Polar paths of diffusion across plant cuticles: new evidence for an old hypothesis

Revisiting plant cuticle biophysics

The plant cuticle is located at the interface of the plant with the environment, thus acting as a protective barrier against biotic and abiotic external stress factors, and regulating water loss. Additionally, it modulates mechanical stresses derived from internal tissues and also from the environment. Recent advances in the understanding of the hydric, mechanical, thermal, and, to a lower extent, optical and electric properties of the cuticle, as well as their phenomenological connections and relationships are reviewed. An equilibrium based on the interaction among the different biophysical properties is essential to ensure plant growth and development. The notable variability reported in cuticle geometry, surface topography, and microchemistry affects the analysis of some biophysical properties of the cuticle. This review aimed to provide an updated view of the plant cuticle, understood as a modification of the cell wall, in order to establish the state-of-the-art biophysics of the plant cuticle, and to serve as an inspiration for future research in the field.

SEM-EDS-based rapid measurement and size-fractionated speciation of airborne particulate matter and associated metals utilizing plant leaves

This study was conducted to assess particulate matter pollution and the accumulation of airborne toxic metals by studying the foliar deposition pattern in an urban environment. To this end, two commonly growing plants (Senna siamea (Lam.) H.S.Irwin & Barneby and Alstonia scholaris (L.) R.Br.) from the busiest traffic squares of the city (Nehru Chowk) in Bilaspur, India, were selected for detailed study. For this purpose, plant leaf samples of both plant species were collected from pollution-affected areas and a reference site (unpolluted) in the city and examined by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) to estimate the accumulation of PM-bound toxic metals at the leaf surfaces. The results of this study showed that the leaves of both plants accumulate PM in different size ranges. Although both plant leaves showed accumulation of PM from respirable suspended particulate matter (RSPM) to ultra-fine particles (UFPs: < 0.1: less than 100 nm) range along with toxic metals, S. siamea retained a higher level of PM than A. scholaris due to better micro-morphological properties on both leaf surfaces. The size of some PM was found to be smaller than the stoma openings. The EDS study proved the presence of harmful airborne toxic metals (Pb, Cd, Cu, Zr, Al, Co, etc.) in these PMs of ambient air. This indicates that toxic metals can enter the leaves through stomatal openings. The results of this study recommended that both plants can be used as a tool to minimise PM pollution.

The effect of formulation composition and adjuvant type on difenoconazole dislodgeable foliar residue

Rigorous risk assessments for those exposed to pesticides are carried out to satisfy crop protection regulatory requirements. Non-dietary risk assessments involve estimating the amount of residue which can be transferred from plant foliage to the skin or clothes, known as dislodgeable foliar residues (DFRs). DFR data are less available than crop residue data as studies are costly and limited by seasonality. European regulatory authorities are reticent to allow extrapolation of study data to different scenarios as the contributory factors have hitherto been poorly identified. This study is the first to use a new laboratory DFR method to investigate how one such factor, pesticide formulation, may affect DFR on a variety of crops. The study used the active substance difenoconazole as both an emulsifiable concentrate (EC 10%) and a wettable powder (WP 10%) with and without adjuvants (Tween 20 and organophosphate tris(2-ethylhexyl)phosphate TEHP) on tomato, French bean and oilseed rape. A comparable DFR% was retained from the WP and EC formulation on most crops except for tomato, where lower DFR% was retained in the case of WP (39 ± 4.7%) compared to EC (60 ± 1.2%). No significant effect of adjuvant addition was observed for either formulation except when mixing TEHP (0.1% w/v) to the EC 10% on French bean, resulting in 8% DFR reduction compared to the EC formulation alone. This research demonstrates the value of a unique DFR laboratory technique in investigating the importance of the formulation and in-tank adjuvants as factors that affect DFR.

Assessment of tree-ring mercury radial translocation and age effect in Masson pine: Implications for historical atmospheric mercury reconstruction

The tree ring has been regarded as an emerging archive to reconstruct historical atmospheric mercury (Hg) trends, but with the large knowledge gaps in the reliability. In this study, we comprehensively evaluated the Hg source, radial translocation and age effect of Masson pine (Pinus massoniana) tree ring at Mt. Jinyun in Chongqing, to assess the suitability of such tree ring as the archive of atmospheric Hg. Results showed that distinct variabilities among Masson pine tree-ring Hg concentration profiles. The Hg concentration significantly increased along with stem height (P < 0.05), indicating the Hg in tree rings mainly derived from foliage uptake atmospheric Hg. We found a distinct age effect that the tree ring of young trees had the higher Hg concentration. Besides, we used the advection-diffusion model to demonstrate how Hg concentration shifted by the advection or/and diffusion in tree rings. The modeling results showed that the advection induced radial translocation during the young growth period of tree was a plausible mechanism to result in the tree-ring Hg record largely different from the trend of anthropogenic Hg emissions in Chongqing. We finally suggest that in further Hg dendrochemistry, better discarding the tree-ring Hg profile of the young growth period to reduce impacts of the radial translocation and age effect.

Effects of uptake pathways on the accumulation, translocation, and metabolism of OPEs in rice: An emphasis on foliar uptake

The often-overlooked importance of foliar absorption on the plant uptake of organic pollutants was investigated by an exposure chamber test. Rice seedlings were exposed to organophosphate esters (OPEs) through 8 scenarios arranged from 3 major uptake pathways: root uptake via solution, foliar uptake via gas, and foliar uptake via particles, to identify the contributions of these 3 uptake pathways and their influences on the translocation and metabolism of OPEs in rice. The concentration of OPEs in rice tissues showed an "additive effect" with the increase of exposure pathways. OPEs in rice shoots mainly originated from foliar uptake through particle (29.6 %-63.5 %) and gaseous (28.5 %-49.4 %) absorptions rather than root uptake (7.86 %-24.2 %) under the exposure condition. In comparison with stomal absorption, wax layer penetration was the main pathway for most OPEs to enter into leaves, especially for those compounds with high octanol-air partition coefficients. Although the subcellular distributions of OPEs in the rice tissues of the foliar exposure were slightly different from those of the root exposure, hydrophobic OPEs were mainly stored in the cell wall with hydrophilic OPEs mainly in the cytosol. The translocation of OPEs from the exposed tissue to the unexposed tissue were significantly negatively correlated with their octanol-water partition coefficients, but their basipetal translocation were limited. The result suggested that the translocation of OPEs within rice is prioritized over their degradation. This study deepens our understanding of the processes behind OPE uptake by rice and highlights the importance of foliar uptake, especially for those via particle absorption.

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.

