Carbon Monoxide Alleviates Salt-Induced Oxidative Damage in Wheat Seedling Leaves

Carbon monoxide （CO）, a by-product released during the degradation of heme by heme oxygenases （EC 1.14.99.3） In animals, is regarded as an important physiological messenger or bioactive molecule involved in many biological events that has been recently reported as playing a major role in mediating the cytoprotectlon against oxidant-induced lung Injury. In the present study, we first determined the protective effect of exogenous CO against salt-induced oxidative damage in wheat seedling leaves. Wheat seedlings treated with 0.01μmol/L hematin as the CO donor demonstrated significant reversal of chlorophyll decay, dry weight, and water loss induced by 300 mmol/L NaCl stress. Interestingly, the increase in lipid peroxidation observed in salt-treated leaves was reversed by 0.01μmol/L hematin treatment. Time-couree analyses showed that application of 0.01μmol/L hematln enhanced gualacol peroxidase, superoxide dismutase, ascorbate peroxidase and catalase activities in wheat seedling leaves subjected to salt stress. These effects are specific for CO because the CO scavenger hemoglobin （1.2 mg/L） blocked the actions of the CO donor hematln. However, higher concentration of the CO donor （1.0μmol/L） did not alleviate dry weight and water loss of salt-stressed wheat seedlings. These results suggest that exogenous application of low levels of a CO donor may be advantageous against salinity toxicity.     

Carbon Monoxide Alleviates Wheat Seed Germination Inhibition and Counteracts Lipid Peroxidation Mediated by Salinity

Recently In animals, endogenous carbon monoxide （CO）, like nitric oxlde, was implicated as another Important physiological messenger or bioactive molecule. However, little information is known about the physlologlcal roles of CO in the whole plant. In the present study, we report that different concentrations of the 130 donor hematin （0.1, 1.0 and 10.0 μmol/L） alleviated wheat （Tilticum aestivum L. Yangmai 158） seed germination Inhlbltlon caused by 250 mmol/L NaCI stress In a dose-dependent manner. These responses were also proved by the addltion of different gaseous CO aqueous solutions from 0.1% to 100.0% of saturation. Among these treatments, the effect of 1.0 μmol/L hematin and 1.0% saturation of CO aqueous solution were the most obvlous. Furthermore, compared with non-hematin treatment, the degradation of storage reserves In wheat seeds was also accelerated. Time-course analyses showed that application of hematln dose-dependently Increased the activities of superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase activities, thus decreasing the lipid peroxidation In germinating wheat seed subjected to salt stress. Meanwhile, the responses of hematin were specific for CO because the addition of the CO scavenger hemoglobln （0.2 g/L） blocked the various actions of 1.0 μmol/L hematin. Taken together, the results of the present study demonstrate that CO, at a low concentration, is able to attenuate the seed germlnation Inhibition produced by salinity stress and counteract the lipid peroxidation in germinating wheat seeds.     

Leaves of Field-Grown Mastic Trees Suffer Oxidative Stress at the Two Extremes of their Lifespan

Leaf senescence is a complex phenomenon occurring in all plant species, but it is still poorly understood in plants grown in Mediterranean field conditions and well-adapted to harsh climatic conditions. To better understand the physiological processes underlying leaf senescence in mastic trees (Pistacia lentiscus L.), we evaluated leaf growth, water and N content, photosystem II (PSII) photochemistry, lipid peroxidation and levels of photosynthetic pigments, antioxidants, abscisic acid, and salicylic acid and jasmonic acid during the complete leaf lifespan, from early expansion to late senescence in relation to natural climatic conditions in the field. While mature leaves suffered from water and N deficit during late spring and summer, both young (emerging) and old (senescing) leaves were most sensitive to photo-oxidative stress, as indicated by reductions in the F v/F m ratio and enhanced lipid peroxidation during late autumn and winter. Reductions in the F v/F m ratio were associated with low α-tocopherol (vitamin E) levels, while very old, senescing leaves additionally showed severe anthocyanin losses. We have concluded that both young (emerging) and old (senescing) leaves suffer oxidative stress in mastic trees, which may be linked in part to suboptimal temperatures during late autumn and winter as well as to low vitamin E levels.     

