Influence of Zn-contaminated soils in the antioxidative defence system of wheat (Triticum aestivum) and maize (Zea mays) at different exposure times: potential use as biomarkers

Effects of particle size on toxicity, bioaccumulation, and translocation of zinc oxide nanoparticles to bok choy (Brassica chinensis L.) in garden soil

The indiscriminate use of zinc oxide nanoparticles (ZnO NPs) in daily life can lead to their release into soil environment. These ZnO NPs can be taken up by crops and translocated to their edible part, potentially causing risks to the ecosystem and human health. In this study, we conducted pot experiments to determine phytotoxicity, bioaccumulation and translocation depending on the size (10 - 30 nm, 80 - 200 nm and 300 nm diameter) and concentration (0, 100, 500 and 1000 mg Zn/kg) of ZnO NPs and Zn ion (Zn2+) in bok choy, a leafy green vegetable crop. After 14 days of exposure, our results showed that large-sized ZnO NPs (i.e., 300 nm) at the highest concentration exhibited greater phytotoxicity, including obstruction of leaf and root weight (42.5 % and 33.8 %, respectively) and reduction of chlorophyll a and b content (50.2 % and 85.2 %, respectively), as well as changes in the activities of oxidative stress responses compared to those of small-sized ZnO NPs, although their translocation ability was relatively lower than that of smaller ones. The translocation factor (TF) values decreased as the size of ZnO NPs increased, with TF values of 0.68 for 10 - 30 nm, 0.55 for 80 - 200 nm, and 0.27 for 300 nm ZnO NPs, all at the highest exposure concentration. Both the results of micro X-ray fluorescence (μ-XRF) spectrometer and bio-transmission electron microscopy (bio-TEM) showed that the Zn elements were mainly localized at the edges of leaves exposed to small-sized ZnO NPs. However, the Zn elements upon exposure to large-sized ZnO NP were primarily observed in the primary veins of leaves in the μ-XRF data, indicating a limitation in their ability to translocate from roots to leaves. This study not only advances our comprehension of the environmental impact of nanotechnology but also holds considerable implications for the future of sustainable agriculture and food safety.

Comparative bioaccumulation, translocation, and phytotoxicity of metal oxide nanoparticles and metal ions in soil-crop system

Exposure of the soil environment to metal nanoparticles (MNPs) has been extensive because of their indiscriminate use and the disposal of MNP products in various applications. In MNP-amended soil, various crops can absorb the nanoparticles, and accumulation of the MNPs in farm products has potential risks for bioconcentration in humans and livestock. Here, we evaluated the comparative bioaccumulation, translocation, and phytotoxicity of MNPs (ZnO and CuO NPs) and metal ions (Zn(NO3)2 and Cu(NO3)2) in four different crops, namely lettuce, radish, bok choy, and tomato. We carried out pot experiments to evaluate the phytotoxicity in the crops from the presence of MNPs and metal ions. Phytotoxicity from different treatments differed depending on the plant species, and metal types. In addition, exposure to Zn and Cu showed positive dose-dependent effects on their bioaccumulation in each crop. However, there were no significant differences in metal bioaccumulation depending on whether the crops were exposed to MNPs or metal ions. By calculating the bioconcentration factor (BCF) and translocation factor (TF), we were able to estimate the biological uptake and translocation abilities of MNPs and metal ions for each crop. It was found that lettuce and radish had greater BCFs than bok choy and tomato, while bok choy and tomato had higher TFs. Also, the uptake and translocation of Zn were better than those of Cu. However, the values for BCF and TF for each crop showed no significant differences between MNP and metal ion exposure. A micro X-ray fluorescence (μ-XRF) spectrometer analysis demonstrated that only Zn elements appeared in the primary veins and edges of all leaves and the storage root of radish. Our study aims to estimate bioaccumulation, translocation, and the implied potential risks from MNPs accumulated in different plant species.

