Unveiling The Potential Tolerance And Physiological Responses Mechanisms of Wheat (Ningmai 16) After Exposure to Nickel In a Soil-plant System

Nickel (Ni) accumulation in soils could lead to critical risks to plants, animals and humans. This study aims to unveil the adverse impacts of Ni on wheat Ningmai 16 and toxicity tolerance mechanisms. Lipid peroxidation was significantly facilitated under high Ni stress, mainly reflecting the notable accumulation of malondialdehyde followed by the increase in glutathione-S-transferase (GST) activities. High Ni contamination caused the decrease in chlorophyll content, with the remarkable inhibition of root activity. Transmission electron microscopy (TEM) micrographs further confirmed the toxicity of Ni and provided significant supporting evidence for the accumulation and localisation of Ni in wheat. The mechanisms adopted in alleviating the oxidative damages induced by Ni were revealed by increasing the soluble sugar and proline content, and inducing the GST related gene expression. Additionally, the cell-wall thickening and vacuole compartmentation were also produced in wheat for improving the tolerance of Ni. Finally, most of biochemical parameters indicated a clearly positive or negative relationship with the available Ni contents, and they are proved as good biomarkers to predict the bioavailability of Ni in a soil-wheat system. We believe that our concluding findings would open a new window for a deeper understanding of ecological risks of an often-underestimated element Ni in future endeavors.

Overexpression of ZNT1 and NRAMP4 from the Ni Hyperaccumulator Noccaea caerulescens Population Monte Prinzera in Arabidopsis thaliana Perturbs Fe, Mn, and Ni Accumulation

Metalliferous soils are characterized by a high content of metal compounds that can hamper plant growth. The pseudometallophyte Noccaea caerulescens is able to grow on metalliferous substrates by implementing both tolerance and accumulation of usually toxic metal ions. Expression of particular transmembrane transporter proteins (e.g., members of the ZIP and NRAMP families) leads to metal tolerance and accumulation, and its comparison between hyperaccumulator N. caerulescens with non-accumulator relatives Arabidopsis thaliana and Thlaspi arvense has deepened our knowledge on mechanisms adopted by plants to survive in metalliferous soils. In this work, two transporters, ZNT1 and NRAMP4, expressed in a serpentinic population of N. caerulescens identified on the Monte Prinzera (Italy) are considered, and their expression has been induced in yeast and in A. thaliana. In the latter, single transgenic lines were crossed to test the effect of the combined over-expression of the two transporters. An enhanced iron and manganese translocation towards the shoot was induced by overexpression of NcZNT1. The combined overexpression of NcZNT1 and NcNRAMP4 did perturb the metal accumulation in plants.

Role of Jasmonic and Salicylic Acid on Enzymatic Changes in the Root of Two Alyssum Inflatum Náyr. Populations Exposed to Nickel Toxicity

Salicylic acid (SA) and jasmonic acid (JA) as plant growth regulators (PGRs) have the potential to ameliorate plant development and tolerance to deleterious effects of toxic metals like nickel (Ni). Therefore, the current study was carried out to evaluate SA and JA's interactive effect on the root antioxidative response of two Alyssum inflatum Nyár. populations against Ni-toxicity. Two A. inflatum species under Ni-stress conditions (0, 100, 200, and 400 µM) were exposed to alone or combined levels of SA (0, 50, and 200 µM) and JA (0, 5, and 10 µM) treatments. Results showed that high Ni doses reduced the roots fresh weight (FW) in two populations than control; however, the use of external PGRs had ameliorated roots biomass by mitigated Ni-toxicity. Under Ni toxicity, SA and JA, especially their combination, induced high Ni accumulation in plants' roots. Moreover, the application of SA and JA alone, as well as combined SA + JA, was found to be effective in the scavenging of hydrogen peroxide (H2O2) by improving the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in both populations under Ni-toxicity. Overall, our results manifest that SA and JA's external use, especially combined SA + JA treatments, ameliorate root biomass and plant tolerance by restricting translocation Ni to the shoot, accumulating in roots, and also enhancing antioxidant defense systems.

