The impact of heavy metals on the activity of some enzymes along the barley root

Barley seedlings 48 h after the onset of germination on filter paper treated for 24 h by 1 mM cadmium (Cd), 3 mM nickel (Ni) or 0.5 mM mercury (Hg) showed similar approximately 45% root growth inhibition. Although root growth inhibition was similar, loss of cell viability evaluated, as Evans blue uptake was distinct among Cd, Ni and Hg treated roots. While Cd and Hg caused cell death along the whole barley root (0–8 mm), Ni induced significant loss of cell viability only in root cells 6–8 mm distance from the root tip. Our results suggest that different metabolic processes are activated in different parts of barley root in relation to distance from the root tip during heavy metal (HM) treatment. Some of them are characteristic for several HMs such as inhibition of ascorbic acid oxidase or glutathione-S-transferase stimulation, while others are specific for individual HMs, e.g. activation of acid phosphatase and lipoxygenase by Cd and Hg, or inhibition of ascorbate peroxidase by Ni and Hg treatment.     

Inhibition of human leukocyte 3-hydroxy-3-methylglutaryl coenzyme A reductase activity by ascorbic acid. An effect mediated by the free radical monodehydroascorbate

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity in microsomes isolated from cultured lymphoid (IM-9) cells or freshly isolated human leukocytes was markedly decreased by either ascorbic acid or its oxidized derivative, dehydroascorbate. Inhibition of IM-9 leukocyte HMG-CoA reductase activity was log linear between 0.01 and 10 mM ascorbic acid (25 and 81% inhibition, respectively) and 0.1 and 10 mM dehydroascorbate (5 and 75% inhibition, respectively). Inhibition was noncompetitive with respect to HMG-CoA (Km = 10.2 microM (RS); ascorbic acid, Ki = 6.4 mM; dehydroascorbate, Ki = 15 mM) and competitive with respect to NADPH (Km = 16.3 microM; acetic acid, Ki = 6.3 mM; dehydroascorbate, Ki = 3.1 mM). Ascorbic acid and dehydroascorbate are interconverted through the free radical intermediate monodehydroascorbate. Reducing agents are required to convert dehydroascorbate to monodehydroascorbate, but prevent formation of the free radical from ascorbate. In microsomes from IM-9 cells, the reducing agent, dithiothreitol, abolished HMG-CoA reductase inhibition by ascorbate but enhanced inhibition by dehydroascorbate. In addition, the concentration of monodehydroascorbate present in ascorbate solutions was directly proportional to the degree of HMG-CoA reductase inhibition by 1.0 mM ascorbate. Fifty per cent inhibition of enzyme activity occurred at a monodehydroascorbate concentration of 14 microM. These data indicate that monodehydroascorbate mediates inhibition of HMG-CoA reductase by both ascorbate and dehydroascorbate. This effect does not appear to be due to free radical-induced membrane lipid modification, however, since both ascorbate and dehydroascorbate inhibited the protease-solubilized, partially purified human liver enzyme. Since inhibition of HMG-CoA reductase occurs at physiological concentrations of ascorbic acid in the human leukocyte (0.2-1.72 mM), this vitamin may be important in the regulation of endogenous cholesterol synthesis in man.     

Oxygen-dependent chemical tumorigenesis in a Nicotiana hybrid: inhibition by ascorbic acid and dinitrophenol

Aqueous solutions of molecular oxygen, per se, or in combination with either pyrogallol or 6-azauracil increased tumorigenesis in Nicotiana suaveolens X Nicotiana langsdorffii seedlings relative to control seedlings. The biological activities of the organic chemicals were O2-dependent, because the substitution of N2 or O2 or the degassing of 0.1-1 mM solutions of the compounds eliminated or greatly reduced their tumorigenic effects. Rates of tumorigenesis exceeded 95% for 0.5 mM solutions of either pyrogallol or 6-azauracil solutions in the presence of l mM O2. Although tumors developed in 20% of seedlings in the presence of 1 mM O2, alone, 4-5 times more tumors were induced by the organic chemical--O2-H2O systems. Dinitrophenol and ascorbic acid, compounds which affect cellular respiration or redox systems, strongly inhibited the chemically-mediated tumorigenesis. Dinitrophenol was equally effective at one-tenth of the molar concentrations of ascorbic acid that were required for the suppressions of oncogenesis. Dehydroascorbic acid was much less inhibitory than ascorbic acid.     

