Salicylic acid enhances nickel stress tolerance by up-regulating antioxidant defense and glyoxalase systems in mustard plants.

Nickel (Ni) is known to be a major carcinogenic heavy metal. Occupational and environmental exposure to Ni has been implicated in human lung and nasal cancers. Currently, the molecular mechanisms of Ni carcinogenicity remain unclear, but studies have shown that Ni-caused DNA damage is an important carcinogenic mechanism. Therefore, we conducted a literature search of DNA damage associated with Ni exposure and summarized known Ni-caused DNA damage effects. In vitro and vivo studies demonstrated that Ni can induce DNA damage through direct DNA binding and reactive oxygen species (ROS) stimulation. Ni can also repress the DNA damage repair systems, including direct reversal, nucleotide repair (NER), base excision repair (BER), mismatch repair (MMR), homologous-recombination repair (HR), and nonhomologous end-joining (NHEJ) repair pathways. The repression of DNA repair is through direct enzyme inhibition and the downregulation of DNA repair molecule expression. Up to now, the exact mechanisms of DNA damage caused by Ni and Ni compounds remain unclear. Revealing the mechanisms of DNA damage from Ni exposure may contribute to the development of preventive strategies in Ni carcinogenicity.

Nickel Carcinogenesis Mechanism: DNA Damage.

Interactive role of epibrassinolide and hydrogen peroxide in regulating stomatal physiology, root morphology, photosynthetic and growth traits in Solanum lycopersicum L. under nickel stress

Arbuscular mycorrhizal fungi alleviate the heavy metal toxicity on sunflower (Helianthus annuus L.) plants cultivated on a heavily contaminated field soil at a WEEE-recycling site.

Soil polluted with heavy metals is a continuous threat to global crop production. The present study deals with growth, biochemical attributes, photosynthetic pigments, antioxidant responses and gyloxalase systems of mustard plants under varying concentrations of nickel (Ni) stress. Ni stress (150 µM) reduced growth (shoot length by 34.46% and root length by 52.49%), chlorophyll (57.63%), gas exchange parameters (PN by 36.84%, A by 55.61%), leaf relative water content (LRWC by 24.34%), and enhanced hydrogen peroxide (H2O2 by3.23 fold) malondialdehyde (MDA by 2.07 fold), and methylglyoxal (MG by 3.32 fold) content. Si (10− 5 M) application ameliorated the negative effects of Ni on growth, chlorophyll content, photosynthetic traits and also elevated the activities of antioxidant enzymes and enzymes associated with the ascorbate glutathione (AsA-GSH) cycle and glyoxylase systems. Nevertheless, Si application to Ni-stressed plants had an additive effect on the enzyme activities of antioxidants and enzymes of AsA-GSH cycle. Exogenous Si supplementation elevated endogenous Si content which decreased root to shoot Ni translocation and maintained optimum osmolyte and secondary metabolite accumulation. We conclude that Si-induced Ni stress tolerance in mustard plants could be correlated with the upregulation of enzymes associated with antioxidant defence, glyoxalase detoxification systems and sufficient primary and secondary osmoprotectant accumulation.

Silicon Alleviates Nickel-Induced Oxidative Stress by Regulating Antioxidant Defense and Glyoxalase Systems in Mustard Plants

With the boom in industrialization, there is an increase in the level of heavy metals in the soil which drastically affect the growth and development of plants. Nickel is an essential micronutrient for plant growth and development, but elevated level of Ni causes stunted growth, chlorosis, nutrient imbalance, and alterations in the defense mechanism of plants in terms of accumulation of osmolytes or change in enzyme activities like guiacol peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD). Ni-induced toxic response was studied in seedlings of finger millet, pearl millet, and oats in terms of seedling growth, lipid peroxidation, total chlorophyll, proline content, and enzymatic activities. On the basis of germination and growth parameters of the seedling, finger millet was found to be the most tolerant. Nickel accumulation was markedly lower in the shoots as compared to the roots, which was the highest in finger millet and the lowest in shoots of oats. Plants treated with a high concentration of Ni showed significant reduction in chlorophyll and increase in proline content. Considerable difference in level of malondialdehyde (MDA) content and activity of antioxidative enzymes indicates generation of redox imbalance in plants due to Ni-induced stress. Elevated activities of POD and SOD were observed with high concentrations of Ni while CAT activity was found to be reduced. It was observed that finger millet has higher capability to maintain homeostasis by keeping the balance between accumulation and ROS scavenging system than pearl millet and oats. The data provide insight into the physiological and biochemical changes in plants adapted to survive in Ni-rich environment. This study will help in selecting the more suitable crop species to be grown on Ni-rich soils.

Raini Verma

Papers

Nickel accumulation and its effect on growth, physiological and biochemical parameters in millets and oats

Relative morpho-physiological responses of millets and oats against lead toxicity