Pollination-induced floral senescence in orchids: Status of oxidative stress

The orchid flowers may stay fresh in unpollinated state from few weeks to months but show rapid senescence upon pollination. Metabolic changes related to this phenomenon are less well understood in orchid flowers. Presently, two orchid species, Aerides multiflora Roxb. and Rhynchostylis retusa (L.) Bl., varying in their floral life span were evaluated for their postpollination-induced responses, involving the oxidative stress. The unpollinated flowers of A. multiflora stayed fresh for 17 days and attained senescence in 5 days after pollination (DAP), while those of R. retusa. remained fresh for 24 days and showed senescence in 7 DAP. After pollination, wilting began in 2 to 3 days in A. multiflora and 3 to 4 days in R. retusa. There was a higher electrolyte leakage accompanied by a concomitant increase in the levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), indicators of oxidative damage in all the organs after pollination while ascorbic acid decreased significantly. The flowers of A. multiflora showed a greater electrolyte leakage, MDA and H₂O₂ contents as compared to those of R. retusa. Ascorbic acid content, on the other hand, was lower in A. multiflora than in R. retusa, suggesting a higher oxidative damage to the floral organs in the former species. An application of triiodobenzoic acid ( an auxin inhibitor; 0.25 mM) and silver nitrate (ethylene inhibitor; 0.25 mM) to pollinated flowers partially prevented the oxidative damage and consequently the senescence, suggesting the involvement of these hormones. AgNO₃ was more effective in delaying senescence.     

Sequential inactivation of zeta-crystallin by o-phthalaldehyde

o-Phthalaldehyde, a bifunctional cross-linking reagent, is commonly used as a probe for the active site of enzymes. In this study, the interaction of o-phthalaldehyde with camel lens zeta-crystallin was examined by activity and fluorescence measurements. Predictably, the oxidoreductase activity of zeta-crystallin was inhibited irreversibly by o-phthalaldehyde in a time- and concentration-dependent manner, and the presence of NADPH with the enzyme appeared to provide a high degree of protection against o-phthalaldehyde inactivation. Interaction of o-phthalaldehyde with zeta-crystallin resulted in formation of isoindole adduct, which exhibited characteristic fluorescence at 415 nm. However, neither inactivation nor modification of the enzyme showed the expected pseudo-first-order kinetics; both events were highly sequential reaching different levels of saturation at different concentrations of o-phthalaldehyde. The modified enzyme had a maximum stoichiometry of 1 mol isoindole/subunit, and bound NADPH to nearly the same extent as unmodified enzyme. Gel filtration experiments suggested that o-phthalaldehyde-modified zeta-crystallin had higher apparent molecular weight than unmodified enzyme, even though the enzyme remained largely monomeric as revealed by electrophoresis on denaturing gel. These results suggested that modification by o-phthalaldehyde might have been so intrusive as to sequentially modify the tetrameric structure of zeta-crystallin.     

An inflammatory cascade leading to hyperresistinemia in humans

Background

Obesity, the most common cause of insulin resistance, is increasingly recognized as a low-grade inflammatory state. Adipocyte-derived resistin is a circulating protein implicated in insulin resistance in rodents, but the role of human resistin is uncertain because it is produced largely by macrophages.

Methods and Findings

The effect of endotoxin and cytokines on resistin gene and protein expression was studied in human primary blood monocytes differentiated into macrophages and in healthy human participants.Inflammatory endotoxin induced resistin in primary human macrophages via a cascade involving the secretion of inflammatory cytokines that circulate at increased levels in individuals with obesity. Induction of resistin was attenuated by drugs with dual insulin-sensitizing and anti-inflammatory properties that converge on NF-κB. In human study participants, experimental endotoxemia, which produces an insulin-resistant state, causes a dramatic rise in circulating resistin levels. Moreover, in patients with type 2 diabetes, serum resistin levels are correlated with levels of soluble tumor necrosis factor α receptor, an inflammatory marker linked to obesity, insulin resistance, and atherosclerosis.

Conclusions

Inflammation is a hyperresistinemic state in humans, and cytokine induction of resistin may contribute to insulin resistance in endotoxemia, obesity, and other inflammatory states.     