An assessment of the role of ethylene in mediating lettuce (Lactuca sativa) root growth at high temperatures

Growth of temperate lettuce (Lactuca sativa) plants aeroponically in tropical greenhouses under ambient root-zone temperatures (A-RZTs) exposes roots to temperatures of up to 40 degrees C during the middle of the day, and severely limits root and shoot growth. The role of ethylene in inhibiting growth was investigated with just-germinated (24-h-old) seedlings in vitro, and 10-d-old plants grown aeroponically. Compared with seedlings maintained at 20 degrees C, root elongation in vitro was inhibited by 39% and root diameter increased by 25% under a temperature regime (38 degrees C/24 degrees C for 7 h/17 h) that simulated A-RZT in the greenhouse. The effects on root elongation were partially alleviated by supplying the ethylene biosynthesis inhibitors aminooxyacetic acid (100-500 microM) or aminoisobutyric acid (5-100 microM) to the seedlings. Application of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid to seedlings grown at 20 degrees C mimicked the high temperature effects on root elongation (1 microM) and root diameter (1 mM). Compared with plants grown at a constant 20 degrees C root-zone temperature, A-RZT plants showed decreased stomatal conductance, leaf relative water content, photosynthetic CO(2) assimilation, shoot and root biomass, total root length, the number of root tips, and root surface area, but increased average root diameter. Addition of 10 microM ACC to the nutrient solution of plants grown at a constant 20 degrees C root-zone temperature mimicked the effects of A-RZT on these parameters but did not influence relative water content. Addition of 30 microM aminoisobutyric acid or 100 microM aminooxyacetic acid to the nutrient solution of A-RZT plants increased stomatal conductance and relative water content and decreased average root diameter, but had no effect on other root parameters or root and shoot biomass or photosynthetic CO(2) assimilation. Although ethylene is important in regulating root morphology and elongation at A-RZT, the failure of ethylene biosynthesis inhibitors to influence shoot carbon gain limits their use in ameliorating the growth inhibition induced by A-RZT.     

Influences of ascorbic acid and gibberellic acid in alleviating effects of salinity in Petunia under in vitro

Salinity is one of the abiotic stresses that limits the growth and productivity of many crops. A possible survival strategy for plant under saline conditions is to use compounds that could minimize the harmful effects of salt stress on the plant development. The objective of the presented study was to investigate the effect of exogenous ascorbic acid (ASA) with or without gibberellic acid (GA3) on key growth and biochemical parameters in two petunia cultivars ‘Prism Rose’ and ‘Prism White’ under saline (150 mM NaCl) and non-saline in vitro condition. Nodal cutting with an axillary buds were used as explants. Application of 1 mM ascorbic acid with or without 0.05 mM gibberellic acid into the MS medium stimulated the length of shoots and the number of new shoots of ‘Prism Rose’; whereas, it decreased the root length and the number of roots of both ‘Prism Rose’ and ‘Prism White’ under non-saline condition. The addition of ascorbic acid with or without gibberellic acid into the MS medium under saline condition, increased the length of plants and the number of new shoots, but did not affect their root number and length. NaCl treatments increased the proline content and lipid peroxidation which was indicated by the accumulation of malondialdehyde (MDA). The study revealed a correlation between chlorophylls a and b content and the leaf pigmentation intensity – parameter a*. Addition of 1 mM ascorbic acid with 0.05 mM gibberellic acid into the MS medium plays a protective role in salinity tolerance by improving the shoot growth and the development as well as increasing the activities of the antioxidant enzymes and other antioxidant substances.     

Loss of Ascorbic Acid from Injured Feline Spinal Cord

Feline spinal cord contains 0.97 mM ascorbic acid, as measured by the dinitrophenylhydrazine method. Greater than 90% is maintained in the reduced form. When functioning normally, the CNS conserves its ascorbic acid with a turnover rate of 2% per h. Following contusion injury severe enough to produce paraplegia, ascorbic acid is rapidly lost from injured spinal tissue. Thus, ascorbic acid is decreased 30% by 1 h and 50% by 3 h following injury. Oxidized ascorbic acid is increased at 1, but not 3, h following impact. As a consequence of its many functions in CNS, loss of ascorbic acid may contribute to derangements in spinal cord function following injury.     