Oxidative Stress and Antioxidant Responses in Young Leaves of Mulberry Plants Grown Under Nitrogen, Phosphorus or Potassium Deficiency

The aim of this study was to associate the generation of reactive oxygen species （ROS） with Induced antloxidant responses and disturbed cellular redox environment in the nitrogen-（N）, phosphorus-（P）, or potassium-（K） deftcient mulberry （Morus alba L. var. Kanva-2） plants. The indicators of oxidative stress and cellular redox environment and antioxldant defense-related parameters were analyzed. Oeficlency of N, P or K suppressed growth, accelerated senescence, and decreased concentrations of chloroplastic pigments and glutathione. Lipid peroxidation and activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase were also increased in these N, P, or K deprived plants. Concentration of hydrogen peroxide Increased in plants deficient in N or P. Oeficlency of N or P particularly altered the cellular redox environment as indicated by changes in the redox couples, namely ascorbic acid/total ascorbate decreased in P-, glutathione sulfydryl/total glutathione decreased in N-, and Increased in P-deficient plants. Activity staining of native gels for superoxide dismutase revealed Increased activity as Indicated by Increased intensity of bands, and induction of few new isoforms in P- and K-deficient plants. Oifferences in the patterns of superoxide dismutase isoforms and redox status （ascorbic acid/total ascorbate and glutathlone sulfydryl/total glutathione） Indicate that N-, P-, or K-deficiency altered antioxidant responses to varying extents in mulberry plants.     

Effects of Cadmium on Polar Lipid Composition and Unsaturation in Maize （Zea mays） in Hydroponic Culture

This study aimed to evaluate the effect of Cd exposure （100 μmol/L） on polar lipid composition, and to examine the level of fatty acid unsaturation in maize （Zea mays L.）. In roots, the level of 16：0 and monounsaturated fatty acids （16：1 ＋ 18：1） decreased in phosphatidylcholine （PC） and phosphatidylethanolamine （PE）. In contrast, the proportion of unsaturated 18-C fatty acid species showed an opposite response to Cd. The content, on the other hand, of PC, PE, digalactosyldiacylglycerol （DGDG）, and steryl lipids increased in roots （2.9-, 1.6-, 5.3-, and 1.7-fold increase, respectively）. These results suggest that a more unsaturated fatty acid composition than found in control plants with a concomitant increase in polar lipids may favor seedling growth during Cd exposure. However, the observed increase in the steryl lipid （SL） ： phospholipid （PL） ratio （twofold）, the decrease in monogalactosyldiacylglycerol （MGDG） ： DGDG ratio, as well as the induction of lipid peroxidation in roots may represent symptoms of membrane injury. In shoots, the unsaturation level was markedly decreased in PC and phosphatidylglycerol （PG） after Cd exposure, but showed a significant increase in sulfoquinovosyldiacylglycerol （SQDG）, MGDG and DGDG. The content of PG and MGDG was decreased by about 65%, while PC accumulated to higher levels （4.4-fold increase）. Taken together, these changes in the polar lipid unsaturation and composition are likely to be due to alterations in the glycerolipid pathway. These results also support the idea that the increase in overall unsaturation plays some role in enabling the plant to withstand the metal exposure.     

Novel Evidence for a Reversible Dissociation of Light-harvesting Complex II from Photosystem II Reaction Center Complex Induced by Saturating Light Illumination in Soybean Leaves

