4
Role of NO in Inducing Secondary Metabolites
Biosynthesis of plant secondary metabolites is regulated by multiple endogenous
signaling pathways. NO has been widely utilized as elicitor to stimulate secondary
metabolite accumulation in several plants ([94, 95]; Table 3). Priming with SNP
has enhanced the phenolic and flavonoid content in fenugreek seeds [116]. Similarly, SNP priming of ripe litchi fruits enhanced the shelf life due to the enhancement of the total phenolic content during postharvest storage [117]. NO is known
to regulate the production of many pharmaceutically important secondary metabolites in plants [95]. Rhodiola sachalinensis A. Bor. is a perennial herb popularly
known for its traditional medicinal properties in China. Nitric oxide induced the
bioactive metabolites including salidroside in this endangered plant while
increased the total content of phenolic and flavonoid compounds in lemon balm
seedlings under in vitro conditions [101]. In another study, the effect of NO donor
was studied on the content of secondary metabolites in Calendula officinalis L.
SNP treatment had significant role in production of total phenolic and flavonoid
content, antioxidant activity, and essential oil of capitule, while it had no effect on
other pigment content. The application of NO donors for induction of the secondary metabolite production in plant cultures is also becoming increasingly popular
[95]. To give few examples, SNP treatment induced catharanthine production in
Catharanthus roseus cells [94, 96 ]. Similarly, the hypericin production by Hypericum perforatum was significantly enhanced by at least fourfold after eliciting with
NO [96, 105]. The accumulation of secondary metabolite such as tannins, saponins, phenols, and total flavonoids is significantly enhanced by high doses of SNP
in Ginkgo biloba callus cultures [106]. The accumulation of phenolic compounds
and glycosides is subsequently followed by an oxidative burst and subsequent
activation of specific enzymes activities such as PAL, SOD, and APX in Gingko
biloba [118]. SNP treatment elicited the accumulation of secondary metabolites in
Echinacea purpurea adventitious roots. Exogenous treatments with SNP also
enhanced the accumulation of phenolics, flavonoids, and caffeic acid derivatives
in this species suggesting the importance of NO accumulation for the secondary
metabolic production [100]. Moreover, the involvement of NO was also suggested
in the accumulation of artemisinin in hairy root cultures of Artemisia annua L. and
taxol production from Taxus chinensis cell cultures [119, 120]. Many previous
studies have shown that NO is being involved in elicited production of secondary
metabolites such as ginseng saponin, hypericin, puerarin, catharanthine
artemisinin, and taxanes in plant cell and tissue cultures [94, 96, 101–103, 105,
120, 121]. These metabolites are highly valuable components of pharmaceuticals
and nutraceuticals. The production and isolation of secondary metabolites from
Ficus religiosa L. in tissue culture are often challenged by callus browning [122].
Adding SNP to the MS medium along with 2,4-dichlorophenoxyacetic acid and 6benzyl amino purine significantly reduced the accumulation of hydrogen peroxide
and phenolic compounds in the callus tissues. Similarly, exogenous NO promoted
callus induction and reduced browning of Chinese yam. Hence, complete
608
P. Santisree et al.
Role of NO in Inducing Secondary Metabolites
Biosynthesis of plant secondary metabolites is regulated by multiple endogenous
signaling pathways. NO has been widely utilized as elicitor to stimulate secondary
metabolite accumulation in several plants ([94, 95]; Table 3). Priming with SNP
has enhanced the phenolic and flavonoid content in fenugreek seeds [116]. Similarly, SNP priming of ripe litchi fruits enhanced the shelf life due to the enhancement of the total phenolic content during postharvest storage [117]. NO is known
to regulate the production of many pharmaceutically important secondary metabolites in plants [95]. Rhodiola sachalinensis A. Bor. is a perennial herb popularly
known for its traditional medicinal properties in China. Nitric oxide induced the
bioactive metabolites including salidroside in this endangered plant while
increased the total content of phenolic and flavonoid compounds in lemon balm
seedlings under in vitro conditions [101]. In another study, the effect of NO donor
was studied on the content of secondary metabolites in Calendula officinalis L.
SNP treatment had significant role in production of total phenolic and flavonoid
content, antioxidant activity, and essential oil of capitule, while it had no effect on
other pigment content. The application of NO donors for induction of the secondary metabolite production in plant cultures is also becoming increasingly popular
[95]. To give few examples, SNP treatment induced catharanthine production in
Catharanthus roseus cells [94, 96 ]. Similarly, the hypericin production by Hypericum perforatum was significantly enhanced by at least fourfold after eliciting with
NO [96, 105]. The accumulation of secondary metabolite such as tannins, saponins, phenols, and total flavonoids is significantly enhanced by high doses of SNP
in Ginkgo biloba callus cultures [106]. The accumulation of phenolic compounds
and glycosides is subsequently followed by an oxidative burst and subsequent
activation of specific enzymes activities such as PAL, SOD, and APX in Gingko
biloba [118]. SNP treatment elicited the accumulation of secondary metabolites in
Echinacea purpurea adventitious roots. Exogenous treatments with SNP also
enhanced the accumulation of phenolics, flavonoids, and caffeic acid derivatives
in this species suggesting the importance of NO accumulation for the secondary
metabolic production [100]. Moreover, the involvement of NO was also suggested
in the accumulation of artemisinin in hairy root cultures of Artemisia annua L. and
taxol production from Taxus chinensis cell cultures [119, 120]. Many previous
studies have shown that NO is being involved in elicited production of secondary
metabolites such as ginseng saponin, hypericin, puerarin, catharanthine
artemisinin, and taxanes in plant cell and tissue cultures [94, 96, 101–103, 105,
120, 121]. These metabolites are highly valuable components of pharmaceuticals
and nutraceuticals. The production and isolation of secondary metabolites from
Ficus religiosa L. in tissue culture are often challenged by callus browning [122].
Adding SNP to the MS medium along with 2,4-dichlorophenoxyacetic acid and 6benzyl amino purine significantly reduced the accumulation of hydrogen peroxide
and phenolic compounds in the callus tissues. Similarly, exogenous NO promoted
callus induction and reduced browning of Chinese yam. Hence, complete
608
P. Santisree et al.