Shade light interaction with salicylic acid in regulating growth of sun (alpine) and shade (prairie) ecotypes of Stellaria longipes

Magnesium (Mg) deficiency in plants is a widespread problem, affecting productivity and quality in agriculture. The mechanism of Mg deficiency inducing antioxidant enzyme activities has not been elucidated in rice. We examined the relationship among abscisic acid (ABA), H₂O₂, and antioxidant enzymes in the leaves of rice seedlings grown under conditions of Mg deficiency. The expression of OsRab16A, an ABA responsive gene, was used to determine the content of ABA. Mg deficiency resulted in increased ABA content in leaves of rice seedlings. The production of H₂O₂ was examined by 3,3-diaminobenzidine staining and a colorimetric method. Mg deficiency also induced H₂O₂ production in leaves, which was blocked by dipehnyleneiodonium chloride (DPI), an NADPH oxidase inhibitor. Tungstate (Tu), an ABA biosynthesis inhibitor, was effective in reducing Mg deficiency-increased ABA content, as well as Mg deficiency-induced H₂O₂ production. Both Tu and DPI were effective in reducing Mg deficiency-induced activities of superoxide dismutase, ascorbate peroxidase, glutathione reductase, and catalase in the leaves. Mg deficiency-induced ABA accumulation may trigger increased production of H₂O₂, which may involve plasma-membrane NADPH oxidase, and, in turn, up-regulates the activities of antioxidant enzymes in leaves of rice seedlings.     

NaCl-induced heme oxygenase in roots of rice seedlings is mediated through hydrogen peroxide

Recent findings have suggested that H₂O₂ is an important signaling molecule for regulating plant responses to abiotic stress. H₂O₂ plays a critical role in NaCl stress. Heme oxygenase (HO) is known to play a protective role against oxidative stress. In this study, we examined the possible involvement of H₂O₂ in regulating NaCl-promoted HO activity in rice roots. Treatment with NaCl increased HO activity and H₂O₂ content in rice roots. As well, NaCl could induce OsHO1 mRNA expression. NaCl (150 mM) and NaNO₃ (150 mM) were equally effective in inducing HO activity. However, mannitol at the concentration (276 mM) iso-osmotic with 150 mM NaCl had no effect on HO activity. NaCl-promoted HO activity and OsHO1 expression in rice roots was reduced by NADPH oxidase inhibitors i.e. dipehnyleneiodonium and imidazole. Moreover, exogenous application of H₂O₂ enhanced the activity of HO and the mRNA level of OsHO1. Our data suggest that H₂O₂ production plays a positive role in NaCl- induced HO activity by enhancing its mRNA level in rice roots.     

Expression of ascorbate peroxidase and glutathione reductase in roots of rice seedlings in response to NaCl and H2O2

The accumulation of H2O2 by NaCl was observed in the roots of rice seedlings. Treatment with NaCl caused an increase in the activities of ascorbate peroxidase (APX) and glutathione reductase (GR) and the expression of OsAPX and OsGR in rice roots. Exogenously applied H2O2 also enhanced the activities of APX and GR and the expression of OsAPX and OsGR in rice roots. The accumulation of H2O2 in rice roots in response to NaCl was inhibited by the NADPH oxidase inhibitors, diphenyleneiodonium chloride (DPI) and imidazole (IMD). However, DPI, IMD, and dimethylthiourea, a H2O2 trap, did not reduce NaCl-enhanced activities of APX and GR and expression of OsAPX and OsGR. It appears that H2O2 is not involved in the regulation of NaCl-induced APX and GR activities and OsAPX and OsGR expression in rice roots.     

The involvement of hydrogen peroxide in abscisic acid-induced activities of ascorbate peroxidase and glutathione reductase in rice roots

We have monitored the changes in antioxidant enzyme activities and H₂O₂ concentrations in roots of rice (Oryza sativa L., cv. Taichung Native 1) seedlings treated with exogenous abscisic acid(ABA). Decrease in superoxide dismutase (SOD) and catalase (CAT) activities was observed in rice roots in the presence of ABA. However, ascorbate peroxide (APX) and glutathione reductase (GR) activities were increased after the ABA treatment. ABA treatment resulted in an increase in H₂O₂ concentrations in rice roots. Pre-treatment with dimethylthiourea, a chemical trap for H₂O₂, and diphenyleneiodonium chloride (DPI), a well known inhibitor of NADPH oxidase, inhibited ABA-induced accumulation of H₂O₂ and ABA-induced activities of APX and GR. ABA-induced accumulation of H₂O₂ was found to be prior to ABA-induced activities of APX and GR. Our results suggest that H₂O₂ is involved in ABA-induced APX and GR activities in rice roots.     