After saturating light illumination for 3 h the potential photochemical efficiency of photosystem Ⅱ （PSII） （FJF,, the ratio of variable to maximal fluorescence） decreased markedly and recovered basically to the level before saturating light illumination after dark recovery for 3 h in both soybean and wheat leaves, indicating that the decline in FJ/Fm is a reversible down-regulation. Also, the saturating light illumination led to significant decreases in the low temperature （77 K） chlorophyll fluorescence parameters F685 （chlorophyll a fluorescence peaked at 685 nm） and F685/F735 （F735, chlorophyll a fluorescence peaked at 735 nm） in soybean leaves but not in wheat leaves. Moreover, trypsin （a protease） treatment resulted in a remarkable decrease in the amounts of PsbS protein （a nuclear gene psbS-encoded 22 kDa protein） in the thylakoids from saturating light-illuminated （SI）, but not in those from darkadapted （DT） and dark-recovered （DRT） soybean leaves. However, the treatment did not cause such a decrease in amounts of the PsbS protein in the thylakoids from saturating light-illuminated wheat leaves. These results support the conclusion that saturating light illumination induces a reversible dissociation of some light-harvesting complex Ⅱ （LHClI） from PSII reaction center complex in soybean leaf but not in wheat leaf.     

Cross-talk between calcium-calmodulin and nitric oxide in abscisic acid signaling in leaves of maize plants

Using pharmacological and biochemical approaches, the signaling pathways between hydrogen peroxide （H2O2）, calcium （Ca^2＋）-calmodulin （CAM）, and nitric oxide （NO） in abscisic acid （ABA）-induced antioxidant defense were investigated in leaves of maize （Zea mays L.） plants. Treatments with ABA, H2O2, and CaCl2 induced increases in the generation of NO in maize mesophyll cells and the activity of nitric oxide synthase （NOS） in the cytosolic and microsomal fractions of maize leaves. However, such increases were blocked by the pretreatments with Ca^2＋ inhibitors and CaM antagonists. Meanwhile, pretreatments with two NOS inhibitors also suppressed the Ca^2＋-induced increase in the production of NO. On the other hand, treatments with ABA and the NO donor sodium nitroprusside （SNP） also led to increases in the concentration of cytosolic Ca^2＋ in protoplasts of mesophyll cells and in the expression of calmodulin 1 （CaM1） gene and the contents of CaM in leaves of maize plants, and the increases induced by ABA were reduced by the pretreatments with a NO scavenger and a NOS inhibitor. Moreover, SNP-induced increases in the expression of the antioxidant genes superoxide dismutase 4 （SOD4）, cytosolic ascorbate peroxidase （cAPX）, and glutathione reductase 1 （GR1） and the activities of the chloroplastic and cytosolic antioxidant enzymes were arrested by the pretreatments with Ca^2＋ inhibitors and CaM antagonists. Our results suggest that Ca^2＋-CaM functions both upstream and downstream of NO production, which is mainly from NOS, in ABA- and H2O2-induced antioxidant defense in leaves of maize plants.     

扑草净对远志幼苗根系活力及氧化胁迫的影响

以远志(Polygala tenuifolia Willd.)为材料,应用组织化学和生物化学的方法研究不同浓度扑草净(0—400 mg/L)对远志幼苗生长、根系活力、膜脂过氧化、活性氧含量及抗氧化酶活性等的影响。10 mg/L扑草净对远志幼苗根系活力、细胞膜完整性及活性氧的积累几乎无显著影响,而25—400 mg/L扑草净处理则显著增加活性氧的积累,明显抑制根系活力且破坏细胞膜完整性;上述结果进一步被膜脂过氧化、质膜完整性、活性氧产生(O.2-和H2O2)的非损伤组织化学染色所证明。远志幼苗可通过多种抗氧化酶(SOD、POD、CAT、APX等)和非酶抗氧化剂(如脯氨酸)的相互协调作用,清除低浓度扑草净胁迫诱发产生的活性氧,减轻对细胞的伤害。研究结果表明,发芽期是远志对扑草净处理的敏感时期,较为安全的扑草净临界浓度为10 mg/L;25mg/L扑草净处理即引起远志幼苗氧化胁迫和膜脂过氧化,使细胞膜的完整性受到破坏,根系活力下降,抑制了远志幼苗的生长发育。该研究为远志抗除草剂胁迫机制及其栽培过程中除草剂的安全合理使用提供理论依据。     

