Alterations in Cd‐induced gene expression under nitrogen deficiency in Hordeum vulgare
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ABSTRACT The inter‐relation between nitrogen availability and cadmium toxicity was studied in roots of barley seedlings with emphasis on the analysis of expression of 10 selected genes relevant for growth in the presence of toxic Cd concentrations. The response to Cd exposure differed quantitatively or qualitatively for the 10 genes in dependence of the N supply. Transcripts of glutathione synthase, glutathione reductase, glutathione peroxidase and dehydroascorbate reductase were measured as parameters involved in antioxidant defence, metallothionein, phosphoenolpyruvate carboxylase and phytochelatin synthase (PCS) were analysed as genes related to heavy metal binding, and vacuolar ATPase subunits VHA‐E and VHA‐c and a NRAMP‐transporter as genes being implicated in Cd transport. Reprogramming of the Cd response was most obvious for PCS and NRAMP whose transcript levels were unaltered and down‐regulated, respectively, in the presence of Cd at adequate N, but strongly up‐regulated upon Cd exposure under conditions of nitrogen deficiency. Different responses to Cd at varying N supply were also seen for the antioxidant genes. The results on gene expression are discussed in context with the changes in biochemical parameters, and underline the importance of evaluating the general growth conditions of a plant when discussing its specific response to a stressor such as Cd. The sequence of the nramp cDNA was filed at the EMBL/GenBank/DDBJ Databases under the accession number AJ514946 .Keywords:
Glutathione reductase
Phosphoenolpyruvate carboxylase
APX
To study the effects of exogenous proline on the ascorbate-glutathione cycle in roots of melon seedlings under salt stress,two melon cultivars( Cucumis melo ‘Yuhuang 'and‘Xuemei') under differing salt tolerances were investigated in a nutrient solution culture system. The results showed that:( 1) The content of reduced ascorbic acid( ASA) and reduced glutathione( GSH) decreased and oxidized glutathione( GSSG) increased in the two melon cultivars under salt stress,with C. melo‘Xuemei'showing a larger range than C. melo‘Yuhuang'.( 2) Exogenous proline had greater effects on‘Xuemei'than on‘Yuhuang'in increasing the content of ASA and GSH while decreasing the content of GSSG,and therefore the ratio of GSH /GSSG increased.( 3) After 3 days salt treatment,‘Xuemei'showed a markedly larger decreasing range in the activities of ascorbate peroxidase( APX),dehydroascorbate reductase( DHAR) and glutathione reductase( GR). Five days later,enzyme activity increased in ‘Yuhuang 'but decreased in ‘Xuemei'with the extension of stress time.( 4) Exogenous proline had larger impact on ‘Xuemei'than on ‘Yuhuang 'in regards to increasing the activities of APX,DHAR and GR. These results indicated that exogenous proline can clean reactive oxygen species( ROS) caused by salt stress through increasing the activities of antioxidant enzyme and non-enzymatic antioxidant content,such as ASA and GSH,and can thus improve the ascorbate-glutathione cycle to protect melon seedlings from damage caused by salt stress.
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Glutathione reductase
Cucumis
Melon
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Glutathione reductase
Biofortification
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The responses of the antioxidant defense system in plant species to drought stress are still relatively unknown. In order to further understand how the system responds to drought stress, the leaves of Fargesia denudata seedlings were investigated. Antioxidant enzyme activities, antioxidant contents, hydrogen perox ide (H2O2), superoxide anion ( ) and MDA contents in the seedling leaves were measured under well watered (WW), moderate drought stressed (MD), and severe drought stressed (SD) treatments. Although drought stress significantly increased H2O2 and levels in F. denudata leaves, only weak lipid peroxidation was observed. This is attributed to the higher superoxide dismutase (SOD), catalase (CAT), ascorbate perox idase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and dehydroascor bate reductase (DHAR) activities in F. denudata leaves during the entire drought period. Reduced and oxi dized ascorbate (AsA and DHA) contents were almost not affected by drought except that DHA under SD showed an obvious increase on day 30. Furthermore, reduced glutathione (GSH) content under drought stress significantly decreased, while oxidized glutathione (GSSG) markedly increased under SD on days 30 and 45 as well as under MD on day 30; as a result, the ratio GSH/GSSG declined considerably. These results indicated that GSH was involved in scavenging H2O2 and under drought stress and it was more sensitive to drought stress in scavenging H2O2 and than AsA. As a result, a highly efficient antioxidant defense system in drought stressed F. denudate leaves operated mainly through the synergistic functioning of SOD, CAT, APX, MDHAR, DHAR, GR, and GSH against oxidative damage.
