Oxyleghemoglobin scavenges nitrogen monoxide and peroxynitrite: a possible role in functioning nodules?

It has been demonstrated that the NO• produced by nitric oxide synthase or by the reduction of nitrite by nitrate reductase plays an important role in plants' defense against microbial pathogens. The detection of nitrosyl Lb in nodules strongly suggests that NO• is also formed in functional nodules. Moreover, NO• may react with superoxide (which has been shown to be produced in nodules by various processes), leading to the formation of peroxynitrite. We have determined the second-order rate constants of the reactions of soybean oxyleghemoglobin with nitrogen monoxide and peroxynitrite. At pH 7.3 and 20°C, the values are on the order of 108 and 104M−1s−1, respectively. In the presence of physiological amounts of CO2 (1.2mM), the second-order rate constant of the reaction of oxyleghemoglobin peroxynitrite is even larger (105M−1s−1). The results presented here clearly show that oxyleghemoglobin is able to scavenge any NO• and peroxynitrite formed in functional nodules. This may help to stop NO• triggering a plant defense reactio

Kinetics and mechanistic studies of the reactions of metleghemoglobin, ferrylleghemoglobin, and nitrosylleghemoglobin with reactive nitrogen species

It is now established that nitrogen monoxide is produced not only in animals but also in plants. However, much less is known about the pathways of generation and the functions of $${\text{NO}}^ \bullet$$ in planta. One of the possible targets of $${\text{NO}}^ \bullet$$ is leghemoglobin (Lb), the hemoprotein found in high concentrations in the root nodules of legumes that establish a symbiosis with nitrogen-fixing bacteria. In analogy to hemoglobin and myoglobin, we have shown that different forms of Lb react not only with $${\text{NO}}^ \bullet$$ , but also with so-called reactive nitrogen species derived from it, among others peroxynitrite and nitrite. Because of the wider active-site pocket, the rate constants measured in this work for $${\text{NO}}^ \bullet$$ and for nitrite binding to metLb are 1order of magnitude larger than the corresponding values for binding of these species to metmyoglobin and methemoglobin. Moreover, we showed that reactive nitrogen species are able to react with two forms of Lb that are produced in vivo but that cannot bind oxygen: ferrylLb is reduced by $${\text{NO}}^ \bullet$$ and nitrite, and nitrosylLb is oxidized by peroxynitrite. The second-order rate constants of these reactions are on the order of 102, 106, and 105M−1s−1, respectively. In all cases, the final reaction product is metLb, a further Lb form that has been detected in vivo. Since a specific reductase is active in nodules, which reduces metLb, reactive nitrogen species could contribute to the recycling of these inactive forms to regenerate deoxyLb, the oxygen-binding form of L

Glutathione plays a fundamental role in growth and symbiotic capacity of Sinorhizobium meliloti

Rhizobia form a symbiotic relationship with plants of the legume family to produce nitrogen-fixing root nodules under nitrogen-limiting conditions. We have examined the importance of glutathione (GSH) during free-living growth and symbiosis of Sinorhizobium meliloti. An S. meliloti mutant strain (SmgshA) which is unable to synthesize GSH due to a gene disruption in gshA, encoding the enzyme for the first step in the biosynthesis of GSH, was unable to grow under nonstress conditions, precluding any nodulation. In contrast, an S. meliloti strain (SmgshB) with gshB, encoding the enzyme involved in the second step in GSH synthesis, deleted was able to grow, indicating that γ- glutamylcysteine, the dipeptide intermediate, can partially substitute for GSH. However, the SmgshB strain showed a delayed-nodulation phenotype coupled to a 75% reduction in the nitrogen fixation capacity. This phenotype was linked to abnormal nodule development. Both the SmgshA and SmgshB mutant strains exhibited higher catalase activity than the wild-type S. meliloti strain, suggesting that both mutant strains are under oxidative stress. Taken together, these results show that GSH plays a critical role in the growth of S. meliloti and during its interaction with the plant partner.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia Molecula

