Mechanisms and Control of Nutrient Uptake in Plants

Dual column chromatography combined with high-resolution mass spectrometry improves coverage of non-targeted analysis of plant root exudates

BACKGROUND

Within the plant kingdom, there is an exceptional amount of chemical diversity that has yet to be annotated. It is for this reason that non-targeted analysis is of interest for those working in novel natural products. To increase the number and diversity of compounds observable in root exudate extracts, several workflows which differ at three key stages were compared: 1) sample extraction, 2) chromatography, and 3) data preprocessing.

RESULTS

Plants were grown in Hoagland's solution for two weeks, and exudates were initially extracted with water, followed by a 24-h regeneration period with subsequent extraction using methanol. Utilizing the second extraction showed improved results with less ion suppression and reduced retention time shifting compared to the first extraction. A single column method, utilizing a pentafluorophenyl column, paired with high-resolution mass spectrometry ionized and correctly identified 34 mock root exudate compounds, while the dual column method, incorporating a pentafluorophenyl column and a porous graphitic carbon column, retained and identified 43 compounds. In a pooled quality control sample of exudate extracts, the single column method detected 1,444 compounds. While the dual method detected fewer compounds overall (1,050), it revealed a larger number of small polar compounds. Three preprocessing methods (targeted, proprietary, and open source) successfully identified 43, 31, and 38 mock root exudate compounds to confidence level 1, respectively.

SIGNIFICANCE

Enhancing signal strength and analytical method stability involves removing the high ionic strength nutrient solution before sampling root exudate extracts. Despite signal intensity loss, a dual column method enhances compound coverage, particularly for small polar metabolites. Open-source software proves a viable alternative for non-targeted analysis, even surpassing proprietary software in peak picking.

Dynamics of Fe, Mn, and potentially harmful elements under reducing conditions in iron ore tailings after dam collapse in the Doce River basin-Brazil: flooded and non-flooded rice cultivations

Potentially harmful element (PHE) bioavailability is important to environmental contamination and must be checked under several soil conditions. This study aimed to assess Fe, Mn, and PHE uptake by rice (Oryza sativa) grown on flooded and non-flooded Fe tailings collected from the Doce River basin after its collapse in Brazil. After 65 days of sowing, shoots and roots were harvested to determine PHE concentrations. The mean concentrations of Mn in shoots and Fe in the roots of rice grown on the flooded tailings were 2140 mg kg-1 and 15,219 mg kg-1, respectively. Mn was extensively translocated from roots to shoots (translocation factor (TF) = 2). Conversely, Fe accumulated in roots (TF = 0.015) and caused morphological damage to this rice organ. The application of macro and micronutrients lessened Fe toxicity in the roots of rice cultivated on the flooded tailings. The flooding of tailings influenced more Fe accumulation than Mn accumulation by rice plants. The PHE Ag, As, Cd, Ni, Hg, Pb, and Sb exhibited low total concentrations (maximum of 9 mg kg-1 for Ni and a minimum of 0.2 mg kg-1 for Cd, Hg, and Sb), and it was not observed an increase in their availability under tailings flooding conditions.

Responses of root characteristics and nitrogen absorption and assimilation to different pH gradients of winter wheat at seedling stage

Nitrogen (N) and rhizosphere pH are the two main factors restricting the growth of winter wheat (Triticum aestivum L.) in North China Plain. Soil nutrient availability is affected by soil acidity and alkalinity. In order to understand the effect of rhizosphere pH value on wheat nitrogen metabolism and the response of wheat growth to pH value at seedling stage, winter wheat varieties 'Aikang 58' (AK58) and 'Bainong 4199' (BN4199) were tested in hydroponics under three pH treatments (pH = 4.0, 6.5, and 9.0). The results showed that the accumulation of dry matter in root and above ground under pH 4.0 and pH 9.0 treatments was lower than that under pH 6.5 treatments, and the root/shoot ratio increased with the increase of pH value. Regardless of pH value, 'BN4199' had higher root dry weight, root length, root surface area, root activity and root tip than 'AK58'. Therefore, wheat that is tolerant to extreme pH is able to adapt to the acid-base environment by changing root characteristics. At pH 4.0, the net H+ outflow rate of wheat roots was significantly lower than that of the control group, and the net NO3- flux of wheat roots was also low. The net H+ outflow occurred at pH 6.5 and 9.0, and at the same time, the net NO3- flux of roots also increased, and both increased with the increase of pH. The activity of nitrate reductase (NR) in stem of pH 9.0 treatment was significantly higher than that of other treatments, while the activity of glutamine synthetase (GS) in root and stem of pH 6.5 treatment was significantly higher than that of other treatments. Under pH 4.0 and pH 9.0 treatments, the activities of NR and GS in 'BN4199' were higher than those in 'AK58', The root respiration of 'BN4199' was significantly higher than that of 'AK58' under pH 4.0 and pH 9.0 treatment, and 'BN4199' had higher NO3- net flux, key enzyme activity of root nitrogen metabolism and root respiration. Therefore, we believe that 'BN4199' has strong resistance ability to extreme pH stress, and high root/shoot ratio and strong root respiration can be used as important indicators for wheat variety screening adapted to the alkaline environment at the seedling stage.