Synthesis and antimycobacterial activities of ring-substituted quinolinecarboxylic acid/ester analogues. Part 1

Structural optimization of recently discovered new chemical entity, 2,8-dicyclopentyl-4-methylquinoline (DCMQ; MIC= 6.25 microg/mL, M. tuberculosis H37Rv) resulted in the synthesis of four new series of ring-substituted quinolinecarboxylic acids/esters constituting 45 analogues. All new derivatives were evaluated for in vitro antimycobacterial activities against M. tuberculosis H37Rv. Certain ring-substituted-2-quinolinecarboxylic acid ester and ring-substituted-2-quinoline acetic acid ester analogues described herein showed moderate to good inhibitory activity. In particular, three analogues methyl 4,5-dicyclopentyl-2-quinolinecarboxylate (3b), methyl 4,8-dicyclopentyl-2-quinolinecarboxylate (3c) and ethyl 2-(2,8-dicyclopentyl-4-quinolyl)acetate (14g) exhibited excellent MIC values of 1.00, 2.00 and 4.00microg/mL, respectively. Results obtained indicate that substitution of the quinoline ring with dicyclopentyl substituent presumably enhances the antimycobacterial activities in the quinoline analogues described herein.     

Comparative response of maize and rice genotypes to heat stress: status of oxidative stress and antioxidants

In the present study, two genotypes each of maize and rice were compared for their response to varying degrees of temperature stress (35/30, 40/35, 45/40°C) with controls growing at 30/25°C. At elevated temperatures of 40/35 and 45/40°C, the rice genotypes were inhibited to a significantly higher extent, especially for their shoot growth compared to maize genotypes. The stress injury measured as damage to membranes, loss of chlorophyll and reduction in leaf water status was significantly higher in rice plants, especially at 45/40°C. The components of oxidative stress particularly the level of malondialdehyde was significantly greater in rice plants while the differences for hydrogen peroxide concentrations were small at 40/35 and 45/40°C. The expression of enzymatic antioxidants like catalase, ascorbate peroxidase and glutathione reductase was found to be higher in maize plants compared to rice plants while no variations existed for superoxide dismutase at 45/40°C. In addition, the non-enzymatic antioxidants like ascorbic acid, glutathione and proline were maintained at significantly greater levels at 45/40°C in maize than in rice genotypes. These findings suggested that maize genotypes were able to retain their growth under high-temperature conditions partly due to their superior ability to cope up with oxidative damage by heat stress compared to rice genotypes. Since, maize and rice belong to C₄ and C₃ plant groups, respectively, these observations may also reflect the relative sensitivity of these plant groups to heat stress.     

Abscisic acid induces heat tolerance in chickpea (Cicer arietinum L.) seedlings by facilitated accumulation of osmoprotectants

The gradual rise of global temperature is of major concern for growth and development of crops. Chickpea (Cicer arietinum L.) is a heat-sensitive crop and hence experiences damage at its vegetative and reproductive stages. Abscisic acid (ABA), a stress-related hormone, is reported to confer heat tolerance, but its mechanism is not fully known, especially whether it involves osmolytes (such as proline, glycine betaine and trehalose) in its action or not. Osmolytes too have a vital role in saving the plants from injurious effects of heat stress by multiple mechanisms. In the present study, we examined the interactive effects of ABA and osmolytes in chickpea plants grown hydroponically at varying temperatures of 30/25°C (control), 35/30, 40/35 and 45/40°C (as day/night (12?h/12?h)): (a) in the absence of ABA; (b) with ABA; and (c) in the presence of its biosynthetic inhibitor fluridone (FLU). The findings indicated severe growth inhibition at 45/40°C that was associated with drastic reduction in endogenous ABA and osmolytes compared to the unstressed plants suggesting a possible relationship between them. Exogenous application of ABA (2.5???M) significantly mitigated the seedling growth at 40/35 and 45/40°C, while FLU application intensified the inhibition. The increase in growth by ABA at stressful temperature was associated with enhancement of endogenous levels of ABA and osmolytes, while this was suppressed by FLU. ABA-treated plants experienced much less oxidative damage measured as malondialdehyde and hydrogen peroxide contents. Exogenous application of proline, glycine betaine and trehalose (10???M) also promoted the growth in heat-stressed plants and their action was not significantly affected with FLU application, suggesting that these osmolytes function downstream of ABA, mediating partially the protective effect of this hormone.     

