Root uptake and translocation of nickel in wheat as affected by histidine

Salicylic acid and jasmonic acid-mediated different fate of nickel phytoremediation in two populations of Alyssum inflatum Nyár

This study investigates Ni phytoremediation and accumulation potential in the presence of salicylic acid (SA) (0, 50 and 200 μM) and jasmonic acid (JA) (0, 5 and 10 μM) in two populations of Alyssum inflatum under various nickel (Ni) doses (0, 100 and 400 μM). By measuring Ni levels in the shoots and roots, values of bioaccumulation coefficient (BAC), biological concentration factor (BCF) and translocation factor (TF) were calculated to quantify Ni accumulation and translocation between plant organs. Additionally, the amounts of histidine (His), citric acid (CA) and malic acid (MA) were explored. The results showed that plant dry weight (DW) [in shoot (29.8%, 8.74%) and in root (21.6%, 24.4%)] and chlorophyll [a (17.1%, 32.5%), b (10.1%, 30.9%)] declined in M and NM populations respectively, when exposed to Ni (400 μM). Conversely, the levels of MA [in shoot (37.0%, 32.0%) and in root (25.5%, 21.2%)], CA [in shoot (17.0%, 10.0%) and in root (47.9%, 37.2%)] and His [in shoot (by 1.59- and 1.34-fold) and in root (by 1.24- and 1.18-fold)] increased. Also, in the presence 400 μM Ni, the highest accumulation of Ni was observed in shoots of M (1392 μg/g DW) and NM (1382 μg/g DW). However, the application of SA and JA (especially in Ni 400 μM + SA 200 μM + JA 5 and 10 μM treatments) mitigated the harmful impact of Ni on physiological parameters. Also, a decreasing trend was observed in the contents of MA, CA, and His. The reduction of these compounds as important chelators of Ni caused a decrease in root-to-shoot Ni transfer and reducing accumulation in the shoots of both populations. The values of phytoremediation indices in both populations exposed to Ni (400 μM) were above one. In presence of the SA and JA, these indices showed a decreasing trend, although the values remained above one (BAC, BCF and TF > 1). Overall, the results indicated that SA and JA can reduce phytoremediation potential of the two populations through different mechanisms.

Proton-coupled cotransporter involves phenanthrene xylem loading in roots

The uptake and translocation of polycyclic aromatic hydrocarbons (PAHs) by staple crops have gained much attention. However, the mechanism on phenanthrene xylem loading across plasma membrane is still unclear. In this study, we investigated the concentration dependence of phenanthrene xylem loading and the relationship between phenanthrene concentration and xylem sap pH. The impacts of metabolic inhibitor, temperature, and dissolved oxygen on phenanthrene concentration in xylem sap were observed as well. The Michaelis-Menten equation fits phenanthrene xylem loading across parenchyma cell membrane well and xylem sap pH decreases with the increase in treated phenanthrene concentration. Metabolic inhibitor, low temperature and low dissolved oxygen can suppress phenanthrene loading into xylem sap. The inhibitory rate of sodium vanadate on xylem sap phenanthrene is between 19.76% and 25.82%. Low temperature reduces phenanthrene concentration in xylem sap by 86.68%. Hypoxia (2 mg L^-1) inhibits phenanthrene loading into xylem by 78.67%. Therefore, it is indicated that H⁺/phenanthrene cotransporter is implicated in phenanthrene loading into xylem. Our work offers a valuable model to understand the mechanism of PAH loading into xylem.

The effect of foliar-applied magnesium on root cell membrane H+-ATPase activity and physiological characteristics of sugar beet

The aim of this study was to investigate the effect of foliar application of Mg on the leaf-to-root translocation of sugar and ATPase activity in the roots of sugar beet (Beta vulgaris L. Jolgeh). Furthermore, the effect of Mg on H⁺ secretion from the roots into the surrounding solution and solubility of Fe(OH)₃ (s) was investigated. Two Mg fertilizer sources i.e., MgSO₄ and Mg-lysine complex (Mg-Lys) were used. A group of plants received only lysine (Lys) and a control treatment free of Mg and Lys was used. Foliar Mg spray significantly increased Fe(OH)₃ (s) solubilization in the root environment, at least in part due to higher passive H⁺ transport from the roots into the solution. The active transport of H⁺ and root activity of ATPase was significantly lower in the plants receiving Mg in comparison with those not receiving Mg. In contrast, the passive transport of H⁺ was higher in the Mg treatments as compared with the control. Our results suggest that foliar applied Mg can moderate the root activity of ATPase pump but it may affect Fe solubility in the root media by enhancing the passive H⁺ permeation across plasma membrane.

The role of the cell walls in Ni binding by plant roots

The role of the cell wall in short-term Ni uptake at different solution Ni levels was investigated in mung bean (Vigna radiata (L.) R. Wilczek) and wheat (Triticum aestivum L., cv. Inna). Both Ni-binding capacity of the CWs and roots are lower for wheat than for mung bean at all Ni levels in the solution. For both plants amounts of Ni associated with roots and root cell walls increased with Ni concentration. The contribution of CWs to Ni absorption by roots depends on Ni level in the medium and plant species. The Ni accumulated in CWs could account for total Ni content of roots (except for wheat in highest Ni treatment). Besides, mung bean plants employ the strategy of reducing Ni accumulation in the root CWs during exposure to excess but not toxic solution Ni level. According to the results, predominant Ni binding in the apoplast of mung bean and wheat roots is observed at both high and low external Ni, which suggests that apoplastic pathway is the main means of Ni transport in the root cortex of these species.