Nitrogen Application Can Optimize Form of Selenium in Soil in Selenium-Rich Areas to Affect Selenium Absorption and Accumulation in Black Wheat

The composition and form of selenium in the soil have significant effects on the selenium content of crops. In this study, we investigated the selenium absorption pathway in plants by studying the interaction between nitrogen fertilizer and soil selenium. Our results showed that the selenium concentration enrichment factors (CEF) varied within the same region due to nitrogen fertilizer application, where they ranged from 1.33 to 5.02. The soil selenium flow coefficient (mobility factor, MF) increased with higher nitrogen application rates. The sum of the MF values for each soil layer treated with nitrogen application rates of 192 kg hm-2 and 240 kg hm-2 was 0.70, which was 64% higher than that for the control group with no nitrogen application. In the 0-20 cm soil layer, the highest summed water-soluble and exchangeable selenium and relative percentage of total selenium (12.45%) was observed at a nitrogen application rate of 240 kg hm-2. In the 20-40 cm soil layer, the highest relative percentage content of water-soluble and exchangeable selenium and total selenium (12.66%) was observed at a nitrogen application rate of 192 kg hm-2. Experimental treatment of black wheat with various concentrations of sodium selenite showed that selenium treatment at 50 μmol L-1 significantly increased the reduced glutathione (GSH) levels in the leaves and roots of seedlings, where the GSH contents increased by 155.4% in the leaves and by 91.5% in the roots. Further analysis of the soil-black wheat system showed that nitrogen application in selenium-rich areas affected the soil selenium flow coefficient and morphological composition, thereby changing the enrichment coefficient for leaves (0.823), transport capacity from leaves to grains (-0.530), and enrichment coefficient for roots (0.38). These changes ultimately affected the selenium concentration in the grains of black wheat.

Nanoplatforms for the Delivery of Nucleic Acids into Plant Cells

Nanocarriers are widely used for efficient delivery of different cargo into mammalian cells; however, delivery into plant cells remains a challenging issue due to physical and mechanical barriers such as the cuticle and cell wall. Here, we discuss recent progress on biodegradable and biosafe nanomaterials that were demonstrated to be applicable to the delivery of nucleic acids into plant cells. This review covers studies the object of which is the plant cell and the cargo for the nanocarrier is either DNA or RNA. The following nanoplatforms that could be potentially used for nucleic acid foliar delivery via spraying are discussed: mesoporous silica nanoparticles, layered double hydroxides (nanoclay), carbon-based materials (carbon dots and single-walled nanotubes), chitosan and, finally, cell-penetrating peptides (CPPs). Hybrid nanomaterials, for example, chitosan- or CPP-functionalized carbon nanotubes, are taken into account. The selected nanocarriers are analyzed according to the following aspects: biosafety, adjustability for the particular cargo and task (e.g., organelle targeting), penetration efficiency and ability to protect nucleic acid from environmental and cellular factors (pH, UV, nucleases, etc.) and to mediate the gradual and timely release of cargo. In addition, we discuss the method of application, experimental system and approaches that are used to assess the efficiency of the tested formulation in the overviewed studies. This review presents recent progress in developing the most promising nanoparticle-based materials that are applicable to both laboratory experiments and field applications.

Tree rings as historical archives of atmospheric mercury: A critical review

Historical concentrations of atmospheric mercury (Hg) are uncertain, as monitoring only began a few decades ago. Tree rings can serve as historical archives of Hg, providing centennial trends. The vast majority of tree-ring Hg studies have been published in the last decade, demonstrating the growing use of tree rings for Hg dendrochemistry. Thus, there is a need for a systematic review on current knowledge of tree rings as archives of atmospheric Hg. In this review, the predominant pathways of Hg uptake to tree rings are discussed, including the initial Hg uptake from the surrounding environment, fixation, and subsequent translocation. Foliar uptake of Hg was found to be the most important uptake route for Hg in tree rings, the root and bark route being negligible. Our summary of the suitability of different tree species indicates that radial translocation is the biggest limiting factor for Hg dendrochemistry, shifting and blurring historical Hg trends. Based on the review findings, Picea (spruce) and Larix (larch) are the most promising genera for Hg dendrochemistry. Additionally, the use of tree-ring Hg archives in combination with other co-located archives, namely lake sediments, peat, and ice, is suggested as it enhances the viability of observed tree-ring historical Hg trends. Finally, we propose future directions and recommendations for research using tree-ring Hg, including sampling protocols, experimental designs, and tree selection.

Global assessment of honeybee exposure to pesticides through guttation consumption: An indicator approach

Guttation consumption is a potential pathway of pesticide residue exposure in honeybees. However, modeling tools for assessing honeybee exposure to pesticide residues in guttation drops are lacking. In this study, we propose an indicator-based approach for qualitatively or quantitatively analyzing the guttation-based exposure pathway, allowing us to conduct region-specific pesticide residue exposure assessments for honeybees. Exposure scores (the product of guttation production and residue level scores) were established to compare or rank honeybee exposure to pesticide residues via guttation intake across locations using three specified indicators (i.e., air temperature, relative humidity, and precipitation intensity). Warm, dry regions had high residue level scores (indicating high residue levels in guttation), whereas cold, wet regions had high guttation production scores (indicating high possibilities of guttation formation on leaf surfaces); their exposure scores were a combination of these two values. We evaluated and ranked honeybee exposure to imidacloprid residue across regions in Brazil, China, the United States, and selected European Union member states, revealing that pesticide application in many Brazilian federative units may raise honeybee risks due to high exposure scores. We also compared the guttation pathway to other common exposure pathways (nectar and pollen), suggesting that for some moderately lipophilic compounds, the guttation exposure pathway may not be ignored and should be further evaluated.

Advances in nanoparticle and organic formulations for prolonged controlled release of auxins

Plant hormones have been well known since Charles Darwin as signaling molecules directing plant metabolism. Their action and transport pathways are at the top of scientific interest and were reviewed in many research articles. Modern agriculture applies phytohormones as supplements to achieve desired physiological plant response. Auxins are a class of plant hormones extensively used for crop management. Auxins stimulate the formation of lateral roots and shoots, seed germination, while extensively high concentrations of these chemicals act as herbicides. Natural auxins are unstable; light or enzyme action leads to their degradation. Moreover, the concentration dependant action of phytohormones denier one-shot injection of these chemicals and require constant slow additive of supplement. It obstructs the direct introduction of auxins. On the other hand, delivery systems can protect phytohormones from degradation and provide a slow release of loaded drugs. Moreover, this release can be managed by external stimuli like pH, enzymes, or temperature. The present review is focused on three auxins: indole-3-acetic, indole-3-butyric, and 1-naphthaleneacetic acids. We collected some examples of inorganic (oxides, Ag, layered double hydroxides) and organic (chitosan, organic formulations) delivery systems. The action of carriers can enhance auxin effects via protection and targeted delivery of loaded molecules. Moreover, nanoparticles can act as nano fertilizers, intensifying the phytohormone effect, providing slow controlled release. So delivery systems for auxins are extremely attractive for modern agriculture opening sustainable management of plant metabolism and morphogenesis.

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.