The Uptake of Rare Trace Elements by Perennial Ryegrass (Lolium perenne L.)

Technological development has increased the use of chemical elements that have hitherto received scant scientific attention as environmental contaminants. Successful management of these rare trace elements (RTEs) requires elucidation of their mobility in the soil-plant system. We aimed to determine the capacity of Lolium perenne (a common pasture species) to tolerate and accumulate the RTEs Be, Ga, In, La, Ce, Nd, and Gd in a fluvial recent soil. Cadmium was used as a reference as a well-studied contaminant that is relatively mobile in the soil-plant system. Soil was spiked with 2.5-283 mg kg-1 of RTE or Cd salts, representing five, 10, 20, and 40 times their background concentrations in soil. For Be, Ce, In, and La, there was no growth reduction, even at the highest soil concentrations (76, 1132, 10.2, and 874 mg kg-1, respectively), which resulted in foliar concentrations of 7.1, 12, 0.11, and 50 mg kg-1, respectively. The maximum no-biomass reduction foliar concentrations for Cd, Gd, Nd, and Ga were 0.061, 0.1, 7.1, and 11 mg kg-1, respectively. Bioaccumulation coefficients ranged from 0.0030-0.95, and increased Ce < In < Nd ≅ Gd < La ≅ Be ≅ Ga < Cd. Beryllium and La were the RTEs most at risk of entering the food chain via L. perenne, as their toxicity thresholds were not reached in the ranges tested, and the bioaccumulation coefficient (plant/soil concentration quotient) trends indicated that uptake would continue to increase at higher soil concentrations. In contrast, In and Ce were the elements least likely to enter the food chain. Further research should repeat the experiments in different soil types or with different plant species to test the robustness of the findings.

Monitoring nutrients in plants with genetically encoded sensors: achievements and perspectives

Understanding mechanisms of nutrient allocation in organisms requires precise knowledge of the spatiotemporal dynamics of small molecules in vivo. Genetically encoded sensors are powerful tools for studying nutrient distribution and dynamics, as they enable minimally invasive monitoring of nutrient steady-state levels in situ. Numerous types of genetically encoded sensors for nutrients have been designed and applied in mammalian cells and fungi. However, to date, their application for visualizing changing nutrient levels in planta remains limited. Systematic sensor-based approaches could provide the quantitative, kinetic information on tissue-specific, cellular, and subcellular distributions and dynamics of nutrients in situ that is needed for the development of theoretical nutrient flux models that form the basis for future crop engineering. Here, we review various approaches that can be used to measure nutrients in planta with an overview over conventional techniques, as well as genetically encoded sensors currently available for nutrient monitoring, and discuss their strengths and limitations. We provide a list of currently available sensors and summarize approaches for their application at the level of cellular compartments and organelles. When used in combination with bioassays on intact organisms and precise, yet destructive analytical methods, the spatiotemporal resolution of sensors offers the prospect of a holistic understanding of nutrient flux in plants.

WAVE-DAMPENED2-LIKE4 modulates the hyper-elongation of light-grown hypocotyl cells

Light, temperature, water, and nutrient availability influence how plants grow to maximize access to resources. Axial growth, the linear extension of tissues by coordinated axial cell expansion, plays a central role in these adaptive morphological responses. Using Arabidopsis (Arabidopsis thaliana) hypocotyl cells to explore axial growth control mechanisms, we investigated WAVE-DAMPENED2-LIKE4 (WDL4), an auxin-induced, microtubule-associated protein and member of the larger WDL gene family shown to modulate hypocotyl growth under changing environmental conditions. Loss-of-function wdl4 seedlings exhibited a hyper-elongation phenotype under light conditions, continuing to elongate when wild-type Col-0 hypocotyls arrested and reaching 150% to 200% of wild-type length before shoot emergence. wdl4 seedling hypocotyls showed dramatic hyper-elongation (500%) in response to temperature elevation, indicating an important role in morphological adaptation to environmental cues. WDL4 was associated with microtubules under both light and dark growth conditions, and no evidence was found for altered microtubule array patterning in loss-of-function wdl4 mutants under various conditions. Examination of hormone responses showed altered sensitivity to ethylene and evidence for changes in the spatial distribution of an auxin-dependent transcriptional reporter. Our data provide evidence that WDL4 regulates hypocotyl cell elongation without substantial changes to microtubule array patterning, suggesting an unconventional role in axial growth control.

Soil Fertility Clock-Crop Rotation as a Paradigm in Nitrogen Fertilizer Productivity Control

The Soil Fertility Clock (SFC) concept is based on the assumption that the critical content (range) of essential nutrients in the soil is adapted to the requirements of the most sensitive plant in the cropping sequence (CS). This provides a key way to effectively control the productivity of fertilizer nitrogen (Nf). The production goals of a farm are set for the maximum crop yield, which is defined by the environmental conditions of the production process. This target can be achieved, provided that the efficiency of Nf approaches 1.0. Nitrogen (in fact, nitrate) is the determining yield-forming factor, but only when it is balanced with the supply of other nutrients (nitrogen-supporting nutrients; N-SNs). The condition for achieving this level of Nf efficiency is the effectiveness of other production factors, including N-SNs, which should be set at ≤1.0. A key source of N-SNs for a plant is the soil zone occupied by the roots. N-SNs should be applied in order to restore their content in the topsoil to the level required by the most sensitive crop in a given CS. Other plants in the CS provide the timeframe for active controlling the distance of the N-SNs from their critical range.