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The objective of this study was to determine the effects of CO2 laser(wavelength 10600 nm,power density 20.1 mW/mm2) on glutathione dependent antioxidative system in wheat seedling under drought stress.Germinating seeds were exposed to CO2 laser radiation for 0 min,1 min,3 min and 5 min,respectively,then they were treated with 10%(W/V) PEG6000 solution for 8 days.When the seedlings were 12-day-old,changes in the concentration of oxidized glutathione(GSSG),reduced glutathione(GSH),ascorbate(AsA) and the activities of glutathione reductase(GR),glutathione-S-transferase(GST),ascorbate peroxidase(APX) were measured to determine the effects of laser.The results showed that suitable laser treatment of seeds improved drought tolerance in wheat seedlings by decreasing the concentration of GSSG and increasing the activities of APX,GR,GST,AsA and GSH concentration.The results suggested that those changes in glutathione dependent antioxidative system were responsible for protection wheat against drought induced oxidative damage.
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To investigate the effects of environmental stresses on ascorbic acid content and its redox status, the effects of freezing and drought on ascorbate and dehydro-ascorbate content and activities of four enzymes involved in the ascorbate-glutathione cycle in some conifers were studied. The results showed that both freezing and drought induced the decrease in ascorbate content and the increase in dehydro-ascorbate content. The activities of ascorbate peroxidase (APX) and monodehydro-ascorbate reductase (MDAR) were decreased by freezing stress. At the beginning of exposure to air, water loss from detached needles induced the increase in the activities of APX and MDAR. Further water loss turned to decrease the APX and MDAR activities. The activities of dehydro-ascorbate reductase (DHAR) and glutathione reductase (GR) were not sensitive to changes in temperature and water content of the needles. It is concluded that moderate temperature or water stresses may induce the acclimation and increase in the ability of the H2O2 scavenging system, while strong stresses decrease the ability and induce injury of plant tissues. Correlation between ascorbate content and activities of related enzymes and cold tolerance of conifers were also reported.
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Malus
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A solution culture experiment in greenhouse was carried out to study the dynamic change of ascorbate-glutathione cycle metabolism in roots and leaves of tomato seedlings under 0.05 mmol/L Cd~(2+) stress and recovery. The results showed that under stress malonaldehyde(MDA) contents in roots and leaves increased ,ascorbate peroxidase(APX)activity rose at the begining of three days and then decreased ,glutathione reductase(GR) activity decreased on the first day and then increased, the content of ascrobate(AsA) and glutathione(GSH) increased and the increase in roots was higher than that of leaves. After recovery the MDA content in leaves declined to control level, while the MDA content in roots duratively increased. The activities of APX and GR and the content of AsA and GSH could recover, which were higher than control. GSH contents in roots duratively maintain high level. There were defferences between the resumptive extent of parameters of leaves and roots.
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In the present study, the effects of heavy metals generating antioxidative defense systems such as superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11) glutathione reductase (GR, EC 1.6.4.2) and catalase (CAT, EC 1.11.1.6) were studied in the leaves of Atriplex plants grown in polluted soil with different heavy metals (Cu, Ni, Pb and Zn). The results showed that the exposure of plants to different levels of metals reduced the dry matter production and height of shoots. The decrease in root growth caused by the toxicity of metals was severe than the decrease in shoot growth. Atriplex showed gradual decrease in height following metal treatments, a four week exposure of A. hortensis var. rubra L. (red) to 25%,50%,75% and 100% contaminated soil gave a respective mean values of 21.4, 12.2, 9.3 and 6.5 cm which were lower in comparison to the plants of the control group. Of the antioxidant enzymes, the results showed that SOD and APX, were diminished by metal toxicity. However, the activity of CAT and GR were increased by the metal stress. Hence, the plants of the three annual arroach species or varieties used, all showed an intermediate level of tolerance according to the imposed treatments. The antioxidative activity seems to be of fundamental importance for adaptive responses of Atriplex plants against the metal toxicity. Abbreviations: SOD, superoxide dismutase; CAT, catalase; APX, ascorbate peroxidase; GR, glutathione reductase; GSH, reduced glutathione; GSSG, oxidized glutathione; ROS, reactive oxygen species; MDHA, monodehydroascorbate; NBT, nitroblue tetrazolium; POD, peroxidase.
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