Leaf and stem anatomical characterization of Euphorbia hirta L., a tolerant species to glyphosate

Euphorbia hirta L. is a weed species that is tolerant to the most used herbicide in agriculture, glyphosate. The anatomical characteristics of plants influence the processes of absorption and translocation of herbicides. The objective of this work was to characterize the anatomy of the aerial vegetative axis (leaves and stem) of E. hirta, to support the establishment of strategies for better control of this species with herbicides. The plants were grown in a greenhouse under controlled conditions. When they reached sizes between 8 and 12 cm, samples of stems and leaves were collected, fixed in FAA 50, and stored in 70% ethanol. Subsequently, the samples were processed following usual light microscopy techniques. In cross-section, the stem of E. hirta has a circular shape. The leaf epidermis is uniseriate composed of isodiametric cells of compact arrangement and with the presence of multicellular trichomes and anthocyanin. As for the morphometric parameters evaluated, the young leaves have a lower thickness in the abaxial epidermis. Based on the anatomical characteristics observed in E. hirta, the main barriers that can act in the absorption of herbicides are the high hairiness and the high content of anthocyanin in the epidermal cells.

Natural variation and drought-induced differences in metabolite profiles of red oak-leaf and Romaine lettuce play a role in modulating the interaction with Salmonella enterica

Nutrients on produce surfaces are vital for successful enteric pathogen colonisation. In this study, we investigated natural variation in metabolite profiles of Romaine 'Parris Island Cos' and red oak-leaf lettuce 'Mascara' under regular and restricted watering conditions. We also investigated the impact of plant drought stress on the Salmonella - lettuce association. Salmonella Newport and Typhimurium were able to persist at higher levels on regularly watered Romaine than red oak-leaf lettuce. Drought treatment to lettuce impaired epiphytic Salmonella association, with S. Newport and Typhimurium being differentially affected. A higher log reduction of both serotypes was measured on drought-subjected red oak-leaf lettuce plants than controls, but S. Typhimurium was unaffected on water deficit-treated Romaine lettuce (p < 0.05). To assess Salmonella interaction with leaf surface metabolites, leaf washes collected from both cultivars were inoculated and found to be able to support S. Newport growth, with higher levels of Salmonella retrieved from Romaine washes (p < 0.05). The lag phase of S. Newport in washes from water restricted red oak-leaf lettuce was prolonged in relation to regularly-watered controls (p < 0.05). Untargeted plant metabolite profiling using electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) revealed natural variation between Romaine and red oak-leaf lettuce profiles for leaf tissue and leaf washes. Metabolite profile shifts were detected in both lettuce types in response to drought stress, but more unique peaks were detected in red oak-leaf than Romaine lettuce after drought treatment. Variation between the two cultivars was in part attributed to naturally higher levels of flavonoids and anthocyanins in red oak-leaf lettuce compared to Romaine. Moreover, red oak-leaf, but not Romaine lettuce, responded to drought by inducing the accumulation of proline, phenolics, flavonoids and anthocyanins. Drought stress, therefore, enhanced the functional food properties of red oak-leaf lettuce. Salmonella growth dynamics in lettuce leaf washes suggested that natural variation and drought-induced changes in metabolite profiles in lettuce could partly explain the differential susceptibility of various lettuce types to Salmonella, although the primary or secondary metabolites mediating this effect remain unknown. Regulated mild water stress should be investigated as an approach to lower Salmonella contamination risk in suitable lettuce cultivars, while simultaneously boosting the health beneficial quality of lettuce.

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.

A mechanism-based fate model of pesticide solutions on the plant surface under aerial application

Pesticide residues on plant surfaces are a primary source of pesticide bioaccumulation in crops. In this context, we propose a mechanism-based model for understanding the pesticide fate on the plant surface following aerial application, taking into account fate modelling of the pesticide spray solution on the plant surface. Using chlorothalonil as an example, the simulation results revealed that the spray solution dissipated rapidly after aerial application, resulting in the formation of a saturated pesticide solution, which facilitated the diffusion process of the pesticide residue from the plant surface into the peel tissue. The proposed model generated higher simulated residue concentrations in the peel or pulp than the current model, owing to the proposed model's assumption of rapid dissipation of the spray solution. This indicated that the proposed model specified the influence of the spray solution on the plant's exposure to residues via the surface deposition pathway, whereas the current modelling approach presented a generic estimate of the residue dissipation on the plant surface that linked to the residue's fate in the soil.

Transgene-free genome editing and RNAi ectopic application in fruit trees: Potential and limitations

For the past fifteen years, significant research advances in sequencing technology have led to a substantial increase in fruit tree genomic resources and databases with a massive number of OMICS datasets (transcriptomic, proteomics, metabolomics), helping to find associations between gene(s) and performance traits. Meanwhile, new technology tools have emerged for gain- and loss-of-function studies, specifically in gene silencing and developing tractable plant models for genetic transformation. Additionally, innovative and adapted transformation protocols have optimized genetic engineering in most fruit trees. The recent explosion of new gene-editing tools allows for broadening opportunities for functional studies in fruit trees. Yet, the fruit tree research community has not fully embraced these new technologies to provide large-scale genome characterizations as in cereals and other staple food crops. Instead, recent research efforts in the fruit trees appear to focus on two primary translational tools: transgene-free gene editing via Ribonucleoprotein (RNP) delivery and the ectopic application of RNA-based products in the field for crop protection. The inherent nature of the propagation system and the long juvenile phase of most fruit trees are significant justifications for the first technology. The second approach might have the public favor regarding sustainability and an eco-friendlier environment for a crop production system that could potentially replace the use of chemicals. Regardless of their potential, both technologies still depend on the foundational knowledge of gene-to-trait relationships generated from basic genetic studies. Therefore, we will discuss the status of gene silencing and DNA-based gene editing techniques for functional studies in fruit trees followed by the potential and limitations of their translational tools (RNP delivery and RNA-based products) in the context of crop production.

Nanoporous silica gel can compete with the flower stigma in germinating and attracting pollen tubes

To find nanoporous substrates with hydrodynamic properties useful for pollen hydration and germination, we used the glassy Silica gel and Vycor scales and pollen with different morphological and physiological traits, that of Crocus vernus, and that of Narcissus poeticus. For in vitro tests, the scales were spread on microscope slides, hand pollinated, and incubated. Pollen germination was evaluated with the stereomicroscope and the tube growth was explored with scanning electron microscopy (SEM). The in vivo tests were carried out by sprinkling the stigmas of the Crocus plants with Silica gel scales and immediately after having pollinated them by hand, the plants were incubated. Three hours later, the stigmas were removed and treated for observation with SEM. In vitro the pollen of both species germinated on Silica gel with percentages similar to those of the in vivo and in vitro controls, accumulating fibrillary material at the interface. The tubes grew perpendicular to the surface of the scales, trying to penetrate the scales to the point of flattening with the apex. On Crocus stigmas sprinkled with Silica gel scales, pollen developed tubes that grew to the scales rather than penetrating the papillae. The results underline the close interaction of pollen with nanoporous artificial material, so much so that its pollen tubes are attracted to the Silica scales more than to the stigma papillae that arises from a mechanism of natural selection.

