Rajesh Kumar Tewari

Modulation of oxidative stress responsive enzymes by excess cobalt

Abstract Excess concentration of cobalt in the growth medium produced visual symptoms of toxicity that intensified with increasing level and duration of metal supply. The tissue concentration of cobalt increased with increasing level of supply. Decreased concentrations of chlorophylls and carotenoids and an increased carotenoids/chlorophyll ratio along with a marked increase in the activities of anti-oxidative enzymes, viz. superoxide dismutase (SOD), ascorbate peroxidase (APOD) and nonspecific peroxidase (POD) suggest strong induction of oxidative stress due to excess cobalt in the growth medium. Decrease in the activity of catalase (CAT)—an iron enzyme, may suggest interference of excess cobalt in iron metabolism of plants, particularly above a 50 μM supply. Decrease in hydrogen peroxide with an increase in cobalt supply has been attributed to increased activities of POD and APOD. Increase in dry matter yield of plants supplied 50 μM cobalt and the decrease in lipid peroxidation with increasing cobalt supply in the range 50–200 μM is suggested as a result from depletion of functional iron as phosphate and/or in ferritin. Appearance of the metal specific toxicity is the likely result of damages predominantly due to enhanced reactive oxygen species (ROS) generation at higher, 300–400 μM, cobalt supplies.

Early Signs of Oxidative Stress in Wheat Plants Subjected to Zinc Deficiency

Abstract Anti-oxidative defense systems in wheat plants were studied as a function of zinc deficiency in solution culture under glasshouse conditions. Zinc (Zn) deficiency enhanced cyanide-insensitive superoxide dismutase activity significantly, and decreased the activity of cyanide-sensitive superoxide dismutase before the appearance of visible effects of Zn deficiency. The plants with incipient deficiency of Zn also had significantly higher activities of nonspecific peroxidase, ascorbate peroxidase, and glutathione reductase. There was an increase in the concentrations of malondialdehyde, H2O2, dehydroascorbate, glutathione-sulfhydryl, and glutathione-disulphide, and the ratios carotenoids/chlorophyll, dehydroascorbate/ascorbate, and glutathione-sulfhydryl/glutathione-disulphide. As the effects of Zn deficiency became more severe, there was greater accumulation of malondialdehyde and H2O2, and the activities superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione reductase declined, particularly that of cyanide-sensitive superoxide dismutase. Restoration of Zn supply significantly increased activities of cyanide-sensitive and total superoxide dismutase and ascorbate peroxidase, and concentration of H2O2, and decreased malondialdehyde significantly within 24 h. Induction of anti-oxidative responses to Zn deficiency occurred rapidly and before symptoms of severe Zn deficiency. There was a depression of anti-oxidative responses as Zn deficiency become more severe, suggesting a break down of these defense systems at the onset of visible effects of Zn deficiency

Sodium nitroprusside-mediated alleviation of iron deficiency and modulation of antioxidant responses in maize plants

The nitric oxide donor sodium nitroprusside (SNP) promotes regreening of Fe-deficient maize plants. The effect is not the outcome of increased tissue Fe but of NO-modulation of oxidative changes that may favour conversions of internal Fe to more readily available ferrous iron.

Morphology and oxidative physiology of boron-deficient mulberry plants

The aim of the study was to induce B deficiency symptoms and to relate the generation of reactive oxygen species (ROS) and altered cellular redox environment with the effects of B deficiency in mulberry (Morus alba L.) cv. Kanva-2 plants. Study was undertaken on antioxidant responses, malondialdehyde (MDA) content as an indicator of oxidative damage and ratio of dehydroascorbate (DHA) to ascorbic acid (AsA) as an index of cellular redox environment in B-deficient (0.0 microM) and B-supraoptimal (33 microM) mulberry plants. B deficiency symptoms appeared as upward cupping of the young emerging leaves. Later on, B-deficient plants developed lenticels like cracks on major vein, petiole and stem. B-deficient leaves had higher water potential (Psi) and relative water content (RWC), contained a lower concentration of B, less chloroplastic pigments and high tissue Fe, Mn and Zn concentrations compared to the controls. Hydrogen peroxide was accumulated in leaves of B-deficient and B-supraoptimal plants. B-supraoptimal plants also showed an increased DHA/AsA ratio. The activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7) and ascorbate peroxidase (APX, EC 1.11.1.11) were increased in B-deficient leaves. The activities of SOD and POD were decreased in B-supraoptimal plants. The results suggest that B deficiency aggravates oxidative stress through enhanced generation of ROS in mulberry plants.

