1-3-dihydroxy-4-4-5-5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole and cobaltous-chloride

In response to flooding/waterlogging, plants develop various anatomical changes including the formation of lysigenous aerenchyma for the delivery of oxygen to roots. Under hypoxia, plants produce high levels of nitric oxide (NO) but the role of this molecule in plant-adaptive response to hypoxia is not known. Here, we investigated whether ethylene-induced aerenchyma requires hypoxia-induced NO. Under hypoxic conditions, wheat roots produced NO apparently via nitrate reductase and scavenging of NO led to a marked reduction in aerenchyma formation. Interestingly, we found that hypoxically induced NO is important for induction of the ethylene biosynthetic genes encoding ACC synthase and ACC oxidase. Hypoxia-induced NO accelerated production of reactive oxygen species, lipid peroxidation, and protein tyrosine nitration. Other events related to cell death such as increased conductivity, increased cellulase activity, DNA fragmentation, and cytoplasmic streaming occurred under hypoxia, and opposing effects were observed by scavenging NO. The NO scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt) and ethylene biosynthetic inhibitor CoCl

Topics: Benzoates; Cobalt; Ethylenes; Imidazoles; Nitrate Reductase; Nitric Oxide; Nitrites; Oxygen; Plant Growth Regulators; Plant Proteins; Plant Roots; Reactive Oxygen Species; Signal Transduction; Stress, Physiological; Triticum

The key player for adaptation to reduced oxygen availability is the transcription factor hypoxia-inducible factor 1 (HIF-1), composed of the redox-sensitive HIF-1alpha and the constitutively expressed HIF-1beta subunits. Under normoxic conditions, HIF-1alpha is rapidly degraded, whereas hypoxia, CoCl(2), or desferroxamine promote protein stabilization, thus evoking its transcriptional activity. Because HIF-1 is regulated by reactive oxygen species, investigation of the impact of reactive nitrogen species was intended. By using different nitric oxide (NO) donors, dose- and time-dependent HIF-1alpha accumulation in close correlation with the release of NO from chemically distinct NO donors was established. Intriguingly, small NO concentrations induced a faster but transient HIF-1alpha accumulation than higher doses of the same NO donor. In contrast, NO attenuated up-regulation of HIF-1alpha evoked by CoCl(2) in a concentration- and time-dependent manner, whereas the desferroxamine-elicited HIF-1alpha signal remained unaltered. To demonstrate an autocrine or paracrine signaling function of NO, we overexpressed the inducible NO synthase and used a coculture system of activated macrophages and tubular cells. Expression of the NO synthase induced HIF-1alpha accumulation, which underscored the role of NO as an intracellular activator for HIF-1. In addition, macrophage-derived NO triggered HIF-1alpha up-regulation in LLC-PK(1) target cells, which points to intercellular signaling properties of NO in achieving HIF-1 accumulation. Our results show that NO does not only modulate the HIF-1 response under hypoxic conditions, but it also functions as a HIF-1 inducer. We conclude that accumulation of HIF-1 occurs during hypoxia but also under inflammatory conditions that are characterized by sustained NO formation.

Topics: Animals; Benzoates; Cell Hypoxia; Cell Line; Cobalt; Coculture Techniques; Deferoxamine; DNA-Binding Proteins; Dose-Response Relationship, Drug; Enzyme Inhibitors; Gene Expression Regulation; Glutathione; Guanylate Cyclase; Hydrazines; Hypoxia-Inducible Factor 1; Hypoxia-Inducible Factor 1, alpha Subunit; Imidazoles; Inflammation; Kidney Tubules, Proximal; Macrophage Activation; Macrophages; Mice; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitrogen Oxides; Nitroso Compounds; Nuclear Proteins; Oxadiazoles; Oxazines; S-Nitrosoglutathione; Spermine; Swine; Transcription Factors