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.

Environmental photochemistry on plants: recent advances and new opportunities for interdisciplinary research

Plants play a central role in the photochemistry of chemicals in the environment. They represent a major atmospheric source of volatile organic compounds (VOCs) but also an important environmental surface for the deposition and photochemical reactions of pesticides, gaseous and particulate pollutants. In this review, we point out the role of plant leaves in these processes, as a support affecting the reactions physically and chemically and as a partner through the release of natural constituents (water, secondary metabolites). We discuss the influence of the chosen support (leaves, needle surfaces or fruit cuticles, extracted cuticular waxes and model surfaces) and other factors (additives, pesticides mixture, and secondary metabolites) on the photochemical degradation kinetics and mechanisms. We also show how plants can be a source of photochemically reactive species which can act as photosensitizers promoting the photodegradation of pesticides or the formation and aging of secondary organic aerosols (SOA) and secondary organic materials (SOM). Understanding the fate of chemicals on plants is a research area located at the interface between photochemistry, analytical chemistry, atmospheric chemistry, microbiology and vegetal physiology. Pluridisciplinary approaches are needed to deeply understand these complex phenomena in a comprehensive way. To overcome this challenge, we summarize future research directions which have been clearly overlooked until now.

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.

Nanotechnology-enabled biofortification strategies for micronutrients enrichment of food crops: Current understanding and future scope

Nutrient deficiency in food crops severely compromises human health, particularly in under privileged communities. Globally, billions of people, particularly in developing nations, have limited access to nutritional supplements and fortified foods, subsequently suffering from micronutrient deficiency leading to a range of health issues. The green revolution enhanced crop production and provided food to billions of people but often falls short with respect to the nutritional quality of that food. Plants may assimilate nutrients from synthetic chemical fertilizers, but this approach generally has low nutrient delivery and use efficiency. Further, the overexposure of chemical fertilizers may increase the risk of neoplastic diseases, render food crops unfit for consumption and cause environmental degradation. Therefore, to address these challenges, more research is needed for sustainable crop yield and quality enhancement with minimum use of chemical fertilizers. Complex nutritional disorders and 'hidden hunger' can be addressed through biofortification of food crops. Nanotechnology may help to improve food quality via biofortification as plants may readily acquire nanoparticle-based nutrients. Nanofertilizers are target specific, possess controlled release, and can be retained for relatively long time periods, thus prevent leaching or run-off from soil. This review evaluates the recent literature on the development and use of nanofertilizers, their effects on the environment, and benefits to food quality. Further, the review highlights the potential of nanomaterials on plant genetics in biofortification, as well as issues of affordability, sustainability, and toxicity.

Translocation and metabolism of the chiral neonicotinoid cycloxaprid in oilseed rape (Brassica napus L.)

Neonicotinoids have been banned in some countries because of increased nontarget resistance and ecological toxicity. Cycloxaprid is a potentially promising substitute, but its metabolism in plants is still poorly understood. The study aims to clarify the translocation of cycloxaprid, identify its metabolites, propose possible metabolic pathways and compare differences between enantiomers in oilseed rape via ¹⁴C tracing technology and HPLC-QTOF-MS. The results showed that most cycloxaprid remained in the treated leaves, and only a small amount translocated to the anthers. Seven metabolites were identified, and the possible metabolic pathway was divided into two phases. Phase Ⅰ metabolism included two metabolites obtained via cleavage of the oxa-bridged seven-membered ring. Phase II metabolism was responsible for glucose conjugate formation. The possible metabolic pathways revealed that the proportion of phase I metabolites gradually decreased over time, and the phase II metabolites transformed from monosaccharide and disaccharide conjugates to trisaccharide and tetrasaccharide conjugates. The levels of metabolites were significantly different between the enantiomers. In particular, the main metabolite was M4, which has confirmed biological toxicity. M2 was the only metabolite detected in rapeseed. The results will promote the scientific application of cycloxaprid in agriculture and could have implications for assessing environmental risk.

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.

Alcohol Ethoxylates Enhancing the Cuticular Uptake of Lipophilic Epoxiconazole Do Not Increase the Rates of Cuticular Transpiration of Leaf and Fruit Cuticles

Surfactants are known to enhance the foliar uptake of agrochemicals by plasticizing the transport-limiting barrier of plant cuticles. The effects of two different polydisperse alcohol ethoxylates with a low degree [mean ethoxylation of 5 ethylene oxide units (EOs)] and a high degree (mean ethoxylation of 10 EOs) of ethoxylation on cuticular barrier properties were investigated. The diffusion of the lipophilic organic molecule ¹⁴C-epoxiconazole and of polar ³H-water across cuticles isolated from six different plant species was investigated. At low surfactant coverages (10 μg cm^-2), the diffusion of water across the cuticles was not affected by the two surfactants. Only at very high surfactant coverages (100-1000 μg cm^-2) was the diffusion of water enhanced by the two surfactants between 5- and 50-fold. Unlike that of water, the diffusion of epoxiconazole was significantly enhanced 12-fold at surfactant coverages of 10 and 100 μg cm² by the surfactant with low ethoxylation (5 EOs), and it decreased to 6-fold at a surfactant coverage of 1000 μg cm^-2. The alcohol ethoxylate with a high degree of ethoxylation (10 EOs) only weakly increased the epoxiconazole diffusion. Our results clearly indicate that those surfactants that significantly enhance the uptake of the lipophilic agrochemicals (e.g., epoxiconazole) at a realistic leaf surface coverage of 10 μg cm^-2, as is applied in the field, do not interfere with cuticular transpiration as an unwanted negative side effect.

Stimuli-Free Transcuticular Delivery of Zn Microelement Using Biopolymeric Nanovehicles: Experimental, Theoretical, and In Planta Studies

This paper reports one-step synthesis of polysaccharide-based nanovehicles, capable of transporting ionic zinc via plant cuticle without auxiliary stimulation. Delivery of highly hydrophilic nutritive microelements via the hydrophobic cuticle of plant foliage is one of the major challenges in modern agriculture. In traditional nutrition via roots, up to 80% of microelements permeate to soil and get wasted; therefore, foliar treatment is an environmentally and economically preferable alternative. Carboxymethyl cellulose (CMC) was modified to amphiphilic N-octylamide-derivative (CMC-8), which spontaneously self-assemble to nanovehicles. It was found that hydrophobic substituents endow a biopolymer with unexpected affinity toward a hydrophilic payload. CMC-8 nanovehicles effectively encapsulated ionic zinc (ZnSO₄) and delivered it upon foliar application to pepper (Capsicum annuum) and tomato (Solanum lycopersicum) plants. Zinc uptake and translocation in plants were monitored by SEM-EDS and fluorescence microscopic methods. In planta monitoring of the carrier was done by labeling nanovehicles with fluorescent carbon dots. Three-dimensional (3-D) structural modeling and conformational dynamics explained the CMC-8 self-assembly mechanism and zinc coordination phenomenon upon introduction of hydrophobic substituents.