Hormetic effects of zinc on growth and antioxidant defense system of wheat plants

Although hormesis induced by heavy metals is a well-known phenomenon, the involved biological mechanisms are not fully understood. Zinc (Zn) is an essential micronutrient for wheat, an important crop contributing to food security as a main staple food; however, excessive Zn is detrimental to the growth of wheat. The aim of this study was to evaluate morphological and physiological responses of two wheat varieties exposed to a broad range of Zn concentrations (0-1000 μM) for 14 days. Hormesis was induced by Zn in both wheat varieties. Treatment with 10-100 μM Zn promoted biomass accumulation by enhancing the photosynthetic ability, the chlorophyll content and the activities of antioxidant enzymes. Increased root/shoot ratio suggested that shoot growth was severely inhibited when Zn concentration exceeded 300 μM by reducing photosynthetic ability and the content of photosynthetic pigments. Excessive Zn accumulation (Zn treatment of 300-1000 μM) in leaf and root induced membrane injuries through lipid peroxidation as malondialdehyde (MDA) content increased with increasing Zn concentration. The results show that MDA content was higher than other treatments by 16.1-151.1% and 15.0-88.3% (XN979) and 36.8-235.7% and 20.6-83.8% (BN207) in the leaves and roots under 1000 μM Zn treatment. To defend against Zn toxicity, ascorbate (AsA), glutathione (GSH), non-protein thiols (NPT) and phytochelatin (PC) content of both wheat varieties (except leaf GSH content of BN207) was increased, while, the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and the content of soluble protein decreased by 300-1000 μM Zn. The results showed that AsA-GSH cycle and NPT and PC content of wheat seedlings play important roles in defending against Zn toxicity. This study contributes new insights into the physiological mechanisms underlying the hormetic response of wheat to Zn, which could be beneficial for optimizing plant health in changing environments and improving risk assessments.

Influence of Seed Source and Soil Contamination on Ecophysiological Responses of Lavandula pedunculata in Rehabilitation of Mining Areas

Mining activities have turned many areas of the Iberian Pyrite Belt (IPB) into extreme environments with high concentrations of metal(loid)s. These harsh conditions can inhibit or reduce the colonization and/or development of most vegetation. However, some species or populations have developed ecophysiological responses to tolerate stress factors and contaminated soils. The main objectives of this study are: (i) to assess the differences in germination, growth, development and physiological behaviour against oxidative stress caused by metal(loid)s in Lavandula pedunculata (Mill.) Cav. from two different origins (a contaminated area in São Domingos mine, SE of Portugal and an uncontaminated area from Serra do Caldeirão, S of Portugal) under controlled conditions; and (ii) to assess whether it is possible to use this species for the rehabilitation of mine areas of the IPB. After germination, seedlings from São Domingos (LC) and Caldeirão (L) were planted in pots with a contaminated soil developed on gossan (CS) and in pots with an uncontaminated soil (US) under controlled conditions. Multielemental concentrations were determined in soils (total and available fractions) and plants (shoots and roots). Germination rate, shoot height, dry biomass and leaf area were determined, and pigments, glutathione, ascorbate and H2O2 contents were measured in plant shoots. Total concentrations of As, Cr, Cu, Pb and Sb in CS, and As in US exceed the intervention and maximum limits for ecosystem protection and human health. The main results showed that L. pedunculata, regardless of the seed origin, activated defence mechanisms against oxidative stress caused by high concentrations of metal(loid)s. Plants grown from seeds of both origins increased the production of AsA to preserve its reduction levels and kept the contents of GSH stable to maintain the cell’s redox state. Plants grown from seeds collected in non-contaminated areas showed a high capacity for adaptation to extreme conditions. This species showed a greater growth capacity when seeds from a contaminated area were sown in uncontaminated soils. Thus, L. pedunculata, mainly grown from seeds from contaminated areas, may be used in phytostabilization programmes in areas with soils with high contents of metal(loid)s.

