Echinacea: Bioactive Compounds and Agronomy.

For centuries, medicinal plants have been used as sources of remedies and treatments for various disorders and diseases. Recently, there has been renewed interest in these plants due to their potential pharmaceutical properties, offering natural alternatives to synthetic drugs. Echinacea, among the world's most important medicinal plants, possesses immunological, antibacterial, antifungal, and antiviral properties. Nevertheless, there is a notable lack of thorough information regarding the echinacea species, underscoring the vital need for a comprehensive review paper to consolidate existing knowledge. The current review provides a thorough analysis of the existing knowledge on recent advances in understanding the physiology, secondary metabolites, agronomy, and ecology of echinacea plants, focusing on E. purpurea, E. angustifolia, and E. pallida. Pharmacologically advantageous effects of echinacea species on human health, particularly distinguished for its ability to safeguard the nervous system and combat cancer, are discussed. We also highlight challenges in echinacea research and provide insights into diverse approaches to boost the biosynthesis of secondary metabolites of interest in echinacea plants and optimize their large-scale farming. Various academic databases were employed to carry out an extensive literature review of publications from 2001 to 2024. The medicinal properties of echinacea plants are attributed to diverse classes of compounds, including caffeic acid derivatives (CADs), chicoric acid, echinacoside, chlorogenic acid, cynarine, phenolic and flavonoid compounds, polysaccharides, and alkylamides. Numerous critical issues have emerged, including the identification of active metabolites with limited bioavailability, the elucidation of specific molecular signaling pathways or targets linked to echinacoside effects, and the scarcity of robust clinical trials. This raises the overarching question of whether scientific inquiry can effectively contribute to harnessing the potential of natural compounds. A systematic review and analysis are essential to furnish insights and lay the groundwork for future research endeavors focused on the echinacea natural products.

Ethylene inhibits ABA-induced stomatal closure via regulating NtMYB184-mediated flavonol biosynthesis in tobacco.

Stomatal movement can be regulated by ABA signaling through synthesis of reactive oxygen species (ROS) in guard cells. By contrast, ethylene triggers the biosynthesis of antioxidant flavonols to suppress ROS accumulation and prevent ABA-induced stomatal closure; however, the underlying mechanism remains largely unknown. In this study, we isolated and characterized the tobacco (Nicotiana tabacum) R2R3-MYB transcription factor NtMYB184, which belongs to the flavonol-specific SG7 subgroup. RNAi suppression and CRISPR/Cas9 mutation (myb184) of NtMYB184 in tobacco caused down-regulation of flavonol biosynthetic genes and decreased the concentration of flavonols in the leaves. Yeast one-hybrid assays, transactivation assays, EMSAs, and ChIP-qPCR demonstrated that NtMYB184 specifically binds to the promoters of flavonol biosynthetic genes via MYBPLANT motifs. NtMYB184 regulated flavonol biosynthesis in guard cells to modulate ROS homeostasis and stomatal aperture. ABA-induced ROS production was accompanied by the suppression of NtMYB184 and flavonol biosynthesis, which may accelerate ABA-induced stomatal closure. Furthermore, ethylene stimulated NtMYB184 expression and flavonol biosynthesis to suppress ROS accumulation and curb ABA-induced stomatal closure. In myb184, however, neither the flavonol and ROS concentrations nor the stomatal aperture varied between the ABA and ABA+ethylene treatments, indicating that NtMYB184 was indispensable for the antagonism between ethylene and ABA via regulating flavonol and ROS concentrations in the guard cells.

A Review on Remediation of Iron Ore Mine Tailings via Organic Amendments Coupled with Phytoremediation.

Mining operations degrade natural ecosystems by generating a large quantity of mine tailings. Mine tailings remain in dams/open ponds without further treatment after valuable metals such as iron ore have been extracted. Therefore, rehabilitation of tailings to mitigate the negative environmental impacts is of the utmost necessity. This review compares existing physical, chemical and amendment-assisted phytoremediation methods in the rehabilitation of mine tailings from the perspective of cost, reliability and durability. After review and discussion, it is concluded that amendment-assisted phytoremediation has received comparatively great attention; however, the selection of an appropriate phytoremediator is the critical step in the process. Moreover, the efficiency of phytoremediation is solely dependent on the amendment type and rate. Further, the application of advanced plant improvement technologies, such as genetically engineered plants produced for this purpose, would be an alternative solution. Further research is needed to determine the suitability of this method for the particular environment.