Irrigation Regimes and Nitrogen Rates as the Contributing Factors in Quinoa Yield to Increase Water and Nitrogen Efficiencies

Sustainable field crop management has been considered to reach the food security issue due to global warming and water scarcity. The effect of deficit irrigation and nitrogen rates on quinoa yield is a challenging issue in those areas. In this regard, the interaction effects of different N rates (0, 125, 250, and 375 kg N ha-1) and irrigation regimes [full irrigation (FI) and deficit irrigation at 0.75 FI and 0.5 FI] on quinoa yield and water and nitrogen efficiencies were evaluated with a two-year field experiment. Increasing nitrogen fertilizer application levels from 250 to 375 kg N ha-1 under FI and deficit irrigation did not cause a significant difference in seed yield and the total dry matter of quinoa. Furthermore, 20% and 34% reductions were observed for nitrogen use efficiency (NUE) and nitrogen yield efficiency with the application of 375 kg N ha-1 compared with that obtained in 250 kg N ha-1 nitrogen fertilizer, respectively. Therefore, a Nitrogen application rate of 250 kg ha-1 and applying 0.75 FI is suggested as the optimum rate to reach the highest seed water use efficiency (0.7 kg m-3) and NUE (0.28 kg m-3) to gain 4.12 Mg ha-1 quinoa seed yield. Under non-limited water resource conditions, an FI and N application rate of 375 kg ha-1 could be used for higher seed yield; however, under water-deficit regimes, an N application rate of 250 kg ha-1 could be adequate. However, questions about which environmental factors impressively restricted the quinoa growth for optimizing the potential yield need further investigation.

CRISPR-Based Genome Editing for Nutrient Enrichment in Crops: A Promising Approach Toward Global Food Security

The global malnutrition burden imparts long-term developmental, economic, social, and medical consequences to individuals, communities, and countries. The current developments in biotechnology have infused biofortification in several food crops to fight malnutrition. However, these methods are not sustainable and suffer from several limitations, which are being solved by the CRISPR-Cas-based system of genome editing. The pin-pointed approach of CRISPR-based genome editing has made it a top-notch method due to targeted gene editing, thus making it free from ethical issues faced by transgenic crops. The CRISPR-Cas genome-editing tool has been extensively used in crop improvement programs due to its more straightforward design, low methodology cost, high efficiency, good reproducibility, and quick cycle. The system is now being utilized in the biofortification of cereal crops such as rice, wheat, barley, and maize, including vegetable crops such as potato and tomato. The CRISPR-Cas-based crop genome editing has been utilized in imparting/producing qualitative enhancement in aroma, shelf life, sweetness, and quantitative improvement in starch, protein, gamma-aminobutyric acid (GABA), oleic acid, anthocyanin, phytic acid, gluten, and steroidal glycoalkaloid contents. Some varieties have even been modified to become disease and stress-resistant. Thus, the present review critically discusses CRISPR-Cas genome editing-based biofortification of crops for imparting nutraceutical properties.

Fertilizers and Fertilization Strategies Mitigating Soil Factors Constraining Efficiency of Nitrogen in Plant Production

Fertilizer Use Efficiency (FUE) is a measure of the potential of an applied fertilizer to increase its impact on the uptake and utilization of nitrogen (N) present in the soil/plant system. The productivity of N depends on the supply of those nutrients in a well-defined stage of yield formation that are decisive for its uptake and utilization. Traditionally, plant nutritional status is evaluated by using chemical methods. However, nowadays, to correct fertilizer doses, the absorption and reflection of solar radiation is used. Fertilization efficiency can be increased not only by adjusting the fertilizer dose to the plant's requirements, but also by removing all of the soil factors that constrain nutrient uptake and their transport from soil to root surface. Among them, soil compaction and pH are relatively easy to correct. The goal of new the formulas of N fertilizers is to increase the availability of N by synchronization of its release with the plant demand. The aim of non-nitrogenous fertilizers is to increase the availability of nutrients that control the effectiveness of N present in the soil/plant system. A wide range of actions is required to reduce the amount of N which can pollute ecosystems adjacent to fields.

Growth and Nutrient Utilization in Basil Plant as Affected by Applied Nutrient Quantity in Nutrient Solution and Light Spectrum

Simple Summary

The growth and nutrient utilization of hydroponic vegetables are largely affected by the nutrient solution management method and light environment. This study was conducted to improve the growth, nutrient absorption efficiency, and nutrient use efficiency of basil plants grown in a plant factory with artificial lighting by controlling the nutrient solution management method and light spectrum. Basil plants were treated with 4 applied nutrient quantities and three red:blue ratios from transplanting to harvest (20 days). Results showed that low applied nutrient quantity significantly improved the nutrient use efficiency and nutrient absorption efficiency. Furthermore, the yield of the basil plant and the absorption of N and K were significantly influenced by different red:blue ratios under low applied nutrient quantity treatments. Therefore, this study has determined the optimal combination of the applied nutrient quantity and red:blue ratio for improving the growth, nutrient use efficiency, and nutrient absorption efficiency of basil plants. The findings of this study can be applied to hydroponic basil production for saving resources and protecting the environment.

