Nalini Pandey

Effect of heavy metals Co2+, Ni2+ and Cd2+ on growth and metabolism of cabbage

Abstract Exposure of cabbage plants to excess (500 μM) of Co 2+ , Ni 2+ and Cd 2+ in sand culture led to increased accumulation of the metals, inhibition of growth and induction of visible symptoms of metal toxicity. In addition to chlorosis, Co 2+ treated plants exhibited reddish purple coloration along leaf margins, Ni 2+ treated plants exhibited black spots near leaf margins, and Cd 2+ treated plants developed purple coloration along leaf margins. At equimolar concentration, inhibition of growth was most severe with excess Cd 2+ and induction of visible symptoms was most severe with excess Ni 2+ . Exposure to excess concentration of the heavy metals decreased the uptake of Fe and its translocation to leaves. Exposure to each Co 2+ , Ni 2+ and Cd 2+ decreased chlorophyll content (Ni 2+ >Cd 2+ >Co 2+ ), concomitant with decrease in the activities of the Fe enzymes—catalase and peroxidase, suggesting reduced availability of Fe for chlorophyll–heme biosynthesis. Each Co 2+ , Ni 2+ and Cd 2+ decreased water potential and transpiration rate, associated with increase in diffusive resistance showing development of water stress. This was further substantiated by enhanced accumulation of proline in the leaves of plants exposed to Co 2+ , Ni 2+ and Cd 2+ .

Chromium interference in iron nutrition and water relations of cabbage

Abstract Cabbage (Brassica oleracea var. capitata cv. Snowball), known to be responsive to potentially toxic elements, was investigated for chromium (Cr3+) effect on iron metabolism and water relations. After 6 weeks growth in sand culture, a set of plants was supplied with 500 μM Cr3+ (CrCl3), superimposed over the full nutrient solution (control). Exposure to excess Cr3+ led to increased accumulation of Cr, more in roots than in leaves, and to the development of toxicity symptoms. In decreasing chlorophyll concentration and the activities of heme enzymes, catalase and peroxidase, the excess Cr3+ effect resembled Fe deficiency. These changes, associated with decrease in Fe accumulation in Cr3+ treated plants, indicate that by reducing absorption of Fe, Cr3+ impairs the Fe requiring steps of chlorophyll and heme biosynthesis. In spite of lower water saturation deficit, the leaves of Cr3+ treated plants showed decrease in leaf water potential, associated with increase in diffusive resistance and lowering of transpiration rate, indicating development of water stress. Enhanced accumulation of proline in Cr3+ treated plants also suggested this. Observed changes in water stress parameters in Cr3+ stressed plants indicate that plant exposure to excess supply of Cr3+ reduces the physiological availability of water.

Enzymic changes in response to zinc nutrition

Summary With a view to evaluating the suitability of Zn induced changes in enzyme activities and for assessing Zn nutrient status, black gram ( Vigna mungo L. cv. IPU 94) was grown under controlled sand culture at five levels of Zn supply ranging from 0.01 to 10 μmol/L. Leaves of 60 d old plants were examined for Zn concentration and activities of fructose 1,6 biphosphate aldolase, carbonic anhydrase, total superoxide dismutase, Cu-Zn SOD, acid phosphatase and ribonuclease, which have been shown to be activated/inhibited by Zn deficiency. Sub-optimal supply of Zn decreased the activities of FBPAse, CA, total SOD and Cu-Zn SOD and increased the activities of APase and RNAse. Activities of the Zn enzymes CA and Cu-Zn SOD, are highly correlated with Zn supply, and suitable as indicators of Zn nutrient status of plants. Activation of APase and RNAse by other micronutrient deficiencies and stress conditions does not favour their use as indicators of Zn nutrient stress.