WGA reduces the level of oxidative stress in wheat seedlings under salinity

Protective effect of exogenous wheat germ agglutinin (WGA) on wheat seedling (Triticum aestivum L.) during salinity stress was studied. In particular, we examined the state of pro- and antioxidant systems as well as the level of peroxide oxidation of lipids and electrolyte leakage under control conditions and when stressed with NaCl. Generation of superoxide anions and activity of both superoxide dismutase (SOD) and peroxidase increased during saline stress. Accumulation of O₂ ^·− resulted in peroxide oxidation of lipids and electrolyte leakage in response to stress. The injurious effect of salinity on root growth of seedlings was manifested by a decreased mitotic index (MI) in apical root meristem. This study show that WGA pretreatment decreased salt-induced superoxide anion generation, SOD and peroxidase activities, levels of lipid peroxidation and electrolytes leakage as well as correlating with a reduction in the inhibition of root apical meristem mitotic activity in salt-treated plants. This suggests that exogenous WGA reduced the detrimental effects of salinity-induced oxidative stress in wheat seedlings. Thus WGA effects on a balance of reactive oxygen species (ROS) and activities of antioxidant enzymes may provide an important contribution to a range of the defense reactions induced by this lectin in wheat plants.     

Riboflavin spraying impairs the antioxidant defense system but induces waterlogging tolerance in tobacco

Riboflavin, which causes plants to produce reactive oxygen species (ROS) when exposed to light, is an excellent photosensitizer for biocidal reactions. This study explores the possible protective role of riboflavin against waterlogging stress in tobacco plants. Tobacco seedlings (4 weeks old) were divided into four groups and pretreated with 0, 0.2, 0.5 or 1.0 mM riboflavin for 1 week, after which all groups were exposed to waterlogging stress for 7 days. We observed delayed leaf senescence and extended survival time, suggesting that riboflavin can confer increased waterlogging tolerance to plants as compared with the control (0 mM riboflavin). Enhanced stomatal closure was observed in the riboflavin-pretreated tobacco. We evaluated the levels of oxidative damage (H₂O₂ and lipid peroxidation), antioxidant enzyme (superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase) activity and antioxidant metabolites (including ascorbate and glutathione) in tobacco leaves that were pretreated with riboflavin. However, the results show that riboflavin pretreatment caused a decrease in chlorophyll content, antioxidant enzyme activity and redox values (AsA/DHA and GSH/GSSG), while causing a significant increase in lipid peroxidation, H₂O₂ accumulation and total ascorbate or glutathione content. In addition, the survival time and stomatal aperture of riboflavin-treated plants were significantly modified by exogenous application of GSH, well-known ROS scavenger. To explain the stomatal closure observed in tobacco plants, we propose a “damage avoidance” hypothesis based on riboflavin-mediated ROS toxicity. The protective function of the photosensitizer riboflavin may be highly significant for farming in frequently waterlogged areas.     

Effects of hematin and carbon monoxide on the salinity stress responses of Cassia obtusifolia L. seeds and seedlings

Aims

The purpose of the present study was to investigate the mechanism of carbon monoxide (CO) and hematin in alleviating the inhibition of Cassia obtusifolia seeds and seedlings. NaCl (100?mM) was used to mimic salinity stress in a series of experiments.

Methods

Varying combinations of CO in a saturated aqueous solution and hematin (1.0?μM) were added to seeds and seedlings under salinity stress. Seed germination indices and seedling parameters were investigated.

Results

Seed germination and seedling growth were significantly inhibited under salinity stress. NaCl-induced inhibitory effects on seed germination and seedling growth were ameliorated by hematin or the CO aqueous solution. Addition of 1.0?μM hematin or 5?% CO-saturated aqueous solution to seeds and seedlings significantly alleviated damage to the plant cells under salinity stress. Hematin and the CO aqueous solution enhanced chlorophyll concentration, total soluble sugars, free proline, and soluble protein, and improved photosystem II (PSII) photochemical efficiency levels, PSII actual photochemical efficiency, and the photochemical quench coefficient. In contrast, the non-photochemical quenching coefficient decreased. Hematin and the CO aqueous solution also enhanced the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and glutathione reductase, thus alleviating oxidative damage, as indicated by decreases in hiobarbituric acid reactive substances, hydrogen peroxide concentration, relative conductivity, and lipoxygenase activity. Heme oxygenase (HO) activity was increased by hematin treatment. Hematin may contribute to endogenous HO-derived CO, since the addition of zinc protoporphyrin IX or hemoglobin reversed the protective effects conferred by hematin specified above.

