Characterization of hydrophilic and lipophilic pathways of Hedera helix L. cuticular membranes: permeation of water and uncharged organic compounds

Comprehensive framework for overcoming scientific challenges related to assessing radioactive ultra-fine (nano/micro) particles transfer at the atmosphere-leaf interface

Food products are prone into contamination after a nuclear emission of radionuclides. While the mechanisms of emission and deposition of ultrafine radioactive particles are well documented, the transfer of these species from the atmosphere into plants is poorly assessed. This is evident in the lack of quantification of particles distributed within plants, especially regarding particles physical-chemical criteria to plant of different properties. Such knowledge gaps raise the concern about the representativeness of risk assessment tools designed for the transfer evaluation of ionic/soluble species to be qualified for simulating insoluble species exposure and proposes a possible underestimation. This highlights the possible need for special particle codes development to be implemented in models for future emissions. In addition, the later tools utilize transfer factors aggregating relevant sub-processes, suggesting another weak point in their overall reliability. As researchers specialized in the nuclear safety and protection, we intend in this perspective, to develop a compressive analysis of the interaction of ultrafine particles with plants of different specificities at different level processes starting from particles retention and gradual translocation to sink organs. This analysis is leveraged in providing insights for possible improvements in the current modeling tools for better real-life scenarios representation.

Quantifying the effect of non-ionic surfactant alkylphenol ethoxylates on the persistence of thiabendazole on fresh produce surface

BACKGROUND

Understanding the role of adjuvants in pesticide persistence is crucial to develop effective pesticide formulations and manage pesticide residues in fresh produce. This study investigated the impact of a commercial non-ionic surfactant product containing alkylphenol ethoxylates (APEOs) on the persistence of thiabendazole on apple and spinach surfaces against the 30 kg m-3 baking soda (sodium bicarbonate, NaHCO3 ) soaking, which was used to remove the active ingredient (AI) in the cuticular wax layer of fresh produce through alkaline hydrolysis. Surface-enhanced Raman scattering (SERS) mapping method was used to quantify the residue levels on fresh produce surfaces at different experimental scenarios. Four standard curves were established to quantify surface thiabendazole in the absence and presence of APEOs, on apple and spinach leaf surfaces, respectively.

RESULTS

Overall, the result showed that APEOs enhanced the persistence of thiabendazole over time. After 3 days of exposure, APEOs increased thiabendazole surface residue against NaHCO3 hydrolysis on apple and spinach surfaces by 5.39% and 10.47%, respectively.

CONCLUSION

The study suggests that APEOs led to more pesticide residues on fresh produce and greater difficulty in washing them off from the surfaces using baking soda, posing food safety concerns. © 2023 Society of Chemical Industry.

Mitigating cadmium accumulation and toxicity in plants: The promising role of nanoparticles

Cadmium (Cd) is a highly toxic heavy metal that adversely affects humans, animals, and plants, even at low concentrations. It is widely distributed and has both natural and anthropogenic sources. Plants readily absorb and distribute Cd in different parts. It may subsequently enter the food chain posing a risk to human health as it is known to be carcinogenic. Cd has a long half-life, resulting in its persistence in plants and animals. Cd toxicity disrupts crucial physiological and biochemical processes in plants, including reactive oxygen species (ROS) homeostasis, enzyme activities, photosynthesis, and nutrient uptake, leading to stunted growth and reduced biomass. Although plants have developed defense mechanisms to mitigate these damages, they are often inadequate to combat high Cd concentrations, resulting in yield losses. Nanoparticles (NPs), typically smaller than 100 nm, possess unique properties such as a large surface area and small size, making them highly reactive compared to their larger counterparts. NPs from diverse sources have shown potential for various agricultural applications, including their use as fertilizers, pesticides, and stress alleviators. Recently, NPs have emerged as a promising strategy to mitigate heavy metal stress, including Cd toxicity. They offer advantages, such as efficient absorption by crop plants, the reduction of Cd uptake, and the enhancement of mineral nutrition, antioxidant defenses, photosynthetic parameters, anatomical structure, and agronomic traits in Cd-stressed plants. The complex interaction of NPs with calcium ions (Ca2+), intracellular ROS, nitric oxide (NO), and phytohormones likely plays a significant role in alleviating Cd stress. This review aims to explore the positive impacts of diverse NPs in reducing Cd accumulation and toxicity while investigating their underlying mechanisms of action. Additionally, it discusses research gaps, recent advancements, and future prospects of utilizing NPs to alleviate Cd-induced stress, ultimately promoting improved plant growth and yield.

Assessing potential soil pollution from plant waste disposal: A modeling analysis of pesticide contamination

Pesticide residues can be taken up by plants after pesticide application, potentially resulting in soil pollution following the disposal of plant wastes at harvest. Currently, there is a lack of simple and efficient methods that can conduct high-throughput simulations to explore this problem across various chemicals and plant species. We present a modeling approach to simulating pesticide residue concentrations in soil as a result of plant waste disposal to assess the impact of plant wastes on agricultural soil pollution with respect to pesticide residues. This modeling approach employs well-established plant uptake models, providing versatility in evaluating different chemicals and plant species. The simulation process was tabulated in the spreadsheet interface, providing users with the flexibility to adjust input values for specific chemicals, plant species, and regions. The simulation results revealed that pesticides with relatively low lipophilicity (i.e., log KOW < 2) had low simulated residue concentrations in the soil as a result of plant waste disposal at harvest, whereas soil concentrations for lipophilic pesticides dramatically rose. This indicated that disposal of plant waste in agricultural soils will not pose significant ecological concerns to pesticides with low lipophilicity. The variability analysis showed that for certain pesticides, environmental factors (such as temperature and humidity) had a significant impact on the simulated residue concentrations in the soil as a result of plant waste disposal, which aided in the assessment of regional ecological risk as well as plant disposal management. Although some modeling aspects such as plant decomposition process, advanced plant uptake models, heterological distribution of residue concentrations in the soil, and plant waste stacking patterns require further research, the proposed approach can be used to assist in managing soil pesticides from plant waste disposal in preliminary stages.

Magnetic iron-based nanoparticles biogeochemical behavior in soil-plant system: A critical review

Increasing attention is being given to magnetic iron-based nanoparticles (MINPs) because of their potential environmental benefits. Owing to the earth abundance and high utilization of MINPs, as well as the significant functions of Fe in sustainable agriculture and environmental remediation, an understanding of the environmental fate of MINPs is indispensable. However, there are still knowledge gaps regarding the largely unknown environmental behaviors and fate of MINPs in soil-plant system. Thus, this review summarizes recent literature on the biogeochemical behavior (uptake, transportation, and transformation) of MINPs in soil and plants. The different possible uptake (e.g., foliar and root adsorption) and translocation (e.g., xylem, phloem, symplastic/apoplastic pathway, and endocytosis) pathways are discussed. Furthermore, drivers of MINPs uptake and transportation (e.g., soil characteristics, fertilizer treatments, copresence of inorganic and organic anions, meteorological conditions, and cell wall pores) in both soil and plant environments are summarized. This review also details the physical, chemical, and biological transformations of MINPs in soil-plant system. More importantly, a metadata analysis from the existing literature was employed to investigate the distinction between MINPs and other engineering nanoparticles biogeochemical behavior. In the future, more attention should be given to understanding the behavior of MINPs in soil-plant system and improving the capabilities of predictive models. This review thus highlights the main knowledge gaps regarding MINPs behavior and fate to provide guidance for their safe application in agrochemicals, crop production, and soil health.

Silica nanoparticles mediated insect pest management

Silicon is known for mitigating the biotic and abiotic stresses of crop plants. Many studies have proved beneficial effects of bulk silicon against biotic stresses in general and insect pests in particular. However, the beneficial effects of silica nanoparticles in crop plants against insect pests were barely studied and reported. By virtue of its physical and chemical nature, silica nanoparticles offer various advantages over bulk silicon sources for its applications in the field of insect pest management. Silica nanoparticles can act as insecticide for killing target insect pest or it can act as a carrier of insecticide molecule for its sustained release. Silica nanoparticles can improve plant resistance to insect pests and also aid in attracting natural enemies via enhanced volatile compounds emission. Silica nanoparticles are safe to use and eco-friendly in nature in comparison to synthetic pesticides. This review provides insights into the applications of silica nanoparticles in insect pest management along with discussion on its synthesis, side effects and future course of action.

