Journal of Medicinal Plants Research Vol. 4(25), pp. 2729-2739, 29 December Special Review, 2010 Available online at http://www.academicjournals.org/JMPR ISSN 1996-0875 ©2010 Academic Journals Review Nitric oxide biochemistry, mode of action and signaling in plants A. N. Misra*, M. Misra and R. Singh Department of Biology and Biotechnology (DBT-BIF and DST-FIST Department), School of Biotechnology, Fakir Mohan University, Jnan Bigyan Vihar, Balasore-756020, India. Accepted 3 August, 2010 Nitric oxide (NO) is a gaseous diatomic radical with a wide variety of physiological and pathological implications in animal, plant and microbes. NO reacts directly with metal complexes and other radicals and indirectly as a reactive nitrogen oxide species with DNA, proteins, and lipids. In animals, NO is a signal transduction element that is synthesized by nitric oxide synthase (NOS) enzyme from L-arginine that functions in many tissues and interacts with multiple target compounds in neurotransmission, vascular smooth muscle relaxation, and platelet inhibition. In plants; NO is synthesized enzymatically by NOS like enzyme, nitrate reductase, nitrite reductase etc. and also by non-enzymatically. NO play a diverse role in plant system including plant growth, stomatal movement, iron homeostasis, protection against biotic and abiotic stresses, senescence etc. Key words: Nitric oxide (NO), nitric oxide synthase (NOS), nitrate reductase (NR), reactive oxygen species (ROS), c-GMP, L-Arginine. INTRODUTION Alfred Nobel was prescribed nitroglycerin to ease his through biomembranes. The half-life of NO in biological chest pain due to heart disease. Hundred years after it tissues is estimated to be less than 6 s (Thomas et al., was discovered that nitroglycerin - one of the key 2001). This short half-life reflects the highly reactive components of dynamite, acts through releasing nitric nature of NO. NO reacts directly with metal complexes oxide as the therapeutic agent. Nitric oxide (NO) is a and other radicals and indirectly as a reactive nitrogen gaseous radical with a wide variety of physiological and oxide species with DNA, proteins, and lipids (Wink and pathological implications in animal, plant and microbes Mitchell, 1998). In animals, NO is a signal transduction (Lamattina et al., 2003; Neill et al., 2003, 2008). element that functions in many tissues and interacts with The biological significance of nitric oxide was multiple target compounds in neurotransmission, vascular recognized by scientific community in 1992. The free smooth muscle relaxation, and platelet inhibition. The radical NO was named as the ‘Molecule of the year’ roles of NO in plants may be equally diverse. To cover a (Koshland, 1992). Subsequently, in the year 1998 the wide array of events in the synthesis and action of NO is Nobel Prize in Physiology and Medicine was awarded to a herculean task. So, in this review, we report an upto three distinguished physicians Robert F Furchgott, Louis date assessment of the biochemistry of evolution, J Ignarro and Ferid Murad for their discoveries localization, mode of action and signaling aspects of NO concerning "the nitric oxide as a signalling molecule in in plants (Figure 1). the cardiovascular system"(Lamattina et al., 2003). Plant researchers did not realize the enormous potential of NO during this period but focused NO as an BIOCHEMISTRY OF NITRIC OXIDE EVOLUTION IN atmospheric pollutant until the mid-1990s. Nitric oxide PLANTS (NO) is a gaseous free radical that diffuses readily In animal systems, NO is synthesized predominantly by the enzyme NO synthase (NOS). NOS converts L-Arg into L-citrulline in a NADPH-dependent reaction that *Corresponding author. E-mail: [email protected]. releases one molecule of NO for each molecule of L-Arg. 2730 J. Med. Plant. Res. Figure 1. Schematic representation of the nitric oxide synthesis. NOS-type enzyme also occurs in plants (Durner et al., 5. Nonenzymatic NO formation at acidic pH. 1998; Foissner et al., 2000). The traditional assay systems for mammalian enzymes have difficulty in the detection and estimation of NOS in plants. So EPR NO synthesis by nitrate reductase (NR) spectroscopy and chemiluminesence methods to detect NOS activity in plants are suggested (Corpas et al., 2004a). The plant NOS have little sequence similarity with Nitrate reductase (NR) has long been known as a source its mammalian counterpart, but still contain domains for NO (Dean and Harper, 1988). The involvement of NR which allow its redox functions to occur (Corpas et al., in NO production has been further established by nia 2004a). mutants and with plants grown in NR-free media Plants also synthesize NO from nitrite. Nitrite- (Planchet et al., 2005). The enzyme NR, reduces nitrate dependent NO production has been observed for Glyci- to nitrite at the expense of NAD(P)H, further catalyzes a ne max (soybean) by Delledonne et al. (1998) and 1-electron transfer from NAD(P)H