Abstract

Quantitative nutrient management has advantages, such as saving resources and improving nutrient utilization, compared with the conventional electrical conductivity management method. The growth and nutrient utilization of vegetables are affected by the integrated environmental conditions such as nutrient supply and light spectrum. This study investigated the effects of applied nutrient quantity (ANQ) (0.5, 1, 2, and 4 times (T) the absorption quantity of nutrients determined in the preliminary experiment, indicated by 0.5T, 1T, 2T, and 4T, respectively) in nutrient solution and red:blue ratio (R:B = 3:7, 7:3, and 9:1, indicated by RB3:7, RB7:3, and RB9:1, respectively) on the growth and nutrient utilization of basil plants in a plant factory with artificial lighting. Results demonstrated that the nutrient use efficiency (NUE) and the nutrient absorption efficiency (NAE) were significantly increased by the ANQ of 0.5T compared with the treatments of 1T, 2T, and 4T, irrespective of R:B ratios. Furthermore, under the ANQ of 0.5T, RB7:3 significantly increased the yield and the absorption of N and K of the basil plant compared with other R:B ratios. Therefore, the ANQ of 0.5T combined with RB7:3 was considered the optimal combination to improve the yield, NUE, and NAE of basil plants in the present study.

The Phytomanagement of PFAS-Contaminated Land

Globally, several hundred thousand hectares of both agricultural and urban land have become contaminated with per- and polyfluoroalkyl substances (PFAS). PFAS compounds are resistant to degradation and are mobile in soil compared to other common contaminants. Many compounds have KD values (matrix/solution concentration quotients) of <10. PFAS compounds endanger the health of humans and ecosystems by leaching into groundwater, exposure via dust, and, to a lesser extent, through plant uptake. This review aims to determine the feasibility of phytomanagement, the use of plants, and the use of soil conditioners to minimize environmental risk whilst also providing an economic return in the management of PFAS-contaminated land. For most sites, PFAS combinations render phytoextraction, the use of plants to remove PFAS from soil, inviable. In contrast, low Bioaccumulation Coefficients (BAC; plant and soil concentration quotients) timber species or native vegetation may be usefully employed for phytomanagement to limit human/food chain exposure to PFAS. Even with a low BAC, PFAS uptake by crop plants may still exceed food safety standards, and therefore, edible crop plants should be avoided. Despite this limitation, phytomanagement may be the only economically viable option to manage most of this land. Plant species and soil amendments should be chosen with the goal of reducing water flux through the soil, as well as increasing the hydrophobic components in soil that may bind the C-F-dominated tails of PFAS compounds. Soil conditioners such as biochar, with significant hydrophobic components, may mitigate the leaching of PFAS into receiving waters. Future work should focus on the interactions of PFAS with soil microbiota; secondary metabolites such as glomalin may immobilize PFAS in soil.

Phytoaccumulation potential of nine plant species for selected nutrients, rare earth elements (REEs), germanium (Ge), and potentially toxic elements (PTEs) in soil

Given the possible benefits of phytoextraction, this study evaluated the potential of nine plant species for phytoaccumulation/co-accumulation of selected nutrients, rare earth elements, germanium, and potentially toxic elements. Plants were grown on 2 kg potted soils for 12 weeks in a greenhouse, followed by a measurement of dry shoot biomass. Subsequently, elemental concentrations were determined using inductively coupled mass spectrometry, followed by the determination of amounts of each element accumulated by the plant species. Results show varying accumulation behavior among plants for the different elements. Fagopyrum esculentum and Cannabis sativa were better accumulators of most elements investigated except for chromium, germanium, and silicon that were better accumulated by Zea mays, the only grass species. F. esculentum accumulated 9, 24, and 10% of Copper, Chromium, and Rare Earth Elements in the mobile/exchangeable element fraction of the soils while Z. mays and C. sativa accumulated amounts of Cr and Ge ∼58 and 17% (for Z. mays) and 20 and 9% (for C. sativa) of the mobile/exchangeable element fraction of the soils. Results revealed co-accumulation potential for some elements e.g., (1) Si, Ge, and Cr, (2) Cu and Pb, (3) P, Ca, Co, and REEs based on chemical similarities/sources of origin.

From mine to mind and mobiles - Lithium contamination and its risk management

With the ever-increasing demand for lithium (Li) for portable energy storage devices, there is a global concern associated with environmental contamination of Li, via the production, use, and disposal of Li-containing products, including mobile phones and mood-stabilizing drugs. While geogenic Li is sparingly soluble, Li added to soil is one of the most mobile cations in soil, which can leach to groundwater and reach surface water through runoff. Lithium is readily taken up by plants and has relatively high plant accumulation coefficient, albeit the underlying mechanisms have not been well described. Therefore, soil contamination with Li could reach the food chain due to its mobility in surface- and ground-waters and uptake into plants. High environmental Li levels adversely affect the health of humans, animals, and plants. Lithium toxicity can be considerably managed through various remediation approaches such as immobilization using clay-like amendments and/or chelate-enhanced phytoremediation. This review integrates fundamental aspects of Li distribution and behaviour in terrestrial and aquatic environments in an effort to efficiently remediate Li-contaminated ecosystems. As research to date has not provided a clear picture of how the increased production and disposal of Li-based products adversely impact human and ecosystem health, there is an urgent need for further studies on this field.