What makes a molecule a pre- or a post-herbicide - how valuable are physicochemical parameters for their design?

Pre-emergence herbicides are taken up by seeds before germination and by roots, hypocotyls, cotyledons, coleoptiles or leaves before emergence, whereas post-emergence herbicides are taken up primarily by foliage and stems. Most modern pre-emergence herbicides are lipophilic, but post-emergence herbicides may be lipophilic or hydrophilic. The metabolic conversion of herbicides to inactive or active metabolites after plant uptake is of major importance for some compound classes. Several herbicides are proherbicides as for example some acetyl-coenzyme A carboxylase (ACCase)-inhibitors. The physicochemical characteristics of proherbicides and herbicides are usually unrelated. A major role can be attributed to the site of action at a cellular level. A great number of herbicides such as photosystem II (PS II)-inhibitors, protoporphyrinogen oxidase (PPO)-inhibitors or carotenoid biosynthesis inhibitors require light for activity. Others, such as cellulose-biosynthesis and mitotic inhibitors seem to be primarily active in belowground organs. Several lipophilic barriers against the uptake of xenobiotics exist in aboveground and belowground plant parts. The relevance of these barriers needs, however, further clarification. Uptake and translocation models are valuable tools for the explanation of the potential movement of compounds. Many factors other than uptake and translocation have, however, to be considered for the design of herbicides. For post-emergence herbicides, ultraviolet (UV) light stability, stability in formulations, and mixability with other agrochemicals have to be kept in mind while, in addition to the aforementioned factors soil interaction plays a major role for pre-emergence herbicides. In our opinion, general physicochemical characteristics of pre- or post-emergence herbicides do, unfortunately not exist yet. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Foliar Delivery of siRNA Particles for Treating Viral Infections in Agricultural Grapevines

Grapevine leafroll disease (GLD) is a globally spreading viral infection that causes major economic losses by reducing crop yield, plant longevity and berry quality, with no effective treatment. Grapevine leafroll associated virus-3 (GLRaV-3) is the most severe and prevalent GLD strain. Here, we evaluated the ability of RNA interference (RNAi), a non-GMO gene-silencing pathway, to treat GLRaV-3 in infected Cabernet Sauvignon grapevines. We synthesized lipid-modified polyethylenimine (lmPEI) as a carrier for long double-stranded RNA (dsRNA, 250-bp-long) that targets RNA polymerase and coat protein genes that are conserved in the GLRaV-3 genome. Self-assembled dsRNA-lmPEI particles, 220 nm in diameter, displayed inner ordered domains spaced 7.3±2 nm from one another, correlating to lmPEI wrapping spirally around the dsRNA. The particles effectively protected RNA from degradation by ribonucleases, and Europium-loaded particles applied to grapevine leaves were detected as far as 60-cm from the foliar application point. In three field experiments, a single dose of foliar administration knocked down GLRaV-3 titer, and multiple doses of the treatment kept the viral titer at baseline and triggered recovery of the vine and berries. This study demonstrates RNAi as a promising platform for treating viral diseases in agriculture.

Biochemical and Metabolic Plant Responses toward Polycyclic Aromatic Hydrocarbons and Heavy Metals Present in Atmospheric Pollution

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are toxic components of atmospheric particles. These pollutants induce a wide variety of responses in plants, leading to tolerance or toxicity. Their effects on plants depend on many different environmental conditions, not only the type and concentration of contaminant, temperature or soil pH, but also on the physiological or genetic status of the plant. The main detoxification process in plants is the accumulation of the contaminant in vacuoles or cell walls. PAHs are normally transformed by enzymatic plant machinery prior to conjugation and immobilization; heavy metals are frequently chelated by some molecules, with glutathione, phytochelatins and metallothioneins being the main players in heavy metal detoxification. Besides these detoxification mechanisms, the presence of contaminants leads to the production of the reactive oxygen species (ROS) and the dynamic of ROS production and detoxification renders different outcomes in different scenarios, from cellular death to the induction of stress resistances. ROS responses have been extensively studied; the complexity of the ROS response and the subsequent cascade of effects on phytohormones and metabolic changes, which depend on local concentrations in different organelles and on the lifetime of each ROS species, allow the plant to modulate its responses to different environmental clues. Basic knowledge of plant responses toward pollutants is key to improving phytoremediation technologies.

The Characteristics of Mercury Flux at the Interfaces between Two Typical Plants and the Air in Leymus chinensis Grasslands

Mercury is a global pollutant. The mercury exchanges between vegetation and the atmosphere are important for the global mercury cycle. Grassland ecosystems occupy more than 25% of the global land area and have different succession processes and ecological functions. The current research regarding mercury exchanges between forests and the atmosphere have attracted much attention, but the research regarding grasslands tends to be rare. To reveal the characteristics of mercury exchanges in grasslands, this study conducted field in-situ monitoring experiments in a Leymus meadow grassland regions of the Songnen Plains in northeastern China. The exchange flux values of the GEM (gaseous element mercury) between the plants and the atmosphere were measured using a dynamic flux bag method (DFB). The experiments were conducted for the purpose of assessing the mercury flux levels between the vegetation and the atmosphere in a typical Leymus chinensis meadow. The goal was to further the understanding of the change characteristics and influential factors and to describe the source and sink actions and dynamics between the grassland vegetation and the atmosphere. The diurnal variation characteristics were as follows: High during the day and low at night, with peaks generally appearing at noon. The growing period was characterized by absorption peaks of atmospheric mercury by the plants. The breeding period was characterized by the peak release of atmospheric mercury by the plants. The change characteristics were as follows: During the growing period, the duration of the plants in a mercury absorption state exceeded 96.5%, which was represented as the net sink of the atmospheric mercury. During the breeding period, the time of mercury release ranged between 46.4% and 66.8%, making the breeding period the net source of atmospheric mercury. The results of this study's analysis indicated that each environmental factor was correlated with the mercury flux, and the environmental factors had different effects on the mercury flux during the different stages of plant growth. The atmospheric mercury concentration levels were the main factor during the growing period. Atmospheric humidity was the main factor during the breeding period. Solar radiation was the decisive factor during the entire experimental period.

Dynamics of moisture diffusion and adsorption in plant cuticles including the role of cellulose

Food production must increase significantly to sustain a growing global population. Reducing plant water loss may help achieve this goal and is especially relevant in a time of climate change. The plant cuticle defends leaves against drought, and so understanding water movement through the cuticle could help future proof our crops and better understand native ecology. Here, via mathematical modelling, we identify mechanistic properties of water movement in cuticles. We model water sorption in astomatous isolated cuticles, utilising three separate pathways of cellulose, aqueous pores and lipophilic. The model compares well to data both over time and humidity gradients. Sensitivity analysis shows that the grouping of parameters influencing plant species variations has the largest effect on sorption, those influencing cellulose are very influential, and aqueous pores less so but still relevant. Cellulose plays a significant role in diffusion and adsorption in the cuticle and the cuticle surfaces.