Chemical composition and antimicrobial,antioxidant, and anti-inflammatory activities of Lepidium sativum seed oil

Lepidium sativum (garden cress) seed oil was examined for its antimicrobial, antioxidant, and anti-inflammatory activities. The oil was obtained by hydrodistillation, where gas chromatography coupled with mass spectrometry that utilized to study its chemical composition. Microdilution method was used to test the antimicrobial effect of oil against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, Klebsiella pneumoniae, and Candida albicans. The antioxidant activity was assessed by radical scavenging activity assay using 2,2-diphenyl-1-picrylhydrazyl radical. The major constituents found in the oil were 7,10-hexadecadienoic acid, 11-octadecenoic acid, 7,10,13-hexadecatrienoic acid, and behenic acid. The minimum inhibitory concentration (MIC) against all pathogens was 47.5 mg/ml, except for Salmonella enterica, which showed MIC of 90 mg/ml. The oil demonstrated antioxidant activity in a dose dependent pattern, with a half maximal inhibitory concentration (IC₅₀) value of 40 mg/ml, and exerted anti-inflammatory activity, wherein 21% protection was shown at a concentration of 300 μg/ml. Thus, L. sativum seed oil shows antimicrobial, antioxidant, and anti-inflammatory properties.     

Differential Sensitivity of Macrocarpa and Microcarpa Types of Chickpea （Cicer arietinum L.） to Water Stress： Association of Contrasting Stress Response with Oxidative Injury

Chickpea (Cicer arietinum L.) is particularly sensitive to water stress at its reproductive phase and, under conditions of water stress, will abort flowers and pods, thus reducing yield potential. There are two types of chickpea: (i) Macrocarpa (“Kabuli”), which has large, rams head‐shaped, light brown seeds; and (ii) Microcarpa (“Desi”), which has small, angular and dark‐brown seeds. Relatively speaking, “Kabuli” has been reported to be more sensitive to water stress than “Desi”. The underlying mechanisms associated with contrasting sensitivity to water stress at the metabolic level are not well understood. We hypothesized that one of the reasons for contrasting water stress sensitivity in the two types of chickpea may be a variation in oxidative injury. In the present study, plants of both types were water stressed at the reproductive stage for 14 d. As a result of the stress, the “Kabuli” type exhibited an 80% reduction in seed yield over control compared with a 64% reduction observed for the “Desi” type. The decrease in leaf water potential (Ψ_w) was faster in the “Kabuli” compared with the “Desi” type. At the end of the water stress period, Ψ_w was reduced to ?2.9 and ?3.1 MPa in the “Desi” and “Kabuli” types, respectively, without any significant difference between them. On the last day of stress, “Kabuli” experienced 20% more membrane injury than “Desi”. The chlorophyll content and photosynthetic rate were significantly greater in “Desi” compared with “Kabuli”. The malondialdehyde and H₂O₂ content were markedly higher at the end of the water stress in “Kabuli” compared with “Desi”, indicating greater oxidative stress in the former. Levels of anti‐oxidants, such as ascorbic acid and glutathione, were significantly higher in “Desi” than “Kabuli”. Superoxide dismutase and catalase activity did not differ significantly between the two types of chickpea, whereas on the 10th day, the activities of ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase were higher in “Desi”. These findings indicate that the greater stress tolerance in the “Desi” type may be ascribed to its superior ability to maintain better water status, which results in less oxidative damage. In addition, laboratory studies conducted by subjecting both types of chickpea to similar levels of polyethylene glycol‐induced water stress and to 10 μ.mol/L abscisic acid indicated a greater capacity of the “Desi” type to deal with oxidative stress than the “Kabuli” type. (Managing editor: Ping He)     

Exogenous Proline Application Reduces Phytotoxic Effects of Selenium by Minimising Oxidative stress and Improves Growth in Bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.) Seedlings

Bean (Phaseolus vulgaris L.) seedlings were subjected to varying selenium levels (1, 2, 4, and 6 ppm) in a hydroponic culture. The germination reached 100% in 48 h in all Se levels except 6 ppm, where it took 72 h. The root and shoot growth was stimulated at 1 and 2 ppm Se levels that was commensurate with increase in chlorophyll content, leaf water content, and cellular respiration. At 4 and 6 ppm Se levels, the growth was inhibited appreciably, which was associated with increase in stress injury measured as damage to membranes and decrease in cellular respiration, chlorophyll, and leaf water content. The oxidative injury as elevation of lipid peroxidation was larger compared to hydrogen peroxide accompanied by reduced levels of enzymatic (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) and non-enzymatic (ascorbic acid and glutathione) antioxidants. Proline content was significantly higher at 1 and 2 ppm Se but diminished considerably at 4 and 6 ppm levels concomitant with the reduced growth. Exogenous application of proline (50 μM) resulted in substantiation of its endogenous levels that antagonised the toxic effects of Se by improving the growth of seedlings. The stress injury was reduced significantly with simultaneous increase in enzymatic and non-enzymatic antioxidants. Especially the components of ascorbate–glutathione cycle showed larger stimulation with proline application. The role of proline in mitigating the toxic effects of Se is discussed.