Alleviation of chromium stress in plants using metal and metal oxide nanoparticles

Chromium (Cr), one of the hazardous pollutants, exists predominantly as Cr(VI) and Cr(III) in the environment. Cr(VI) is more toxic than Cr(III) due to its high mobility and solubility. Elevated levels of Cr in agricultural soil due to various anthropogenic activities cause Cr accumulation in plants, resulting in a significant reduction in plant yield and quality due to Cr-induced physiological, biochemical and molecular alterations. It can infiltrate the food chain through crop plants and cause harmful effects in humans via biomagnification. Cr(VI) is linked to cancer in humans. Therefore, mitigation strategies are required to remediate Cr-polluted soils and limit its accumulation in plants for safe food production. Recent research on metal and metal oxide nanoparticles (NPs) has shown that they can effectively reduce Cr accumulation and phytotoxicity. The effects of these NPs are influenced by their type and dose, exposure method, plant species and experimental settings. In this review, we present an up-to-date compilation and comprehensive analysis of the existing literature regarding the process of uptake and distribution of Cr and impact and potential mechanisms of metal and metal oxide nanoparticles led mitigation of Cr-induced stress in plants. We have also discussed recent developments, existing research gaps and future research directions in the field of Cr stress mitigation by NPs in plants. Overall, this review can provide valuable insights in reducing Cr accumulation and toxicity using metal and metal oxide nanoparticles, thereby promoting safe and sustainable cultivation of food and phytostabilization of Cr-polluted soil.

Kinetics of Lipophilic Pesticide Uptake by Living Maize

We report the uptake of a lipophilic fungicide into the cuticle of living leaves of young maize from droplets of a suspension concentrate. The action of a "coffee-ring" effect is demonstrated during fungicide formulation drying, and the fungicide particle distribution is quantified. We develop a simple, two-dimensional model of uptake leading to a "reservoir" of cuticular fungicide. This model allows inferences of physicochemical properties for fungicides inside the cuticular medium. The diffusion coefficient closely agrees with literature penetration experiments (D_cut ≈ 10^-18 m² s^-1). The logarithm of the inferred cuticle-water partition coefficient log₁₀ K_cw = 6.03 ± 0.04 is consistent with ethyl acetate as a model solvent for the maize cuticle. Two limiting kinetic uptake regimes are inferred from the model for short and long times, with the transition resulting from longitudinal saturation of the cuticle beneath the droplet. We discuss the strengths, limitations, and generalizability of our model within the "cuticle reservoir" approximation.

Divergent effects of cerium oxide nanoparticles alone and in combination with cadmium on nutrient acquisition and the growth of maize (Zea mays)

INTRODUCTION

The increasing use of cerium nanoparticles (CeO₂-NPs) has made their influx in agroecosystems imminent through air and soil deposition or untreated wastewater irrigation. Another major pollutant associated with anthropogenic activities is Cd, which has adverse effects on plants, animals, and humans. The major source of the influx of Cd and Ce metals in the human food chain is contaminated food, making it an alarming issue; thus, there is a need to understand the factors that can reduce the potential damage of these heavy metals.

METHODS

The present investigation was conducted to evaluate the effect of CeO₂-10-nm-NPs and Cd (alone and in combination) on Zea mays growth. A pot experiment (in sand) was conducted to check the effect of 0, 200, 400, 600, 1,000, and 2,000 mg of CeO₂-10 nm-NPs/kg^-1 dry sand alone and in combination with 0 and 0.5 mg Cd/kg^-1 dry sand on maize seedlings grown in a partially controlled greenhouse environment, making a total of 12 treatments applied in four replicates under a factorial design. Maize seedling biomass, shoot and root growth, nutrient content, and root anatomy were measured.

RESULTS AND DISCUSSION

The NPs were toxic to plant biomass (shoot and root dry weight), and growth at 2,000 ppm was the most toxic in Cd-0 sets. For Cd-0.5 sets, NPs applied at 1,000 ppm somewhat reverted Cd toxicity compared with the contaminated control (CC). Additionally, CeO₂-NPs affected Cd translocation, and variable Ce uptake was observed in the presence of Cd compared with non-Cd applied sets. Furthermore, CeO₂-NPs partially controlled the elemental content of roots and shoots (micronutrients such as B, Mn, Ni, Cu, Zn, Mo, and Fe and the elements Co and Si) and affected root anatomy.

Environmental microplastics: Classification, sources, fates, and effects on plants

Microplastic (MP) pollution has become a global concern due to the generation of extensive plastic waste and products (370 million metric tons in 2020) that are difficult to biodegrade. Therefore, MPs have attracted a great deal of research attention, and many new findings regarding MPs (over 9000 papers published in the last 3 years) have been reported. MPs generally exert adverse effects on plants. As MPs accumulate in agricultural ecosystems, many studies have sought to understand the sources and fates of MPs and their effects on various plants. However, there have been few reviews of the properties of MPs, their effects on plants, and their interactions with other factors (e.g., drought, heat, ultraviolet light, plant hormones, heavy metals, and other pollutants) remain poorly understood. In this review, we performed scientometrics analyses of research papers (January 1, 2019, to September 30, 2022) in this field. We focused on the recent progress in the classification of MPs and their sources, circulation, and deposition in agricultural ecosystems. We review MP uptake and transport in plants, as well as factors (size, type, and environmental factors) that affect MP uptake, the positive and negative effects of MPs on plants, and the mechanisms of MP impacts on plants. We discuss current issues and future perspectives concerning research into plant interactions with MPs, along with some promising methods to manage the MP issue.

ZnO quantum dots outperform nanoscale and bulk particles for enhancing tomato (Solanum lycopersicum) growth and nutritional values

Tomato (Solanum lycopersicum) seedlings were exposed by foliar or root applications to Zn in different nanoscale and non-nanoscale forms (40 mg Zn/L) under hydroponic conditions for 15 days. Under foliar exposure, ZnO QDs significantly promoted tomato growth, while ZnO NPs and BPs had lower impacts. ZnO QDs increased fresh weight and plant height by 42.02 % and 21.10 % relative to the untreated controls, respectively. The ionic control (ZnSO₄·7H₂O, 176.6 mg/L) decreased fresh weight by 39.31 %. ZnO QDs also significantly increased the Chla/Chlb ratio, as well as carotenoids and protein content by 7.70 %, 8.90 % and 26.33 %, respectively, over the untreated controls, suggesting improvement in seedling photosynthetic performance. Antioxidant enzyme (POD, PPO and PAL) activities in ZnO QDs treated shoots were significantly decreased by 31.1 %, 17.8 % and 48.3 %, respectively, indicating no overt oxidative damage from exposure. Importantly, the translocation factor of Zn (TF_Zn) in the foliar exposure of the ZnO QDs treatment was 73.2 %, 97.1 % and 276.9 % greater than the NPs, BPs, and ionic controls, respectively. Overall, these findings clearly demonstrate that foliar spray of nanoscale nutrients at the appropriate concentration and size can significantly increase crop growth and be a sustainable approach to nano-enabled agriculture.

A novel approach for measuring membrane permeability for organic compounds via surface plasmon resonance detection

Well-known methods for measuring permeability of membranes include static or flow diffusion chambers. When studying the effects of organic compounds on plants, the use of such model systems allows to investigate xenobiotic behavior at the cuticular barrier level and obtain an understanding of the initial penetration processes of these substances into plant leaves. However, the use of diffusion chambers has disadvantages, including being time-consuming, requiring sampling, or a sufficiently large membrane area, which cannot be obtained from all types of plants. Therefore, we propose a new method based on surface plasmon resonance imaging (SPRi) to enable rapid membrane permeability evaluation. This study presents the methodology for measuring permeability of isolated cuticles for organic compounds via surface plasmon resonance detection, where the selected model analyte was the widely used pesticide metazachlor. Experiments were performed on the cuticles of Ficus elastica, Citrus pyriformis, and an artificial PES membrane, which is used in passive samplers for the detection of xenobiotics in water and soils. The average permeability for metazachlor was 5.23 × 10^-14 m² s^-1 for C. pyriformis, 1.34 × 10^-13 m² s^-1 for F. elastica, and 7.74 × 10^-12 m² s^-1 for the PES membrane. We confirmed that the combination of a flow-through diffusion cell and real-time optical detection of transposed molecules represents a promising method for determining the permeability of membranes to xenobiotics occurring in the environment. This is necessary for determining a pesticide dosage in agriculture, selecting suitable membranes for passive samplers in analytics, testing membranes for water treatment, or studying material use of impregnated membranes.