Strategies for probing absorption and translocation of foliar-applied nutrients

This article comments on:

Li C, Wu J, Pax F, Blamey F, Wang L, Zhou L, Paterson DJ, van der En A, Fernández V, Lombi E, Wang Y, Kopittke PM. 2021. Non-glandular trichomes of sunflower are important in the absorption and translocation of foliar-applied Zn. Journal of Experimental Botany 72, 5079–5092.

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.

Strawberry fruit skins are far more permeable to osmotic water uptake than to transpirational water loss

Water movements through the fruit skin play critical roles in many disorders of strawberry (Fragaria × ananassa Duch.) such as water soaking, cracking and shriveling. The objective was to identify the mechanisms of fruit water loss (dry skin, transpiration) and water uptake (wet skin, osmosis). Fruits were held above dried silica gel or incubated in deionized water. Water movements were quantified gravimetrically. Transpiration and osmotic uptake increased linearly with time. Abrading the thin cuticle (0.62 g m^-2) increased rates of transpiration 2.6–fold, the rates of osmotic uptake 7.9-fold. The osmotic potential of the expressed juice was nearly the same for green and for white fruit but decreased in red fruit stages. Fruit turgor was low throughout development, except for green fruit. There was no relationship between the rates of water movement and fruit osmotic potential. The skin permeance for transpiration and for osmotic uptake were both high (relative to other fruit species) but were two orders of magnitude greater for osmotic uptake than for transpiration. Incubating fruit in isotonic solutions of osmolytes of different sizes resulted in increases in fruit mass that depended on the osmolyte. The rate of osmotic uptake decreased asymptotically as molecular size of the osmolyte increased. When transpiration and osmotic uptake experiments were conducted sequentially on the same fruit, the rates of transpiration were higher for fruit previously incubated in water. Fluorescence microscopy revealed considerable microcracking in a fruit previously incubated in water. Our findings indicate that the high permeance for osmotic uptake is accounted for by an extremely thin cuticle and by viscous water flow through microcracks and along polar pathways.

Agro-Nanotechnology as an Emerging Field: A Novel Sustainable Approach for Improving Plant Growth by Reducing Biotic Stress

In the present era, the global need for food is increasing rapidly; nanomaterials are a useful tool for improving crop production and yield. The application of nanomaterials can improve plant growth parameters. Biotic stress is induced by many microbes in crops and causes disease and high yield loss. Every year, approximately 20–40% of crop yield is lost due to plant diseases caused by various pests and pathogens. Current plant disease or biotic stress management mainly relies on toxic fungicides and pesticides that are potentially harmful to the environment. Nanotechnology emerged as an alternative for the sustainable and eco-friendly management of biotic stress induced by pests and pathogens on crops. In this review article, we assess the role and impact of different nanoparticles in plant disease management, and this review explores the direction in which nanoparticles can be utilized for improving plant growth and crop yield.

Silica nanoparticles enhance disease resistance in Arabidopsis plants

In plants, pathogen attack can induce an immune response known as systemic acquired resistance that protects against a broad spectrum of pathogens. In the search for safer agrochemicals, silica nanoparticles (SiO2 NPs; food additive E551) have recently been proposed as a new tool. However, initial results are controversial, and the molecular mechanisms of SiO2 NP-induced disease resistance are unknown. Here we show that SiO2 NPs, as well as soluble Si(OH)4, can induce systemic acquired resistance in a dose-dependent manner, which involves the defence hormone salicylic acid. Nanoparticle uptake and action occurred exclusively through the stomata (leaf pores facilitating gas exchange) and involved extracellular adsorption in the air spaces in the spongy mesophyll of the leaf. In contrast to the treatment with SiO2 NPs, the induction of systemic acquired resistance by Si(OH)4 was problematic since high Si(OH)4 concentrations caused stress. We conclude that SiO2 NPs have the potential to serve as an inexpensive, highly efficient, safe and sustainable alternative for plant disease protection.

Cutin:cutin-acid endo-transacylase (CCT), a cuticle-remodelling enzyme activity in the plant epidermis

Cutin is a polyester matrix mainly composed of hydroxy-fatty acids that occurs in the cuticles of shoots and root-caps. The cuticle, of which cutin is a major component, protects the plant from biotic and abiotic stresses, and cutin has been postulated to constrain organ expansion. We propose that, to allow cutin restructuring, ester bonds in this net-like polymer can be transiently cleaved and then re-formed (transacylation). Here, using pea epicotyl epidermis as the main model, we first detected a cutin:cutin-fatty acid endo-transacylase (CCT) activity. In-situ assays used endogenous cutin as the donor substrate for endogenous enzymes; the exogenous acceptor substrate was a radiolabelled monomeric cutin-acid, 16-hydroxy-[3H]hexadecanoic acid (HHA). High-molecular-weight cutin became ester-bonded to intact [3H]HHA molecules, which thereby became unextractable except by ester-hydrolysing alkalis. In-situ CCT activity correlated with growth rate in Hylotelephium leaves and tomato fruits, suggesting a role in loosening the outer epidermal wall during organ growth. The only well-defined cutin transacylase in the apoplast, CUS1 (a tomato cutin synthase), when produced in transgenic tobacco, lacked CCT activity. This finding provides a reference for future CCT protein identification, which can adopt our sensitive enzyme assay to screen other CUS1-related enzymes.

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.

Enhancing mixed toluene and formaldehyde pollutant removal by Zamioculcas zamiifolia combined with Sansevieria trifasciata and its CO2 emission

Indoor air pollutants comprise both polar and non-polar volatile organic compounds (VOCs). Indoor potted plants are well known for their innate ability to improve indoor air quality (IAQ) by detoxification of indoor air pollutants. In this study, a combination of two different plant species comprising a C3 plant (Zamioculcas zamiifolia) and a crassulacean acid metabolism (CAM) plant (Sansevieria trifasciata) was used to remove polar and non-polar VOCs and minimize CO₂ emission from the chamber. Z. zamiifolia and S. trifasciata, when combined, were able to remove more than 95% of pollutants within 48 h and could do so for six consecutive pollutant's exposure cycles. The CO₂ concentration was reduced from 410 down to 160 ppm inside the chamber. Our results showed that using plant growth medium rather than soil had a positive effect on decreasing CO₂. We also re-affirmed the role of formaldehyde dehydrogenase in the detoxification and metabolism of formaldehyde and that exposure of plants to pollutants enhances the activity of this enzyme in the shoots of both Z. zamiifolia and S. trifasciata. Overall, a mixed plant of Z. zamiifolia and S. trifasciata was more efficient at removing mixed pollutants and reducing CO₂ than individual plants.