Counteraction of Salinity Stress on Wheat Plants by Grain Soaking in Ascorbic Acid, Thiamin or Sodium Salicylate

The interactive effects of salinity stress (40, 80, 120 and 160 mM NaCl) and ascorbic acid (0.6 mM), thiamin (0.3 mM) or sodium salicylate (0.6 mM) were studied in wheat (Triticum aestivum L.). The contents of cellulose, lignin of either shoots or roots, pectin of root and soluble sugars of shoots were lowered with the rise of NaCl concentration. On the other hand, the contents of hemicellulose and soluble sugars of roots, starch and soluble proteins of shoots, proline of either shoots or roots, and amino acids of roots were raised. Also, increasing NaCl concentration in the culture media increased Na⁺ and Ca²⁺ accumulation and gradually lowered K⁺ and Mg²⁺ concentration in different organs of wheat plant. Grain soaking in ascorbic acid, thiamin or sodium salicylate could counteract the adverse effects of NaCl salinity on the seedlings of wheat plant by suppression of salt stress induced accumulation of proline.     

Abscisic Acid accumulation is not required for proline accumulation in wilted leaves

Leaves from dark-grown barley (Hordeum vulgare L. var Larker) seedlings grown in the presence and absence of fluridone were used to determine whether or not abscisic acid (ABA) accumulation was necessary for proline to accumulate in wilted tissue. Wilted tissue (polyethylene glycol-treated) leaves from fluridone-grown seedlings did not accumulate ABA but did accumulate proline at a rate that was not different from the non-fluridone-treated leaves. Thus ABA accumulation is not required for wilting-induced proline accumulation in barley leaves. Proline accumulation in wilted leaves from the wilty tomato (Lycopersicon esculentum) mutant, flacca, was compared to that in the wild type, Rheinlands Ruhm. Proline accumulated in wilted leaves from flacca. The rate of accumulation was faster in flacca compared to the rate in the wild type because the wilty mutant wilted faster. ABA accumulated in wilted leaves from the wild type but not in the wilty mutant. This result is a further confirmation that ABA accumulation is not required for wilting-induced proline accumulation. These results are significant in that proline accumulation in barley leaves can be induced independently by any one of three treatments: wilting, ABA, or salt.     

Peroxidase and phenylalanine ammonia-lyase activities,phenolic acid contents,and allelochemicals-inhibited root growth of soybean

The influence of the allelochemicals ferulic (FA) and vanillic (VA) acids on peroxidase (POD, EC 1.11.1.7) and phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) activities and their relationships with phenolic acid (PhAs) contents and root growth of soybean (Glycine max (L.) Merr.) were examined. Three-day-old seedlings were cultivated in nutrient solution containing FA or VA (0.1 to 1 mM) for 48 h. Both compounds (at 0.5 and 1 mM) decreased root length (RL), fresh weight (FW) and dry weight (DW) and increased PhAs contents. At 0.5 and 1 mM, FA increased soluble POD activity (18% and 47%, respectively) and cell wall (CW)-bound POD activity (61% and 34%), while VA increased soluble POD activity (33% and 17%) but did not affect CW-bound POD activity. At 1 mM, FA increased (82%) while VA reduced (32%) PAL activities. The results are discussed on the basis of the role of these compounds on phenylpropanoid metabolism and root growth and suggest that the effects caused on POD and PAL activities are some of the many mechanisms by which allelochemicals influence plant growth.     