Foliar-applied manganese and phosphorus in deficient barley: Linking absorption pathways and leaf nutrient status

Foliar fertilization delivers essential nutrients directly to plant tissues, reducing excessive soil fertilizer applications that can lead to eutrophication following nutrient leaching. Foliar nutrient absorption is a dynamic process affected by leaf surface structure and composition, plant nutrient status, and ion physicochemical properties. We applied multiple methods to study the foliar absorption behaviors of manganese (Mn) and phosphorus (P) in nutrient-deficient spring barley (Hordeum vulgare) at two growth stages. Nutrient-specific chlorophyll a fluorescence assays were used to visualize leaf nutrient status, while laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to visualize foliar absorption pathways for P and Mn ions. Rapid Mn absorption was facilitated by a relatively thin cuticle with a low abundance of waxes and a higher stomatal density in Mn-deficient plants. Following absorption, Mn accumulated in epidermal cells and in the photosynthetically active mesophyll, enabling a fast (6 h) restoration of Mn-dependent photosynthetic processes. Conversely, P-deficient plants developed thicker cuticles and epidermal cell walls, which reduced the penetration of P across the leaf surface. Foliar-applied P accumulated in trichomes and fiber cells above leaf veins without reaching the mesophyll and, as a consequence, no restoration of P-dependent photosynthetic processes was observed. This study reveals new links between leaf surface morphology, foliar-applied ion absorption pathways, and the restoration of affected physiological processes in nutrient-deficient leaves. Understanding that ions may have different absorption pathways across the leaf surface is critical for the future development of efficient fertilization strategies for crops in nutrient-limited soils.

Diffusion of volatile organics and water in the epicuticular waxes of petunia petal epidermal cells

Plant cuticles are a mixture of crystalline and amorphous waxes that restrict the exchange of molecules between the plant and the atmosphere. The multicomponent nature of cuticular waxes complicates the study of the relationship between the physical and transport properties. Here, a model cuticle based on the epicuticular waxes of Petunia hybrida flower petals was formulated to test the effect of wax composition on diffusion of water and volatile organic compounds (VOCs). The model cuticle was composed of an n-tetracosane (C₂₄ H₅₀ ), 1-docosanol (C₂₂ H₄₅ OH), and 3-methylbutyl dodecanoate (C₁₇ H₃₄ O₂ ), reflecting the relative chain length, functional groups, molecular arrangements, and crystallinity of the natural waxes. Molecular dynamics simulations were performed to obtain diffusion coefficients for compounds moving through waxes of varying composition. Simulated VOC diffusivities of the model system were found to highly correlate with in vitro measurements in isolated petunia cuticles. VOC diffusivity increased up to 30-fold in completely amorphous waxes, indicating a significant effect of crystallinity on cuticular permeability. The crystallinity of the waxes was highly dependent on the elongation of the lattice length and decrease in gap width between crystalline unit cells. Diffusion of water and higher molecular weight VOCs were significantly affected by alterations in crystalline spacing and lengths, whereas the low molecular weight VOCs were less affected. Comparison of measured diffusion coefficients from atomistic simulations and emissions from petunia flowers indicates that the role of the plant cuticle in the VOC emission network is attributed to the differential control on mass transfer of individual VOCs by controlling the composition, amount, and dynamics of scent emission.

Role of Silica Nanoparticles in Abiotic and Biotic Stress Tolerance in Plants: A Review

The demand for agricultural crops continues to escalate with the rapid growth of the population. However, extreme climates, pests and diseases, and environmental pollution pose a huge threat to agricultural food production. Silica nanoparticles (SNPs) are beneficial for plant growth and production and can be used as nanopesticides, nanoherbicides, and nanofertilizers in agriculture. This article provides a review of the absorption and transportation of SNPs in plants, as well as their role and mechanisms in promoting plant growth and enhancing plant resistance against biotic and abiotic stresses. In general, SNPs induce plant resistance against stress factors by strengthening the physical barrier, improving plant photosynthesis, activating defensive enzyme activity, increasing anti-stress compounds, and activating the expression of defense-related genes. The effect of SNPs on plants stress is related to the physical and chemical properties (e.g., particle size and surface charge) of SNPs, soil, and stress type. Future research needs to focus on the “SNPs–plant–soil–microorganism” system by using omics and the in-depth study of the molecular mechanisms of SNPs-mediated plant resistance.

Recent insights into the impact, fate and transport of cerium oxide nanoparticles in the plant-soil continuum

The advent of the nanotechnology era offers a unique opportunity for sustainable agriculture provided that the exposure and toxicity are adequately assessed and properly controlled. The global production and application of cerium oxide nanoparticles (CeO₂-NPs) in various industrial sectors have tremendously increased. Most of the nanoparticles end up in water and soil where they interact with soil microorganisms and plants. Investigating the uptake, translocation and accumulation of CeO₂-NPs is critical for its safe application in agriculture. Plant uptake of CeO₂-NPs may lead to their accumulation in different plant tissues and interference with key metabolic processes of plants. Soil microbes can also be affected by increasing CeO₂-NPs in soil, leading to changes in the physiology and enzymatic activity of soil microorganisms. The interactions between CeO₂-NPs, microbes and plants in the agricultural system need systemic research in ecologically relevant conditions. In the present review, The uptake pathways and in-planta translocation of CeO₂-NPs,and their impact on plant morphology, nutritional values, antioxidant enzymes and molecular determinants are presented. The role of CeO₂-NPs in modifying soil microbial community in plant rhizosphere is also discussed. Overall, the review aims to provide a comprehensive account on the behaviour of CeO₂-NPs in soil-plant systems and their potential impacts on the soil microbial community and plant health.

Non-glandular trichomes of sunflower are important in the absorption and translocation of foliar-applied Zn

Trichomes are potentially important for absorption of foliar fertilizers. A study has shown that the non-glandular trichromes (NGTs) of sunflower (Helianthus annuus) accumulated high concentrations of foliar-applied zinc (Zn); however, the mechanisms of Zn accumulation in the NGTs and the fate of this Zn are unclear. Here we investigated how foliar-applied Zn accumulates in the NGTs and the subsequent translocation of this Zn. Time-resolved synchrotron-based X-ray fluorescence microscopy and transcriptional analyses were used to probe the movement of Zn in the NGTs, with the cuticle composition of the NGTs examined using confocal Raman microscopy. The accumulation of Zn in the NGTs is both an initial preferential absorption process and a subsequent translocation process. This preferred absorption is likely because the NGT base has a higher hydrophilicity, whilst the subsequent translocation is due to the presence of plasmodesmata, Zn-chelating ligands, and Zn transporters in the NGTs. Furthermore, the Zn sequestered in the NGTs was eventually translocated out of the trichome once the leaf Zn concentration had decreased, suggesting that the NGTs are also important in maintaining leaf Zn homeostasis. This study demonstrates for the first time that trichomes have a key structural and functional role in the absorption and translocation of foliar-applied Zn.

Asymmetric water transport in dense leaf cuticles and cuticle-inspired compositionally graded membranes

Most of the aerial organs of vascular plants are covered by a protective layer known as the cuticle, the main purpose of which is to limit transpirational water loss. Cuticles consist of an amphiphilic polyester matrix, polar polysaccharides that extend from the underlying epidermal cell wall and become less prominent towards the exterior, and hydrophobic waxes that dominate the surface. Here we report that the polarity gradient caused by this architecture renders the transport of water through astomatous olive and ivy leaf cuticles directional and that the permeation is regulated by the hydration level of the cutin-rich outer cuticular layer. We further report artificial nanocomposite membranes that are inspired by the cuticles' compositionally graded architecture and consist of hydrophilic cellulose nanocrystals and a hydrophobic polymer. The structure and composition of these cuticle-inspired membranes can easily be varied and this enables a systematic investigation of the water transport mechanism.

