Although nitric oxide synthase (NOS) proteins homologous to mammalian NOS are absent in terrestrial plants (embryophytes), they are present in various algal groups. Of the 367 algal species for which genome data is available on the NCBI database, 40 proteins belonging to 36 species in various algal classes have been identified. The sporadic distribution of NOS orthologues across the algae phylogenetic tree raises the question of why this enzyme is absent in most species. Genome and recent transcriptome sequencing in Klebsormidiophyceae provided an opportunity to study the evolution of NOS sequences in closely related organisms. Based on a dataset comprising 18 species, including 13 Klebsormidium species, we showed that only eight species possess complete or partial NOS sequences. Both in silico and experimental approaches suggest that the divergence observed in Klebsormidiophyceae NOS genes, compared to their human homologs, reflect specific modifications, including putative pseudogenization. Indeed, although copies of genes encoding NOS are expressed in certain species of algae, some are evolving into non-functional copies through the accumulation of mutations, which could affect the synthesis of a functional protein. This process may be considered relatively recent in Charophytes history since the presence or absence of a gene can be observed in very closely related species.

Nitric oxide (NO) gas continues to be a widely studied and versatile treatment given its broad spectrum of physiological effects such as pulmonary vasodilation, improvement of oxygenation, anti-inflammatory, and antimicrobial effects. The idea of administering a pulsed dose of inhaled NO (PiNO) at the beginning of inhalation was developed in the last 20 years as an alternative to continuous inhalation of NO (CiNO) through the respiratory cycle. Across multiple studies, PiNO has repeatedly demonstrated similarly efficacious pulmonary vasodilation and oxygenation improvement as CiNO administration while consistently reducing total NO exposure and nitrogen dioxide (NO2) formation. PiNO has proven to be an effective adjunctive treatment for patients with primary pulmonary hypertension among spontaneously breathing patients. In patients with chronic obstructive pulmonary disease (COPD), PiNO reduced pulmonary vascular resistance (PVR) in the short term, though further research remains necessary to demonstrate long-term benefits. Similarly, PiNO use in patients with interstitial lung disease has been associated with subjective improvements in exercise tolerance and quality of life. The effect of PiNO on PVR was also confirmed in mechanically ventilated subjects. In this setting, PiNO reduced anesthesia-associated hypoxemia and improved shunt fraction and oxygenation. Overall, the scientific body of evidence surrounding PiNO supports it as a safe, effective, and efficient alternative to CiNO delivery that can be utilized in a wide range of clinical settings. Future research may continue to expand the application of PiNO to different clinical settings.

Nitric oxide (•NO) is a central regulator of plant development and stress responses, but recent evidence shows that reactive nitrogen signaling involves more than •NO alone. Nitroxyl (HNO), the one-electron-reduced and protonated form of •NO, has emerged as a distinct signaling molecule in plants with unique chemical and functional properties. Unlike •NO, HNO is a non-radical, thiophilic species that acts as a selective redox modulator rather than a freely diffusible messenger. Improved detection methods have confirmed endogenous HNO formation in plant cells, with basal nanomolar concentrations under optimal conditions and reversible changes during key developmental stages and stress responses, such as senescence and hypoxia. HNO production and stability are closely regulated by intracellular redox status and interconvert dynamically with •NO through non-enzymatic reactions involving cellular reductants such as ascorbate, hydrogen sulfide, and low-molecular-weight thiols. This interplay establishes the •NO/HNO balance as a redox-sensitive signaling switch, increasing the informational capacity of reactive nitrogen networks. Functional and transcriptomic studies indicate that HNO participates in hormone signaling, especially in ethylene-mediated pathways, and supports plant adaptation to redox-related stresses. This review summarizes current knowledge of HNO chemistry, regulation, detection, and function in plants, and identifies key open questions. Including HNO in plant signaling frameworks provides a more nuanced and comprehensive view of redox-regulated plant physiology.

Reactive nitrogen species (RNS) are signalling molecules triggering several defence responses during plant stress. The highest importance has nitric oxide (NO), involved in the post-translational modifications, including protein S-nitrosation of target cysteine residues. Aminoaldehyde dehydrogenases (AMADHs) catalyze the NAD(P)[+]-dependent oxidation of various ω-amino aldehydes to the corresponding amino acids. Here, we focused on the dynamic redox regulation of AMADH activity in pea (Pisum sativum). We used the reversible S-nitrosation approach and studied the effect of NO donors on the activity of two AMADHs. LC-MS/MS analysis combined with structural mapping revealed selective modification of spatially accessible cysteine residues, whereas the catalytic Cys294 was detected predominantly in the methylthionylated form, consistent with its largely reduced state under the applied experimental conditions. These findings suggest that S-nitrosation modulates PsAMADH activity in a structurally constrained manner without directly disrupting the catalytic core. Inhibition of AMADH activity in roots of different pea genotypes was accompanied by increased RNS/NO accumulation, suggesting that nitrosative modulation of PsAMADH activity represents an important component of redox regulation in vivo.