Effect of nitrate supply on the in-vivo synthesis and distribution of trifollin A,a Rhizobium trifolii-binding lectin,in Trifolium repens seedlings

In-vivo synthesis of the white-clover lectin, trifoliin A, was examined by the incorporation of labeled amino acids into protein during heterotrophic growth of intact Trifolium repens L. seedlings. Lectin synthesis was quantified by measuring the level of labeled protein immunoprecipitated from root exudate, from the hapten (2-deoxyglucose) eluate of the roots, and from root and shoot homogenates. The presence of labeled trifoliin A was confirmed by non-denaturing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by fluorography and comparison with trifoliin A standards. In-vivo-labeled trifoliin A was detected in seedling root homogenate 2 h after the addition of labeled amino acids and on the root surface by 8 h. Incorporation of labeled amino acids into protein and trifoliin A was greatest with 2-d-old seedlings and was greater when the plants were grown continuously in the dark than when they were exposed to 14 h light daily. Significantly more labeled lectin accumulated on the root surface of seedlings grown with 1.5 mM KNO₃ than of seedlings grown either without N or with 15.0 mM KNO₃. The labeled lectin from the root surface in all nitrate treatments and from the rootexudate samples of seedlings grown N-free and with 1.5 mM KNO₃ was fully able to bind to Rhizobium trifolii. In contrast, only 2% of the immunoprecipitable protein found in the root exudate of seedlings grown with 15.0 mM KNO₃ was able to bind to the bacteria. Thus, excess nitrate does not repress the synthesis of trifoliin A in the root, but does affect the distribution and activity of this newly synthesized lectin in a way which reduces its ability to interact with R. trifolii. By using Western blot analysis, much more total trifoliin A is detected in the homogenates of shoots than roots. However, greater than 80% of the total labeled protein and 85–90% of the total labeled lectin were found in the root homogenates of 2-d-old dark-grown seedlings incubated for 5 h with labeled amino acids. In addition, Western blot analysis indicated that the shoot homogenate contained smaller-molecular-weight peptides which reacted with the specific anti-trifoliin A antibody. These studies indicate that stored trifoliin A in the seed is degraded in the shoots during seedling development, while newly synthesized trifoliin A in the roots is excreted to the root surface and external environment.Abbreviations IgG immunoglobulin G - LPS lipopolysaccharide - PBS 10 mM potassium-phosphate buffer, pH 7.0, containing 0.8% NaCl - PBS-T 20 mM phosphate-buffered saline, pH 7.4, containing 0.05% Tween 20 - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Paraquat-induced Oxidative Stress in Drosophila melanogaster: Effects of Melatonin, Glutathione, Serotonin, Minocycline, Lipoic Acid and Ascorbic Acid

The efficacy of melatonin, glutathione, serotonin, minocycline, lipoic acid and ascorbic acid in counteracting the toxicity of paraquat in Drosophila melanogaster was examined. Male Oregon wild strain flies were fed for 5 days with control food or food containing the test substance. They were transferred in groups of five to vials containing only filter paper soaked with 20 mM paraquat in 5% sucrose solution. Survival was determined 24 and 48 h later. All the substances assayed increased the survival of D. melanogaster. At equimolar concentrations (0.43 mM) melatonin was more effective than serotonin, lipoic acid and ascorbic acid. However, lower concentrations of glutathione (0.22 mM) and minocycline (0.05 mM) were as efficient as melatonin. The highest survival rate (38.6%) after 48 h of paraquat treatment was found with 2.15 mM of lipoic acid. No synergistic effect of melatonin with glutathione, serotonin, minocycline, lipoic acid and ascorbic acid was detected.     

Factors increasing ethylene production enhance the sensitivity of root growth to auxins

Light inhibits root elongation, increases ethylene production and enhances the inhibitory action of auxins on root elongation of pea ( Pisum sativum L. cv. Weibulls Marma) seedlings. To investigate the role of ethylene in the interaction between light and auxin, the level of ethylene production in darkness was increased to the level produced in light by supplying 1-aminocyclopropane-1-carboxylic acid (ACC) or benzylaminopurine (BAP). Ethylene production was measured in excised root tips after treatment of intact seedlings for 24 h, while root growth was measured after 48 h. Auxin, at a concentration causing a partial inhibition of root elongation, did not increase ethylene production significantly. A 4-fold increase in ethylene production, caused either by light, 0.1 μ M ACC or 0.1 μ M BAP, inhibited root elongation by 40–50%. The auxins 2,4-dichlorophenoxyacetic acid and indolebutyric acid applied at 0.1 μ M inhibited root elongation by 15–25% in darkness but by 50–60% in light. Supply of ACC or BAP in darkness enhanced the inhibitory effects of auxins to about the same extent as in light. The inhibition caused by the auxins as well as by the BAP was associated with swelling of the root tips. ACC and BAP treatment synergistically increased the swelling caused by auxins. We conclude that auxin and ethylene, when applied or produced in partially inhibitory concentrations, act synergistically to inhibit root elongation and increase root diameter. The effect of light on the response of the roots to auxins is mediated by a light-induced increase in ethylene production.     