Foliar water and solute absorption: an update

The absorption of water and solutes by plant leaves has been recognised since more than two centuries. Given the polar nature of water and solutes, the mechanisms of foliar uptake have been proposed to be similar for water and electrolytes, including nutrient solutions. Research efforts since the 19th century focussed on characterising the properties of cuticles and applying foliar sprays to crop plants as a tool for improving crop nutrition. This was accompanied by the development of hundreds of studies aimed at characterising the chemical and structural nature of plant cuticles from different species and the mechanisms of cuticular and, to a lower extent, stomatal penetration of water and solutes. The processes involved are complex and will be affected by multiple environmental, physico-chemical and physiological factors which are only partially clear to date. During the last decades, the body of evidence that water transport across leaf surfaces of native species may contribute to water balances (absorption and loss) at an ecosystem level has grown. Given the potential importance of foliar water absorption for many plant species and ecosystems as shown in recent studies, the aim of this review is to first integrate current knowledge on plant surface composition, structure, wettability and physico-chemical interactions with surface-deposited matter. The different mechanisms of foliar absorption of water and electrolytes and experimental procedures for tracing the uptake process are discussed before posing several outstanding questions which should be tackled in future studies.

Optimising the foliar uptake of zinc oxide nanoparticles: Do leaf surface properties and particle coating affect absorption?

Foliar absorption of zinc (Zn) is limited by several barriers, the first of which is the leaf cuticle. In this study, we investigated the absorption of Zn from Zn oxide nanoparticles (ZnO-NPs) in wheat (Triticum aestivum cv Gladius) and sunflower (Helianthus annuus cv Hyoleic 41) to determine the importance of NP surface coating for Zn absorption. Fourier transform infrared (FTIR) spectroscopy showed a higher polysaccharide content in the wheat cuticle than sunflower, indicated by a more pronounced glycosidic bond at 1020 cm^-1 , but wax and cutin content were similar. Scanning electron microscopy (SEM) revealed that trichome density was twice as high in wheat (3600 ± 900 cm^-2 ) as in sunflower (1600 cm^-2 ) and stomatal density four times higher in sunflower (6400 ± 800 cm^-2 in wheat and 22 900 cm^-2 in sunflower). Suspensions of ZnO-NPs with coatings of different hydrophobicity were applied to leaves to compare Zn absorption using X-ray fluorescence microscopy (XFM) and inductively coupled plasma mass spectroscopy (ICP-MS). Absorption of Zn was similar between wheat and sunflower when Zn was applied at 1000 mg Zn l^-1 , but much less Zn was absorbed from all ZnO products than from soluble Zn fertiliser. Particle coating did not affect Zn absorption, but it may facilitate particle adhesion to leaves, providing a longer-term source of resupply of Zn ions to the leaves. Differences in leaf surface characteristics did not affect Zn absorption, indicating that the cuticle is the main pathway of absorption under these conditions.

Co-addition of humic substances and humic acids with urea enhances foliar nitrogen use efficiency in sugarcane (Saccharum officinarum L.)

Humic substances (HS) and humic acids (HA) are proven to enhance nutrient uptake and growth in plants. Foliar application of urea combined with HS and HA offers an alternative strategy to increase nitrogen use efficiency (NUE). The objective of this study was to understand the effects of foliar application of HA and HS along with urea on NUE and response of different biometric, biochemical and physiological traits of sugarcane with respect to cultivar, mode of foliar application, geographic location and intervals of foliar application. To study this, two different independent Experiments were conducted in green house facilities at two different agro-climatic zones (USA and Brazil) using two different predominant varieties, modes and intervals of foliar applications. The three different foliar applications used in this study were (1) urea (U), (2) mixture of urea and HS (U+HS) and (3) HA (U+HA). In both Experiments, ¹⁵N (nitrogen isotope) recovery or NUE was higher in U+HS followed by U+HA. However, magnitude of NUE changed according to the differences in two Experiments. Results showed that foliar application of U+HS and U+HA was rapidly absorbed and stored in the form of protein and starch. Also induced changes in photosynthesis, intrinsic water use efficiency, protein, total soluble sugars and starch signifying a synergistic effect of U+HS and U+HA on carbon and nitrogen metabolism. These results showed promising use of HS and HA with urea to improve NUE in sugarcane compared to using the urea alone. Simultaneously, mode, quantity, and interval of foliar application should be standardized based on the geographic locations and varieties to optimize the NUE.

Nanoparticle Charge and Size Control Foliar Delivery Efficiency to Plant Cells and Organelles

Fundamental and quantitative understanding of the interactions between nanoparticles and plant leaves is crucial for advancing the field of nanoenabled agriculture. Herein, we systematically investigated and modeled how ζ potential (-52.3 mV to +36.6 mV) and hydrodynamic size (1.7-18 nm) of hydrophilic nanoparticles influence delivery efficiency and pathways to specific leaf cells and organelles. We studied interactions of nanoparticles of agricultural interest including carbon dots (CDs, 0.5 and 5 mg/mL), cerium oxide (CeO₂, 0.5 mg/mL), and silica (SiO₂, 0.5 mg/mL) nanoparticles with leaves of two major crop species having contrasting leaf anatomies: cotton (dicotyledon) and maize (monocotyledon). Biocompatible CDs allowed real-time tracking of nanoparticle translocation and distribution in planta by confocal fluorescence microscopy at high spatial (∼200 nm) and temporal (2-5 min) resolution. Nanoparticle formulations with surfactants (Silwet L-77) that reduced surface tension to 22 mN/m were found to be crucial for enabling rapid uptake (<10 min) of nanoparticles through the leaf stomata and cuticle pathways. Nanoparticle-leaf interaction (NLI) empirical models based on hydrodynamic size and ζ potential indicate that hydrophilic nanoparticles with <20 and 11 nm for cotton and maize, respectively, and positive charge (>15 mV), exhibit the highest foliar delivery efficiencies into guard cells (100%), extracellular space (90.3%), and chloroplasts (55.8%). Systematic assessments of nanoparticle-plant interactions would lead to the development of NLI models that predict the translocation and distribution of nanomaterials in plants based on their chemical and physical properties.

Predicting plant cuticle-water partition coefficients for organic pollutants using pp-LFER model

Predicting plant cuticle-water partition coefficients (K_cw) and understanding the partition mechanisms are crucial to assess environmental fate and risk of organic pollutants. Up to now, experimental K_cw values are determined for only hundreds of compounds because of high experimental cost. For this reason, computational models, which can predict K_cw values based on chemical structures, are promising approaches to evaluate new compounds. In this study, a large dataset consisting of 279 logK_cw values for 125 unique compounds were collected and curated. A poly-parameter linear free energy relationship (pp-LFER) model was developed with stepwise multiple linear regression based on this dataset. The resulted pp-LFER model has good predictability and robustness as indicated by determination coefficient (R²_adj,tra) of 0.93, bootstrapping coefficient (Q²_BOOT) of 0.92, external validation coefficient (Q²_ext) of 0.94 and root mean square error of 0.52 log units. Contribution analysis of different interactions indicated that dispersion and hydrophobic interactions have the highest positive contribution (56%) to increase the partition of pollutants onto plant cuticles. In addition, for organic pollutions containing benzene ring (13-31%), double bond (9-17%) or nitrogen-containing heterocycles (9-17%), π/n-electron pairs interactions exhibit obvious positive contributions to logK_cw. In conclusion, the proposed pp-LFER model is beneficial for predicting logK_cw of potential organic pollutants directly from their molecular structures.