Wheat Leaf Antioxidative Status—Variety-Specific Mechanisms of Zinc Tolerance during Biofortification

In this study, we evaluated the leaf antioxidative responses of three wheat varieties (Srpanjka, Divana, and Simonida) treated with two different forms of zinc (Zn), Zn-sulfate and Zn-EDTA, in concentrations commonly used in agronomic biofortification. Zn concentration was significantly higher in the flag leaves of all three wheat varieties treated with Zn-EDTA compared to control and leaves treated with Zn-sulfate. Both forms of Zn increased malondialdehyde level and total phenolics content in varieties Srpanjka and Divana. Total glutathione content was not affected after the Zn treatment. Zn-sulfate increased the activities of glutathione reductase (GR) and guaiacol peroxidase (GPOD) in both Srpanjka and Divana, while glutathione S-transferase (GST) was only induced in var. Srpanjka. Chelate form of Zn increased the activities of GST and GPOD in both Simonida and Divana. Catalase activity was shown to be less sensitive to Zn treatment and was only induced in var. Srpanjka treated with Zn-EDTA where GPOD activity was not induced. Concentrations of Zn used for agronomic biofortification can induce oxidative stress in wheat leaves. The antioxidative status of wheat leaves could be a good indicator of Zn tolerance, whereas wheat genotype and chemical form of Zn are the most critical factors influencing Zn toxicity.

Risk assessment and ecotoxicological diagnosis of soil from a chemical industry park in Nanjing, China

Soil pollution due to the activities of industrial parks, is becoming an increasingly serious issue, particularly throughout China. Therefore, it is essential to explore the soil pollution characteristics and its ecotoxicological effects on model species, such as higher plant species, in typical industrial areas. In this study, concentrations of heavy metals and polycyclic aromatic hydrocarbons (PAHs) were examined in the soil collected from 10 sampling sites at a chemical industry park in Nanjing, China. The pollution index was used to assess the heavy metal pollution level of soils, while the hazard index (HI) and carcinogenic risk index (RI) were calculated to assess the human health risk of soil PAHs. In addition, wheat (Triticum aestivum L.) was used as the model species to evaluate the ecotoxicological effects of polluted soil in pot experiments. Results showed that the content of heavy metals and PAHs varied greatly in soil samples, among which the heavy metal pollution at S1, S2 and S3 was the most serious. The health risk assessment of PAHs indicated that non-carcinogenic and carcinogenic values for all soil samples were below the threshold levels. Statistical analysis of the correlation between contaminated soil and toxic effects in wheat found that the significance values of regression equations were all less than 0.05 for chlorophyll content, peroxidase (POD) and amylase (AMS) activity. This indicates that the chlorophyll content, POD and AMS activity in wheat leaves could be suitable biomarkers for evaluation of the combined toxicity of multiple pollutants. This study provides a reference for future research on the risk assessment of soil containing multiple pollutants from industrial chemical parks.

Plants' genetic variation approach applied to zinc contamination: secondary metabolites and enzymes of the antioxidant system in Pfaffia glomerata accessions

Zinc (Zn) is a micronutrient, but its excessive concentration can impair plant growth and development. Fertilizers, liming materials, pesticides and fungicides containing Zn have contributed to increase its concentration in agricultural soils. The aim of the present study is to evaluate the effect of Zn excess on the non-enzymatic (anthocyanin and β-ecdysone) and enzymatic (superoxide dismutase-SOD and guaiacol peroxidase-GPX) antioxidant system of two P. glomerata accessions (JB and GD) grown in hydroponic system and soil, under short- and long-term exposure times. Three Zn levels (2, 100 and 200 μM) and two short-term exposure times (7 and 14 d) were tested in the hydroponic experiment. Three Zn levels (2, 100 and 200 mg kg^-1) and two long-term exposure times (34 and 74 d) were tested in the soil experiment. The effects of Zn excess on P. glomerata accessions depended on the growth system and exposure time. Zinc excess in both tested growth systems resulted in significant change in the tissue oxidative process (MDA concentration) in both accessions, as well as broadened the antioxidant system response, which was based on antioxidant enzymes (SOD and GPX) and secondary metabolites (anthocyanins and β-ecdysone). The highest anthocyanin concentration was observed in accession JB, which was grown in hydroponics, but tissue anthocyanin concentration increased in both accessions, regardless of growth medium and exposure time. The β-ecdysone concentration in the roots increased in both accessions, but accession GD was more responsive to Zn excess. There was significant physiological variation in P.glomerata accessions in response to Zn excess.

