NO release by nitric oxide donors in vitro and in planta

Nitric oxide mediates humic acids-induced root development and plasma membrane H+-ATPase activation

It is widely reported that some humic substances behave as exogenous auxins influencing root growth by mechanisms that are not yet completely understood. This study explores the hypothesis that the humic acids' effects on root development involve a nitric oxide signaling. Maize seedlings were treated with HA 20 mg C L(-1), IAA 0.1 nM, and NO donors (SNP or GSNO), in combination with either the auxin-signaling inhibitor PCIB, the auxin efflux inhibitor TIBA, or the NO scavenger PTIO. H(+)-transport-competent plasma membrane vesicles were isolated from roots to investigate a possible link between NO-induced H(+)-pump and HA bioactivity. Plants treated with either HA or SNP stimulated similarly the lateral roots emergence even in the presence of the auxin inhibitors, whereas NO scavenger diminished this effect. These treatments induced H(+)-ATPase stimulation by threefold, which was abolished by PTIO and decreased by auxin inhibitors. HA-induced NO synthesis was also detected in the sites of lateral roots emergence. These data depict a new scenario where the root development stimulation and the H(+)-ATPase activation elicited by either HA or exogenous IAA depend essentially on mechanisms that use NO as a messenger induced site-specifically in the early stages of lateral root development.

Proteomics reveals the overlapping roles of hydrogen peroxide and nitric oxide in the acclimation of citrus plants to salinity

Hydrogen peroxide (H(2)O(2)) and nitric oxide (*NO) are key reactive species in signal transduction pathways leading to activation of plant defense against biotic or abiotic stress. Here, we investigated the effect of pre-treating citrus plants (Citrus aurantium L.) with either of these two molecules on plant acclimation to salinity and show that both pre-treatments strongly reduced the detrimental phenotypical and physiological effects accompanying this stress. A proteomic analysis disclosed 85 leaf proteins that underwent significant quantitative variations in plants directly exposed to salt stress. A large part of these changes was not observed with salt-stressed plants pre-treated with either H(2)O(2) or sodium nitroprusside (SNP; a *NO-releasing chemical). We also identified several proteins undergoing changes either in their oxidation (carbonylation; 40 proteins) and/or S-nitrosylation (49 proteins) status in response to salinity stress. Both H(2)O(2) and SNP pre-treatments before salinity stress alleviated salinity-induced protein carbonylation and shifted the accumulation levels of leaf S-nitrosylated proteins to those of unstressed control plants. Altogether, the results indicate an overlap between H(2)O(2)- and *NO-signaling pathways in acclimation to salinity and suggest that the oxidation and S-nitrosylation patterns of leaf proteins are specific molecular signatures of citrus plant vigour under stressful conditions.

Induction of matrix metalloproteinase-1 and glioma cell motility by nitric oxide

High grade gliomas invariably recur due in a large part to tumor cells permeating normal brain in an inaccessible, diffuse manner. Previous work demonstrates that the expression of matrix metalloproteinases (MMP) contributes to this characteristic. Not only can MMPs assist a cell in traversing its environment by clearing extracellular matrix molecules, but they can also impact non-traditional downstream signals that affect a cell's ability to interact and respond to its surroundings. Contributions to the induction of MMP expression and functional significance in glioma are still under investigation. Evidence in other cancer settings indicates that nitric oxide (NO) may play a role in tumor/cell progression that can influence MMP production. Matrix metalloproteinase-1 (MMP-1), also known as interstitial collagenase, and the constitutive nitric oxide synthases (NOS) have been shown to be over-expressed in high grade gliomas. In the current study we investigated the potential involvements of NO with regard to MMP-1 and functional glioma cell movement. With the treatment of the NO donor sodium nitroprusside (SNP), there was significant induction of MMP-1 mRNA, secreted MMP-1 protein and motility of glioma cell lines within 48 h. RNA inhibition of MMP-1 through transient transfection of three MMP-1 specific siRNAs revealed a marked abrogation of the NO-mediated induction of motility. In addition, application of the NOS inhibitor N(omega)-Nitro-L-arginine methyl ester (L-NAME) impaired movement of glioma cells. These data provide evidence for a regulatory axis of high grade glioma cell movement from NO through MMP-1, with NOS inhibitor results showing promise for future pharmacologic investigation.