Phytomelatonin interferes with flavonols biosynthesis to regulate ROS production and stomatal closure in tobacco.

Flavonols are well-known antioxidants that prevent stomatal closure via interfering with ROS signaling. Phytomelatonin regulates stomatal closure, but the signaling pathways are still largely unknown. Here, we investigated the role of flavonols in phytomelatonin-mediated stomatal closure in tobacco plants. The application of melatonin induced stomatal closure through NADPH oxidase-mediated ROS production. Transgenic tobacco plants overexpressing soybean GmSNAT1 (coding for serotonin N-acetyltransferase that catalyzes the penultimate step in phytomelatonin biosynthesis) had higher phytomelatonin concentration, accumulated more ROS in guard cells and were more sensitive to melatonin-induced stomatal closure than the wild-type plants, which was associated with the higher expression of PMTR1-homologous genes. Exogenous melatonin decreased flavonol concentrations in guard cells and the expression of flavonoid-related genes in wild-type and transgenic tobacco plants, and these inhibitory effects were more obvious in GmSNAT1-overexpressing plants than the wild type. However, the melatonin-mediated stomatal closure and ROS production were diminished by the application of kaempferol (a type of flavonol). Additionally, transgenic tobacco plants with increased expression of NtFLS (encoding flavonol synthase) were less sensitive to melatonin-induced stomatal closure. In conclusion, phytomelatonin hampers the biosynthesis of flavonols in guard cells, which results in high concentration of ROS and induces stomatal closure in tobacco plants.

Microplastics have rice cultivar-dependent impacts on grain yield and quality, and nitrogenous gas losses from paddy, but not on soil properties.

Microplastics might affect the nitrogen (N)-use efficiency, crop production, and reactive N losses in agricultural system. However, it remains unclear whether the effects are dependent on crop cultivar. Here, a pot experiment was conducted to evaluate the effects of a typical polyethylene (PE) microplastics addition on grain yield and amino acid content, N-use efficiency, ammonia (NH3) volatilization and nitrous oxide (N2O) emission, and properties of paddy soil planted with common rice Nangeng 5055 (NG) and hybrid rice Jiafengyou 6 (JFY). The results showed that PE addition significantly reduced the grain yield and total grain amino acid content of hybrid rice by 23% and 1.7%, respectively. In addition, PE addition significantly decreased the N agronomic and recovery efficiencies of hybrid rice by 30% and 27%, respectively. For paddy soil in which hybrid rice was grown, PE addition significantly increased NH3 volatilization by 72%, but exerted no influence on N2O emission. Interestingly, the N2O emission from NG+PE treatment was 15% significantly lower than that from NG treatment, which was associated with decreased gene copies of nirK (by 50%) and nirS (by 84%) in NG+PE treatment. Generally, no significant change in soil properties was found as result of microplastics addition regardless of the cultivar. In conclusion, the impacts of microplastics on rice production and quality, N-use efficiency and nitrogenous gas losses from paddy soil are cultivar-dependent.

Physiological and Molecular Changes in Cherry Red Tobacco in Response to Iron Deficiency Stress.

The genotype CR60 is a spontaneous Cherry Red variant (containing granular red dapples on flue-cured leaves) of the Yunyan 87 (Y87) tobacco; it accumulates higher concentration of iron (Fe) in leaves than Y87, but the physiological differences between them remain largely unknown. We investigated the physiological and molecular mechanisms of CR60 in response to Fe deficiency under hydroponic conditions. Our results showed no significant phenotypic difference between Y87 and CR60 at optimal (40 µM) and high Fe (160 and 320 µM) concentrations. By contrast, CR60 exhibited higher tolerance to Fe deficiency (0 µM) than Y87, as shown by higher concentrations of chlorophyll in CR60 leaves after 21-day Fe-deficiency stress. Transcriptome profiling coupled with RT-PCR analyses found that the expression of IRT1 and several genes associated with chlorophyll biosynthesis and photosynthesis (e.g., PRO, GSA, FD1, PsbO, and PC) was higher in CR60 than Y87. These results indicated that CR60 maintains sufficient Fe uptake, chlorophyll biosynthesis and photosynthetic rate when subjected to Fe starvation.