Role of Jasmonic and Salicylic Acid on Enzymatic Changes in The Root of Two Alyssum Inflatum Náyr. Populations Exposed to Nickel Toxicity

Salicylic acid (SA) and jasmonic acid (JA) as plant growth regulators (PGRs) have the potential to ameliorate plant development and tolerance to deleterious effects of toxic metals like nickel (Ni). Therefore, the current study was carried out to evaluate SA and JA's interactive effect on the root antioxidative response of two Alyssum inflatum Nyár. populations against Ni-toxicity. Two A. inflatum species under Ni-stress conditions (0, 100, 200, and 400 µM) were exposed to alone or combined levels of SA (0, 50, and 200 µM) and JA (0, 5, and 10 µM) treatments. Results showed that high Ni doses reduced the roots fresh weight (FW) in two populations than control; however, the use of external PGRs had ameliorated roots biomass by mitigated Ni-toxicity. Under Ni toxicity, SA and JA, especially their combination, induced high Ni accumulation in plants' roots. Moreover, the application of SA and JA alone, as well as combined SA + JA, was found to be effective in the scavenging of hydrogen peroxide (H2O2) by improving the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in both populations under Ni-toxicity. Overall, our results manifest that SA and JA's external use, especially combined SA + JA treatments, ameliorate root biomass and plant tolerance by restricting translocation Ni to the shoot, accumulating in roots, and also enhancing antioxidant defense systems.

Difference between Selenite and Selenate in the Regulation of Growth and Physiological Parameters of Nickel-Exposed Lettuce

Nickel is an essential plant micronutrient; however, even at low concentrations, it may be phytotoxic. Selenium is a beneficial element with an alleviating effect that has been confirmed in the case of many abiotic stresses, including metal toxicity. The aim of this study is to assess the effect of two forms of Se (Se(IV) or Se(VI)) on the phytotoxicity, accumulation, and translocation of Ni in lettuce. Nickel causes a reduction in lettuce growth and vitality of roots, probably through increased lipid peroxidation. The application of Se(IV) to a Ni-contaminated medium resulted in a further reduction of growth, especially in the presence of 6 µM Se(IV). The growth-promoting effect of Se was found only in the 2 µM Se(VI)/10 µM Ni treatment. The application of 6 µM Se, regardless of the Se form, to the Ni-containing substrate caused an increase in shoot Ni concentration. In turn, a decrease in root Ni content was found for all Se treatments. The strong aggravation of Ni phytotoxicity in the presence of 6 µM Se(IV) was most likely related to the accumulation of high Se concentration in the roots, and the combination of high root Ni accumulation caused irreversible dysregulation of cell metabolism.

Inability to accumulate Ni in a genus of hyperaccumulators: the paradox of Odontarrhena sibirica (Brassicaceae)

Main conclusion Odontarrhena is a highly diverse genus of Ni-hyperaccumulators. Here, we demonstrate substantial inability to accumulate Ni in the facultative serpentinophyte O. sibirica, which seems a unique case among the numerous species of the genus that grow on ultramafic soils. Abstract Odontarrhena is the most diverse genus of Ni-accumulating plants in W Eurasia, with most taxa growing obligatorily or facultatively on ultramafic soils. A notable exception may be O. sibirica, a facultative serpentinophyte from the E Mediterranean and W Asia in which accumulation ability is still enigmatic. We addressed this issue using observational and experimental methods. Atomic Absorption Analysis of 33 herbarium specimens and plant and soil samples from seven ultramafic and non-ultramafic sites in Greece revealed shoot Ni values always much lower than 1000 µg g−1, non-significant differences between plants from the two soil types and no relationship with soil pH. Only two Turkish specimens from waste mines had shoot Ni concentration > 1000 µg g−1. The reasons for this deviating result remain obscure, but may be associated with inherent peculiarities of the local populations. When cultivated together with congeneric Ni-accumulating species on the same natural ultramafic soil, only O. sibirica was unable to accumulate the metal. Although plant growth was stimulated in hydroponics at relatively low NiSO4 levels (50–150 µM), as typical for hyperaccumulators, Ni-accumulation occurred only at higher concentrations which had a toxic effect. This peculiar combination of Ni-response traits could be the result of a partial evolutionary loss of ability with respect to all other Ni-accumulating congeneric species. For this, O. sibirica could represent a unique model system for further studies on the evolutionary dynamics, physiological mechanisms and genetic control of metal accumulation and homeostasis.