Molecular characterization and environmental impacts of water-soluble organic compounds of bio-oil from the thermochemical treatment of domestic sewage sludge

Water-soluble organic compounds derived from bio-oil (WOCB) are regarded as potential risk sources of sludge thermochemical treatment. This study showed that 10.35 mg of water-soluble organic carbon and 1.32 mg of water-soluble organic nitrogen were released per gram of sludge when the final temperature of thermochemical treatment was 600 °C. WOCB was mainly formed at 300-500 °C. Furthermore, FT-ICR MS results indicated that high temperatures promoted deamination reactions, and low molecular weight (LMW) compounds with low oxygen number polymerized into aromatic compounds with increasing temperature. Noteworthily, WOCB released at 20-600 °C showed strong phytotoxicity to wheat. LMW compounds with lignin/carboxylic rich alicyclic molecules (CRAM)-like structures derived from low temperatures (200-400 °C) induced this inhibitory effect, but lipids containing nitrogen and sulfur from high temperatures (400-600 °C) can act as nutrients to promote wheat growth. This study provides theoretical support for the risk control and benefits assessments of sludge thermochemical treatment.

Shoot and Root Traits Underlying Genotypic Variation in Early Vigor and Nutrient Accumulation in Spring Wheat Grown in High-Latitude Light Conditions

Plants with improved nutrient use efficiency are needed to maintain and enhance future crop plant production. The aim of this study was to explore candidate traits for pre-breeding to improve nutrient accumulation and early vigor of spring wheat grown at high latitudes. We quantified shoot and root traits together with nutrient accumulation in nine contrasting spring wheat genotypes grown in rhizoboxes for 20 days in a greenhouse. Whole-plant relative growth rate was here correlated with leaf area productivity and plant nitrogen productivity, but not leaf area ratio. Furthermore, the total leaf area was correlated with the accumulation of six macronutrients, and could be suggested as a candidate trait for the pre-breeding towards improved nutrient accumulation and early vigor in wheat to be grown in high-latitude environments. Depending on the nutrient of interest, different root system traits were identified as relevant for their accumulation. Accumulation of nitrogen, potassium, sulfur and calcium was correlated with lateral root length, whilst accumulation of phosphorus and magnesium was correlated with main root length. Therefore, special attention needs to be paid to specific root system traits in the breeding of wheat towards improved nutrient accumulation to counteract the suboptimal uptake of some nutrient elements.

Selenate and selenite uptake, accumulation and toxicity in Lemna minuta

The kinetics of Se uptake and toxicity to Lemna were studied over a period of 14 days of exposure to Se(IV) or Se(VI). The growth of Lemna stopped immediately after exposure to 5.0 mg/L of Se(IV) or Se(VI). The content of chlorophyll and phaeopigments of Lemna exposed to 5.0 mg/L of Se(IV) was two to three times less than in the control after 3 d exposure. Lemna took up Se rapidly within the first 3 d. The Se content in Lemna along with the exposure time fitted well the two-compartment and the hyperbolic model, which demonstrates that the mechanism of Se(IV) and Se(VI) uptake in Lemna is not only through passive diffusion, but also through other processes such as ion channel proteins or transporters. The kinetic bioconcentration factors (BCFs) were 231 and 42 for 0.5 mg/L Se(IV) and Se(VI) exposure, respectively. The uptake rate of Lemna reached 263 mg/kg/d and 28 mg/kg/d in the Se(IV) and Se(VI) treatments, respectively. This study showed that Se(IV) has a faster accumulation rate than Se(VI), but a higher toxicity, indicating Lemna could be a good candidate to remove Se(IV) from water, producing Se-enriched biomass which may eventually also be considered for use as Se-enriched feed supplement or fertilizer.

Zinc uptake from ZnSO4 (aq) and Zn-EDTA (aq) and its root-to-shoot transport in soybean plants (Glycine max) probed by time-resolved in vivo X-ray spectroscopy

This study investigated the dynamic of zinc (Zn) uptake and the root-to-shoot Zn-transport when supplied as ZnSO4 (aq) or Zn-EDTA (aq) in soybean seedlings using in vivo X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XANES). The time-resolved X-ray fluorescence showed that plants absorbed ca. 10-fold more Zn from ZnSO4 (aq) than from Zn-EDTA (aq). However, the uptake velocity did not influence the amount of Zn in the stem. It let furthermore appear that the plants were able to reduce the absorption of Zn from Zn-EDTA (aq) earlier than ZnSO4 (aq). Thus, the entrance of Zn2+ into the roots is not necessarily accompanied by SO42-(aq). Regardless the source, the Zn distribution and its transport in the stem were spatially correlated to the bundles and cortex nearby the epidermal cells. Its chemical speciation showed that Zn is neither transported as ZnSO4(aq) nor as Zn-EDTA(aq), indicating that these compounds are retained in the roots or biotransformed on in the root-solution interface. Zn2+ was long-distance transported complexed by organic molecules such as histidine, malate, and citrate, and the proportion of ligands was affected by the concentration of Zn2+ in the stem rather than by the type of Zn source.

