Biotechnological Perspective of Reactive Oxygen Species (ROS)-Mediated Stress Tolerance in Plants

All environmental cues lead to develop secondary stress conditions like osmotic and oxidative stress conditions that reduces average crop yields by more than 50% every year. The univalent reduction of molecular oxygen (O2) in metabolic reactions consequently produces superoxide anions (O2•−) and other reactive oxygen species (ROS) ubiquitously in all compartments of the cell that disturbs redox potential and causes threat to cellular organelles. The production of ROS further increases under stress conditions and especially in combination with high light intensity. Plants have evolved different strategies to minimize the accumulation of excess ROS like avoidance mechanisms such as physiological adaptation, efficient photosystems such as C4 or CAM metabolism and scavenging mechanisms through production of antioxidants and antioxidative enzymes. Ascorbate-glutathione pathway plays an important role in detoxifying excess ROS in plant cells, which includes superoxide dismutase (SOD) and ascorbate peroxidase (APX) in detoxifying O2•−radical and hydrogen peroxide (H2O2) respectively, monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) involved in recycling of reduced substrates such as ascorbate and glutathione. Efficient ROS management is one of the strategies used by tolerant plants to survive and perform cellular activities under stress conditions. The present chapter describes different sites of ROS generation and and their consequences under abiotic stress conditions and also described the approaches to overcome oxidative stress through genomics and genetic engineering

Oxidative stress and inflammatory markers in the exhaled breath condensate of children with OSA

Obstructive sleep apnea (OSA) in children has been associated with systemic inflammation and oxidative stress. Limited evidence indicates that pediatric OSA is associated with oxidative stress and inflammation in the airway. The objective of this study is to assess the hypothesis that levels of oxidative stress and inflammatory markers in the exhaled breath condensate (EBC) of children with OSA are higher than those of control subjects. Participants were children with OSA and control subjects who underwent overnight polysomnography. Morning levels of hydrogen peroxide (H2O2) and sum of nitrite and nitrate (NO (x) ) in EBC of participants were measured. Twelve subjects with moderate-to-severe OSA (mean age +/- standard deviation: 6.3 +/- 1.7 years; apnea-hypopnea index-AHI, 13.6 +/- 10.1 episodes/h), 22 subjects with mild OSA (6.7 +/- 2.1 years; AHI, 2.8 +/- 1 episodes/h) and 16 control participants (7.7 +/- 2.4 years; AHI, 0.6 +/- 0.3 episodes/h) were recruited. Children with moderate-to severe OSA had higher log-transformed H2O2 concentrations in EBC compared to subjects with mild OSA, or to control participants: 0.4 +/- 1.1 versus -0.9 +/- 1.3 (p = 0.015), or versus -1.2 +/- 1.2 (p = 0.003), respectively. AHI and % sleep time with oxygen saturation of hemoglobin < 95% were significant predictors of log-transformed H2O2 after adjustment by age and body mass index z score (p < 0.05). No significant differences were demonstrated between the three study groups in terms of EBC NO (x) levels. Children with moderate-to-severe OSA have increased H2O2 levels in morning EBC, an indirect index of altered redox status in the respiratory tract

Clinical, functional and biochemical changes during recovery from COPD exacerbations

The pathways underlying chronic obstructive pulmonary disease exacerbations (ECOPD) remain unclear. This study describes the clinical., functional and biochemical changes during recovery from ECOPD. Thirty hospitalized patients with Anthonisen's typed ECOPD were evaluated on days 0 (admission), 3, 10 and 40. A five-symptom score (TSS), performance status and quality of life were evaluated. Post-bronchodilator spirometry, blood gases, oxidative stress, C-reactive protein (CRP), serum amyloid-A (SAA), tumor necrosis factor-alpha (TNF-alpha), interteukin-6 (IL-6) and fibrinogen were also measured. Patients were classified as early- or late-recoverers, based on whether dyspnea had returned to pre-exacerbation level by day 10. Most clinical, functional and biochemical parameters improved during follow-up. CRP and IL-6 levels reduced on Day 3 (p < 0.05), whereas SAA on Day 10 (p < 0.01). TNF-alpha was reduced on Days 3 and 10, but on Day 40 its levels returned to baseline. Fibrinogen and WBC reduced only by day 40. TSS and dyspnea were correlated inversely with FEV(1) on days 3, 10 and 40. Although late-recoverers had lower FEV(1) on admission, none of the reported measurements on admission and day 3 predicted early recovery. During recovery from ECOPD, symptomatic improvement correlates only with post-bronchoditator FEV(1) whereas systemic inflammatory burden subsidence does not correlate with clinical and functional changes. Although late-recoverers have tower FEV(1) on admission, none of the measured parameters is able to predict early symptomatic recovery. (C) 2008 Elsevier Ltd. All rights reserved

Roles of sodium hydrosulfide and sodium nitroprusside as priming molecules during drought acclimation in citrus plants

Emerging evidence suggests that the gaseous molecules hydrogen sulfide (H2S) and nitric oxide (NO) enhances plant acclimation to stress; however, the underlying mechanism remains unclear. In this work, we explored if pretreatment of citrus roots with NaHS (a H2S donor) or sodium nitroprusside (SNP, a NO donor) for 2 days (d) could elicit long-lasting priming effects to subsequent exposure to PEG-associated drought stress for 21 d following a 5 d acclimation period. Detailed physiological study documented that both pretreatments primed plants against drought stress. Analysis of the level of nitrite, NOx, S-nitrosoglutahione reductase, Tyr-nitration and S-nitrosylation along with the expression of genes involved in NO-generation suggested that the nitrosative status of leaves and roots was altered by NaHS and SNP. Using a proteomic approach we characterized S-nitrosylated proteins in citrus leaves exposed to chemical treatments, including well known and novel S-nitrosylated targets. Mass spectrometry analysis also enabled the identification of 42 differentially expressed proteins in PEG alone-treated plants. Several PEG-responsive proteins were down-regulated, especially photosynthetic proteins. Finally, the identification of specific proteins that were regulated by NaHS and SNP under PEG conditions provides novel insight into long-term drought priming in plants and in a fruit crop such as citrus in particular

Application of sodium nitroprusside results in distinct antioxidant gene expression patterns in leaves of mature and senescing Medicago truncatula plants

Sodium nitroprusside (SNP) represents one of the most commonly used NO donors in biological sciences, which acts as a signal molecule in plants responsible for the regulation of the expression of many defense-related enzymes. This study attempts to provide novel insight into the effect of application of low (100 μΜ) and high (2.5 mM) concentrations of SNP on antioxidant gene expression (cAPX, GST, FeSOD, CAT, and AOX) in mature (40 day) and senescing (65 day) Medicago truncatula plants. Quantitative real-time RT-PCR suggests that low concentration of SNP applied in mature leaves leads to an overall induction of antioxidant gene expression, while increasing concentration results in suppression of these genes. Conversely, older plants demonstrate a much more variable regulation which appears to be time dependent. The observed transcriptional regulation pattern in mature M. truncatula plants comes in support of the previously documented protective or damaging effect of SNP depending on concentration applied, whereas senescing M. truncatula plants demonstrated a general suppression in antioxidant gene expression levels regardless of SNP concentration, indicative of reduced overall plant defense capacity against free radicals