Raising the pH of the Pulsing Solution Improved the Acropetal Transport of NAA and 2,4-D and Their Efficacy in Reducing Floret Bud Abscission of Red Cestrum Cut Flowers

The use of auxins to improve the vase life of cut flowers is very limited. Previous studies demonstrated that a pulse treatment of Red Cestrum (Cestrum elegans Schlecht.) cut flowers with 2,4-dichlorophenoxyacetic acid (2,4-D) significantly reduced floret bud abscission, whereas 1-naphthaleneacetic acid (NAA) was ineffective. This difference resulted, at least in part, from the higher acropetal transport capability of 2,4-D compared to that of NAA. The present research focused on examining the factors affecting the acropetal transport, and hence the efficacy of the two auxins in reducing floret bud abscission of Red Cestrum cut flowers. We assumed that the differential acropetal transport capability of the two auxins results from the difference in their dissociation constants (pKa), with values of 2.75 and 4.23 for 2,4-D and NAA, respectively, which affects their pH-dependent physicochemical properties. Thus, increasing the pH of the pulsing solution above the pKa of both auxins might improve their acropetal movement. Indeed, the results of the present research show that raising the pH of the pulsing solution to pH 7.0 and above improved the efficacy of the two auxins in reducing floret bud abscission, with a higher effect on 2,4-D than that on NAA. Raising the pH of the pulsing solution decreased the adsorption and/or uptake of the two auxins by the cells adjacent to the xylem vessels, leading to an increase in their acropetal transport. The high pH of the pulsing solution increased the dissociation and hence decreased the lipophilicity of the auxin molecules, leading to improved acropetal movement. This effect was corroborated by the significant reduction in their 1-octanol/water partition coefficient (K OW ) values with the increase in the pH. A significant increase in the CeIAA1 transcript level was obtained in response to 2,4-D pulsing at pH 7.0 and 8.25 and to NAA pulsing at pH 8.25, indicating that the acropetally transported auxins were taken up by the cells under these conditions. Our data suggest that raising the pH of the pulsing solution would significantly contribute to the increased efficacy of auxins in improving the vase life of cut flowers.

Chitosan-Based Agronanochemicals as a Sustainable Alternative in Crop Protection

The rise in the World's food demand in line with the increase of the global population has resulted in calls for more research on the production of sustainable food and sustainable agriculture. A natural biopolymer, chitosan, coupled with nanotechnology could offer a sustainable alternative to the use of conventional agrochemicals towards a safer agriculture industry. Here, we review the potential of chitosan-based agronanochemicals as a sustainable alternative in crop protection against pests, diseases as well as plant growth promoters. Such effort offers better alternatives: (1) the existing agricultural active ingredients can be encapsulated into chitosan nanocarriers for the formation of potent biocides against plant pathogens and pests; (2) the controlled release properties and high bioavailability of the nanoformulations help in minimizing the wastage and leaching of the agrochemicals' active ingredients; (3) the small size, in the nanometer regime, enhances the penetration on the plant cell wall and cuticle, which in turn increases the argochemical uptake; (4) the encapsulation of agrochemicals in chitosan nanocarriers shields the toxic effect of the free agrochemicals on the plant, cells and DNA, thus, minimizing the negative impacts of agrochemical active ingredients on human health and environmental wellness. In addition, this article also briefly reviews the mechanism of action of chitosan against pathogens and the elicitations of plant immunity and defense response activities of chitosan-treated plants.

The permeation barrier of plant cuticles: uptake of active ingredients is limited by very long-chain aliphatic rather than cyclic wax compounds

BACKGROUND

The barrier to diffusion of organic solutes across the plant cuticle is composed of waxes consisting of very long-chain aliphatic (VLCA) and, to varying degrees, cyclic compounds like pentacyclic triterpenoids. The roles of both fractions in controlling cuticular penetration by organic solutes, e.g. the active ingredients (AI) of pesticides, are unknown to date. We studied the permeability of isolated leaf cuticular membranes from Garcinia xanthochymus and Prunus laurocerasus for lipophilic azoxystrobin and theobromine as model compounds for hydrophilic AIs.

RESULTS

The wax of P. laurocerasus consists of VLCA (12%) and cyclic compounds (88%), whereas VLCAs make up 97% of the wax of G. xanthochymus. We show that treating isolated cuticles with methanol almost quantitatively releases the cyclic fraction while leaving the VLCA fraction essentially intact. All VLCAs were subsequently removed using chloroform. In both species, the permeance of the two model compounds did not change significantly after methanol treatment, whereas chloroform extraction had a large effect on organic solute permeability.

CONCLUSION

The VLCA wax fraction makes up the permeability barrier for organic solutes, whereas cyclic compounds even in high amounts have a negligible role. This is of significance when optimizing the foliar uptake of pesticides. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

In Vivo Evaluation of Zn Foliar Uptake and Transport in Soybean Using X-ray Absorption and Fluorescence Spectroscopy

Understanding the mechanisms of absorption and transport of foliar nutrition is a key step towards the development of advanced fertilization methods. This study employed X-ray fluorescence (XRF) and X-ray absorption near edge spectroscopy (XANES) to trace the in vivo absorption and transport of ZnO and ZnSO4(aq) to soybean leaves (Glycine max). XRF maps monitored over 48 h showed a shape change of the dried ZnSO4(aq) droplet, indicating Zn2+ absorption. Conversely, these maps did not show short movement of Zn from ZnO. XRF measurements on petioles of leaves that received Zn2+ treatments clarified that the Zn absorption and transport in the form of ZnSO4(aq) was faster that of ZnO. Solubility was the major factor driving ZnSO4(aq) absorption. XANES speciation showed that in planta Zn is transported coordinated with organic acids. Because plants demand Zn during their entire lifecycle, the utilization of sources with different solubilities can increase Zn use efficiency.

Nanoparticle Size and Coating Chemistry Control Foliar Uptake Pathways, Translocation, and Leaf-to-Rhizosphere Transport in Wheat

Nanoenabled foliar-applied agrochemicals can potentially be safer and more efficient than conventional products. However, limited understanding about how nanoparticle properties influence their interactions with plant leaves, uptake, translocation through the mesophyll to the vasculature, and transport to the rest of the plant prevents rational design. This study used a combination of Au quantification and spatial analysis to investigate how size (3, 10, or 50 nm) and coating chemistry (PVP versus citrate) of gold nanoparticles (AuNPs) influence these processes. Following wheat foliar exposure to AuNPs suspensions (∼280 ng per plant), adhesion on the leaf surface was increased for smaller sizes, and PVP-AuNPs compared to citrate-AuNPs. After 2 weeks, there was incomplete uptake of citrate-AuNPs with some AuNPs remaining on the outside of the cuticle layer. However, the fraction of citrate-AuNPs that had entered the leaf was translocated efficiently to the plant vasculature. In contrast, for similar sizes, virtually all of the PVP-AuNPs crossed the cuticle layer after 2 weeks, but its transport through the mesophyll cells was lower. As a consequence of PVP-AuNP accumulation in the leaf mesophyll, wheat photosynthesis was impaired. Regardless of their coating and sizes, the majority of the transported AuNPs accumulated in younger shoots (10-30%) and in roots (10-25%), and 5-15% of the NPs <50 nm were exuded into the rhizosphere soil. A greater fraction of larger sizes AuNPs (presenting lower ζ potentials) was transported to the roots. The key hypotheses about the NPs physical-chemical and plant physiology parameters that may matter to predict leaf-to-rhizosphere transport are also discussed.

Mathematical Modeling of Diffusion of a Hydrophilic Ionic Fertilizer in Plant Cuticles: Surfactant and Hygroscopic Effects

The agricultural industry requires improved efficacy of sprays being applied to crops and weeds to reduce their environmental impact and increase financial returns. One way to improve efficacy is by enhancing foliar penetration. The plant leaf cuticle is the most significant barrier to agrochemical diffusion within the leaf. The importance of a mechanistic mathematical model has been noted previously in the literature, as each penetration experiment is dictated by its specific parameters, namely plant species, environmental conditions such as relative humidity and spray formulation including adjuvant addition. A mechanistic mathematical model has been previously developed by the authors, focusing on plant cuticle diffusion of calcium chloride through tomato fruit cuticles including pore swelling, ion binding and evaporation, along with the ability to vary the active ingredient concentration and type, relative humidity and plant species. Here we further develop this model to include adjuvant effects as well as the hygroscopic nature of deliquescent ionic solutions with evaporation on the cuticle surface. These modifications to a penetration and evaporation model provide a novel addition to the literature and allow the model to be applied to many types of evaporating ionic hygroscopic solutions on many types of substrates, not just plant cuticles. We validate our theoretical model results against appropriate experimental data, discuss key sensitivities and relate theoretical predictions to physical mechanisms. The important governing mechanisms influencing surfactant enhanced penetration of ionic active through plant cuticles were found to be aqueous pore radius, pore density, cuticle thickness and initial contact angle of the applied droplet; ion binding, relative humidity and evaporation including hygroscopic water absorption parameters for point of deliquescence. The sensitivity analysis indicated surfactants increase penetration by changing the point of deliquescence of a solution, which alters the water absorption and the initial contact angle, which alters the number of pores under the droplet. The results of the validation and sensitivity analysis imply that this model accounts for many of the mechanisms governing penetration in plant cuticles.