Survey of 17 elements, including rare earth elements, in chilled and non-chilled cauliflower cultivars

This study investigated if genetic diversity among cauliflower cultivars (white 'Xenia' F1, green 'Vitaverde' F1, purple 'Graffiti' F1, orange 'Sunset' F1, romanesco 'Celio' F1) and transplant chilling are reflected in the content of 17 elements in mature curds. Transplants at 40 days after sowing were exposed to 4 °C (chilling) and 18 °C (control) for 7 days and then planted in the field till harvest maturity. The lowest Ag, Al, Co, and Li contents were found in 'Celio' F1 cauliflower, which also had the highest Ba and Sr levels. Orange curds of 'Sunset' F1 were the richest in Al, and high in Li, Sc, and Sn. Chilling applied to the transplants increased Ag, Ba, Co, Sc, Sr, and Tb, and decreased the Y content of mature curds. Transplant chilling can permanently alter plant metabolism, and subsequently may affect the mineral composition of the curds.

Chemometric Assessment of Soil Pollution and Pollution Source Apportionment for an Industrially Impacted Region around a Non-Ferrous Metal Smelter in Bulgaria

The present study deals with the assessment of pollution caused by a large industrial facility using multivariate statistical methods. The primary goal is to classify specific pollution sources and to apportion their involvement in the formation of the total concentration of the chemical parameters being monitored. This aim is accomplished by intelligent data analysis based on cluster analysis, principal component analysis and principal component regression analysis. Five latent factors are found to explain over 80% of the total variance of the system being conditionally named “organic”, “non-ferrous smelter”, “acidic”, “secondary anthropogenic contribution” and “natural” factor. The apportionment models designate the contribution of the identified sources quantitatively and help in the interpretation of risk assessment and management actions. Since the study takes into account pollution uptake from soil to a cabbage plant, the data interpretation could help in introducing biomonitoring aspects of the assessment. The chemometric expertise helps in revealing hidden relationships between the objects and the variables involved to achieve a better understanding of specific pollution events in the soil of a severely industrially impacted region.

Suspended cells of metallicolous and nonmetallicolous Viola species tolerate, accumulate and detoxify zinc and lead

We studied the zinc and lead accumulation and tolerance level of suspended cells of four Viola species with different metallophyte statuses: Viola lutea ssp. westfalica (obligate metallophyte), V. tricolor (facultative metallophyte), V. arvensis (accidental metallophyte) and V. uliginosa (nonmetallophyte), in order to determine the correlation between cell and plant tolerance. Cells of all studied species/genotypes were tolerant to metal concentrations applied to the medium for 24, 48 and 72 h, more for zinc than for lead, as estimated by cell viability using the alamarBlue assay. Viable cells of each analyzed species/genotype accumulated zinc and particularly lead in very high amounts after treatment with 2000 μM for 72 h (1500-4500 mg kg^-1, 24 000-32 000 mg kg^-1, respectively), determined by atomic absorption spectrometry. The bioaccumulation factor values confirmed the cells' hyperaccumulation strategy. The cell-activated detoxification mechanism, consisting in deposition of metals in the cell wall and vacuoles, as shown by transmission electron microscopy with X-ray microanalysis, allows the cells to survive despite the high level of metal accumulation. These results indicate innate high tolerance to zinc and lead in violets with different metallophyte statuses and also in the nonmetallophyte, suggesting that evolutionarily developed hypertolerance may occurs in this group as a whole.

A trophic framework for animal origins

Metazoans emerged in a microbial world and play a unique role in the biosphere as the only complex multicellular eukaryotes capable of phagocytosis. While the bodyplan and feeding mode of the last common metazoan ancestor remain unresolved, the earliest multicellular stem-metazoans likely subsisted on picoplankton (planktonic microbes 0.2-2 μm in diameter) and dissolved organic matter (DOM), similarly to modern sponges. Once multicellular stem-metazoans emerged, they conceivably modulated both the local availability of picoplankton, which they preferentially removed from the water column for feeding, and detrital particles 2-100 μm in diameter, which they expelled and deposited into the benthos as waste products. By influencing the availability of these heterotrophic food sources, the earliest multicellular stem-metazoans would have acted as ecosystem engineers, helping create the ecological conditions under which other metazoans, namely detritivores and non-sponge suspension feeders incapable of subsisting on picoplankton and DOM, could emerge and diversify. This early style of metazoan feeding, specifically the phagocytosis of small eukaryotic prey, could have also encouraged the evolution of larger, even multicellular, eukaryotic forms less prone to metazoan consumption. Therefore, the first multicellular stem-metazoans, through their feeding, arguably helped bridge the strictly microbial food webs of the Proterozoic Eon (2.5-0.541 billion years ago) to the more macroscopic, metazoan-sustaining food webs of the Phanerozoic Eon (0.541-0 billion years ago).