Assessment of phytotoxicity of leachates from landfilled waste and dust from foundry

The study assesses the contamination, classification and phytotoxicity of foundry waste. The presented results are a part of the research on the agrotechnical use of foundry waste. Landfilled foundry waste (LFW) and dust samples were taken from one of the Polish foundries. An analysis of the waste and its leachate composition was conducted. Phytotoxicity tests were carried out using Lepidium sativum. The aim of the phytotoxicity study was to evaluate germination and root growth after 72 h and the accumulation of heavy metals after 7 days. LFW was least contaminated with heavy metals and metalloids compared to dust. The composition of the foundry dusts depended on the unit of the foundry, from which it was collected. It was found that electric arc furnace dust (EAFD) was the most polluted by heavy metals among the dust samples. According to the requirements of Polish regulations most of tested waste were classified as non-hazardous, and EAFD as hazardous waste due to high Pb concentration in leachate. Phytotoxicity tests have shown a low phytotoxicity of the leachate from most of the tested waste. The results of the accumulation test showed that an excess of metal and metalloids in leachate was not directly related to its accumulation in plants. A negative correlation between EC, Cu, Co, Fe, Pb, Cr, K, Na, sulfate, fluoride, ammonia, phenol and formaldehyde concentration in leachate and GI was found. It was stated that the Fe, Mn, As and Se in plants was significantly correlated with concentrations in leachate.

Unraveling the crucial role of the ascorbate-glutathione cycle in the resilience of Cistus monspeliensis L. to withstand high As concentrations

Cistus monspeliensis L. is a species that grows spontaneously in contaminated mining areas of the Iberian Pyrite Belt. This species can accumulate high concentrations of As in the shoots without visible signs of phytotoxicity. In order to understand the physiological mechanisms underlying this tolerance, C. monspeliensis was grown in an Arenosol irrigated with aqueous nutrient solutions containing increasing concentrations of As (0, 1500, 5000, 10000, 15000 µM) and the effects of this metalloid on plant development and on the defence mechanisms against oxidative stress were monitored. Independently of the treatment, As was mainly retained in the roots. The plants with the highest concentrations of As in the shoots (> 5000 µM) showed toxicity symptoms such as chlorosis, low leaf size and decrease in biomass production and also nutritional deficiencies. Most of the studied physiological parameters (pigments, glutathione, ascorbate and antioxidative enzymes) showed significant correlation with As concentration in roots and shoots. Pigments, especially anthocyanins, were negatively affected even in the treatments with the lowest As concentrations. Glutathione increased significantly in roots at low As levels while in shoots this increase occurred in all As treatments. Ascorbate decreased in both tissues with As addition. The highest concentrations of As in shoots of C. monspeliensis triggered defence mechanisms against oxidative stress, namely by inducing the expression of genes coding antioxidative enzymes.

Comparative study of the phytotoxicity of ZnO nanoparticles and Zn accumulation in nine crops grown in a calcareous soil and an acidic soil