Growth and graviresponsiveness of primary roots of Zea mays seedlings deficient in abscisic acid and gibberellic acid

The objective of this research was to determine if gibberellic acid (GA) and/or abscisic acid (ABA) are necessary for graviresponsiveness by primary roots of Zea mays. To accomplish this objective we measured the growth and graviresponsiveness of primary roots of seedlings in which the synthesis of ABA and GA was inhibited collectively and individually by genetic and chemical means. Roots of seedlings treated with Fluridone (an inhibitor of ABA biosynthesis) and Ancymidol (an inhibitor of GA biosynthesis) were characterized by slower growth rates but not significantly different gravicultures as compared to untreated controls. Gravicurvatures of primary roots of d-5 mutants (having undetectable levels of GA) and vp-9 mutants (having undectable levels of ABA) were not significantly different from those of wild-type seedlings. Roots of seedlings in which the biosynthesis of ABA and GA was collectively inhibited were characterized by gravicurvatures not significantly different for those of controls. These results (1) indicate that drastic reductions in the amount of ABA and GA in Z. mays seedlings do not significantly alter root graviresponsiveness, (2) suggest that neither ABA nor GA is necessary for root gravicurvature, and (3) indicate that root gravicurvature is not necessarily proportional to root elongation.     

Effects of pH on NaCl tolerance of American elm (<Emphasis Type="Italic">Ulmus americana</Emphasis>) seedlings inoculated with <Emphasis Type="Italic">Hebeloma crustuliniforme</Emphasis> and <Emphasis Type="Italic">Laccaria bicolor</Emphasis>

In the present study, we investigated the effects of pH treatments on NaCl tolerance in mycorrhizal and non-mycorrhizal American elm. American elm (Ulmus americana) seedlings were inoculated with Hebeloma crustuliniforme, Laccaria bicolor or with both mycorrhizal fungi and subsequently subjected to different pH solutions (pH 3, 6 and 9) containing 0 mM (control) and 60 mM NaCl for 4 weeks. Inoculation with the mycorrhizal fungi did not have a large effect on seedling dry weights when the pH and NaCl treatments were considered independently. However, when the inoculated seedlings were treated with 60 mM NaCl at pH 3 or 6, shoot to root ratios and root hydraulic conductivity were higher compared with non-inoculated plants, likely reflecting changes in seedling water flow properties. At pH 6, transpiration rates were about twofold lower in non-inoculated plants treated with NaCl compared with non-treated controls. For NaCl-treated H. crustuliniforme- and L. bicolor-inoculated plants, the greatest reduction of transpiration rates was at pH 9. Treatment with 60 mM NaCl reduced leaf chlorophyll concentrations more in non-inoculated compared with inoculated plants, with the greatest, twofold, decrease occurring at pH 6. At pH 3, root Na concentrations were higher in inoculated than non-inoculated seedlings; however, there was no effect of inoculation on root Na concentrations at pH 6 and 9. Contrary to the roots, the leaves of inoculated plants had lower Na concentrations at pH 6 and 9, but not at pH 3. The results point to an interaction between ECM fungi and root zone pH for salt tolerance of American elm.     

