metabolites have been identified in higher plants. Most of them are synthesized
from primary metabolites including carbohydrates, lipids, and amino acids [21,
22]. Secondary metabolites significantly contribute to develop specific aroma,
tastes, and colors in plants that are in turn responsible for plant interactions with
environment and defense against pathogens. In economic point of view, they are
the major sources for natural products, pharmaceuticals, food additives, and
flavors. The accumulation of secondary metabolites can be influenced by various
genetic and environmental factors [23, 24 ]. Secondary metabolites including
toxoids, polysaccharides, and flavones serve as key components for plant interaction with the biotic and abiotic cues in their vicinity. Indeed, these are the signals
of plant communication during symbiosis, seed dispersal, and plant completion
with other plants [25].
Secondary metabolites are not essential to life but essential for survival. Indeed
the specific phytochemical profile of species can be used for systematic classification of species in chemotaxonomy. Majority of the plants have four chemically
distinct metabolite groups such as terpenes, phenolics, nitrogen, and sulfurcontaining secondary metabolites [25]. Terpenes constitute the largest group of
secondary metabolites usually derived from acetyl-coA or glycolytic intermediates. Terpenes are structurally diverse group including monoterpenes, sesquiterpenes, diterpene, triterpenes, and polyterpenes that constitute toxins and feeding
deterrents in plants. Carotenoids, insecticides like pyrethroid, and phytohormone
abscisic acid are the most popular examples of terpenes in plants [26]. Phenols are
aromatic compounds derived from the shikimic acid pathway, having a significant
role in plant defense against various bacterial, fungal pests, and disease. Few
examples of phenols which include lignin, flavonoids, isoflavonoids, and coumarin derivatives play effectively against a range of plant pathogens, protect cells
from UV-B radiation and oxidative stress, and promote symbiotic associations.
Phytoalexins, thionins, defensins, and glutathiones are the well-known sulfurcontaining secondary metabolites [26–28]. They are useful in plant growth as
source of reduced sulfur, in stress responses as volatiles defensive substances. The
nitrogen-containing secondary metabolites including alkaloids and cyanogenic
glucosides and nonproteins amino acids such as canavanine and azetidine-2
carboxylic acid are biosynthesized from common amino acids. These metabolites
are mostly toxic and offer defense against pathogenic microbes and herbivoral
animals and insects.
2
Production of Secondary Metabolites in Plants Under
Abiotic Stress
Plants have potential to adopt some strategies to neutralize the effects of various
abiotic stresses. External stress factors such as high and low temperature, salinity,
alkalinity, UV, heavy metals, and drought can significantly affect the synthesis of
secondary metabolites profiles (Table 1; [27]). The released secondary metabolites
25 Nitric Oxide as a Signal in Inducing Secondary Metabolites During Plant Stress
599
from primary metabolites including carbohydrates, lipids, and amino acids [21,
22]. Secondary metabolites significantly contribute to develop specific aroma,
tastes, and colors in plants that are in turn responsible for plant interactions with
environment and defense against pathogens. In economic point of view, they are
the major sources for natural products, pharmaceuticals, food additives, and
flavors. The accumulation of secondary metabolites can be influenced by various
genetic and environmental factors [23, 24 ]. Secondary metabolites including
toxoids, polysaccharides, and flavones serve as key components for plant interaction with the biotic and abiotic cues in their vicinity. Indeed, these are the signals
of plant communication during symbiosis, seed dispersal, and plant completion
with other plants [25].
Secondary metabolites are not essential to life but essential for survival. Indeed
the specific phytochemical profile of species can be used for systematic classification of species in chemotaxonomy. Majority of the plants have four chemically
distinct metabolite groups such as terpenes, phenolics, nitrogen, and sulfurcontaining secondary metabolites [25]. Terpenes constitute the largest group of
secondary metabolites usually derived from acetyl-coA or glycolytic intermediates. Terpenes are structurally diverse group including monoterpenes, sesquiterpenes, diterpene, triterpenes, and polyterpenes that constitute toxins and feeding
deterrents in plants. Carotenoids, insecticides like pyrethroid, and phytohormone
abscisic acid are the most popular examples of terpenes in plants [26]. Phenols are
aromatic compounds derived from the shikimic acid pathway, having a significant
role in plant defense against various bacterial, fungal pests, and disease. Few
examples of phenols which include lignin, flavonoids, isoflavonoids, and coumarin derivatives play effectively against a range of plant pathogens, protect cells
from UV-B radiation and oxidative stress, and promote symbiotic associations.
Phytoalexins, thionins, defensins, and glutathiones are the well-known sulfurcontaining secondary metabolites [26–28]. They are useful in plant growth as
source of reduced sulfur, in stress responses as volatiles defensive substances. The
nitrogen-containing secondary metabolites including alkaloids and cyanogenic
glucosides and nonproteins amino acids such as canavanine and azetidine-2
carboxylic acid are biosynthesized from common amino acids. These metabolites
are mostly toxic and offer defense against pathogenic microbes and herbivoral
animals and insects.
2
Production of Secondary Metabolites in Plants Under
Abiotic Stress
Plants have potential to adopt some strategies to neutralize the effects of various
abiotic stresses. External stress factors such as high and low temperature, salinity,
alkalinity, UV, heavy metals, and drought can significantly affect the synthesis of
secondary metabolites profiles (Table 1; [27]). The released secondary metabolites
25 Nitric Oxide as a Signal in Inducing Secondary Metabolites During Plant Stress
599