Transpiration from Tomato Fruit Occurs Primarily via Trichome-Associated Transcuticular Polar Pores

Nonstomatal water loss by transpiration through the hydrophobic cuticle is ubiquitous in land plants, but the pathways along which this occurs have not been identified. Tomato (Solanum lycopersicum) provides an excellent system in which to study this phenomenon, as its fruit are astomatous and a major target for desiccation resistance to enhance shelf life. We screened a tomato core collection of 398 accessions from around the world and selected seven cultivars that collectively exhibited the lowest and highest degrees of transpirational water loss for a more detailed study. The transpirational differences between these lines reflected the permeances of their isolated cuticles, but this did not correlate with various measures of cuticle abundance or composition. Rather, we found that fruit cuticle permeance has a strong dependence on the abundance of microscopic polar pores. We further observed that these transcuticular pores are associated with trichomes and are exposed when the trichomes are dislodged, revealing a previously unreported link between fruit trichome density and transpirational water loss. During postharvest storage, limited self-sealing of the pores was detected for certain cultivars, in contrast with the stem scar, which healed relatively rapidly. The abundance of trichome-associated pores, together with their self-sealing capacity, presents a promising target for breeding or engineering efforts to reduce fruit transpirational water loss.

Structure-function analysis of the maize bulliform cell cuticle and its potential role in dehydration and leaf rolling

The hydrophobic cuticle of plant shoots serves as an important interaction interface with the environment. It consists of the lipid polymer cutin, embedded with and covered by waxes, and provides protection against stresses including desiccation, UV radiation, and pathogen attack. Bulliform cells form in longitudinal strips on the adaxial leaf surface, and have been implicated in the leaf rolling response observed in drought-stressed grass leaves. In this study, we show that bulliform cells of the adult maize leaf epidermis have a specialized cuticle, and we investigate its function along with that of bulliform cells themselves. Bulliform cells displayed increased shrinkage compared to other epidermal cell types during dehydration of the leaf, providing a potential mechanism to facilitate leaf rolling. Analysis of natural variation was used to relate bulliform strip patterning to leaf rolling rate, providing further evidence of a role for bulliform cells in leaf rolling. Bulliform cell cuticles showed a distinct ultrastructure with increased cuticle thickness compared to other leaf epidermal cells. Comparisons of cuticular conductance between adaxial and abaxial leaf surfaces, and between bulliform-enriched mutants versus wild-type siblings, showed a correlation between elevated water loss rates and presence or increased density of bulliform cells, suggesting that bulliform cuticles are more water-permeable. Biochemical analysis revealed altered cutin composition and increased cutin monomer content in bulliform-enriched tissues. In particular, our findings suggest that an increase in 9,10-epoxy-18-hydroxyoctadecanoic acid content, and a lower proportion of ferulate, are characteristics of bulliform cuticles. We hypothesize that elevated water permeability of the bulliform cell cuticle contributes to the differential shrinkage of these cells during leaf dehydration, thereby facilitating the function of bulliform cells in stress-induced leaf rolling observed in grasses.

Toxicity, uptake and transport mechanisms of dual-modal polymer dots in penny grass (Hydrocotyle vulgaris L.)

The use of polymers such as plastic has become an important part of daily life, and in aqueous environments, these polymers are considered as pollutants. When macropolymers are reduced to the nanoscale, their small particle size and large specific surface area facilitate their uptake by plants, which has a significant impact on aquatic plants. Therefore, it is essential to study the pollution of nanoscale polymers in the aquatic environment. In this work, we prepared nanoscale polymer dots (Pdots) and explored their toxicity, uptake and transport mechanisms in penny grass. From toxicological studies, in the absence of other nutrients, the cell structure, physiological parameters (total soluble protein and chlorophyll) and biochemical parameters (malondialdehyde) do not show significant changes over at least five days. Through in vivo fluorescence and photoacoustic (PA) imaging, the transport location can be visually detected accurately, and the transport rate can be analyzed without destroying the plants. Moreover, through ex vivo fluorescence imaging, we found that different types of Pdots have various uptake and transport mechanisms in stems and blades. It may be due to the differences in ligands, particle sizes, and oil-water partition coefficients of Pdots. By understanding how Pdots interact with plants, a corresponding method can be developed to prevent them from entering plants, thus avoiding the toxicity from accumulation. Therefore, the results of this study also provide the basis for subsequent prevention work.

Relationship between the amount and composition of epicuticular wax and tolerance of Ipomoea biotypes to glyphosate

Ipomoea species are troublesome weeds in crop systems through Brazil. Drought stress typically reduces glyphosate efficacy by reducing the foliar uptake of herbicides and their translocation. Using both glyphosate tolerant (GT) and sensitive (GS) plants from Ipomoea grandifolia, I. indivisa and I. purpurea species, this research aimed to (a) correlate amounts of epicuticular wax and tolerance to glyphosate in plants and (b) determine the effect of drought stress (DStress) on changes in the quantity and chemical composition of plant epicuticular waxes. The dose that causes 50% inhibition of growth (GR50) of the biotypes varied between 62 and 1208 (I. grandifolia), 159 and 913 (I. indivisa), and 389 and 1925 g a.e. ha-1 of glyphosate (I. purpurea). There was low inverse correlation (-0.46) between the amount of epicuticular wax and the sensitivity to glyphosate. GT biotypes of the species presented greater plastic capacities than GS biotypes for increasing the amount of epicuticular wax under DStress. The three Ipomoea species exhibited different chemical profiles of waxes supported by IR spectra, which allows for their differentiation. For I. grandifolia and I. purpurea, there was an increase in the polar components in the state without DStress, while for the species I. indivisa, no differences in infrared spectra were detected between the two water conditions.

Ecophysiology with barley eceriferum (cer) mutants: the effects of humidity and wax crystal structure on yield and vegetative parameters

BACKGROUND AND AIMS

In addition to preventing water loss, plant cuticles must also regulate nutrient loss via leaching. The eceriferum mutants in Hordeum vulgare (barley) potentially influence these functions by altering epicuticular wax structure and composition.

METHODS

Cultivar 'Bonus' and five of its cer mutants were grown under optimal conditions for vegetative growth and maturation, and nine traits were measured. Nutrient and water amounts going through the soil and the amount of simulated rain as deionized water, affecting phyllosphere humidity, delivered during either the vegetative or maturation phase, were varied. Cer leaf genes and three wilty (wlt) mutations were characterized for reaction to toluidine blue and the rate of non-stomatal water loss.

KEY RESULTS

Vegetative phase rain on 'Bonus' significantly decreased kernel weight and numbers by 15-30 %, while in cer.j59 and .c36 decreases of up to 42 % occurred. Maturation phase findings corroborated those from the vegetative phase. Significant pleiotropic effects were identified: cer.j59 decreased culm and spike length and 1000-kernel weight, .c36 decreased kernel number and weight, .i16 decreased spike length and .e8 increased culm height. Excepting Cer.zv and .ym mutations, none of the other 27 Cer leaf genes or wlt mutations played significant roles, if any, in preventing water loss. Cer.zv and .ym mutants lost non-stomatal water 13.5 times faster than those of Cer.j, .yi, .ys and .zp and 18.3 times faster than those of four cultivars and the mutants tested here.

