Participation of NO in plant response to temperature extremes is also
well documented in literature [12]. An increase in NO synthesis associated
with cold acclimation was observed in Helianthus annuus and Capsicum annuum
[12, 74, 79, 80 ]. Transgenic cucumber plants overexpressing CsNOA1 constitutively
had greater accumulation of soluble sugars and starch and a lower chilling damage
index, while suppression of CsNOA1 expression resulted in opposite effects [78].
Furthermore, exogenous application of an NO donor can induce cold acclimation
through synthesis of osmolytes such as glycine betaine and proline and
reprogramming of lipid signaling and composition [74, 81]. Similarly, high-temperature treatment increased NO levels in leaves of Nicotiana tabacum and Medicago
sativa [9]. While exogenous NO has been able to reduce heat-induced cellular
damage, depleting endogenous NO levels by cPTIO reversed these beneficial effects
[12, 84]. SNP treatment recovered relative water content, chlorophyll content,
and electrolyte leakage in heat-stressed Zingiber officinale, Festuca arundinacea,
Triticum aestivum, and Zea mays [12, 82, 83]. NO plays a significant role in
mitigating heat-induced oxidative stress in plants by maintenance of cellular redox
hemostasis and through moderation of carotenoid content [68].
NO mitigate heavy metal stresses in plants mainly by upregulation of antioxidant
defense, by regulating cellular free metal concentration, or by excluding the heavy
metal in the root zone, thereby preventing the accumulation at toxic concentrations
[15, 84–86]. SNP supplementation decreased Cd accumulation in roots and stems
while increasing the photosynthetic and antioxidant activity in Arachis hypogaea
[15]. In rice, exogenous NO treatment has increased Cd tolerance by increasing
pectin and hemicellulose content in the root cell walls and decreasing Cd sequestration in leaf soluble fractions [85]. Moreover, the involvement of NO has also seen in
protection of chlorophyll against Cd stress in H. annuus and Cu stress in Lolium
perenne [86]. Similarly, NO treatment raised photosynthetic rate, antioxidant activity, and reduced MDA content in Vigna unguiculata and antioxidant gene transcription in Triticum aestivum under Al stress [87]. NO also plays a critical role in
promoting antioxidant enzymes activities and inducing the activity of H
+
-ATPase
under metals stress in tomato plants. The role of NO in alleviating other heavy metals
has been reviewed by few authors in recent years [15, 86].
Ozone exposure induced NO generation and flavonol accumulation in
Ginkgo biloba cells [3]. Further, a study in poplar has indicated increased activity
of phenylalanine ammonia-lyase (PAL) due to de-nitrosylation and also Snitrosylation of nearly 172 proteins due to ozone fumigation [89]. Similarly studies
indicate that upregulation of flavonoids and chalcone synthase gene responsible for
flavonoid production by UV-B requires NO in A. thaliana and Betula pendula plants
[90]. Pretreated with SNP prevented the oxidative stress progression in UV-Bexposed Phaseolus vulgaris seedlings by decreasing H 2 O 2 content, increasing the
thiol group content, and upregulation of active oxygen scavenging genes [91]. These
studies suggest that UV-B-enhanced NO levels protect the microtubule organization
as well as microtubule-related processes by in-plant cells against disrupting effects
of UV-B [92]. All these evidence presents NO as a key regulator in maintaining
cellular osmotic and redox status in plants under stress.
25 Nitric Oxide as a Signal in Inducing Secondary Metabolites During Plant Stress
607
well documented in literature [12]. An increase in NO synthesis associated
with cold acclimation was observed in Helianthus annuus and Capsicum annuum
[12, 74, 79, 80 ]. Transgenic cucumber plants overexpressing CsNOA1 constitutively
had greater accumulation of soluble sugars and starch and a lower chilling damage
index, while suppression of CsNOA1 expression resulted in opposite effects [78].
Furthermore, exogenous application of an NO donor can induce cold acclimation
through synthesis of osmolytes such as glycine betaine and proline and
reprogramming of lipid signaling and composition [74, 81]. Similarly, high-temperature treatment increased NO levels in leaves of Nicotiana tabacum and Medicago
sativa [9]. While exogenous NO has been able to reduce heat-induced cellular
damage, depleting endogenous NO levels by cPTIO reversed these beneficial effects
[12, 84]. SNP treatment recovered relative water content, chlorophyll content,
and electrolyte leakage in heat-stressed Zingiber officinale, Festuca arundinacea,
Triticum aestivum, and Zea mays [12, 82, 83]. NO plays a significant role in
mitigating heat-induced oxidative stress in plants by maintenance of cellular redox
hemostasis and through moderation of carotenoid content [68].
NO mitigate heavy metal stresses in plants mainly by upregulation of antioxidant
defense, by regulating cellular free metal concentration, or by excluding the heavy
metal in the root zone, thereby preventing the accumulation at toxic concentrations
[15, 84–86]. SNP supplementation decreased Cd accumulation in roots and stems
while increasing the photosynthetic and antioxidant activity in Arachis hypogaea
[15]. In rice, exogenous NO treatment has increased Cd tolerance by increasing
pectin and hemicellulose content in the root cell walls and decreasing Cd sequestration in leaf soluble fractions [85]. Moreover, the involvement of NO has also seen in
protection of chlorophyll against Cd stress in H. annuus and Cu stress in Lolium
perenne [86]. Similarly, NO treatment raised photosynthetic rate, antioxidant activity, and reduced MDA content in Vigna unguiculata and antioxidant gene transcription in Triticum aestivum under Al stress [87]. NO also plays a critical role in
promoting antioxidant enzymes activities and inducing the activity of H
+
-ATPase
under metals stress in tomato plants. The role of NO in alleviating other heavy metals
has been reviewed by few authors in recent years [15, 86].
Ozone exposure induced NO generation and flavonol accumulation in
Ginkgo biloba cells [3]. Further, a study in poplar has indicated increased activity
of phenylalanine ammonia-lyase (PAL) due to de-nitrosylation and also Snitrosylation of nearly 172 proteins due to ozone fumigation [89]. Similarly studies
indicate that upregulation of flavonoids and chalcone synthase gene responsible for
flavonoid production by UV-B requires NO in A. thaliana and Betula pendula plants
[90]. Pretreated with SNP prevented the oxidative stress progression in UV-Bexposed Phaseolus vulgaris seedlings by decreasing H 2 O 2 content, increasing the
thiol group content, and upregulation of active oxygen scavenging genes [91]. These
studies suggest that UV-B-enhanced NO levels protect the microtubule organization
as well as microtubule-related processes by in-plant cells against disrupting effects
of UV-B [92]. All these evidence presents NO as a key regulator in maintaining
cellular osmotic and redox status in plants under stress.
25 Nitric Oxide as a Signal in Inducing Secondary Metabolites During Plant Stress
607