Remediation of heavy metal-contaminated iron ore tailings by applying compost and growing perennial ryegrass (Lolium perenne L.).

Improper disposal of heavy metal-contaminated iron ore tailings poses a significant risk to the surrounding environments. Adding compost and growing ryegrass could be a cost-effective long-term solution for remediation of iron ore tailings. We conducted a glasshouse study to investigate the impact of compost amendment (0, 50, 75 and 100% w/w) on growth and accumulation of heavy metals (Cu, Fe, Mn, Pb, Ni and Zn) and As in shoots of perennial ryegrass (Lolium perenne L.) grown in two iron ore tailings (Site A and Site B mines, Pilbara, Western Australia). Ryegrass was harvested 45 and 60 days after sowing. Site A iron ore tailings had total concentrations (mg kg-1) of Fe (449,000), Mn (6900), Zn (109), Co (16) and As (7.3). Site B mine tailings had total concentrations (mg kg-1) of Fe (457,000), Ni (21), Zn (109) and As (45). Both tailings had low cation exchange capacity, organic matter, air porosity and near-neutral pH, but varied in particle size distribution (Site A-clay loam and Site B-sandy loam). Ryegrass germination was higher in the extract of Site B than Site A tailings. Increasing compost-to-tailings ratio increased dry shoot biomass at 45 days. The heavy metal/metalloid concentrations in shoots significantly decreased with increasing compost-to-tailings ratio, except for Cu and Zn. The bioconcentration factor (BCF) of heavy metals (metal concentration in shoot/total metal concentration in substrate) significantly decreased with an increasing proportion of compost in growth substrate. The BCF was >1 for Zn and Cu, and <1 for other heavy metals. A high concentration of organic matter in compost treatments likely contributed to the enhanced mobilisation of Cu and Zn for plant uptake. In contrast, compost stabilised other metals/metalloids in the tailings to decrease their uptake by ryegrass and maintain plant growth despite relatively high Mn, Fe, As and Pb concentrations in iron ore tailings.

Co-Cropping Indian Mustard and Silage Maize for Phytoremediation of a Cadmium-Contaminated Acid Paddy Soil Amended with Peat.

Co-cropping is an eco-friendly strategy to improve the phytoremediation capacity of plants growing in soils contaminated with heavy metals such as cadmium (Cd). This study was conducted to investigate the effects of co-cropping Indian mustard (Brassicajuncea) and silage maize (Zeamays) and applying peat on the phytoremediation of a Cd-contaminated acid paddy soil via characterizing plant growth and Cd uptake in pot experiments. There were six planting patterns (Control: no plants; MI-2 and MI-4: mono-cropping of Indian mustard at low and high densities, respectively; MS: mono-cropping of silage maize; CIS-2 and CIS-4: co-cropping of Indian mustard at low and high densities with silage maize, respectively) and two application rates of peat (NP: 0; WP: 30 g kg-1). When Indian mustard and silage maize were co-cropped, the shoot biomass of Indian mustard plants per pot was significantly (p < 0.05) lower than that obtained in the mono-cropping systems, with a substantial reduction (55-72%) in the same plant density group. The shoot biomass of silage maize plants in the mono-cropping systems did not differ significantly from that in the co-cropping systems regardless of the density of Indian mustard. The growth-promoting effect of the peat application was more pronounced in Indian mustard than silage maize. Under the low density of Indian mustard, the co-cropping systems significantly (p < 0.05) decreased Cd uptake by silage maize. Additionally, soil amendment with peat significantly (p < 0.05) increased shoot Cd removal rate and Cd translocation factor value in the co-cropping systems. Taken together, the results demonstrated that silage maize should be co-cropped with Indian mustard at an appropriate density in Cd-polluted soils to achieve simultaneous remediation of Cd-contaminated soils (via Indian mustard) and production of crops (here, silage maize). Peat application was shown to promote the removal of Cd from soil and translocation of Cd into shoots and could contribute to enhanced phytoremediation of Cd-contaminated acid paddy soil.