Nickel hyperaccumulation in New Caledonian Hybanthus (Violaceae) and occurrence of nickel-rich phloem in Hybanthus austrocaledonicus

Background and Aims Hybanthus austrocaledonicus (Violaceae) is a nickel (Ni) hyperaccumulator endemic to New Caledonia. One of the specimens stored at the local herbarium had a strip of bark with a remarkably green phloem tissue attached to the sheet containing over 4 wt% Ni. This study aimed to collect field samples from the original H. austrocaledonicus locality to confirm the nature of the green ‘nickel-rich phloem’ in this taxon and to systematically assess the occurrence of Ni hyperaccumulation in H. austrocaledonicus and Hybanthus caledonicus populations. Methods X-ray fluorescence spectroscopy scanning of all collections of the genus Hybanthus (236 specimens) was undertaken at the Herbarium of New Caledonia to reveal incidences of Ni accumulation in populations of H. austrocaledonicus and H. caledonicus. In parallel, micro-analytical investigations were performed via synchrotron X-ray fluorescence microscopy (XFM) and scanning electron microscopy with X-ray microanalysis (SEM-EDS). Key Results The extensive scanning demonstrated that Ni hyperaccumulation is not a characteristic common to all populations in the endemic Hybanthus species. Synchrotron XFM revealed that Ni was exclusively concentrated in the epidermal cells of the leaf blade and petiole, conforming with the majority of (tropical) Ni hyperaccumulator plants studied to date. SEM-EDS of freeze-dried and frozen-hydrated samples revealed the presence of dense solid deposits in the phloem bundles that contained >8 wt% nickel. Conclusions The occurrence of extremely Ni-rich green phloem tissues appears to be a characteristic feature of tropical Ni hyperaccumulator plants.

Biotolerance of Orechromis niloticus to Nickel (Ni) Inside the Agodi Reservoir at Ibadan, Nigeria

Orechromis niloticus (Tilapia) that was rarely found in feeder Ogunpa River was more invasive in the receiving Agodi Reservoir and this provoked an examination of the remote causes. .Sampled water temperature and pH were measured with standard analytical methods while Ni, Co and Cr concentrations in water and fish were selectively tested using Atomic Absorption Spectrophotometer (AAS).Data obtained were subjected to analysis of variance and linear regression to establish clear relationships. On the average, temperature was 27.15ºC, pH 7.56, Ni 0.27 mg/L, Co 0.75 mg/L and Cr 0.005 mg/Lin Ogunpa River, while in Agodi Reservoir, temperature was 27.42ºC, pH 7.57, Ni 0.17 mg/L, Co 0.19 mg/L and Cr 0.005 mg/L. The temperature and pH values were higher in Agodi Reservoir than in the Ogunpa River but only the concentrations of Ni and Co in Ogunpa River were higher than in Agodi Reservoir. Using the FAO/WHO permissible limits, only the Ni concentration appeared potent in influencing Tilapia eco-dynamics. Ni accumulation could be lethal and must have affected the fish relocation and distribution, thus, a conclusion that Ni concentration and its synergistic effects with temperature could be responsible for the migration of the fish into the Agodi Reservoir.