Regulation of solute flux through plasmodesmata in the root meristem

Plasmodesmata permit solutes to move between cells nonspecifically and without having to cross a membrane. This symplastic connectivity, while straightforward to observe using fluorescent tracers, has proven difficult to quantify. We use fluorescence recovery after photobleaching, combined with a mathematical model of symplastic diffusion, to assay plasmodesmata-mediated permeability in the Arabidopsis (Arabidopsis thaliana) root meristem in wild-type and transgenic lines, and under selected chemical treatments. The permeability measured for the wild type is nearly 10-times greater than previously reported. Plamodesmal permeability remains constant in seedlings treated with auxin (30 mM indoleacetic acid for 2 and 24 h; 100 nm indoleacetic acid for 2 h); however, permeability is diminished in two lines previously reported to have impaired plasmodesmal function as well as in wild-type seedlings treated for 24 h with 0.6 mM tryptophan. Moreover, plasmodesmal permeability is strongly altered by applied hydrogen peroxide within 2 h of treatment, being approximately doubled at a low concentration (0.6 mM) and nearly eliminated at a higher one (6 mM). These results reveal that the plasmodesmata in the root meristem carry a substantial flux of small molecules and that this flux is subject to rapid regulation.     

Regulation of Nitrate Reductase during Early Seedling Growth (A Role for Asparagine and Glutamine)

Growth systems that either permit (wet system) or prevent (dry system) the hydrolysis of endosperm reserves in maize (Zea mays) seedlings were developed to study the effect of endosperm reserves on the acquisition of external nitrogen. Three-day-old seedlings treated with 5 mM KNO3 for 24 h had higher levels of nitrate reductase (NR) activity and protein in shoot and root tissues in the dry relative to the wet system. This suggests that the induction of NR is sensitive to products of hydrolysis of endosperm reserves. Asparagine (1 mM) or glutamine (1 mM), potential products of that hydrolysis, inhibited the induction of NADH-dependent root NR in the dry system by about 70%. The inhibition of the induction of NR activity in the wet system was only about 35%, suggesting that the enzyme in the wet system was already partially repressed at 3 d. At 5 d, when asparagine and glutamine levels in the plant tissue had decreased, the induction of root NR activity was inhibited to a similar extent in the two growth systems by amide additions. The shoot enzyme was less sensitive to amide additions, and 10 mM concentrations of either amide was required for a 65% inhibition.     

O-Benzylhydroxylamine: An Inhibitor of Phenylpropanoid Metabolism in Plants

O-Benzylhydroxylamine (OBHA) is a potent inhibitor of phenylalanineammonialyase (PAL, EC 4.3.1.5 [EC] ) and phenylpropanoid metabolismas evidenced by its effects on three plant species [soybean(Glycine max (L.) Merr.), buckwheat (Fagopyrum esculentum Moench.),and mung bean (Vigna radiata L.)]. When supplied to roots, OBHA(10^–5 M) did not significantly inhibit light- or dark-growthof soybean seedlings, but reduced (25%) soluble hydroxyphenoliccompound accumulation in light-grown axes. Higher concentrations(510^–5 M) of OBHA caused reductions (25%) in axis freshweight of light-grown seedlings (72 h), but did not lower axisweight of dark-grown seedlings. Anthocyanin accumulation inhypocotyls of intact mung bean seedlings was reduced by 25%after 3 days light growth after treatment with OBHA (10^–5M) via root feeding. Anthocyanin content of excised, etiolatedbuckwheat hypocotyls floated on solutions of OBHA (10^–5M) and incubated in the light for 24 h was reduced by 40%. L-Phenylalanineand t-cinnamic acid, intermediates of phenylpropanoid metabolism,were able to partially reverse this inhibition in buckwheat.Extractable PAL activity (specific activity basis) in soybeanaxes was substantially reduced (20% in dark, 40% in light) asearly as 24 h after root feeding with OBHA (10^–5 M). Reductionof PAL activity (specific activity or per axis basis) by OBHAcompared to control levels, continued throughout a time courseof 96 h. Kinetic studies on soybean PAL revealed a K_m of 1.1mM for L-phenylalanine and an apparent K_i of 3.5 µM forOBHA. (Received May 31, 1985; Accepted August 6, 1985)     

Amelioration of salinity tolerance in <Emphasis Type="Italic">Solanum tuberosum</Emphasis> L. by exogenous application of ascorbic acid