The increasing use of zinc oxide nanoparticles (ZnO NPs) in agriculture and consumer products has created the need to evaluate their impact on crops. Nine crops were investigated: wheat, maize, radish, bean, lettuce, tomato, pea, cucumber, and beet. The toxic effects of ZnO NPs on seed germination, plant growth, and biochemical parameters, including photosynthetic pigments, protein and malondialdehyde (MDA) content, reactive oxygen species (ROS), enzymes of the antioxidant defence system, as well as the Zn translocation in the plants were investigated using pots containing non-contaminated or ZnO NP-contaminated soil at concentrations of 20, 225, 450, and 900 mg Zn kg^-1. Two soils with different physicochemical properties, namely a calcareous soil and an acidic soil, were used. The total and available Zn in the soils were correlated with the Zn in the plants (roots and shoots) and the observed effects. In the calcareous soil, the available Zn was very low and the phytotoxicity was limited to a slight reduction in the biomass for wheat, cucumber, and beet at the highest concentration. Only beet showed an increase in photosynthetic pigments. The parameters related to oxidative stress were affected to different degrees depending on the crop, with the exceptions of maize, lettuce, pea, and beet. In the acidic soil, the available Zn was high, and the germination of bean, tomato, lettuce, and beet, and the growth of most of the crops were seriously affected. The calculated EC50 values (growth) in the acidic soil ranged from 110 to 520 mg Zn kg^-1. The photosynthetic pigments and most of the markers of oxidative stress were negatively affected in maize, wheat, bean, and pea. However, these changes were not always associated with a decrease in plant weight. In summary, soil pH and plant species are key factors affecting the Zn availability and phytotoxicity of ZnO NPs.

Transcriptional profiling of catalase genes in juglone-treated seeds of maize (Zea mays L.) and wheat (Triticum aestivum L.)

The major aim of the present study was to investigate the influence of juglone (JU; 5-hydroxy-1,4-naphthoquinone) treatments on the expression level of Cat1, Cat2 and Cat3 genes, encoding the respective catalase isozymes in maize (Zea mays L.) and wheat (Triticum aestivum L.) seeds. In parallel, germination efficiency, catalase (CAT) activity and hydrogen peroxide (H₂O₂) content in juglone-exposed cereal seeds were assessed. Juglone applications significantly stimulated abundance of three target catalase transcripts as well as induced CAT activity and generation of H₂O₂ in both maize and wheat kernels. Furthermore, germination process of juglone-affected maize seeds was more severe suppressed than in case of wheat kernels. The role of juglone in triggering the oxidative stress as well as antioxidative responses in seeds of the studied model cereal species are discussed.

Drastic Change in Zinc Speciation during Anaerobic Digestion and Composting: Instability of Nanosized Zinc Sulfide

Zinc (Zn) is a potentially toxic trace element that is present in large amounts in organic wastes (OWs) spread on agricultural lands as fertilizer. Zn speciation in OW is a crucial parameter to understand its fate in soil after spreading and to assess the risk associated with agricultural recycling of OW. Here, we investigated changes in Zn speciation from raw OWs up to digestates and/or composts for a large series of organic wastes sampled in full-scale plants. Using extended X-ray absorption fine structure, we show that nanosized Zn sulfide (nano-ZnS) is a major Zn species in raw liquid OWs and a minor species in raw solid OWs. Whatever the characteristics of the raw OW, anaerobic digestion always favors the formation of nano-ZnS (>70% of zinc in digestates). However, after 1 to 3 months of composting of OWs, nano-ZnS becomes a minor species (<10% of zinc). In composts, Zn is mostly present as amorphous Zn phosphate and Zn sorbed to ferrihydrite. These results highlight (i) the influence of OW treatment on Zn speciation and (ii) the chemical instability of nano-ZnS formed in OW in anaerobic conditions.

Modulating the antioxidant system by exogenous 2-(3,4-dichlorophenoxy) triethylamine in maize seedlings exposed to polyethylene glycol-simulated drought stress

Maize (Zea mays L.), an important agricultural crop, suffers from drought stress frequently during its growth period, thus leading to a decline in yield. 2-(3,4-Dichlorophenoxy) triethylamine (DCPTA) regulates many aspects of plant development; however, its effects on crop stress tolerance are poorly understood. We pre-treated maize seedlings by adding DCPTA to a hydroponic solution and then subjected the seedlings to a drought condition [15% polyethylene glycol (PEG)-6000 treatment]. The activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR) were enhanced under drought stress and further enhanced by the DCPTA application. The activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and catalase (CAT) declined continuously under drought stress; however, the activities partially recovered with DCPTA application. Up-regulation of the activities and transcript levels of APX, GR, MDHAR and DHAR in the DCPTA treatments contributed to the increases in ascorbate (AsA) and glutathione (GSH) levels and inhibited the increased generation rate of superoxide anion radicals (O2·-), the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA), and the electrolyte leakage (EL) induced by drought. These results suggest that the enhanced antioxidant capacity induced by DCPTA application may represent an efficient mechanism for increasing the drought stress tolerance of maize seedlings.