Boron inhibits cadmium uptake in wheat (Triticum aestivum) by regulating gene expression.

Various nutrients (Mg, Zn, Fe, Mn, Si, etc.) can supress cadmium (Cd) uptake and alleviate Cd toxicity, but the mechanisms are not the same. In this study, the molecular mechanism governing the effects of boron (B) on uptake of Cd in hydroponically grown wheat was characterized. As compared to control (0 µM Cd), B concentration per plant decreased by 22% and 29% under 5 µM Cd and 50 µM Cd treatment respectively. In addition, B application decreased Cd concentration and accumulation in whole wheat. Correlation analysis of different elements show that there was a highly negative correlation between concentrations of B and Cd (r = -0.854 with significant correlation) in wheat. Additionally, 16,543 differentially expressed genes (DEGs) (7666 up- and 8877 down-regulated) were detected between 0 and 5 µM Cd treatments in wheat roots by transcriptome sequencing. Gene ontology functional category and Kyoto encyclopedia of genes and genomes pathway analyses indicated that the DEGs were involved in biological process, cellular component, and molecular function. Five highly homologous genes to Cd transporters were identified; these genes were involved in metal ion binding, transmembrane ion transport, and protein transport. According to the qRT-PCR results, expression of all these genes was down-regulated in the 462 µM of B treatment compared with the 46.2 µM of B treatment regardless of the Cd treatments (0.5 or 5 µM Cd). These results suggest that B is an inhibitor of Cd uptake, and the down-regulation of five highly homologous genes could be associated with decreased uptake of Cd after B application.

Magnesium reduces cadmium accumulation by decreasing the nitrate reductase-mediated nitric oxide production in Panax notoginseng roots.

Panax notoginseng is a traditional medicinal herb in China. However, the high capacity of its roots to accumulate cadmium (Cd) poses a potential risk to human health. Our previous study showed that nitrate reductase (NR)-dependent nitric oxide (NO) production promoted Cd accumulation in P. notoginseng root cell walls. In this study, the role of Mg in the regulation of NO production and Cd accumulation in P. notoginseng roots was characterized. Exposure of P. notoginseng roots to increasing concentrations of Cd resulted in a linear increase in NO production. The application of 2 mM Mg for 24 h significantly alleviated Cd-induced NO production and Cd accumulation in roots, which coincided with a significant decrease in the NR activity. Western analysis suggested that Mg increased the interaction between the 14-3-3 protein and NR, which might have been a reason for the Mg-mediated decrease in NR activity and NO production under Cd stress. These results suggested that Mg-mediated alleviation of Cd-induced NO production and Cd accumulation is achieved by enhancement of the interaction between the 14-3-3 protein and NR in P. notoginseng roots.

Interactions of humates and chlorides with cadmium drive soil cadmium chemistry and uptake by radish cultivars.

In contrast to some salts such as chlorides (Cl) that enhance cadmium (Cd) phyto-uptake, complex soil organics like humates (HA) potentially minimise Cd uptake, but are depleted in soils low in organic matter. Organically-depleted and salt-affected areas frequently coincide in (semi)arid agroecosystems where inappropriate management practices may load topsoils with Cd. We evaluated the impact of HA (0-100 mg/kg) and NaCl (0-60 mM) in Cd-contaminated (0-5 mg/kg) soil on the chemical changes in the rhizosphere and Cd uptake by two radish (Raphanus sativus L.) cultivars. In the rhizosphere solution the significant HAxCd interaction resulted in a decrease in Cd concentration with increasing HA rates, whereas the NaClxCd interaction was brought about by an increase in Cd concentration with NaCl rising. Also, the NaClxCd interaction increased Cd concentration in radish hypocotyl with increasing NaCl addition; in contrast, the HAxCd interaction reduced Cd concentration in hypocotyl, notably at the highest Cd rate, with increasing soil humification. The addition of HA acted as a biostimulant in both radish cultivars and decreased Cd accumulation (up to 44%), whereas NaCl stress reduced the root growth and enhanced total Cd accumulation (by almost 50%). Dose-dependent severity of Cd toxicity was confirmed in both cultivars by reduced growth and progressive (up to 2 orders of magnitude) Cd accumulation (vs. uncontaminated soil). Ion speciation modelling suggested that chemistry of deprotonated humates and chlorides is crucial for complexation of the most bioavailable Cd2+ species, thus driving Cd mobility within the soil matrix, including uptake by plants. Detected differences between the tested cultivars (e.g. lower Cd concentration in Sparkler vs. Cherry Belle) and their impacts on rhizosphere chemistry and Cd soil-plant acquisition/root-hypocotyl-shoot (re)distribution, suggest that genetic improvements (by developing and introducing salt- and/or metal-resistant varieties) should be exploited in phytoremediation of contaminated soils or for minimising metal accumulation in sustainable food production.