Cell Penetration, Herbicidal Activity, and in-vivo-Toxicity of Oligo-Arginine Derivatives and of Novel Guanidinium-Rich Compounds Derived from the Biopolymer Cyanophycin

Oligo-arginines are thoroughly studied cell-penetrating peptides (CPPs, Figures 1 and 2). Previous in-vitro investigations with the octaarginine salt of the phosphonate fosmidomycin (herbicide and anti-malaria drug) have shown a 40-fold parasitaemia inhibition with P. falciparum, compared to fosmidomycin alone (Figure 3). We have now tested this salt, as well as the corresponding phosphinate salt of the herbicide glufosinate, for herbicidal activity with whole plants by spray application, hoping for increased activities, i.e. decreased doses. However, both salts showed low herbicidal activity, indicating poor foliar uptake (Table 1). Another pronounced difference between in-vitro and in-vivo activity was demonstrated with various cell-penetrating octaarginine salts of fosmidomycin: intravenous injection to mice caused exitus of the animals within minutes, even at doses as low as 1.4 μmol/kg (Table 2). The results show that use of CPPs for drug delivery, for instance to cancer cells and tissues, must be considered with due care. The biopolymer cyanophycin is a poly-aspartic acid containing argininylated side chains (Figure 4); its building block is the dipeptide H-βAsp-αArg-OH (H-Adp-OH). To test and compare the biological properties with those of octaarginines we synthesized Adp8-derivatives (Figure 5). Intravenouse injection of H-Adp8-NH2 into the tail vein of mice with doses as high as 45 μmol/kg causes no symptoms whatsoever (Table 3), but H-Adp8-NH2 is not cell penetrating (HEK293 and MCF-7 cells, Figure 6). On the other hand, the fluorescently labeled octamers FAM-(Adp(OMe))8-NH2 and FAM-(Adp(NMe2))8-NH2 with ester and amide groups in the side chains exhibit mediocre to high cell-wall permeability (Figure 6), and are toxic (Table 3). Possible reasons for this behavior are discussed (Figure 7) and corresponding NMR spectra are presented (Figure 8).

Direct determination of surfactant effects on the uptake of gaseous parent and alkylated PAHs by crop leaf surfaces

The partitioning of atmospheric polycyclic aromatic hydrocarbons (PAHs) into crop systems raises concerns about their potential harm to ecosystem and human health. To assess parent and alkylated PAHs accumulation accurately, the uptake of individual 7-isopropyl-1-methylphenanthrene (Retene), 3-methyl-phenanthrene (3-MP) and phenanthrene (Phe) by living maize, soybean and potato leaf surfaces, as well as the effects of cationic cetyltrimethylammonium bromide (CTMAB) and anionic sodium dodecyl benzene sulfonate (SDBS), were examined in situ using fiber-optic fluorimetry. For each of three PAH chemicals, the uptake achieved equilibrium between the air and living crop leaf surfaces within the 120-h monitoring period. There is inter-chemical and inter-species variability in terms of both the time required reaching equilibrium, the equilibrated adsorption concentration (EAC) and the overall air-surfaces mass transfer coefficient (kAS). The EAC of the three PAHs for each of the three crops' leaf surfaces increased with the number of alkyl substitutions on the aromatic ring. For any given PAHs, the EAC values followed the sequence of potato > soybean > maize, which was dominantly controlled by their leaf surface polarity index ((O+N)/C). The presence of CTMAB and SDBS increased the EAC of PAHs in the three crops' leaf surfaces by 6.5-17.1%, due to the plasticizing effect induced by the surface-sorbed surfactants, and the enhancement degree was closely associated with leaf-wax content and lg KOW values of PAHs. In addition, the two surfactants promoted the kAS values of the three chemicals by 7.7-23.3%. These results demonstrated that surfactants promoted the uptake of PAHs onto the crop leaf surfaces, potentially threatening the agricultural product safety.

Physico-chemical properties of plant cuticles and their functional and ecological significance

Most aerial plant surfaces are covered with a lipid-rich cuticle, which is a barrier for the bidirectional transport of substances between the plant and the surrounding environment. This review article provides an overview of the significance of the leaf cuticle as a barrier for the deposition and absorption of water and electrolytes. After providing insights into the physico-chemical properties of plant surfaces, the mechanisms of foliar absorption are revised with special emphasis on solutes. Due to the limited information and relative importance of the leaf cuticle of herbaceous and deciduous cultivated plants, an overview of the studies developed with Alpine conifers and treeline species is provided. The significance of foliar water uptake as a phenomenon of ecophysiological relevance in many areas of the world is also highlighted. Given the observed variability in structure and composition among, for example, plant species and organs, it is concluded that it is currently not possible to establish general permeability and wettability models that are valid for predicting liquid-surface interactions and the subsequent transport of water and electrolytes across plant surfaces.

Residual transpiration as a component of salinity stress tolerance mechanism: a case study for barley

BACKGROUND

While most water loss from leaf surfaces occurs via stomata, part of this loss also occurs through the leaf cuticle, even when the stomata are fully closed. This component, termed residual transpiration, dominates during the night and also becomes critical under stress conditions such as drought or salinity. Reducing residual transpiration might therefore be a potentially useful mechanism for improving plant performance when water availability is reduced (e.g. under saline or drought stress conditions). One way of reducing residual transpiration may be via increased accumulation of waxes on the surface of leaf. Residual transpiration and wax constituents may vary with leaf age and position as well as between genotypes. This study used barley genotypes contrasting in salinity stress tolerance to evaluate the contribution of residual transpiration to the overall salt tolerance, and also investigated what role cuticular waxes play in this process. Leaves of three different positions (old, intermediate and young) were used.

RESULTS

Our results show that residual transpiration was higher in old leaves than the young flag leaves, correlated negatively with the osmolality, and was positively associated with the osmotic and leaf water potentials. Salt tolerant varieties transpired more water than the sensitive variety under normal growth conditions. Cuticular waxes on barley leaves were dominated by primary alcohols (84.7-86.9%) and also included aldehydes (8.90-10.1%), n-alkanes (1.31-1.77%), benzoate esters (0.44-0.52%), phytol related compounds (0.22-0.53%), fatty acid methyl esters (0.14-0.33%), β-diketones (0.07-0.23%) and alkylresorcinols (1.65-3.58%). A significant negative correlation was found between residual transpiration and total wax content, and residual transpiration correlated significantly with the amount of primary alcohols.

CONCLUSIONS

Both leaf osmolality and the amount of total cuticular wax are involved in controlling cuticular water loss from barley leaves under well irrigated conditions. A significant and negative relationship between the amount of primary alcohols and a residual transpiration implies that some cuticular wax constituents act as a water barrier on plant leaf surface and thus contribute to salinity stress tolerance. It is suggested that residual transpiration could be a fundamental mechanism by which plants optimize water use efficiency under stress conditions.

Nonlinear Porous Diffusion Modeling of Hydrophilic Ionic Agrochemicals in Astomatous Plant Cuticle Aqueous Pores: A Mechanistic Approach

The agricultural industry requires improved efficacy of sprays being applied to crops and weeds in order to reduce their environmental impact and deliver improved financial returns. Enhanced foliar uptake is one means of improving efficacy. The plant leaf cuticle is known to be the main barrier to diffusion of agrochemicals within the leaf. The usefulness of a mathematical model to simulate uptake of agrochemicals in plant cuticles has been noted previously in the literature, as the results of each uptake experiment are specific to each formulation of active ingredient, plant species and environmental conditions. In this work we develop a mathematical model and numerical simulation for the uptake of hydrophilic ionic agrochemicals through aqueous pores in plant cuticles. We propose a novel, nonlinear, porous diffusion model for ionic agrochemicals in isolated cuticles, which extends simple diffusion through the incorporation of parameters capable of simulating: plant species variations, evaporation of surface droplet solutions, ion binding effects on the cuticle surface and swelling of the aqueous pores with water. We validate our theoretical results against appropriate experimental data, discuss the key sensitivities in the model and relate theoretical predictions to appropriate physical mechanisms. Major influencing factors have been found to be cuticle structure, including tortuosity and density of the aqueous pores, and to a lesser extent humidity and cuticle surface ion binding effects.

