Nitric Oxide: Its Generation and Interactions with Other Reactive Signaling Compounds.

Nitric oxide (NO) is an immensely important signaling molecule in animals and plants. It is involved in plant reproduction, development, key physiological responses such as stomatal closure, and cell death. One of the controversies of NO metabolism in plants is the identification of enzymatic sources.

Role of nitric oxide in regulating stomatal apertures.

During stomatal closure, nitric oxide (NO) operates as one of the key intermediates in the complex, abscisic acid (ABA)-mediated, guard cell signaling network that regulates this process. However, data concerning the role of NO in stomatal closure that occurs in turgid vs. dehydrated plants is limited.

Tools to investigate reaction oxygen species-sensitive signaling proteins.

The thiol groups ofcysteine residues on proteins are attractive oxidative targets for modification by reactive oxygen species, such as hydrogen peroxide (H2O2). Such modification can lead to important cellular signaling processes that ultimately result in modification of the physiology of the organism. To identify such proteins that are amenable to oxidative modification, different methods can be used.

Differential requirement for NO during ABA-induced stomatal closure in turgid and wilted leaves.

Abscisic acid (ABA)-induced stomatal closure is mediated by a complex, guard cell signalling network involving nitric oxide (NO) as a key intermediate. However, there is a lack of information concerning the role of NO in the ABA-enhanced stomatal closure seen in dehydrated plants. The data herein demonstrate that, while nitrate reductase (NR)1-mediated NO generation is required for the ABA-induced closure of stomata in turgid leaves, it is not required for ABA-enhanced stomatal closure under conditions leading to rapid dehydration.

The histidine kinase AHK5 integrates endogenous and environmental signals in Arabidopsis guard cells.

Background: Stomatal guard cells monitor and respond to environmental and endogenous signals such that the stomatal aperture is continually optimised for water use efficiency. A key signalling molecule produced in guard cells in response to plant hormones, light, carbon dioxide and pathogen-derived signals is hydrogen peroxide (H(2)O(2)). The mechanisms by which H(2)O(2) integrates multiple signals via specific signalling pathways leading to stomatal closure is not known.

Expression analysis of Arabidopsis vacuolar sorting receptor 3 reveals a putative function in guard cells.

Vacuolar sorting receptors (VSRs) are responsible for the proper targeting of soluble cargo proteins to their destination compartments. The Arabidopsis genome encodes seven VSRs. In this work, the spatio-temporal expression of one of the members of this gene family, AtVSR3, was determined by RT-PCR and promoter::reporter gene fusions.

Nitric oxide synthesis and signalling in plants.

As with all organisms, plants must respond to a plethora of external environmental cues. Individual plant cells must also perceive and respond to a wide range of internal signals. It is now well-accepted that nitric oxide (NO) is a component of the repertoire of signals that a plant uses to both thrive and survive.

Ethylene-induced stomatal closure in Arabidopsis occurs via AtrbohF-mediated hydrogen peroxide synthesis.

Ethylene is a plant hormone that regulates many aspects of growth and development. Despite the well-known association between ethylene and stress signalling, its effects on stomatal movements are largely unexplored. Here, genetic and physiological data are provided that position ethylene into the Arabidopsis guard cell signalling network, and demonstrate a functional link between ethylene and hydrogen peroxide (H(2)O(2)).

ABA-induced NO generation and stomatal closure in Arabidopsis are dependent on H2O2 synthesis.

Nitric oxide (NO) and hydrogen peroxide (H(2)O(2)) are key signalling molecules produced in response to various stimuli and involved in a diverse range of plant signal transduction processes. Nitric oxide and H(2)O(2) have been identified as essential components of the complex signalling network inducing stomatal closure in response to the phytohormone abscisic acid (ABA). A close inter-relationship exists between ABA and the spatial and temporal production and action of both NO and H(2)O(2) in guard cells.

Proteomic identification of glyceraldehyde 3-phosphate dehydrogenase as an inhibitory target of hydrogen peroxide in Arabidopsis.

Hydrogen peroxide (H2O2) is now recognised as a key signalling molecule in eukaryotes. In plants, H2O2 is involved in regulating stomatal closure, gravitropic responses, gene expression and programmed cell death. Although several kinases, such as oxidative signal-inducible 1 (OXI1) kinase and mitogen-activated protein kinases are known to be activated by exogenous H2O2, little is known about the proteins that directly react with H2O2.

Fungal elicitor induces singlet oxygen generation, ethylene release and saponin synthesis in cultured cells of Panax ginseng C. A. Meyer.

Singlet oxygen is a high-energy molecular oxygen species. As one of the most active intermediates involved in chemical and biochemical reactions, singlet oxygen plays essential roles in plant responses to UV and strong light. Here, we report that Cle, an elicitor derived from fungal cell walls, induces the generation of singlet oxygen in cell cultures of ginseng, Panax ginseng.

