances) [9, 10]. These
interactions have a largely negative effect on the germination, growth, development,
propagation, and behavior of other organisms [7, 11, 12].
There are different classifications of secondary metabolites based on the content
or absence of nitrogen in the molecules as well as their biosynthetic pathway or
precursor. The most common classifications divide the secondary metabolites into
two main groups: nitrogen-containing and non-nitrogenous compounds, each of
which is subdivided into subgroups (Table 1).
Depending on the biosynthetic pathway, the secondary metabolites are divided
into three main groups: (1) Terpenoids; (2) Flavonoids and concomitant phenolic
and polyphenolic compounds; (3) Nitrogen-containing alkaloids and sulfurcontaining compounds [14] (Fig. 1).
Terpenoids are the largest and most diverse family of natural products, ranging
from linear to polycyclic molecule structures, and ranging in size from five-carbon
(C5) hemiterpenes to natural rubber containing thousands of isoprene units (C5). All
16 Deranged Physiology of Peach
379