Aluminum stress differentially affects physiological performance and metabolic compounds in cultivars of highbush blueberry.

Aluminum (Al) toxicity is one of the major factors that limit the growth and production of crops in acid soils. Highbush blueberry (Vaccinium corymbosum L.) cultivars differing in resistance to Al toxicity regarding root growth and photosynthetic performance were used. In this study, we compared the physiological and metabolic strategies to cope with Al toxicity among the highbush blueberry cultivars [two new ones (Camellia and Cargo) and three established ones (Brigitta (Al-resistant), Star and Duke)]. Aluminum concentration in roots and leaves increased in all cultivars after 24 and 48 h of exposure to Al, but less so in roots of cultivar Camellia and leaves of cultivar Cargo. These two cultivars displayed minor effects of Al exposure in terms of photosynthetic activity in comparison with the established cultivars. Furthermore, Cargo did not vary fluorescence parameters, whereas Camellia exhibited a decrease in effective quantum yield (ΦPSII) and electron transport rate (ETR) and a change in non-photochemical quenching (NPQ) and maximum quantum yield (Fv/Fm) under Al after 48 h. The Al treatment increased total phenols in leaves of Brigitta, Cargo, and Camellia, whereas antioxidant activity increased in Star and Cargo after 48 h. Aluminum exposure decreased malate concentration in roots of all cultivars, but no change was noted in fumarate concentration. The antioxidant activity correlated with photosynthetic performance and the total phenol concentration in the leaves of new cultivars exposed to Al, suggesting enhanced resistance in the short-term experiment. The principal component analysis separated the new from the established cultivars. In conclusion, the new cultivars appear to be more Al-resistant than the established ones, with Star being most Al-sensitive. Regarding the Al-resistance mechanisms of the new cultivars, it is suggested that Camellia could have a root Al-exclusion mechanism under Al toxicity. This mechanism could be explained by low Al concentration in roots, suggesting that this cultivar could exude organic acid, allowing to chelate Al in the rhizosphere. Nonetheless, further researches are needed to confirm this assumption.

Accumulation and distribution of arsenic and cadmium in winter wheat (Triticum aestivum L.) at different developmental stages.

Arsenic (As) and cadmium (Cd) are known to be toxic to humans, and elevated concentrations have been documented in food crops worldwide. However, little is known regarding their uptake, translocation, and distribution in wheat plants during plant development. A series of experiments were conducted to investigate the spatial distribution and dynamics of As and Cd in two wheat cultivars (cv. JN12 and JM85; the latter is a low grain Cd accumulator) at different developmental stages. Root concentrations of As decreased by 84%, and those of Cd by 67%, from tillering to maturity. In contrast, As concentrations in the stems increased 3.1-fold. A significant decrease in root As accumulation was observed at the mature stage, whereas root Cd accumulation decreased largely at the elongation stage. The concentrations of Cd in all leaves and As in new leaves increased as plant growth advanced. However, As concentrations in old leaves decreased significantly from grain filling to maturity. In both cultivars, the upward transfer toward younger parts of shoots was greater in the case of Cd than of As. The remobilization of As and Cd from stems and roots differed between the two cultivars. Arsenic concentrations in rachis, glumes, and grain in JM85 were significantly higher than those in JN12, whereas As concentrations in roots and stems did not differ between the cultivars. Grain Cd was significantly higher in JN12 than in JM85, but Cd concentrations in rachis and glumes were similar between the cultivars. The difference in grain Cd concentration between the two cultivars depended on root and stem Cd remobilization and redistribution from rachis to glumes and grain; in contrast, accumulation of As in grain was influenced by As remobilization from the leaves and stem to the spike.