The present investigation envisaged revealing the role of exogenous application of ascorbic acid in increasing resistance against NaCl stress. Shoot apices from 60-d-old, in vitro-grown plants of two commercially important cultivars of Solanum tuberosum L., cvs. Desiree and Cardinal, were inoculated on Murashige and Skoog (MS) medium supplemented with 0.5 mM ascorbic acid for 72 h as a pretreatment. Pretreated and non-pretreated shoot apices were transferred to MS medium containing different concentrations of NaCl (0–140 mM; eight treatments). Results were recorded for morphological (shoot length, shoot number, root length, root number, and number of nodes) and biochemical features (protein, peroxidase, catalase, and superoxide dismutase activities) after 60 d of salt treatment. Similarly, 60-d-old, well-proliferated callus cultures were also pretreated with ascorbic acid for 24 h and transferred to an optimized callus proliferation medium containing different concentrations of salt. Results were recorded after 60 d of salt treatment for percentage relative fresh weight growth and biochemical parameters. Salinity severely inhibited all the growth parameters in both the cultivars. Pretreatment with ascorbic acid to both salt-treated plants and callus cultures showed significant differences with respect to almost all of the growth and biochemical parameters studied. Protein content as well as catalase and superoxide dismutase activities increased significantly in both the cultivars, although peroxidase activity showed a decreasing trend in ascorbic acid-pretreated plants as well as callus cultures.     

Metal uptake,antioxidant status and membrane potential in maize roots exposed to cadmium and nickel

Root growth of the seedlings of maize cultivars Premia and Blitz exposed to 2 μM cadmium (Cd), nickel (Ni) or both metals acting simultaneously (Cd + Ni) for 72 h was significantly reduced but not ceased. The effect was more pronounced in the seedlings of the cv. Blitz. The heavy metals (HMs) contents increased significantly in the roots. Simultaneous application of metals had an antagonistic effect on either Cd or Ni uptake in Premia but not in Blitz. In control roots the contents of ascorbic acid (AsA) and dehydroascorbic acid (DHA) were lower and gluthatione (GSH) content was higher in Premia than in Blitz. A decrease of AsA content was induced by all metal treatments in Premia but only by Cd + Ni in Blitz while an increase was induced by single metals in this cultivar. All metal treatments increased DHA contents in both cultivars. GSH content decreased significantly in Premia treated with Cd or Cd + Ni, and in Blitz treated with Ni. Unlike the contents of AsA, DHA and GSH, the increased metal concentrations in root cells did not affect the membrane potential (E _M). The changes in antioxidant contents depended on both, maize genotypes and HMs treatments. Nevertheless, the results indicated a role of antioxidative system in minimizing the effects of oxidative stress and protecting cell membranes in both maize cultivars.     

Enhancing effects of 24-epibrassinolide and Putrescine on the antioxidant capacity and free radical scavenging activity of <Emphasis Type="Italic">Raphanus sativus</Emphasis> seedlings under Cu ion stress

The present investigation recorded significant restoration of seedling growth (root length, shoot length and fresh weight) upon application of 24-epibrassinolide (EBL) and putrescine (Put) to 7-day-old seedlings of Raphanus sativus L. cv. Pusa chetki grown under copper (Cu) ion stress. EBL and Put with/or without Cu ion treated seedlings showed increased titers of ascorbic acid, total phenols and proline when compared with Cu-stressed seedlings. Differential responses in the activities of guaiacol peroxidase (GPOX) and catalase (CAT) were noted for EBL and Put alone or with/or without Cu ion treatment. Decreased activities of glutathione reductase (GR) and superoxide dismutase (SOD) noted for EBL and Put alone were observed to enhance significantly when applied in combination with Cu ion solution. A remarkable decrease in malondialdehyde contents was observed in seedlings treated with EBL and Put alone and with/or without Cu ion stress. Enhanced free radical scavenging activities were also recorded for seedlings given EBL and Put alone or in combination over Cu ion stressed seedlings. Maximum DPPH activity was observed in seedlings treated with Put and EBL 10⁻⁹ M + Put. Significant enhancements in deoxyribose and reducing power activities were too recorded for Put, EBL and Put + 10⁻⁹ M EBL treatments. Improved seedling growth, antioxidant levels (ascorbic acid, total phenols and proline) and enzymic (GPOX, CAT, SOD and GR) activities and free radical scavenging capacities along with reduced membrane damage in seedlings given EBL and Put with/or without Cu stress suggests significant and positive interactions of EBL and Put in alleviating the Cu ion induced oxidative damage in radish seedlings.