Antioxidant responses of edible and model plant species subjected to subtoxic zinc concentrations

Zinc (Zn) is a common heavy metal in polluted soils, as it is a widespread pollutant deriving both from natural sources and anthropogenic activities. The antioxidant tolerance/defence mechanisms against oxidative stress induced by subtoxic concentrations of Zn (50 and 150 μM ZnSO4) were studied in a widespread edible plant (lettuce; Lactuca sativa L.) and in an important model plant (Arabidopsis thaliana (L.) Heynh.). After 10 days (Arabidopsis) and 20 days (lettuce) of Zn exposure, Zn uptake/translocation was evaluated in both roots and shoots, while indicators of oxidative stress and stress intensity, total antioxidant capacity, and enzymatic and non-enzymatic antioxidative defence were measured in leaves. From an overall comparison of the two species, Zn root uptake in Arabidopsis subjected to 50 and 150 μM ZnSO4 was approximately 3- and 5-fold lower than in lettuce, while Zn translocation from roots to apical leaves was more efficient in Arabidopsis (23.7 vs 21.3% at 50 μM ZnSO4 and 19.3 vs 12.9% at 150 μM ZnSO4). Generally, a higher degree of Zn-induced oxidative stress (863.8 vs 21.3 μg g-1 FW H2O2 and 1.33 vs 0.75 μM g-1 FW MDAeq at 150 μM ZnSO4) and antioxidant response (441.2 vs 258.5 mM g-1 FW TEAC and 91.0 vs 54.9% RSA at 150 μM ZnSO4) were found in lettuce. The aim of this study is understanding (a) if subtoxic Zn levels can affect Zn uptake and translocation in the studied species and (b) if this eventual Zn absorption can influence plant oxidative status/antioxidant response. Considering that soil contamination by Zn can affect crop production and quality, the results of this research could be important for environmental, nutritional and human health issues.

Comparative effect of ZnO NPs, ZnO bulk and ZnSO4 in the antioxidant defences of two plant species growing in two agricultural soils under greenhouse conditions

The present study has investigated the toxicity of ZnO NPs to bean (Phaseolus vulgaris) and tomato (Solanum lycopersicon) crops grown to maturity under greenhouse conditions using an acidic (soil pH5.4) and a calcareous soil (soil pH8.3). The potentially available Zn in the soils and the Zn accumulation in the leaves from NPs applied to the soil (3, 20 and 225mgZnkg^-1) and changes in the chlorophylls, carotenoids and oxidative stress biomarkers were measured at 15, 30, 60 and 90days and compared with those caused by bulk ZnO and ZnSO₄. The available Zn in the soil and the leaf Zn content did not differ among the Zn chemical species, except in the acidic soil at the highest concentration of Zn applied as Zn ions, where the highest values of the two variables were found. The ZnO NPs showed comparable Zn toxicity or biostimulation to their bulk counterparts and Zn salts, irrespective of certain significant differences suggesting a higher activity of the Zn ion. The treatments altered the photosynthetic pigment concentration and induced oxidative stress in plants. ROS formation was observed at Zn plant concentrations ranging from 590 to 760mgkg^-1, but the effects on the rest of the parameters were highly dependent on the plant species, exposure time and especially soil type. In general, the effects were higher in the acidic soil than in the calcareous soil for the bean and the opposite for the tomato. The similar uptakes and toxicities of the different Zn forms suggest that the Zn ions derived from the ZnO NPs exerted a preferential toxicity in plants. However, several results obtained in soils treated with NPs at 3mgZnkg^-1 soil indicated that may exist other underlying mechanisms related to the intrinsic nanoparticle properties, especially at low NP concentrations.