Cadmium stress increases antioxidant enzyme activities and decreases endogenous hormone concentrations more in Cd-tolerant than Cd-sensitive wheat varieties.

The different wheat varieties have different tolerance to cadmium stress, while the mechanisms underlying the Cd tolerance are still poorly understood. A pot experiment was conducted to study the changes of antioxidant enzyme activities and endogenous hormones in wheat (Triticum aestivum) genotypes differing in cadmium (Cd) accumulation (low = Pingan 8 and high = Bainong 160) in different growth stages under Cd stress. The Cd treatment (3 mg/kg) increased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) and concentrations of malondialdehyde (MDA) and abscisic acid (ABA); in contrast, it reduced the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular carbon dioxide concentration (Ci) and the concentrations of gibberellin (GA3), auxin (IAA) and zeatin nucleoside (ZR) in wheat leaves compared to the CK (without Cd). The antioxidant enzyme activities were higher in Bainong 160 than Pingan 8 under Cd stress. In addition, the changes in endogenous hormone concentration were smaller in Bainong 160 than Pingan 8 leaves. The correlation coefficients of Bainong 160 and Pingan 8 were 0.87 and 0.66, respectively. Our results suggest that high Cd accumulation (greater Cd tolerance) in Bainong 160 is associated with higher photosynthetic parameters, higher activities of antioxidant enzyme and higher concentration of hormones than Pingan 8.

Zinc and Cadmium Mapping in the Apical Shoot and Hypocotyl Tissues of Radish by High-Resolution Secondary Ion Mass Spectrometry (NanoSIMS) after Short-Term Exposure to Metal Contamination.

Zinc (as an essential phytonutrient) and cadmium (as a toxic but readily bioavailable nonessential metal for plants) share similar routes for crossing plant biomembranes, although with a substantially different potential for translocation into above-ground tissues. The in situ distribution of these metals in plant cells and tissues (particularly intensively-dividing and fast-growing areas) is poorly understood. In this study, 17-day-old radish (Raphanus sativus L.) plants grown in nutrient solution were subjected to short-term (24 h) equimolar contamination (2.2 µM of each 70Zn and Cd) to investigate their accumulation and distribution in the shoot apex (leaf primordia) and edible fleshy hypocotyl tissues. After 24-h exposure, radish hypocotyl had similar concentration (in µg/g dry weight) of 70Zn (12.1 ± 1.1) and total Cd (12.9 ± 0.8), with relatively limited translocation of both metals to shoots (concentrations lower by 2.5-fold for 70Zn and 4.8-fold for Cd) as determined by inductively-coupled plasma mass spectrometry (ICP-MS). The in situ Zn/Cd distribution maps created by high-resolution secondary ion mass spectrometry (NanoSIMS, Cameca, Gennevilliers, France) imaging corresponded well with the ICP-MS data, confirming a similar pattern and uniform distribution of 70Zn and Cd across the examined areas. Both applied techniques can be powerful tools for quantification (ICP-MS) and localisation and visualisation (NanoSIMS) of some ultra-trace isotopes in the intensively-dividing cells and fast-growing tissues of non-metalophytes even after short-term metal exposure. The results emphasise the importance of the quality of (agro)ecosystem resources (growing media, metal-contaminated soils/waters) in the public health risk, given that, even under low contamination and short-term exposure, some of the most toxic metallic ions (e.g., Cd) can relatively rapidly enter the human food chain.

Zinc and cadmium mapping by NanoSIMS within the root apex after short-term exposure to metal contamination.