Effect of NaCl stress on H2O2 metabolism in rice leaves

The effect of NaCl stress on H₂O₂ metabolismin detached rice leaves was studied. NaCl (200 mM)treatment did not cause the accumulation ofH₂O₂ and resulted in no increase in lipidperoxidation and membrane leakage of leaf tissues. The activities of peroxidase, ascorbate peroxidase,superoxide dismutase, and glutathione reductase wereobserved to be greater in NaCl-stressed rice leavesthan in control leaves. However, glycolate oxidasewas lower in NaCl-treated rice leaves than in thecontrol leaves. There was no difference in catalaseactivity between NaCl and control treatments. Theseresults suggest that some antioxidant enzymes can beactivated in response to oxidative stress induced byNaCl.     

OsHK3 is a crucial regulator of abscisic acid signaling involved in antioxidant defense in rice

In this study, the role of the rice(Oryza sativa L.)histidine kinase Os HK3 in abscisic acid(ABA)-induced antioxidant defense was investigated. Treatments with ABA, H2O2,and polyethylene glycol(PEG) induced the expression of Os HK3 in rice leaves, and H2O2 is required for ABA-induced increase in the expression of Os HK3 under water stress. Subcellular localization analysis showed that Os HK3 is located in the cytoplasm and the plasma membrane. The transient expression analysis and the transient RNA interference test in rice protoplasts showed that Os HK3 is required for ABA-induced upregulation in the expression of antioxidant enzymes genes and the activities of antioxidant enzymes. Further analysis showed that Os HK3 functions upstream of the calcium/calmodulin-dependent protein kinase Os DMI3 and the mitogen-activated protein kinase Os MPK1 to regulate the activities of antioxidant enzymes in ABA signaling. Moreover, Os HK3was also shown to regulate the expression of nicotinamide adenine dinucleotide phosphate oxidase genes, Osrboh B and Osrboh E, and the production of H2O2 in ABA signaling. Our data indicate that Os HK3 play an important role in the regulation of ABA-induced antioxidant defense and in the feedback regulation of H2O2 production in ABA signaling.     

Cell wall peroxidase activity,hydrogen peroxide level and NaCl-inhibited root growth of rice seedlings

The changes in cell-wall peroxidase (POD) activity and H₂O₂ level in roots of NaCl-stressed rice seedlings and their correlation with root growth were investigated. Increasing concentrations of NaCl from 50 to 150 mM progressively reduced root growth and increased ionically bound cell-wall POD activity. NaCl had no effect on covalently bound cell-wall POD activities. The reduction of root growth by NaCl is closely correlated with the increase in H₂O₂ level. Exogenous H₂O₂ was found to inhibit root growth of rice seedlings. Since ammonium and proline accumulation are associated with root growth inhibition caused by NaCl, we determined the effects of NH₄Cl or proline on root growth, cell-wall POD activity and H₂O₂level in roots. External application of NH₄Cl or proline markedly inhibited root growth, increased cell-wall POD activity and increased H₂O₂ level in roots of rice seedlings in the absence of NaCl. An increase in cell-wall POD activity and H₂O₂ level preceded inhibition of root growth caused by NaCl, NH₄Cl or proline. NaCl or proline treatment also increased NADH-POD and diamine oxidase (DAO) activities in roots of rice seedlings, suggesting that NADH-POD and DAO contribute to the H₂O₂ generation in the cell wall of NaCl- or proline-treated roots. NH₄Cl treatment increased NADH-POD activity but had no effect on DAO activity, suggesting that NADH-POD but not DAO is responsible for H₂O₂ generation in cell wall of NH₄Cl-treated roots.     

Overexpression of OsRab7B3, a Small GTP-Binding Protein Gene,Enhances Leaf Senescence in Transgenic Rice

Rab family proteins are small GTP-binding proteins involved in intracellular trafficking. They play critical roles in several plant development processes. Different expression patterns of 46 Rabs in the rice genome were examined in various rice tissues and in leaves treated with plant growth regulators and under senescence conditions. One of the OsRab genes, OsRab7B3, closely associated with senescence in expression pattern, was chosen for functional analysis. Expression of sGFP under the control of the OsRab7B3 promoter increased in leaves when ABA and NaCl were applied or when kept in dark. In transgenic rice overexpressing OsRab7B3, the senescence-related genes were upregulated and leaf senescence was significantly enhanced under dark conditions. Moreover, leaf yellowing occurred earlier in the transgenic plants than in the wild type at the ripening stage. Hence it is suggested that OsRab7B3 act as a stress–inducible gene that plays an important role in the leaf senescence process.     