to nitrite resulting in Helianthus annuus (sunflower) by Rockel et al. (2002), NO formation in cell free systems also (Neill et al., 2003). green algae Chlamydomonas reinhardtii (Sakihama et al., NO production by NR in vitro was reported to be higher in 2002) and Scenedesmus obliquus, and the anoxic condition yhat is in pure nitrogen (or argon) than in cyanobacterium Anabaena doliolum (Mallick et al., 1999). oxygenic condition – pure air (Planchet et al., 2005). The In some if not all of these cases, NO is likely to be low yield of NO in oxygenic cell free system is attributed produced by nitrate reductase (NR), which reduces to autoxidation of NO or by its reaction with ROS nitrate to nitrite and can further reduce nitrite to NO. produced simultaneously by NR (Yamasaki and Sakihama, 2000). Modulations of NR activity by reversible serine phosphorylation also modulate NO Nitrite-dependent NO production production (Rockel et al., 2002). Lea et al. (2004) reported a dirurnal opposite pattern to the wild type (low Several plant systems use nitrite as a substrate for NO in day and high in night) of NO emission from plants synthesis: constitutively expressing NR where serine was replaced with aspartic acid. - + A plasma membrane-bound, root-specific enzyme, NO2 + e- + 2H NO + H2O nitrite-NO oxidoreductase (Ni-NOR), may also function as This reaction is mediated by the enzyme nitrite reuctase a further source of NO. This enzyme was identified biochemically via its NO-generating activity. However, (NiR) localized in various compartments of the plant cell: unlike NR, it does not use NAD(P)H as a cofactor, but 1. Cytosolic NiR (cNiR) uses cytochrome c as an electron donor in vitro and has 2. A plasma membrane-bound NiR (PM NiR) a comparatively reduced pH optimum (Stohr and 3. Mitochondrial electron transport Stremlau, 2006). 4. Xanthine dehydrogenase/oxidase Other enzymes may also be involved in NO production Misra et al. 2731 Figure 2. Enzyme sources and compartmentalization of the production of NO in plants. (Corpas et al., 2004b). For example, in animals, xanthine species (ROS). NO reacts readily and reversibly with oxidoreductase (XOR), under hypoxic conditions, can either thiol groups in the cysteine residues of proteins or produce NO in preference to H2O2 (Millar et al., 1998). with the tripeptide glutathione (GSH) probably leading to However, Planchet and Kaiser (2006b) were unable to protein S-nitrosylation in NO signalling. Glutathione observe any NO production from recombinant xanthine concentrations are typically 2 to 3 mM in plant cells (Ball oxidase in plants. Xanthine oxidase/dehydrogenase et al., 2004) and thus, formation of S-nitrosylated (XDH). XDH has also been occasionally suggested as a glutathione (GSNO) could have a large impact on the source for NO using nitrite and xanthine as a substrate concentration of free NO. GSNO is metabolized by the (Millar et al., 1998). However recombinant XDH, gave no enzyme GSNO reductase (Diaz et al., 2003) and this evidence for NO production by the enzyme itself enzyme may be instrumental in controlling the (Planchet et al., 2005). bioavailability of NO and the formation of protein S-NO Nonenzymatic NO production can occur at pH below groups, thereby regulating such NO-regulated processes 4.5, since the pKa of nitrous acid is about 3.2. in plants (Feechan et al., 2005). NO can also interact with transition metals, particularly with haem as in guanylyl 2 HNO2 NO + NO2 + H2O 2 NO + 2 O2 + H2O cyclase or in haemoglobins (Perazzolli et al., 2004). The process of NO removal in plants is shown in Figure 3. These conditions exist in the apoplast of plant cells (Bethke et al., 2004a). A comprehensive summary of the enzymes for the Mode of action and signaling in plants production of NO and compartmentalization of NO synthesis in plants is given in Figure 2. Nitric oxide perception in plants Nitric oxide (NO) has emerged as an important endogenous signalling molecule in plants that mediates Removal of nitric oxide in plants many developmental and physiological processes NO is a reactive free radical molecule. So, it is likely that including NO synthesized in living systems by different pathways is 1. Xylogenesis, rapidly removed or metabolized after inducing the initial 2. programmed cell death, signalling events. Also an increased in the rates of NO 3. Pathogen defence, accumulation or emission not necessarily reflect an 4. Flowering, increased generation but it may actually reflect reduced 5. Stomatal closure, and rates of removal. Nitric oxide is unstable and readily react 6. Gravitropism (Delledonne,2005; Lamattina et al., 2003; with oxygen to form nitrite and nitrate (Gladwin et al., Neil et al., 2003) 2005). In both animals and plants, NO is often produced at the Experimental evidence in support of such signalling roles Same time and in the same place as reactive oxygen for NO has typically been obtained via the application of 2732 J.