Zinc as a micronutrient and cadmium as a nonessential toxic element share similar pathways for entering plant tissues and thus may be antagonistic. In nutrient solution culture, 17-day-old radish (Raphanus sativus L) plants were exposed to short-term (24 h) equimolar metal contamination (2.2 µM of each 70Zn and total Cd) to investigate the in situ Zn/Cd distribution in the apical root tissues using high-resolution secondary ion mass spectrometry (NanoSIMS) imaging. Inductively-coupled plasma mass spectrometry analysis of bulk root tissue confirmed large root uptake of both metal elements. After 24-h exposure the total root concentration (in µg/g DW) of 70Zn was 180 ±â€¯24 (mean±SE) and of total Cd 352 ±â€¯11. NanoSIMS mapping was performed on the cross sections of the radish root apex as a crucial component in root growth and uptake of water and nutrients from soil. Elemental maps of 70Zn and 114Cd isotopes revealed greater enrichment of both metals in the outer epidermal root layer than in cortical tissues and especially stele, confirming the epidermal root cells as preferential sites of metal uptake, and indicating relatively slow and less-intensive metal transport into other parts (edible hypocotyl, shoot) of metal-sensitive radish. NanoSIMS has been confirmed as a powerful tool for spatial detection and visualisation of some ultra-trace metal isotopes (e.g. 70Zn) in the fast-growing root tips. However, precise (sub)cellular mapping of diffusible metallic ions (Cd, Zn) remains a technically-challenging task in plant specimens given an unavoidable compromise between optimising methodology for structural preservation vs. authentic in vivo ion localisation.

Zinc-biofortified wheat accumulates more cadmium in grains than standard wheat when grown on cadmium-contaminated soil regardless of soil and foliar zinc application.

Zinc (Zn)-biofortified wheat may contribute to decreasing widespread human Zn deficiency. Such genotypes may also accumulate cadmium (Cd) in grains that would expect to be decreased by Zn application. However, the influence of soil and foliar Zn application on grain Cd accumulation in Zn-biofortified versus standard wheat is unknown. In our experiment, we grew standard (Faisalabad-2008) and Zn-biofortified (Zincol-2016) wheats in pots having uncontaminated (T0) or Cd-spiked (8 mg kg-1) soil. Plants in Cd-amended pots were treated with no Zn (T1), 8 mg Zn kg-1 to soil at sowing (T2), 0.5% w/v ZnSO4·7H2O to foliage at booting and heading (T3), or soil (as in T2) + foliar (as in T3) Zn application (T4). Only in the uncontaminated control, grain yield of Faisalabad-2008 was greater than Zincol-2016. Any Zn application to Zincol-2016 grown in Cd-spiked pots increased grain yield compared with the uncontaminated control. In both cultivars, grain Zn concentration was influenced more by foliar than soil Zn application. However, Zincol-2016 had 6 to 14 mg more Zn kg-1 in grains than Faisalabad-2008 in the comparable treatments. Cadmium exposure (T1 vs. T0) decreased grain yield of only Faisalabad-2008, and decreased grain Zn concentration only in Zincol-2016. Without any Zn application, grain Cd concentration in both cultivars exposed to Cd was above the permissible level (0.20 mg kg-1). Zinc application decreased grain Cd concentration, although it remained above the permissible level in both cultivars except in Faisalabad-2008 when treated with soil + foliar Zn. Foliar Zn application decreased grain Cd concentration more than soil Zn application, and more in Zincol-2016 than Faisalabad-2008. In the comparable Cd-spiked treatments, Zincol-2016 had 73 to 134% higher grain Cd concentration than Faisalabad-2008. The Zn-biofortified genotypes accumulating toxic metals may pose serious health issues. Therefore, future breeding for biofortification should focus on the selective accumulation of Zn.

Humic acids decrease uptake and distribution of trace metals, but not the growth of radish exposed to cadmium toxicity.