Characterization of five CIPK genes expressions in maize under water stress

ABA, H₂O₂ and Ca²⁺ play critical roles as signals in the adaptive responses of plants to water and other stresses. They accumulate in plant cells under water and other stresses and induce changes in stress-related gene expressions. CIPKs, protein kinases associated with a calcineurin B-like calcium sensor, play a role in the regulation of stress gene expression in plants. However, it is still unclear whether ABA and H₂O₂ are key inducers that regulate the changes in CIPK expressions under water stress. In this study, five stress-inducible CIPKs in maize were retrieved from Database. They were designated as ZmCIPK1, 3, 8, 17 and 18, based on their homologies with known CIPK sequences. The expressions of the five ZmCIPKs in maize leaves and roots were analyzed and found to be regulated by PEG, CaCl₂, ABA and H₂O₂ to different extents. Moreover, the effect of ABA and H₂O₂ on the expressions of ZmCIPKs under water stress was in an organ-dependent manner.     

Hydrogen peroxide is involved in the regulation of rice (Oryza sativa L.) tolerance to salt stress

In the present study, we investigated the salt tolerance mechanism of two rice cultivars (Zhenghan-2 and Yujing-6), which show different tolerance to drought and disease. NaCl induced higher extent of lipid peroxide and ion leakage in Yujing-6 roots than those in Zhenghan-2 roots. H₂O₂ accumulation in Zhenghan-2 roots was lower than that in Yujing-6 roots under salt stress. Comparatively, NaCl treatment did not increase O₂ ^? contents in both rice roots, however, O₂ ^? level in Yujing-6 roots was higher than that in Zhenghan-2 roots under both control and salt stress conditions. Ascorbate peroxidases (APX) activity increased more significantly in Zhenghan-2 roots than that in Yujing-6 roots. The activity of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and glucose-6-phosphate dehydrogenase (G6PDH) was similarly enhanced in both rice roots under salt stress; however, they showed higher levels in Zhenghan-2 roots than in Yujing-6 roots. Exogenous H₂O₂ could enhance APX, CAT, POD, SOD and G6PDH activities in a concentration-dependent manner in both rice roots. Diphenylene iodonium (DPI), a plasma membrane (PM) NADPH oxidase inhibitor, which counteracted the NaCl-induced H₂O₂ accumulation, markedly decreased the activity of above enzymes. Moreover, ion leakage increased dramatically in Zhenghan-2 roots and reached to the similar level of Yujing-6 roots under NaCl+DPI treatment. Taken together, H₂O₂, which is mainly generated from PM NADPH oxidase, is involved in Zhenghan-2 rice tolerance to salt stress by enhancing the cellular antioxidant level.     

OsDMI3‐mediated activation of OsMPK1 regulates the activities of antioxidant enzymes in abscisic acid signalling in rice

In rice, the Ca²⁺/calmodulin (CaM)‐dependent protein kinase (CCaMK) OsDMI3 has been shown to be required for abscisic acid (ABA)‐induced antioxidant defence. However, it is not clear how OsDMI3 participates in this process in rice. In this study, the cross‐talk between OsDMI3 and the major ABA‐activated MAPK OsMPK1 in ABA‐induced antioxidant defence was investigated. ABA treatment induced the expression of OsDMI3 and OsMPK1 and the activities of OsDMI3 and OsMPK1 in rice leaves. In the mutant of OsDMI3, the ABA‐induced increases in the expression and the activity of OsMPK1 were substantially reduced. But in the mutant of OsMPK1, the ABA‐induced increases in the expression and the activity of OsDMI3 were not affected. Pretreatments with MAPKK inhibitors also did not affect the ABA‐induced activation of OsDMI3. Further, a transient expression analysis in combination with mutant analysis in rice protoplasts showed that OsMPK1 is required for OsDMI3‐induced increases in the activities of antioxidant enzymes and the production of H₂O₂. Our data indicate that there exists a cross‐talk between OsDMI3 and OsMPK1 in ABA signalling, in which OsDMI3 functions upstream of OsMPK1 to regulate the activities of antioxidant enzymes and the production of H₂O₂ in rice.     