Heavy metals, Co, Ni, Cu, Zn and Cd, produce oxidative damage and evoke differential antioxidant responses in spinach

Exposure of 10-d-old spinach (Spinacea oleracea L.) plants to excess (500 µM) concentrations of Co, Ni, Cu, Zn and Cd in sand culture inhibited growth, induced toxicity symptoms, oxidative damage and changes in the antioxidant defense system. The severity of the metal-induced effects varied with the metals and the duration of exposure to excess supply of the metals. Each metal induced chlorosis. In addition, excess Co, Ni and Cd also produced metal specific toxic effects. Excess supply of each metal caused lipid peroxidation (TBARS). Their effectiveness in producing oxidative damage was in the order: Ni > Co > Cd > Cu >Zn. Of all the metals, Ni was also most effective in lowering the concentration of the chloroplast pigments (Chl, Car). While each metal increased the concentration of ascorbate and activated the key enzymes of the ascorbate-glutathione cycle, excess Cd and Zn were more effective in this regard. Each metal increased the activity of SOD and POD and decreased the activity of CAT. Enhancement in SOD activity and inhibition of CAT activity suggested high build-up of H2O2, possibly the main cause of oxidative stress, induced in response to excess supply of the heavy metals.

Induction of oxidative stress and antioxidant responses in Vigna mungo by zinc stress

Significant changes were observed in the antioxidant systems in the leaves of black gram (Vigna mungo L., var. DPU-88-31) grown under deficient and excess supply of Zn. Plant grown with Zn supply ranging from 0.01 to 10.0 μM under glasshouse conditions showed optimal growth and biomass yield at 1.0 μM Zn supply. Deficient (0.001 and 0.01 μM) as well as excess (2.0 and 10.0 μM) supply of Zn decreased the concentrations of chlorophyll, carotenoids, and nonprotein thiols and increased that of ascorbate. The activity of superoxide dismutase and carbonic anhydrase was decreased at deficient levels and increased with increase in Zn supply up to 10 μM. At both stages of growth, the activities of antioxidant enzymes, such as catalase and ascorbate peroxidase, were decreased, whereas the activities of glutathione reductase and peroxidase were increased at both deficient and excess supply of Zn. An accumulation of hydrogen peroxide and thiobarbituric acid-reactive substances was observed in Zn-stressed leaves, indicating oxidative damage. Different responses to deficient and excess supply of Zn were observed in the production of oxidative damage.

Impairment in reproductive development is a major factor limiting yield of black gram under zinc deficiency

Black gram [Vigna mungo (L.) Hepper] cv. IPU 94 plants grown in sand culture with deficient zinc (0.1 µM Zn) nutrition and those deprived of normal (1 µM) Zn supply at the initiation of flowering, showed decrease in dry matter production and especially seed yield. These plants showed a decrease in the size of anthers and stigmatic heads, pollen producing capacity of the anthers and stigmatic exudations. Zn deficiency caused structural alterations in exine and retarded germination of pollen grains and tube growth. The pollen extracts and stigmatic exudates of the Zn-deficient plants showed increase in activity of acid phosphatase isoforms and inhibition of esterase isoforms. Zn deficiency led to decrease in number of pods, seeds per pod and seed mass, altered seed coat topography and reduced seeds germinability. Low seed yield under Zn deficiency is attributed to a role of Zn in pollen function, as also in pollen-pistil interaction conducive to fertilization and development of seeds.

The impact of foliar boron sprays on reproductive biology and seed quality of black gram

An experiment was conducted under glass house condition to study the effect of foliar application of boron (B) on reproductive biology and seed quality of black gram (Vigna mungo). Black gram (V. mungo L. var. DPU-88-31) was grown under controlled sand culture condition at deficient and sufficient B levels. After 32 days of sowing B deficient plants were sprayed with three concentrations of B (0.05%, 0.1% and 0.2% borax) at three different stages of reproductive development, i.e. prior to flowering, initiation of bud formation and after bud formation. Deficient B supply decreased the anther and pollen size, pollen tube growth, pollen viability as well as stigmatic receptivity which were increased by foliar B application. Foliar spray at all the three concentrations and at all stages increased the yield parameters like number of pods, pod size and number of seeds formed per plant. Foliar B application also improved the seed yield and seed quality in terms of storage seed proteins (albumin, globulin, glutenin and prolamin) and carbohydrates (sugars and starch) in black gram. The foliar application of B in appropriate doses (particularly 0.1%) after bud formation made quantitative and qualitative improvement in seed yield of black gram by supplementing additional/critical B requirements for reproductive development.