In situ investigation into surfactant effects on the clearance of polycyclic aromatic hydrocarbons adsorbed onto soybean leaf surfaces

The partitioning of polycyclic aromatic hydrocarbons (PAHs) in agricultural crop leaves, contributes to the exposure of organisms to these chemicals through the dietary pathway. To precisely predict the fate of PAHs and crop safety, the clearance of three-ringed phenanthrene (Phe) and four-ringed pyrene (Pyr) adsorbed individually onto living soybean leaf surfaces, as well as the effects of two surfactants, namely, an ionic surfactant (sodium dodecylbenzene sulfonate, SDBS) and a non-ionic surfactant (polyoxyethyleneglycol dodecyl ether, Brij35), were investigated in situ using the laser-induced nanosecond time-resolved fluorescence (LITRF) method. The effects varied significantly with surfactant types primarily in terms of the elimination rates and the final residues of PAH chemicals. With increasing SDBS and Brij35 concentrations, volatilization rate constants (kC) of both Phe and Pyr initially decreased at fast rates and then at more moderate rates later on, resulting from the plasticizing effect of surfactants adsorbed on leaf surfaces. In addition, the photolysis rate constants (kP) decreased with the presence of SDBS but increased with the presence of Brij35. Overall, the total clearance rates of PAHs (kT) adsorbed onto living soybean leaf surfaces were inhibited by the presence of SDBS but promoted by the presence of Brij35. These observations show that surfactants may significantly alter the clearance of PAHs in agricultural systems, and the potential impact of surfactants on crop safety is closely related to surfactant types in natural environments.

Rethinking how volatiles are released from plant cells

For plant volatile organic compounds (VOCs) to be emitted, they must cross membrane(s), the aqueous cell wall, and sometimes the cuticle, before moving into the gas phase. It is presumed that VOC movement through each barrier occurs via passive diffusion. However, VOCs, which are primarily nonpolar compounds, will preferentially partition into membranes, making diffusion into aqueous compartments slow. Using Fick's first law, we calculated that to achieve observed VOC emission rates by diffusion alone would necessitate toxic VOC levels in membranes. Here, we propose that biological mechanisms, such as those involved in trafficking other hydrophobic compounds, must contribute to VOC emission. Such parallel biological pathways would lower barrier resistances and, thus, steady-state emission rates could be maintained with significantly reduced intramembrane VOC concentrations.

The contribution of spray formulation component variables to foliar uptake of agrichemicals

BACKGROUND

The objective of the present study was to determine the contribution of the active ingredient (AI) and surfactant, and their concentrations, to the foliar uptake of agrichemicals, and to examine the physical properties that would need to be included in a model for foliar uptake.

RESULTS

All spray formulation component variables significantly affected uptake, explaining 73% of the deviance. The deviance explained by each factor ranged from 43% (AI concentration nested within AI) to 5.6% (surfactant). The only significant interaction was between AI and surfactant, explaining 15.8% of the deviance. Overall, 90% of the deviance could be explained by the variables and their first-order interactions.

CONCLUSIONS

Uptake increased with increasing lipophilicity of the AI at concentrations below those causing precipitation on the leaf surface. AI concentration had a far greater (negative) effect on the uptake of the lipophilic molecule epoxiconazole. The uptake of 2-deoxy-D-glucose (DOG) and 2,4-dichlorophenoxyacetic acid (2,4-D) increased with increasing hydrophile-lipophile balance (HLB) of the surfactant, the effect of HLB being far greater on the hydrophilic molecule DOG. However, the differences observed in epoxiconazole uptake owing to the surfactant were strongly positively related to the spread area of the formulation on the leaf surface. For all AIs, uptake increased in a similar manner with increasing molar surfactant concentration.

Penetration and Toxicity of Nanomaterials in Higher Plants

Nanomaterials (NMs) comprise either inorganic particles consisting of metals, oxides, and salts that exist in nature and may be also produced in the laboratory, or organic particles originating only from the laboratory, having at least one dimension between 1 and 100 nm in size. According to shape, size, surface area, and charge, NMs have different mechanical, chemical, electrical, and optical properties that make them suitable for technological and biomedical applications and thus they are being increasingly produced and modified. Despite their beneficial potential, their use may be hazardous to health owing to the capacity to enter the animal and plant body and interact with cells. Studies on NMs involve technologists, biologists, physicists, chemists, and ecologists, so there are numerous reports that are significantly raising the level of knowledge, especially in the field of nanotechnology; however, many aspects concerning nanobiology remain undiscovered, including the interactions with plant biomolecules. In this review we examine current knowledge on the ways in which NMs penetrate plant organs and interact with cells, with the aim of shedding light on the reactivity of NMs and toxicity to plants. These points are discussed critically to adjust the balance with regard to the risk to the health of the plants as well as providing some suggestions for new studies on this topic.

Mechanistic modelling of toxicokinetic processes within Myriophyllum spicatum

Effects of chemicals are, in most cases, caused by internal concentrations within organisms which rely on uptake and elimination kinetics. These processes might be key components for assessing the effects of time-variable exposure of chemicals which regularly occur in aquatic systems. However, the knowledge of toxicokinetic patterns caused by time-variable exposure is limited, and gaining such information is complex. In this work, a previously developed mechanistic growth model of Myriophyllum spicatum is coupled with a newly developed toxicokinetic part, providing a model that is able to predict uptake and elimination of chemicals, as well as distribution processes between plant compartments (leaves, stems, roots) of M. spicatum. It is shown, that toxicokinetic patterns, at least for most of the investigated chemicals, can be calculated in agreement with experimental observations, by only calibrating two chemical- specific parameters, the cuticular permeability and a plant/water partition coefficient. Through the model-based determination of the cuticular permeabilities of Isoproturon, Iofensulfuron, Fluridone, Imazamox and Penoxsulam, their toxicokinetic pattern can be described with the model approach. For the use of the model for predicting toxicokinetics of other chemicals, where experimental data is not available, equations are presented that are based on the log (P oct/wat) of a chemical and estimate parameters that are necessary to run the model. In general, a method is presented to analyze time-variable exposure of chemicals more in detail without conducting time and labour intensive experiments.

Measurement of partition coefficients for selected polycyclic aromatic hydrocarbons between isolated plant cuticles and water

Partition coefficients between plant cuticles and water (Kcutw) were measured for 10 selected polycyclic aromatic hydrocarbons (PAHs) to evaluate the sorption capacity of plant cuticular layers for hydrophobic organic chemicals. The partitioning properties of PAHs between cuticles and water were evaluated by using (1) isolated cuticular layers and (2) leaf homogenate. The abaxial and adaxial cuticular layers of Euonymus japonicus were isolated by enzymatic digestion. A third-phase partitioning method using poly(dimethylsiloxane) (PDMS) was used to obtain Kcutw. The Kcutw values for the selected PAHs showed no significant differences between the abaxial and adaxial cuticular layers and ranged between 10(4.1) and 10(7.6). These values are close to or slightly higher than their 1-octanol/water partition coefficient (log Kow), indicating high sorption capacity of plant cuticles. On the contrary, partition coefficients between the lipid tissues of homogenized leaves and water were lower than those obtained using isolated cuticular layers by factors of 3.7-190, which is likely due to the breakdown of lipid layers. This indicates that the sorption of hydrophobic organic chemicals by plant leaves is better evaluated using isolated cuticles and that the sorption potential of plant leaves may be underestimated when leaf homogenates are used.