Differences in growth and physiological traits of Populus cathayana populations as affected by enhanced UV-B radiation and exogenous ABA

During one growing season, the effects of enhanced ultraviolet-B (UV-B) radiation, exogenous abscisic acid (ABA) and their combination on biomass accumulation, gas exchange, endogenous ABA, the concentration of UV-absorbing compounds, antioxidant system and on the carbon (C) and nitrogen (N) content and C/N ratio were investigated in two contrasting Populus cathayana Rehd. populations, originating from high and low altitudes in south-west China. Exogenous ABA was sprayed to the leaves, and enhanced UV-B treatments were applied using a square-wave system to expose the seedlings to ambient (1×) or twice ambient (2×) doses of biologically effective UV-B radiation (UV-B_BE). Enhanced UV-B radiation significantly decreased height, basal diameter, total leaf area, total biomass, net CO₂ assimilation rate (A), stomatal conductance (g_s), transpiration rate (E) and carbon (C) content in leaves, and significantly increased the activities of superoxide dismutase (SOD) and guaiacol peroxidase (GPx), and the contents of hydrogen peroxide (H₂O₂) and malonaldehyde (MDA), as well as the accumulation of UV-absorbing compounds and endogenous ABA concentrations among different organs in both populations. In contrast, exogenous ABA induced a significant decrease in A and significant increases in the activities of SOD and GPx, in the content of H₂O₂ and MDA, and in the endogenous ABA concentrations. Compared with the low altitude population, the high altitude population was more tolerant to enhanced UV-B and exogenous ABA. Significant interactions between UV-B and ABA were observed in A, E, and in the activities of SOD and GPx, as well as in endogenous ABA in the leaves and roots of both populations. Across all treatments, the C and N contents of leaves were strongly correlated with their contents in stems and roots. Additionally, the N content of leaves and stems were significantly correlated with the C content of stems.     

水稻磷脂氢谷胱甘肽过氧化物酶在蛋白质水平上的组织和诱导表达特征

蛋白质是生命活动的主要承担分子,了解蛋白质在有机体中的时空分布对于正确解析蛋白质的功能十分重要．磷脂氢谷胱甘肽过氧化物酶 (PHGPx) 是目前发现的唯一能够直接还原膜上脂类过氧化物的抗氧化酶,在保护生物膜免受过氧化损伤方面有着重要作用．采用Western blot技术,分析了水稻PHGPx (OsPHGPx) 在水稻不同组织以及多种胁迫条件下的蛋白质表达特征．结果表明,OsPHGPx在成熟水稻植株内主要分布于叶组织中,以旗叶中含量最高,而在水稻幼苗中则在茎及叶组织中均检测到较强的杂交信号．OsPHGPx在幼苗中的表达受到H₂O₂和NaCl的强烈诱导,但植物激素对其表达的影响较弱．H₂O₂和NaCl的诱导效果呈现出时间及剂量的相关性,当用0.5 mmol/L H₂O₂处理12 h或用500 mmol/L NaCl处理24 h,此时OsPHGPx表达量达到最大值．对H₂O₂清除剂二甲基硫脲处理的水稻幼苗,外源H₂O₂的再处理并不能诱导OsPHGPx的表达,而NaCl的诱导效果并不受影响,说明H₂O₂可能并不介导NaCl诱导OsPHGPx的表达．这些结果为进一步研究OsPHGPx在水稻中生物学功能奠定了基础．     

Effects of salt stress on ion content,antioxidant enzymes and protein profile in different tissues of Broussonetia papyrifera

Although some plant responses to salinity have been characterized, the precise mechanisms by which salt stress damages plants are still poorly understood especially in woody plants. In the present study, the physiological and biochemical responses of Broussonetia papyrifera, a tree species of the family, Moraceae, to salinity were studied. In vitro-produced plantlets of B. papyrifera were treated with varying levels of NaCl (0, 50, 100 and 150 mM) in hydroponic culture. Changes in ion contents, accumulation of H₂O₂, as well as the activities and isoform profiles of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the leaves, stems and roots were investigated. Under salt stress, there was higher Na⁺ accumulation in roots than in stems and leaves, and Ca^2 +, Mg^2 + and P^3 + content, as well as K⁺/Na⁺ ratio were affected. NaCl treatment induced an increase in H₂O₂ contents in the tissues of B. papyrifera. The work demonstrated that activities of antioxidant defense enzymes changed in parallel with the increased H₂O₂ and salinity appeared to be associated with differential regulation of distinct SOD and POD isoenzymes. Moreover, SDS-PAGE analysis of total proteins extracted from leaves and roots of control and NaCl-treated plantlets revealed that in the leaves salt stress was associated with decrease or disappearance of some protein bands, and induction of a new protein band after exposure to 100 and 150 mM NaCl. In contrast, NaCl stress had little effect on the protein pattern in the roots. In summary, these findings may provide insight into the mechanisms of the response of woody plants to salt stress.