CONCLUSIONS

Using yield to measure the net effect of phyllosphere humidity and wax crystal structure revealed that the former is far more important than the latter. The amenable experimental setup described here can be used to delve deeper. Significant pleiotropic effects were identified for mutations in four Cer genes, of which one is known to participate in wax biosynthesis. Twenty-seven Cer leaf genes and three wlt mutations have little if any effect on water loss.

Comparative functional analyses of DWARF14 and KARRIKIN INSENSITIVE 2 in drought adaptation of Arabidopsis thaliana

Functional analyses of various strigolactone-deficient mutants have demonstrated that strigolactones enhance drought resistance; however, the mechanistic involvement of the strigolactone receptor DWARF14 (D14) in this trait remains elusive. In this study, loss-of-function analysis of the D14 gene in Arabidopsis thaliana revealed that d14 mutant plants were more drought-susceptible than wild-type plants, which was associated with their larger stomatal aperture, slower abscisic acid (ABA)-mediated stomatal closure, lower anthocyanin content and delayed senescence under drought stress. Transcriptome analysis revealed a consistent alteration in the expression levels of many genes related to the observed physiological and biochemical changes in d14 plants when compared with the wild type under normal and dehydration conditions. A comparative drought resistance assay confirmed that D14 plays a less critical role in Arabidopsis drought resistance than its paralog karrikin receptor KARRIKIN INSENSITIVE 2 (KAI2). In-depth comparative analyses of the single mutants d14 and kai2 and the double mutant d14 kai2, in relation to various drought resistance-associated mechanisms, revealed that D14 and KAI2 exhibited a similar effect on stomatal closure. On the other hand, D14 had a lesser role in the maintenance of cell membrane integrity, leaf cuticle structure and ABA-induced leaf senescence, but a greater role in drought-induced anthocyanin biosynthesis, than KAI2. Interestingly, a possible additive relationship between D14 and KAI2 could be observed in regulating cell membrane integrity and leaf cuticle development. In addition, our findings also suggest the existence of a complex interaction between the D14 and ABA signaling pathways in the adaptation of Arabidopsis to drought.

A Permeable Cuticle, Not Open Stomata, Is the Primary Source of Water Loss From Expanding Leaves

High rates of water loss in young, expanding leaves have previously been attributed to open stomata that only develop a capacity to close once exposed to low humidity and high abscisic acid (ABA) levels. To test this model, we quantified water loss through stomata and cuticle in expanding leaves of Quercus rubra. Stomatal anatomy and density were observed using scanning electron microscopy. Leaves of Q. rubra less than 5 days after emergence have no stomata; therefore, water loss from these leaves must be through the cuticle. Once stomata develop, they are initially covered in a cuticle and have no outer cuticular ledge, implying that the majority of water lost from leaves in this phase of expansion is through the cuticle. Foliar ABA levels are high when leaves first expand and decline exponentially as leaves expand. Once leaves have expanded to maximum size, ABA levels are at a minimum, an outer cuticular ledge has formed on most stomata, cuticular conductance has declined, and most water loss is through the stomata. Similar sequences of events leading to stomatal regulation of water loss in expanding leaves may be general across angiosperms.

Barriers to Efficient Foliar Uptake of dsRNA and Molecular Barriers to dsRNA Activity in Plant Cells

Foliar application of dsRNA to elicit an RNA interference (RNAi) response is currently under consideration as a crop protection strategy. To access the RNAi machinery of a plant, foliarly applied dsRNAs must traverse the plant cuticle, avoid nuclease degradation, and penetrate the cell wall and plasma membrane. Application methods and co-formulants have been identified by Bayer Crop Science researchers and others that can help bypass barriers to dsRNA uptake in plants leading to an RNAi response in greenhouse grown, young plants and cell cultures. However, these advances in dsRNA delivery have yet to yield systemic RNAi silencing of an endogenous gene target required for product concepts such as weed control. Systemic RNAi silencing in plants has only been observed with the GFP transgene in Nicotiana benthamiana. Because biologically meaningful whole plant RNAi has not been observed for endogenous gene products in N. benthamiana or in other plant species tested, under growing conditions including field production, the regulatory risk assessment of foliarly applied dsRNA-based products should not consider exposure scenarios that include systemic response to small RNAs in treated plants.

Effects of cuticular wax content and specific leaf area on accumulation and partition of PAHs in different tissues of wheat leaf

An indoor simulation experiment was conducted to explore the effects of cuticular wax content and specific leaf area (SLA) on accumulation and distribution of PAHs in different tissues of wheat leaf. Three levels (0, 1.25, 6.0 mg L^-1) of mixed solution of five PAHs (Σ₅PAHs) including phenanthrene (PHE), anthracene (ANT), pyrene (PYR), benz[a]anthracene (BaA), and benzo[a]pyrene (BaP) were sprayed on leaves of seven varieties of winter wheat for every other day during 20 consecutive days. Shoot and root biomass of wheat under 6.0 mg L^-1 Σ₅PAHs exposure were 5.87 and 0.33 g, which were significantly (p < 0.05) lower than those (7.14 and 0.65 g) without spraying Σ₅PAHs solution, respectively. Elevated Σ₅PAHs concentration in spraying solution significantly (p < 0.0001) decreased cuticular wax content (59.1 and 65.1 vs. 67.8 mg g^-1) in leaves of wheat but exerted slight effects on SLA. Regardless of spraying Σ₅PAHs or not, SLA in leaves of Jiaomai (269-276 cm² g^-1) and Zhengmai (265-285 cm² g^-1) and cuticular wax content (104-118 mg g^-1) in leaves of Zhengmai were significantly higher than other varieties of wheat, respectively. Σ₅PAHs concentration in cuticular waxes ranged from 24,616 to 106,353 μg kg^-1, which was 2~3 orders and 1~2 orders of magnitude higher than that in mesophylls (46.0-535 μg kg^-1) and leaves (785-5366 μg kg^-1). There was a significant (r = 0.46, p < 0.05, n = 28) positive correlation between SLA and Σ₅PAHs concentration in wheat leaves when spraying 1.25 mg L^-1 of Σ₅PAHs. The present study indicated that cuticular wax content was significantly (p < 0.01) positive correlated with Σ₅PAHs concentration in the leaves and the translocation factor (TF_w-m) of PHE, ANT, PYR, and Σ₅PAHs from cuticular wax to mesophyll. Based on principal component analysis (PCA), cuticular wax content was the main limiting factor for folia uptake of PAHs in winter wheat. The present study suggested that cuticular wax could play significant roles in foliar uptake of PAHs of wheat via affecting their accumulation in cuticular wax and translocation to mesophyll.