The physiological mechanisms underlying the ability of Cistus monspeliensis L. from São Domingos mine to withstand high Zn concentrations in soils

Cistus monspeliensis L. is a species that grows spontaneously in contaminated mining areas from the Iberian Pyrite Belt. This species can have high concentrations of Zn in the shoots without visible signs of phytotoxicity. In order to understand the physiological mechanisms underlying this tolerance, C. monspeliensis was grown at several concentrations of Zn(2+) (0, 500, 1000, 1500, 2000µM) and the effects of this metal on plant development and on the defence mechanisms against oxidative stress were evaluated. Independently of the treatment, Zn was mainly retained in the roots. The plants with the highest concentrations of Zn showed toxicity symptoms such as chlorosis, low leaf size and decrease in biomass production. At 2000µM of Zn, the dry biomass of the shoots decreased significantly. High concentrations of Zn in shoots did not induce deficiencies of other nutrients, except Cu. Plants with high concentrations of Zn had low amounts of chlorophyll, anthocyanins and glutathione and high contents of H2O2. The highest concentrations of Zn in shoots of C. monspeliensis triggered defence mechanisms against oxidative stress, namely by triggering antioxidative enzyme activity and by direct reactive oxygen species (ROS) scavenging through carotenoids, that are unaffected by stress due to stabilisation by ascorbic acid.

Expression Patterns of Genes Involved in Ascorbate-Glutathione Cycle in Aphid-Infested Maize (Zea mays L.) Seedlings

Reduced forms of ascorbate (AsA) and glutathione (GSH) are among the most important non-enzymatic foliar antioxidants in maize (Zea mays L.). The survey was aimed to evaluate impact of bird cherry-oat aphid (Rhopalosiphum padi L.) or grain aphid (Sitobion avenae F.) herbivory on expression of genes related to ascorbate-glutathione (AsA-GSH) cycle in seedlings of six maize varieties (Ambrozja, Nana, Tasty Sweet, Touran, Waza, Złota Karłowa), differing in resistance to the cereal aphids. Relative expression of sixteen maize genes encoding isoenzymes of ascorbate peroxidase (APX1, APX2, APX3, APX4, APX5, APX6, APX7), monodehydroascorbate reductase (MDHAR1, MDHAR2, MDHAR3, MDHAR4), dehydroascorbate reductase (DHAR1, DHAR2, DHAR3) and glutathione reductase (GR1, GR2) was quantified. Furthermore, effect of hemipterans’ attack on activity of APX, MDHAR, DHAR and GR enzymes, and the content of reduced and oxidized ascorbate and glutathione in maize plants were assessed. Seedling leaves of more resistant Z. mays varieties responded higher elevations in abundance of target transcripts. In addition, earlier and stronger aphid-triggered changes in activity of APX, MDHAR, DHAR and GR enzymes, and greater modulations in amount of the analyzed antioxidative metabolites were detected in foliar tissues of highly resistant Ambrozja genotype in relation to susceptible Tasty Sweet plants.

Too much is bad--an appraisal of phytotoxicity of elevated plant-beneficial heavy metal ions

Heavy metal ions such as cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn) are considered essential/beneficial for optimal plant growth, development, and productivity. However, these ions readily impact functions of many enzymes and proteins, halt metabolism, and exhibit phytotoxicity at supra-optimum supply. Nevertheless, the concentrations of these heavy metal ions are increasing in agricultural soils worldwide via both natural and anthropogenic sources that need immediate attention. Considering recent breakthroughs on Co, Cu, Fe, Mn, Mo, Ni, and Zn in soil-plant system, the present paper: (a) overviews the status in soils and their uptake, transport, and significance in plants; (b) critically discusses their elevated level-mediated toxicity to both plant growth/development and cell/genome; (c) briefly cross talks on the significance of potential interactions between previous plant-beneficial heavy metal ions in plants; and (d) highlights so far unexplored aspects in the current context.