Nickel; whether toxic or essential for plants and environment - A review

Nickel (Ni) is becoming a toxic pollutant in agricultural environments. Due to its diverse uses from a range of common household items to industrial applications, it is essential to examine Ni bioavailability in soil and plants. Ni occurs in the environment (soil, water and air) in very small concentrations and eventually taken up by plants through roots once it becomes available in soil. It is an essential nutrient for normal plant growth and development and required for the activation of several enzymes such as urease, and glyoxalase-I. Ni plays important roles in a wide range of physiological processes including seed germination, vegetative and reproductive growth, photosynthesis as well as in nitrogen metabolism. Therefore, plants cannot endure their life cycle without adequate Ni supply. However, excessive Ni concentration can lead to induce ROS production affecting numerous physiological and biochemical processes such as photosynthesis, transpiration, as well as mineral nutrition and causes phytotoxicity in plants. ROS production intensifies the disintegration of plasma membranes and deactivates functioning of vital enzymes through lipid peroxidation. This review article explores the essential roles of Ni in the life cycle of plant as well as its toxic effects in details. In conclusion, we have proposed different viable approaches for remediation of Ni-contaminated soils.

Nickel accumulation by the green algae-like Euglena gracilis

Nickel accumulation and nickel effects on cellular growth, respiration, photosynthesis, ascorbate peroxidase (APX) activity, and levels of thiols, histidine and phosphate-molecules were determined in Euglena gracilis. Cells incubated with 0.5-1mM NiCl₂ showed impairment of O₂ consumption, photosynthesis, Chl a+b content and APX activity whereas cellular integrity and viability were unaltered. Nickel accumulation was depressed by Mg²⁺ and Cu²⁺, while Ca²⁺, Co²⁺, Mn²⁺ and Zn²⁺ were innocuous. The growth half-inhibitory concentrations for Ni²⁺ in the culture medium supplemented with 2 or 0.2mM Mg²⁺ were 0.43 or 0.03mM Ni²⁺, respectively. Maximal nickel accumulation (1362mg nickel/Kg DW) was achieved in cells exposed to 1mM Ni²⁺ for 24h in the absence of Mg²⁺ and Cu²⁺; accumulated nickel was partially released after 72h. GSH polymers content increased or remained unchanged in cells exposed to 0.05-1mM Ni²⁺; however, GSH, cysteine, γ-glutamylcysteine, and phosphate-molecules all decreased after 72h. Histidine content increased in cells stressed with 0.05 and 0.5mM Ni²⁺ for 24h but not at longer times. It was concluded that E. gracilis can accumulate high nickel levels depending on the external Mg²⁺ and Cu²⁺ concentrations, in a process in which thiols, histidine and phosphate-molecules have a moderate contribution.

Hidden Nickel Deficiency? Nickel Fertilization via Soil Improves Nitrogen Metabolism and Grain Yield in Soybean Genotypes

Nickel (Ni)-a component of urease and hydrogenase-was the latest nutrient to be recognized as an essential element for plants. However, to date there are no records of Ni deficiency for annual species cultivated under field conditions, possibly because of the non-appearance of obvious and distinctive symptoms, i.e., a hidden (or latent) deficiency. Soybean, a crop cultivated on soils poor in extractable Ni, has a high dependence on biological nitrogen fixation (BNF), in which Ni plays a key role. Thus, we hypothesized that Ni fertilization in soybean genotypes results in a better nitrogen physiological function and in higher grain production due to the hidden deficiency of this micronutrient. To verify this hypothesis, two simultaneous experiments were carried out, under greenhouse and field conditions, with Ni supply of 0.0 or 0.5 mg of Ni kg^-1 of soil. For this, we used 15 soybean genotypes and two soybean isogenic lines (urease positive, Eu3; urease activity-null, eu3-a, formerly eu3-e1). Plants were evaluated for yield, Ni and N concentration, photosynthesis, and N metabolism. Nickel fertilization resulted in greater grain yield in some genotypes, indicating the hidden deficiency of Ni in both conditions. Yield gains of up to 2.9 g per plant in greenhouse and up to 1,502 kg ha^-1 in field conditions were associated with a promoted N metabolism, namely, leaf N concentration, ammonia, ureides, urea, and urease activity, which separated the genotypes into groups of Ni responsiveness. Nickel supply also positively affected photosynthesis in the genotypes, never causing detrimental effects, except for the eu3-a mutant, which due to the absence of ureolytic activity accumulated excess urea in leaves and had reduced yield. In summary, the effect of Ni on the plants was positive and the extent of this effect was controlled by genotype-environment interaction. The application of 0.5 mg kg^-1 of Ni resulted in safe levels of this element in grains for human health consumption. Including Ni applications in fertilization programs may provide significant yield benefits in soybean production on low Ni soil. This might also be the case for other annual crops, especially legumes.