Glutathione plays a fundamental role in growth and symbiotic capacity of Sinorhizobium meliloti

Rhizobia form a symbiotic relationship with plants of the legume family to produce nitrogen-fixing root nodules under nitrogen-limiting conditions. We have examined the importance of glutathione (GSH) during free-living growth and symbiosis of Sinorhizobium meliloti. An S. meliloti mutant strain (SmgshA) which is unable to synthesize GSH due to a gene disruption in gshA, encoding the enzyme for the first step in the biosynthesis of GSH, was unable to grow under nonstress conditions, precluding any nodulation. In contrast, an S. meliloti strain (SmgshB) with gshB, encoding the enzyme involved in the second step in GSH synthesis, deleted was able to grow, indicating that γ- glutamylcysteine, the dipeptide intermediate, can partially substitute for GSH. However, the SmgshB strain showed a delayed-nodulation phenotype coupled to a 75% reduction in the nitrogen fixation capacity. This phenotype was linked to abnormal nodule development. Both the SmgshA and SmgshB mutant strains exhibited higher catalase activity than the wild-type S. meliloti strain, suggesting that both mutant strains are under oxidative stress. Taken together, these results show that GSH plays a critical role in the growth of S. meliloti and during its interaction with the plant partner.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia Molecula

(Homo)glutathione Deficiency Impairs Root-knot Nematode Development in Medicago truncatula

Root-knot nematodes (RKN) are obligatory plant parasitic worms that establish and maintain an intimate relationship with their host plants. During a compatible interaction, RKN induce the redifferentiation of root cells into multinucleate and hypertrophied giant cells essential for nematode growth and reproduction. These metabolically active feeding cells constitute the exclusive source of nutrients for the nematode. Detailed analysis of glutathione (GSH) and homoglutathione (hGSH) metabolism demonstrated the importance of these compounds for the success of nematode infection in Medicago truncatula. We reported quantification of GSH and hGSH and gene expression analysis showing that (h)GSH metabolism in neoformed gall organs differs from that in uninfected roots. Depletion of (h)GSH content impaired nematode egg mass formation and modified the sex ratio. In addition, gene expression and metabolomic analyses showed a substantial modification of starch and γ-aminobutyrate metabolism and of malate and glucose content in (h)GSH-depleted galls. Interestingly, these modifications did not occur in (h)GSH-depleted roots. These various results suggest that (h)GSH have a key role in the regulation of giant cell metabolism. The discovery of these specific plant regulatory elements could lead to the development of new pest management strategies against nematodes

Low loss coatings for the VIRGO large mirrors

présentée par L. PinardThe goal of the VIRGO program is to build a giant Michelson type interferometer (3 kilometer long arms) to detect gravitational waves. Large optical components (350 mm in diameter), having extremely low loss at 1064 nm, are needed. Today, the Ion beam Sputtering is the only deposition technique able to produce optical components with such performances. Consequently, a large ion beam sputtering deposition system was built to coat large optics up to 700 mm in diameter. The performances of this coater are described in term of layer uniformity on large scale and optical losses (absorption and scattering characterization). The VIRGO interferometer needs six main mirrors. The first set was ready in June 2002 and its installation is in progress on the VIRGO site (Italy). The optical performances of this first set are discussed. The requirements at 1064 nm are all satisfied. Indeed, the absorption level is close to 1 ppm (part per million), the scattering is lower than 5 ppm and the R.M.S. wavefront of these optics is lower than 8 nm on 150 mm in diameter. Finally, some solutions are proposed to further improve these performances, especially the absorption level (lower than 0.1 ppm) and the mechanical quality factor Q of the mirrors (thermal noise reduction)

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Oxyleghemoglobin scavenges nitrogen monoxide and peroxynitrite: A possible role in functioning nodules?

ISSN:0949-8257ISSN:1432-132

Kinetics and mechanistic studies of the reactions of metleghemoglobin, ferrylleghemoglobin, and nitrosylleghemoglobin with reactive nitrogen species

ISSN:0949-8257ISSN:1432-132