Conclusions

Based on the experimental results, we conclude that hematin and CO induce advantageous effects on the attenuation of salt-stress inhibition of C. obtusifolia seeds and seedlings and alleviate oxidative damage by conferring beneficial cytoprotection and activating anti-oxidant enzymes.     

茉莉酸对小麦幼苗UV-B抗性的生理学效应研究

以小麦品种‘西农88’(Triticum aestivum L.,cv.Xinong 88)为材料,研究了外源施加不同浓度茉莉酸(1、2.5、5、10 mmol/L)对UV-B辐射(1.5 kJ·m-2·d-1)下小麦幼苗光合色素、抗氧化酶、丙二醛、游离脯氨酸、紫外吸收物、花青素、根系活力等生理指标以及对其生长的影响,探讨了茉莉酸在UV-B辐射胁迫中的可能作用及其作用机制.研究结果表明,外源茉莉酸对小麦幼苗生理指标产生显著影响,并且表现出浓度效应,其中较低浓度的茉莉酸(1 mmol/L和2.5 mmol/L)能明显提高小麦幼苗的UV-B抗性.表现为低浓度茉莉酸显著提高UV-B辐射下小麦幼苗叶片中的总叶绿素含量、过氧化氢酶(CAT)、过氧化物酶(POD)和超氧化物歧化酶(SOD)活性.并且外源施加的茉莉酸还能够增加小麦幼苗的游离脯氨酸含量,降低脂质过氧化水平,提高花青素含量,增强根系活力.可见,茉莉酸通过提高小麦幼苗的抗氧化酶活性,增加渗透调节物含量以及保护性色素含量,从而缓解膜脂过氧化程度和提高防御物质含量,进而增强植物抵抗UV-B辐射胁迫的能力,保证小麦幼苗正常生长.     

Salinity-induced changes in two cultivars of Vigna radiata: responses of antioxidative and proline metabolism

The influence of increasing salinity stress on plant growth, antioxidant enzymes and proline metabolism in two cultivars of Vigna radiata L. (cv. Pusa Bold and cv. CO 4) was investigated. Salt stress was imposed on 30-days-old cultivars with four different concentrations of NaCl (0, 100, 200 and 300 mM). The roots and shoots of CO 4 showed greater reduction in fresh weight, dry weight and water content when compared to Pusa Bold with increasing salt stress. Under salinity stress, the roots and shoots of CO 4 exhibited higher Na⁺: K⁺ ratio than Pusa Bold. The activities of reactive oxygen species (ROS) scavenging enzymes and reduced glutathione (GSH) concentration were found to be higher in the leaves of Pusa Bold than in CO 4, whereas oxidized glutathione (GSSG) concentration was found to be higher in the leaves of CO 4 compared to those in Pusa Bold. Our studies on oxidative damage in two Vigna cultivars showed lower levels of lipid peroxidation and H₂O₂ concentration in Pusa Bold than in CO 4 under salt stress conditions. High accumulation of proline and glycine betaine under salt stress was also observed in Pusa Bold when compared to CO 4. The activities of proline biosynthetic enzymes were significantly high in Pusa Bold. However, under salinity stress, Pusa Bold showed a greater decline in proline dehydrogenase (ProDH) activity compared to CO 4. Our data in this investigation demonstrate that oxidative stress plays a major role in salt-stressed Vigna cultivars and Pusa Bold has efficient antioxidative characteristics which could provide better protection against oxidative damage in leaves under salt-stressed conditions.