Oxidative stress and antioxidant responses of mulberry (Morus alba) plants subjected to deficiency and excess of manganese

The aim of the study was to relate the effects of deficiency and excess of Mn with the generation of reactive oxygen species (ROS) and altered cellular redox environment in mulberry (Morus alba L.) cv. Kanva-2 plants. Mn deficiency symptom appeared as mild interveinal chlorosis in middle leaves. Mn-excess did not produce any specific symptom. Leaf water potential (Ψ) was increased in Mn-deficient and Mn-excess mulberry plants. Mn-deficient leaves contained less Mn, less chloroplastic pigments and high tissue Fe, Zn and Cu concentrations. Starch content was increased with increasing Mn supply. While reducing sugar content increased in Mn-deficient and Mn-excess plants as well, non-reducing sugars remained unaffected in Mn-deficient plants and decreased in Mn-excess plants. Moreover, study of antioxidative responses, oxidative stress (H2O2 and lipid peroxidation) and cellular redox environment [dehydroascorbate (DHA)/ascorbic acid (AsA) ratio] in Mn-stressed mulberry plants was also undertaken. Both hydrogen peroxide and lipid peroxidation were enhanced in the leaves of Mn-deficient plants. Increased H2O2 concentration in Mn-excess leaves did not induce oxidative damage as indicated by no change in lipid peroxidation. The ratio of the redox couple (DHA/AsA) was increased both in Mn-deficient or Mn-excess plants. The activities of superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) increased in Mn-deficient plants. The activity of ascorbate peroxidase (EC 1.11.1.11) increased with increasing Mn supply. The results suggest that deficiency or excess of Mn induces oxidative stress through enhanced ROS generation and disturbed redox couple in mulberry plants.

The spatial patterns of oxidative stress indicators co-locate with early signs of natural senescence in maize leaves

Reactive oxygen species play a crucial role for various physiological and developmental processes in plants. Here, we report a spatial pattern of oxidative stress and antioxidant defence within maize leaf. Localization of hydrogen peroxide in different region of leaf clearly exhibits well-defined increasing pattern of accumulation from the base to the leaf tip. Lipid peroxidation, an index of oxidative damage, also showed a similar pattern-like hydrogen peroxide that is lowest at the base and highest at the leaf tip. NADPH oxidase, an enzyme responsible for superoxide anion generation, showed highest activity in the leaf tip and least in the leaf base regions. Superoxide dismutase (SOD) activity was increased from the base to the leaf tip. Peroxidases, DAB-peroxidase (DAB-POD) and guaiacol-peroxidase (G-POD), catalase (CAT) and glutathione reductase (GR) also showed increases in their activities from the base to the leaf tip. Ascorbate peroxidase (APX), however, showed a reverse trend—highest at the base and least in the leaf tip. The decrease in APX and increases in the activities of other antioxidant enzymes SOD, CAT, DAB-POD, G-POD and GR along with H2O2 and lipid peroxidation, ascorbate/dehydroascorbate and non-protein thiol levels from the base to the leaf tip clearly exhibit a spatial pattern prior to the onset of visible signs of senescence in the maize leaf.

Overproduction of stromal ferredoxin:NADPH oxidoreductase in H2O2-accumulating Brassica napus leaf protoplasts

Abstract The isolation of Brassica napus leaf protoplasts induces reactive oxygen species generation and accumulation in the chloroplasts. An activated isoform of NADPH oxidase-like protein was detected in the protoplasts and the protoplast chloroplasts. The purpose of this study is to define the NADH oxidase-like activities in the H2O2-accumulating protoplast chloroplasts. Proteomic analysis of this protein revealed an isoform of ferredoxin:NADPH oxidoreductase (FNR1). While leaves highly expressed the LFNR1 transcript, protoplasts decreased the expression significantly. The protoplast chloroplasts predominantly expressed soluble FNR1 proteins. While the albino leaves of white kale (Brassica oleracea var. acephala f. tricolor cv. white pigeon) expressed FNR1 protein at the same level as B. napus leaves, the protoplasts of albino leaves displayed reduced FNR1 expression. The albino leaf protoplasts of white kale generated and accumulated H2O2 in the cytoplasm and on the plasma membrane. Intracellular pH showed that the chloroplasts were acidic, which suggest that excess H+ was generated in chloroplast stroma. NADPH content of the protoplast chloroplasts increased by over sixfold during the isolation of protoplasts. This study reports a possibility of mediating electrons to oxygen by an overproduced soluble FNR, and suggests that the FNR has a function in utilizing any excess reducing power of NADPH.

Role of Nitric Oxide in Adventitious Root Development

Nitric oxide (NO) is a gaseous free radical and a diffusible signalling molecule. NO influences plant growth and development. NO also affects the plant responses to various stresses. Treatments of NO producers (SNP, sodium nitroprusside; SNAP, S-Nitroso-N-acetylpenicillamine) and NO scavenger (PTIO, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide) revealed that NO is involved in the induction of new rootlets. Severe decline in the number of new rootlets by PTIO treatment indicates that NO acts downstream of auxin action in the process of root development. NO producers (SNP and SNAP) activated NADPH oxidase-like activity, resulting in a greater superoxide anion generation and a higher number of new rootlets from the adventitious root explants. A severe inhibition of NADPH oxidase-like activity and decline in root biomass of SNP and SNAP treated root explants in the presence of the NADPH oxidase inhibitor (diphenyl iodonium, DPI), further supports the involvement of NADPH oxidase-like activity in adventitious root development. The number of rootlets induced per explant and NADPH oxidase-like activity were related to NO content present in adventitious root of Panax ginseng. NO and superoxide anion generation at the site of root emergence strongly suggest the key roles of NO and ROS in root development.