Antioxidant responses of pea genotypes to zinc deficiency

The effects of Zn deficiency on antioxidant responses of two pea (Pisum sativum L.) genotypes, a Zn-efficient IPFD-99-13 and Zn-inefficient KPMR-500, grown in sand culture were studied. In the pea genotype KPMR-500, Zn deficiency decreased dry matter yield, tissue Zn concentration, and antioxidant enzyme activities istronger than in the genotype IPFD-99-13. Genotype IPFD-99-13 developed more efficient antioxidant system to scavenge ROS than genotype KPMR-500. Zinc deficiency produced oxidative damage to pea genotypes due to enhanced accumulation of TBARS and H2O2 and decreased activities of antioxidant enzymes (Cu/Zn superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX)). In the leaves of IPFD-99-13 genotype, the higher activity of ROS-scavenging enzyme, e.g., SOD, CAT, POD, and glutathione reductase, and antioxidants, such as ascorbate and non-protein thiols, led to the lower accumulation of H2O2 and lipid peroxides. These results suggest that, by maintaining an efficient antioxidant defense system, the IPFD-99-13 genotype shows a lower sensivity to Zn deficiency than the KPMR-500 genotype.

Improving reproductive efficiency of chickpea by foliar application of zinc

Zinc deficiency is not only the cause of low productivity of crops, but it also results in low zinc content in seeds, which leads to poor dietary zinc intake. To study the effect of zinc foliar application on improving plant yield and seed zinc content for human consumption, chickpea plants were raised in refined sand culture with deficient (0.2 µM) and sufficient (1µM) supply of zinc under glass-house conditions. Prior to initiation of the reproductive phase, zinc was applied as 0.1% ZnSO4 foliar spray to both zinc sufficient and deficient plants. The plants exposed to different zinc treatments were studied for pollen and stigma structure and their involvement in fertilization and seed yield. Zinc deficiency induces flower abortion, pollen, and ovule infertility leading to low seed set and ultimately its yield. Foliar application of ZnSO4 to zinc deficient plants at the time of initiation of flowering partially reverses the adverse effect of zinc deficiency on pollen-stigma morphology, pollen fertility, and greatly enhanced seed yield of plants. Zinc foliar application improved not only the boldness and vigor of seeds in zinc-deficient plants, but also the seed zinc content in zinc-deficient seeds as well as the sufficient ones.

Antioxidant Status of Vigna mungo L. in Response to Sulfur Nutrition

Black gram (Vigna mungo L. var. DPU-88-31), an edible legume, was grown at 1, 2, 4, 6, and 8 meq S L−1 to study the effect of deficient and excess level of sulfur on oxidative metabolism. Plants supplied by 4 meq S L−1 showed optimum yield. Sulfur deficient plants (1 and 2 meq S L−1) showed reduction in growth and chlorosis of young leaves. Tissue sulfur and cysteine concentration was increased with increasing sulfur supply. The thresholds for critical concentration of sulfur deficiency and toxicity were 0.315% and 0.434% dry weight. Biomass and photoassimilatory pigments were decreased and carbohydrates (sugar and starch) were accumulated in leaves of sulfur deficient and excess plants. Accumulation of hydrogen peroxide and thiobarbituric acid reactive substances in sulfur deficient and excess plants caused oxidative damage in plants which was also evident by the increase in the activity of superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione reductase, and concentration of ascorbate and nonprotein thiols.