Transport properties of the mung bean (Vigna radiata) non-aerial hypocotyl membrane: permselectivity to hydrophilic compounds

BACKGROUND

Aerial plant surfaces are covered by a lipophilic cuticular membrane (CM) that restricts the transport of water and small solutes. Non-aerial tissues do not exhibit such a barrier. Recent data have shown that large relative to CM hydrophilic agrochemicals were able to pass at high rates through the non-aerial coleoptile.

RESULTS

A moderately large hydrophilic solute like PEG 1000 with a mean molar volume of 782 cm(3) mol(-1) was rejected by the non-aerial hypocotyl. Uptake of smaller solutes like urea (46.5 cm(3) mol(-1) ) was fast and with 99% after 1 day. Cut-off size estimations suggest a pore size diameter below 1.5 nm.

CONCLUSION

Aerial and non-aerial CM differ largely in their absolute barrier properties. This difference is related to the absence of embedded cuticular waxes in the non-aerial hypocotyl membrane, which make the CM physically dense and cause low solubility of hydrophilic solutes. The free volume for diffusion at the interface of the non-aerial hypocotyl cuticle to the environment is much larger resulting in higher penetration rates. It is suggested that diffusion through the non-aerial hypocotyl does not proceed in a real channel system with continuous aqueous phase but is more like transport through a filter with restricted diffusion in the pore openings.

Foliar sorption of emerging and priority contaminants under controlled conditions

Agricultural irrigation water contains a variety of contaminants that can be introduced into the food chain through intake by irrigated crops. This paper describes an experiment under controlled conditions designed to simulate sprinkle irrigation with polluted water at two different relative humidities (40 and 90%). Specifically, shed lettuce-heart leaves were spiked with an aqueous solution containing organic microcontaminants, including pharmaceuticals (ibuprofen, diclofenac, clofibric acid, and carbamazepine), fragrances (tonalide), biocides (triclosan), insecticides (lindane), herbicides (atrazine), phenolic estrogen (bisphenol A), and polycyclic aromatic hydrocarbons (phenanthrene and pyrene). Following an incubation period (48 h), the treated leaves were rinsed with water, and both the solution used to rinse them and the leaves themselves were independently analyzed to investigate the foliar sorption and uptake of the spiked organic contaminants through cuticle. The results showed that the foliar sorption of emerging and priority microcontaminants in leaves wetted by irrigation practices is related to their polarity (logD(ow)) and volatility (logk(H)), regardless of their compound class and the relative humidity. The results thus underscore the need to improve the quality of reclaimed water in crop irrigation, particularly when sprinkle irrigation is used.

Aqueous pathways dominate permeation of solutes across Pisum sativum seed coats and mediate solute transport via diffusion and bulk flow of water

The permeability of seed coats to solutes either of biological or anthropogenic origin plays a major role in germination, seedling growth and seed treatment by pesticides. An experimental set-up was designed for investigating the mechanisms of seed coat permeation, which allows steady-state experiments with isolated seed coats of Pisum sativum. Permeances were measured for a set of organic model compounds with different physicochemical properties and sizes. The results show that narrow aqueous pathways dominate the diffusion of solutes across pea seed coats, as indicated by a correlation of permeances with the molecular sizes of the compounds instead of their lipophilicity. Further indicators for an aqueous pathway are small size selectivity and a small effect of temperature on permeation. The application of an osmotic water potential gradient across isolated seed coats leads to an increase in solute transfer, indicating that the aqueous pathways form a water-filled continuum across the seed coat allowing the bulk flow of water. Thus, the uptake of organic solutes across pea testae has two components: (1) by diffusion and (2) by bulk water inflow, which, however, is relevant only during imbibition.

Plant uptake of pesticides and human health: dynamic modeling of residues in wheat and ingestion intake

Human intake of pesticide residues from consumption of processed food plays an important role for evaluating current agricultural practice. We take advantage of latest developments in crop-specific plant uptake modeling and propose an innovative dynamic model to estimate pesticide residues in the wheat-environment system, dynamiCROP. We used this model to analyze uptake and translocation of pesticides in wheat after foliar spray application and subsequent intake fractions by humans. Based on the evolution of residues in edible parts of harvested wheat we predict that between 22 mg and 2.1 g per kg applied pesticide are taken in by humans via consumption of processed wheat products. Model results were compared with experimentally derived concentrations in wheat ears and with estimated intake via inhalation and ingestion caused by indirect emissions, i.e. the amount lost to the environment during pesticide application. Modeled and measured concentrations in wheat fitted very well and deviate from less than a factor 1.5 for chlorothalonil to a maximum factor 3 for tebuconazole. Main aspects influencing pesticide fate behavior are degradation half-life in plant and time between pesticide application and crop harvest, leading to variations in harvest fraction of at least three orders of magnitude. Food processing may further reduce residues by approximately 63%. Intake fractions from residues in sprayed wheat were up to four orders of magnitude higher than intake fractions estimated from indirect emissions, thereby demonstrating the importance of exposure from consumption of food crops after direct pesticide treatment.

In vitro human skin permeation and cutaneous metabolism of catechins from green tea extract and green tea extract-loaded chitosan microparticles

Catechins are major antioxidants in green tea (Camellia sinensis or Camellia assamica), but because they do not permeate the skin well, the application of green tea in cosmetic products has so far been limited. This study aims to evaluate the cutaneous absorption of catechins from an extract of green tea and from a green tea extract-loaded chitosan microparticle. The catechin skin metabolism was also examined. The results suggest that chitosan microparticles significantly improve the ability of catechins to permeate skin. The cutaneous metabolism of the catechins significantly affected their permeation profiles. Epicatechin (EC) and epigallocatechin (EGC) penetrated the skin more than epigallocatechin gallate (EGCG) and epicatechin gallate (ECG). The galloyl groups in EGCG and ECG were enzymatically hydrolysed to EGC and EC, respectively. Dehydroxylation of catechins was also observed. Chitosan microparticles effectively prevented enzymatic changes of the catechins; therefore, chitosan microparticles are here found to be the promising carriers for enhancing the skin permeation.

Phylloplane location of glucosinolates in Barbarea spp. (Brassicaceae) and misleading assessment of host suitability by a specialist herbivore

Glucosinolates are plant secondary metabolites used in host plant recognition by insects specialized on Brassicaceae, such as the diamondback moth (DBM), Plutella xylostella. Their perception as oviposition cues by females would seem to require their occurrence on the leaf surface, yet previous studies have reached opposite conclusions about whether glucosinolates are actually present on the surface of crucifer leaves. DBM oviposits extensively on Barbarea vulgaris, despite its larvae not being able to survive on this plant because of its content of feeding-deterrent saponins. Glucosinolates and saponins in plant tissue and mechanically removed surface waxes from leaves of Barbarea spp. were analyzed with high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). Surface waxes from leaves of Barbarea spp. contained glucosinolates, but not feeding-deterrent saponins. Our research is the first to show that glucosinolates are present on the leaf surface of Barbarea spp., but not in other crucifers investigated, resolving some conflicting results from previous studies. Our research is also the first to quantify glucosinolates on the leaf surface of a crucifer, and to show that the concentrations of glucosinolates found on the leaf surface of Barbarea spp. are sufficient to be perceived by ovipositing DBM.

Abscisic acid deficiency causes changes in cuticle permeability and pectin composition that influence tomato resistance to Botrytis cinerea

A mutant of tomato (Solanum lycopersicum) with reduced abscisic acid (ABA) production (sitiens) exhibits increased resistance to the necrotrophic fungus Botrytis cinerea. This resistance is correlated with a rapid and strong hydrogen peroxide-driven cell wall fortification response in epidermis cells that is absent in tomato with normal ABA production. Moreover, basal expression of defense genes is higher in the mutant compared with the wild-type tomato. Given the importance of this fast response in sitiens resistance, we investigated cell wall and cuticle properties of the mutant at the chemical, histological, and ultrastructural levels. We demonstrate that ABA deficiency in the mutant leads to increased cuticle permeability, which is positively correlated with disease resistance. Furthermore, perturbation of ABA levels affects pectin composition. sitiens plants have a relatively higher degree of pectin methylesterification and release different oligosaccharides upon inoculation with B. cinerea. These results show that endogenous plant ABA levels affect the composition of the tomato cuticle and cell wall and demonstrate the importance of cuticle and cell wall chemistry in shaping the outcome of this plant-fungus interaction.