An update on nitric oxide and its benign role in plant responses under metal stress

Nitric Oxide as a Signal in Inducing Secondary Metabolites During Plant Stress

“…Later four major sources for NO generation have been deciphered in plants: nitrate reductase (NR) pathway, NOS pathway [14], and other enzymatic and nonenzymatic pathways [15]. Oxidative NO synthesis from L-arginine through NOS activity has been reported across the kingdoms including prokaryotes, unicellular eukaryotes, invertebrates, and mammals.…”

“…NR, in addition to its primary nitrate (NO_3) oxidoreductase activity, is capable of reducing NO 2 to NO with low efficacy [18]. Additionally, NO can also be produced through reductive pathways by assimilatory nitrate reductase, or through the mitochondrial electron transport system, or from xanthine dehydrogenase/oxidase [15]. The reductive NO synthesis from NO 2 can occur in cytoplasm, mitochondria, chloroplast, peroxisomes, and the apoplast of the plant cells [18].…”

“…In the past decade, researchers deployed different methods to elucidate NOdependent processes including NOS/NR activity assays, NO-binding fluorescent dyes, and various pharmacologic approaches using NO donors including sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine and NO scavengers 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), and quantification of effectors by radioimmunoassay or liquid chromatography tandem-mass spectrometry [9,15,17,19]. The recent use of targeted nanodonors and nanoshutters has enhanced the specificity while reducing the pleiotropic responses and artifacts encountered with pharmacological compounds [12,16].…”

“…Heavy metal contamination in soil, air, and water may alter the chemical and metabolite composition of plants leading to poor production and quality [15]. Metals such as aluminum, cadmium, lanthanum, nickel, europium, and silver are known to influence secondary metabolite production due to either inactivation or stimulation of enzymes involved in their production [36,37].…”

“…Metals such as aluminum, cadmium, lanthanum, nickel, europium, and silver are known to influence secondary metabolite production due to either inactivation or stimulation of enzymes involved in their production [36,37]. For instance, metal ions in the growth medium regulate the anthocyanin biosynthesis by inhibiting activity of PAL [15]. Cu 2+ and Cd 2+ have been shown to induce secondary metabolites such as shikonin, digitalin, and betalains [63].…”