Pulmonary function tests are performed throughout the day, yet time-of-day effects on spirometry and pulmonary diffusing capacities for nitric oxide (DLNO) and carbon monoxide (DLCO) are poorly characterized, and DLNO's diurnal behavior is unknown. We examined whether these measurements vary in healthy men and derived within-day limits of change. Thirty-eight men (median age, 29.8 years) underwent up to six testing sessions during one waking day. Each session included spirometry (FVC, FEV1, SVC, and FEV1/FVC), followed by single-breath DLNO/DLCO testing to obtain DLCO, DLNO, alveolar volume (VA), transfer coefficients KCO and KNO, and the DLNO/DLCO ratio. Time-of-day effects were assessed using linear mixed-effects models with subject-specific random intercepts; within-subject variability was quantified using the within-subject standard deviation. After quality filtering and multiplicity adjustment, FVC, FEV1, SVC, DLNO, DLCO, and VA decreased across the day (q ≤ 0.014). KCO declined before but not after false-discovery-rate adjustment (p = 0.041, q = 0.058); FEV1/FVC, KNO, and DLNO/DLCO did not change significantly. Within-day variability ranged from 1.5% for SVC to 3.5% for DLCO. One-sided 95% within-day change limits were approximately 11 mL/min/mmHg for DLNO (z-score, 0.59), 2.8 mL/min/mmHg for DLCO (z-score, 0.59), 0.28 L for VA (z-score, 0.35), and 0.27 for DLNO/DLCO. Spirometric volumes and absolute diffusing capacities declined from morning to evening, consistent with decreasing VA, whereas ratio and transfer-coefficient indices were largely stable. Serial measurements should be performed at consistent times. These limits reflect measurement error plus short-term physiological or procedural variation and are specific to this device, protocol, and population.

The activity of S-nitrosoglutathione reductase (ADH5/GSNOR) has been proposed being essential to limit oxidative stress and preserve mitochondrial quality control. Here we identify a redox-dependent ATM-CHK2-SOD1 signaling axis that drives ADH5/GSNOR transcription in SH-SY5Y cells expressing the ALS-associated SOD1[G93A] mutant. ATM-CHK2 activation promotes the interaction of SOD1 with CHK2, leading to SOD1 nuclear translocation and binding to the ADH5 promoter. Pharmacological inhibition of ATM or CHK2 abolishes these effects. ADH5/GSNOR overexpression protects cells from SOD1[G93A]-induced toxicity suggesting that the modulation of GSNOR activity may represent a potential strategy to restore redox homeostasis in ALS.

6-Phosphogluconate dehydrogenase (6PGDH) functions in the oxidative phase of the pentose phosphate pathway (oxiPPP), together with glucose-6-phosphate dehydrogenase (G6PDH). These two enzymes play central roles in cellular NADPH generation. In pepper fruit, two genes were identified in the transcriptome, designated Ca6PGDH1 and Ca6PGDH2, which appear to encode a peroxisomal and a plastidial putative isozyme, respectively. During ripening, Ca6PGDH1 exhibited only minor changes in its expression, whereas Ca6PGDH2 was markedly downregulated. The expression patterns of both genes diverged in response to exposure to a nitric oxide (NO)-enriched atmosphere and melatonin, while both NO and melatonin treatments partially mitigated the downregulation of Ca6PGDH2 but not that of Ca6PGDH1. At the enzymatic level, the total 6PGDH activity exhibited a modest decline during ripening. Isoenzymatic analysis using non-denaturing polyacrylamide gel electrophoresis revealed three distinct isozymes, designated 6PGDH I to III, in order of increasing electrophoretic mobility. In vitro assays examining the effects of various reducing agents, including glutathione (GSH) and l-cysteine (L-Cys), as well as signaling molecules such as NO, peroxynitrite (ONOO[-]), hydrogen sulfide (H2S), and cyanide, showed that the NO donors and H2S exerted inhibitory effects on some isozymes, with the strongest inhibition observed for Ca6PGDH III whereas reducing compounds (GSH and Cys) protected against these inhibitory effects. Together, these results highlight Ca6PGDH as a redox-sensitive enzyme that may contribute to metabolic and signaling homeostasis during pepper fruit ripening.

Nitric oxide (NO) is a direct regulator of mitochondrial respiration. Nitrate (NO3[-]) and nitrite (NO2[-]) are good sources of NO, but whether their effects on mitochondrial respiration differ between in vivo and in vitro administration remains unclear. In Study 1, 8 participants consumed NO3[-] -rich beetroot juice (BR) (∼12.8 mmol NO3[-]) and NO3[-] -depleted placebo beetroot juice (PL) (∼0.08 mmol NO3[-]) acutely and chronically for 2 weeks in a randomised, double-blind, crossover design. A substrate-uncoupler-inhibitor titration (SUIT) protocol was used to assess mitochondrial respiration using high-resolution respirometry (oxygen tension: ∼200-450 μM) in permeabilized muscle fibres. In Study 2, skeletal muscle samples were collected from 11 participants. In a randomised, crossover design, different doses (0, 1.5, and 3.0 μM) of sodium nitrite (NaNO2) were administered to permeabilized muscle fibres. Mitochondrial respiration was measured using the same SUIT protocol under lower oxygen tension (∼50-200 μM). Although muscle NO3[-] concentration significantly increased after both acute and chronic BR supplementation, mitochondrial respiration and exercise performance did not differ between PL and BR in either condition. Similarly, absolute oxygen flux across different respiratory states were not different between different doses of NaNO2. However, the leak control ratio, reflecting the degree of uncoupling of mitochondrial respiration, was significantly higher with 3.0 μM NaNO2 administration (0.12 ± 0.05) compared to 0 μM NaNO2 administration (0.09 ± 0.04, P = 0.03). These findings, involving both in vivo and in vitro administration approaches, albeit in the presence of relatively high oxygen concentrations, suggest that neither NO3[-] nor NO2[-] improves mitochondrial respiration, at least in young healthy adults.