Naturally-occurring highly-complexed and polymerised organics such as humic acids (HA), due to their large negative charge, play a crucial role in biogeochemistry of trace metals (TM). Toxic (Cd) as well as essential (Zn, Cu, Mn) TM bind strongly to HA, but how these organo-metalic forms influence metal uptake by plants is poorly understood. A solution culture study was conducted to characterize the effects of different concentrations of HA (0-225mg/L) on the growth and element uptake/distribution in roots, shoots and hypocotyls of radish (Raphanus sativus L.) exposed to Cd (0.5mg/L) contamination. After 10-d-exposure to applied treatments, Cd induced phytotoxicity; in contrast, different concentrations of HA had no influence on biomass, but decreased concentration of most TM in examined tissues (Cu by 4.2-fold, Zn by 2.2-fold, Cd by 1.6-fold and Mn by 34%) and their total plant accumulation (Cu by 73%, Cd by 39%, Zn by 29% and Mn by 22%). HA influenced the transport/distribution of TM, decreasing accumulation in roots and increasing their translocation/deposition in shoots, with no effect on TM content in edible hypocotyls. Chemical speciation modelling of the rooting medium confirmed predominance of free metallic forms in the control (no HA) and the pronounced organo-metal complexation in the HA treatments. The results provide evidence of strong capacity of HA to decrease phytoavailability and uptake of Cd, Zn, Cu and Mn while being non-toxic even at relatively high concentration (225mg/L). Thus, HA, as naturally present soil components, control mobility and phyto-extraction of most TM as well as their phyto-accumulation.

Molecular regulation of aluminum resistance and sulfur nutrition during root growth.

MAIN CONCLUSION: Aluminum toxicity and sulfate deprivation both regulate microRNA395 expression, repressing its low-affinity sulfate transporter ( SULTR2;1 ) target. Sulfate deprivation also induces the high-affinity sulfate transporter gene ( SULTR12 ), allowing enhanced sulfate uptake. Few studies about the relationships between sulfate, a plant nutrient, and aluminum, a toxic ion, are available; hence, the molecular and physiological processes underpinning this interaction are poorly understood. The Al-sulfate interaction occurs in acidic soils, whereby relatively high concentrations of trivalent toxic aluminum (Al3+) may hamper root growth, limiting uptake of nutrients, including sulfur (S). On the other side, Al3+ may be detoxified by complexation with sulfate in the acid soil solution as well as in the root-cell vacuoles. In this review, we focus on recent insights into the mechanisms governing plant responses to Al toxicity and its relationship with sulfur nutrition, emphasizing the role of phytohormones, microRNAs, and ion transporters in higher plants. It is known that Al3+ disturbs gene expression and enzymes involved in biosynthesis of S-containing cysteine in root cells. On the other hand, Al3+ may induce ethylene biosynthesis, enhance reactive oxygen species production, alter phytohormone transport, trigger root growth inhibition and promote sulfate uptake under S deficiency. MicroRNA395, regulated by both Al toxicity and sulfate deprivation, represses its low-affinity Sulfate Transporter 2;1 (SULTR2;1) target. In addition, sulfate deprivation induces High Affinity Sulfate Transporters (HAST; SULTR1;2), improving sulfate uptake from low-sulfate soil solutions. Identification of new microRNAs and cloning of their target genes are necessary for a better understanding of the role of molecular regulation of plant resistance to Al stress and sulfate deprivation.

Opportunities and challenges in the use of mineral nutrition for minimizing arsenic toxicity and accumulation in rice: A critical review.

Growing rice on arsenic (As)-contaminated soil or irrigating with As-contaminated water leads to significant accumulation of As in grains. Moreover, rice accumulates more As into grains than other cereal crops. Thus, rice consumption has been identified as a major route of human exposure to As in many countries. Inorganic As species are carcinogenic and could pose a considerable health risk to humans even at low dietary concentration. Genotypic variation and concentration of nutrients such as iron, manganese, phosphate, sulfur and silicon are the two main factors that affect As accumulation in rice grains. Therefore, in addition to better growth and yield of plants, application of specific nutrients in optimum quantities offers an added benefit of decreasing As content in rice grains. These nutrient elements influence speciation of As in rhizosphere, compete with As for root uptake and interfere with As translocations to the shoot and ultimately accumulation in grains. This papers critically appraises the methods, forms and rate of application, mechanisms and extent of efficiency of different mineral nutrients in decreasing As accumulation in rice grains.