Net ammonium and nitrate fluxes in wheat roots under different environmental conditions as assessed by scanning ion-selective electrode technique

Wheat is one of the most important food crops in the world, its availability affects global food security. In this study, we investigated variations in NH4(+) and NO3(-) fluxes in the fine roots of wheat using a scanning ion-selective electrode technique in the presence of different nitrogen (N) forms, N concentrations, and pH levels as well as under water stress. Our results show that the fine roots of wheat demonstrated maximum NH4(+) and NO3(-) influxes at 20 mm and 25 mm from the root tip, respectively. The maximal net NH4(+) and NO3(-) influxes were observed at pH 6.2 in the presence of a 1/4 N solution. We observed N efflux in two different cultivars following the exposure of roots to a 10% PEG-6000 solution. Furthermore, the drought-tolerant cultivar generally performed better than the drought-intolerant cultivar. Net NH4(+) and NO3(-) fluxes may be determined by plant growth status, but environmental conditions can also affect the magnitude and direction of N flux. Interestingly, we found that NO3(-) was more sensitive to environmental changes than NH4(+). Our results may be used to guide future hydroponic experiments in wheat as well as to aid in the development of effective fertilisation protocols for this crop.

Remediation of nutrient-rich waters using the terrestrial plant, Pandanus amaryllifolius Roxb

Effective control of eutrophication is generally established through the reduction of nutrient loading into waterways and water bodies. An economically viable and ecologically sustainable approach to nutrient pollution control could involve the integration of retention ponds, wetlands and greenways into water management systems. Plants not only play an invaluable role in the assimilation and removal of nutrients, but they also support fauna richness and can be aesthetically pleasing. Pandanus amaryllifolius, a tropical terrestrial plant, was found to establish well in hydrophytic conditions and was highly effective in remediating high nutrient levels in an aquatic environment showing 100% removal of NO3(-)-N up to 200 mg/L in 14 days. Phosphate uptake by the plant was less efficient with 64% of the PO4(-)-P removed at the maximum concentration of 100 mg/L at the end of 6 weeks. With its high NO3(-)-N and PO4(3-)-P removal efficiency, P. amaryllifolius depleted the nutrient-rich media and markedly contained the natural colonization of algae. The impediment of algal growth led to improvements in the water quality with significant decreases in turbidity, pH and electrical conductivity. In addition, the plants did not show stress symptoms when grown in high nutrient levels as shown by the changes in their biomass, total soluble proteins and chlorophyll accumulation as well as photochemical efficiency. Thus, P. amaryllifolius is a potential candidate for the mitigation of nutrient pollution in phytoremediation systems in the tropics as the plant requires low maintenance, is tolerant to the natural variability of weather conditions and fluctuating hydro-periods, and exhibit good nutrient removal capabilities.

Ion gradients in xylem exudate and guttation fluid related to tissue ion levels along primary leaves of barley

The concentration of ions in plant cells and tissues is an essential factor in determining physiological function. In the present study, we established that concentration gradients of mobile ions exist in both xylem exudates and tissues within a barley (Hordeum vulgare) primary leaf. For K(+) and NO3 (-) , ion concentrations generally decreased from the leaf base to the tip in both xylem exudates and tissues. Ion gradients were also found for Pi and Cl(-) in the xylem. The hydathode strongly absorbed Pi and re-translocated it to the rest of the plant, whereas Cl(-) was extruded. The ion concentration gradients developed early during leaf growth, increased as the tissue aged and remained under both high and low transpiration conditions. Measurement of the expression profiles of Pi, K(+) and NO3 (-) transporters along the longitudinal axis of the leaf revealed that some transporters are more expressed at the hydathode, but for most transporters, there was no significant variation along the leaf. The mechanisms by which longitudinal ion gradients develop in leaves and their physiological functions are discussed.

pH affects ammonium, nitrate and proton fluxes in the apical region of conifer and soybean roots

The effect of pH on nitrate and ammonium uptake in the high-affinity transport system and low-affinity transport system ranges was compared in two conifers and one crop species. Many conifers grow on acidic soils, thus their preference for ammonium vs nitrate uptake can differ from that of crop plants, and the effect of pH on nitrogen (N) uptake may differ. Proton, ammonium and nitrate net fluxes were measured at seedling root tips and 5, 10, 20 and 30 mm from the tips using a non-invasive microelectrode ion flux measurement system in solutions of 50 or 1500 microM NH(4)NO(3) at pH 4 and 7. In Glycine max and Pinus contorta, efflux of protons was observed at pH 7 while pH 4 resulted in net proton uptake in some root regions. Pseudotsuga menziesii roots consistently showed proton efflux behind the root tip, and thus appear better adapted to maintain proton efflux in acid soils. P. menziesii's ability to maintain ammonium uptake at low pH may relate to its ability to maintain proton efflux. In all three species, net nitrate uptake was greatest at neutral pH. Net ammonium uptake in G. max and net nitrate uptake in P. menziesii were greatly reduced at pH 4, particularly at high N concentration, thus N concentration should be considered when determining optimum pH for N uptake. In P. menziesii and G. max, net N uptake was greater in 1500 than 50 microM NH(4)NO(3) solution, but flux profiles of all ions varied among species.