Gibberellin-regulated XET is differentially induced by auxin in rice leaf sheath bases during gravitropic bending.

The asymmetric distribution of auxin plays a fundamental role in plant gravitropism, yet little is understood about how its lateral distribution stimulates growth. In the present work, the asymmetric distribution not only of auxin, but also that of gibberellins (GAs), was observed in rice leaf sheath bases following gravistimulation. Gravistimulation induced the transient accumulation of greater amounts of both IAA and GA in the lower halves of the leaf sheath bases of rice seedlings.

Nitric oxide mediates gravitropic bending in soybean roots.

Plant roots are gravitropic, detecting and responding to changes in orientation via differential growth that results in bending and reestablishment of downward growth. Recent data support the basics of the Cholodny-Went hypothesis, indicating that differential growth is due to redistribution of auxin to the lower sides of gravistimulated roots, but little is known regarding the molecular details of such effects. Here, we investigate auxin and gravity signal transduction by demonstrating that the endogenous signaling molecules nitric oxide (NO) and cGMP mediate responses to gravistimulation in primary roots of soybean (Glycine max).

Mitogen-activated protein kinases mediate the oxidative burst and saponin synthesis induced by chitosan in cell cultures of Panax ginseng.

Chitosan (CHN) specially induced the activities of 39 kD and 42 kD protein kinases in ginseng cells, which could be suppressed by an inhibitor of mitogen-activated protein kinase (MAPK) pathway, PD98059. The immunoprecipitation (IP) using MAPK antibody or kinase assay in vitro also showed that CHN-induced 42 kD and 39 kD protein kinases belonged to the MAPK family. PD98059 suppressed CHN-induced transcriptions of ginseng squalene synthase and ginseng squalene epoxidase genes (gss and gse), CHN-induced accumulation of beta-Amyrin synthase (beta-AS) and synthesis of saponin.

Induction of defence gene expression by oligogalacturonic acid requires increases in both cytosolic calcium and hydrogen peroxide in Arabidopsis thaliana.

Responses to oligogalacturonic acid (OGA) were determined in transgenic Arabidopsis thaliana seedlings expressing the calcium reporter protein aequorin. OGA stimulated a rapid, substantial and transient increase in the concentration of cytosolic calcium ([Ca2+]cyt) that peaked after ca. 15 s.

Cytochrome c, glutathione, and the possible role of redox potentials in apoptosis.

The redox environment of the cell is now thought to be extremely important to control the activity of many proteins. During apoptosis, the intracellular redox potential (E(h)) becomes more positive, with possible consequences for the mechanisms of apoptosis. Glutathione and cytochrome c might both influence and be influenced by the cellular redox environment and therefore be important in the progression of apoptosis.

ABA, hydrogen peroxide and nitric oxide signalling in stomatal guard cells.

Increased synthesis and redistribution of the phytohormone abscisic acid (ABA) in response to water deficit stress initiates an intricate network of signalling pathways in guard cells leading to stomatal closure. Despite the large number of ABA signalling intermediates that are known in guard cells, new discoveries are still being made. Recently, the reactive oxygen species hydrogen peroxide (H2O2) and the reactive nitrogen species nitric oxide (NO) have been identified as key molecules regulating ABA-induced stomatal closure in various species.

New equations for redox and nano-signal transduction.

Cells maintain redox potentials (Eh) in intracellular compartments, sometimes referred to as redox environments. These potentials are often very reducing, for example in the cytoplasm, but throughout the cell different potentials are maintained, commensurate with the functionality of that particular part of the cell. Furthermore, within a simple cellular compartment, "hot-spots" of redox poise may be maintained.

Nitric oxide mediates elicitor-induced saponin synthesis in cell cultures of Panax ginseng.

The elicitor oligogalacturonic acid (OGA) stimulated nitric oxide (NO) accumulation in the growth medium of ginseng suspension cultures and induced increased nitric oxide synthase (NOS) activity in ginseng cells. OGA also stimulated accumulation of saponin, transcription of genes encoding squalene synthase (sqs) and squalene epoxidase (sqe), two early enzymes of saponin synthesis, and the accumulation of β-amyrin synthase protein (β-AS). Saponin accumulation, sqs and sqe gene expression, and increases in β-AS content were also induced by exposure to NO via the NO donor sodium nitroprusside (SNP).

Nitric oxide signalling in plants.

Recently nitric oxide (NO) has emerged as a key signalling molecule in plants. Here we review the potential sources of endogenous NO, outline the biological processes likely to be mediated by NO, and discuss the downstream signalling processes by which NO exerts its cellular effects. It will be important to develop methods to quantify intracellular NO synthesis and release.

Hydrogen peroxide and nitric oxide as signalling molecules in plants.

It is now clear that hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) function as signalling molecules in plants. A wide range of abiotic and biotic stresses results in H(2)O(2) generation, from a variety of sources. H(2)O(2) is removed from cells via a number of antioxidant mechanisms, both enzymatic and non-enzymatic.