Two calcineurin B-like calcium sensors, interacting with protein kinase CIPK23, regulate leaf transpiration and root potassium uptake in Arabidopsis

Calcium signalling involves sensor proteins that decode temporal and spatial changes in cellular Ca2+ concentration. Calcineurin B-like proteins (CBLs) represent a unique family of plant calcium sensors that relay signals by interacting with a family of protein kinases, designated as CBL-interacting protein kinases (CIPKs). In a reverse genetic screen for altered drought tolerance, we identified a loss-of-function allele of CIPK23 as exhibiting a drought-tolerant phenotype. In the cipk23 mutant, reduced transpirational water loss from leaves coincides with enhanced ABA sensitivity of guard cells during opening as well as closing reactions, without noticeable alterations in ABA content in the plant. We identified the calcium sensors CBL1 and CBL9 as CIPK23-interacting proteins that targeted CIPK23 to the plasma membrane in vivo. Expression analysis of the CIPK23, CBL1 and CBL9 genes suggested that they may function together in diverse tissues, including guard cells and root hairs. In addition, expression of the CIPK23 gene was induced by low-potassium conditions, implicating a function of this gene product in potassium nutrition. Indeed, cipk23 mutants displayed severe growth impairment on media with low concentrations of potassium. This phenotype correlates with a reduced efficiency of K+ uptake into the roots. In support of the conclusion that CBL1 and CBL9 interact with and synergistically serve as upstream regulators of CIPK23, the cbl1 cbl9 double mutant, but not the cbl1 or cbl9 single mutants, exhibit altered phenotypes for stomatal responses and low-potassium sensitivity. Together with the recent identification of the potassium channel AKT1 as a target of CIPK23, these results imply that plasma membrane-localized CBL1- and CBL9-CIPK23 complexes simultaneously regulate K+ transport processes in roots and in stomatal guard cells.

Put the metal to the petal: metal uptake and transport throughout plants

Compared to other organisms, plants have expanded families of transporters that are involved in the uptake and efflux of metals. Fortunately, in many cases, the examination of double mutants has been sufficient to overcome the challenge of studying functionally redundant gene families. Plants that lack two heavy-metal-transporting P-type ATPase family members (HMA2 and HMA4) reveal a function for these transporters in Zn translocation from roots to shoots. Likewise, the phenotype of plants that lack two natural resistance associated macrophage protein (NRAMP) homologs (NRAMP3 and NRAMP4) implicate these metal uptake proteins in the mobilization of vacuolar Fe stores during seed germination. Most families of metal transporters are ubiquitous but the Yellow Stripe1-Like (YSL) family is plant specific and YSL family members have been implicated in the transport of metals that are complexed with a plant specific chelator called nicotianamine (NA).

Strategies for the engineered phytoremediation of toxic element pollution: mercury and arsenic

Plants have many natural properties that make them ideally suited to clean up polluted soil, water, and air, in a process called phytoremediation. We are in the early stages of testing genetic engineering-based phytoremediation strategies for elemental pollutants like mercury and arsenic using the model plant Arabidopsis. The long-term goal is to develop and test vigorous, field-adapted plant species that can prevent elemental pollutants from entering the food-chain by extracting them to aboveground tissues, where they can be managed. To achieve this goal for arsenic and mercury, and pave the way for the remediation of other challenging elemental pollutants like lead or radionucleides, research and development on native hyperaccumulators and engineered model plants needs to proceed in at least eight focus areas: (1) Plant tolerance to toxic elementals is essential if plant roots are to penetrate and extract pollutants efficiently from heterogeneous contaminated soils. Only the roots of mercury- and arsenic-tolerant plants efficiently contact substrates heavily contaminated with these elements. (2) Plants alter their rhizosphere by secreting various enzymes and small molecules, and by adjusting pH in order to enhance extraction of both essential nutrients and toxic elements. Acidification favors greater mobility and uptake of mercury and arsenic. (3) Short distance transport systems for nutrients in roots and root hairs requires numerous endogenous transporters. It is likely that root plasma membrane transporters for iron, copper, zinc, and phosphate take up ionic mercuric ions and arsenate. (4) The electrochemical state and chemical speciation of elemental pollutants can enhance their mobility from roots up to shoots. Initial data suggest that elemental and ionic mercury and the oxyanion arsenate will be the most mobile species of these two toxic elements. (5) The long-distance transport of nutrients requires efficient xylem loading in roots, movement through the xylem up to leaves, and efficient xylem unloading aboveground. These systems can be enhanced for the movement of arsenic and mercury. (6) Aboveground control over the electrochemical state and chemical speciation of elemental pollutants will maximize their storage in leaves, stems, and vascular tissues. Our research suggests ionic Hg(II) and arsenite will be the best chemical species to trap aboveground. (7) Chemical sinks can increase the storage capacity for essential nutrients like iron, zinc, copper, sulfate, and phosphate. Organic acids and thiol-rich chelators are among the important chemical sinks that could trap maximal levels of mercury and arsenic aboveground. (8) Physical sinks such as subcellular vacuoles, epidermal trichome cells, and dead vascular elements have shown the evolutionary capacity to store large quantities of a few toxic pollutants aboveground in various native hyperaccumulators. Specific plant transporters may already recognize gluthione conjugates of Hg(II) or arsenite and pump them into vacuole.