Tomato and Pepper Leaf Parts Contribute Differently to the Absorption of Foliar-Applied Potassium Dihydrogen Phosphate.

Foliar fertilisation is an application technique that is increasingly being used in agriculture and offers the possibility of providing nutrients directly to the site of highest demand. Especially for phosphorus (P), foliar application is an interesting alternative to soil fertilisation, but foliar uptake mechanisms are poorly understood. To gain a better understanding of the importance of leaf surface features for foliar P uptake, we conducted a study with tomato (Solanum lycopersicum) and pepper (Capsicum annuum) plants, which have different leaf surface traits. For this purpose, drops of 200 mM KH2PO4 without surfactant were applied onto the adaxial or abaxial leaf side or to the leaf veins and the rate of foliar P absorption was evaluated after one day. Additionally, leaf surfaces were characterised in detail by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), estimating also leaf surface wettability and free energy, among other parameters. While the leaves of pepper hardly contained any trichomes, the abaxial side and the leaf veins of tomato leaves were densely covered with trichomes. The cuticle of tomato leaves was thin (approximately 50 nm), while that of pepper was thick (approximately 150-200 nm) and impregnated with lignin. Due to the fact that trichomes were most abundant in the leaf veins of tomato, dry foliar fertiliser drop residues were observed to be anchored there, and the highest P uptake occurred via tomato leaf veins, resulting in 62% increased P concentration. However, in pepper, the highest rate of P absorption was recorded after abaxial-side P treatment (+66% P). Our results provide evidence that different leaf parts contribute unequally to the absorption of foliar-applied agrochemicals, which could potentially be useful for optimising foliar spray treatments in different crops.

Foliar P Application Cannot Fully Restore Photosynthetic Capacity, P Nutrient Status, and Growth of P Deficient Maize (Zea mays L.).

The essential plant nutrient phosphorus (P) is key for numerous structures and processes in crops and its deficiency can severely restrict yield and quality. As soil P availability for plant uptake is often limited, foliar P application can be an alternative means of supplying P to the plants during the growth period. This study was aimed at investigating the effect of foliar P application on photosynthetic parameters, P nutritional status, and growth of P deficient maize over time. Plants of Zea mays L. cv. Keops were grown with deficient and sufficient amounts of P in hydroponics. Foliar P treatments were applied to P deficient plants and several physiological parameters were monitored for 21 days. The variables measured were leaf gas exchange parameters, SPAD values, foliar P absorption, re-translocation rates, and plant biomass production. Foliar P application significantly increased CO2-assimilation and SPAD values and additionally enhanced biomass production in all plant components. Elemental analysis revealed increased tissue P concentrations following foliar P application compared to P deficient plants. While increased growth of P-deficient plants was steadily promoted by foliar P spraying for the entire experimental period, the positive effect on CO2 assimilation and P concentration was transient and vanished some days after the foliar treatment. P deficiency markedly impaired the efficiency of physiological processes of maize plants. As a conclusion, foliar P fertilisation improved physiological and agronomical plant parameters over time, but failed to restore plant functionality of P deficient maize plants during a prolonged experimental period.

Foliar water uptake does not contribute to embolism repair in beech (Fagus sylvatica L.).

BACKGROUND AND AIMS: Foliar water uptake has recently been suggested as a possible mechanism for the restoration of hydraulically dysfunctional xylem vessels. In this paper we used a combination of ecophysiological measurements, X-ray microcomputed tomography and cryo-scanning electron microscopy during a drought treatment to fully evaluate this hypothesis. KEY RESULTS: Based on an assessment of these methods in beech (Fagus sylvatica L.) seedlings we were able to (1) confirm an increase in the amount of hydraulically redistributed water absorbed by leaves when the soil water potential decreased, and (2) locate this redistributed water in hydraulically active vessels in the stem. However, (3) no embolism repair was observed irrespective of the organ under investigation (i.e. stem, petiole or leaf) or the intensity of drought. CONCLUSIONS: Our data provide evidence for a hydraulic pathway from the leaf surface to the stem xylem following a water potential gradient, but this pathway exists only in functional vessels and does not play a role in embolism repair for beech.

Uptake, subcellular distribution, and translocation of foliar-applied phosphorus: Short-term effects on ion relations in deficient young maize plants.

One crucial aspect for successful foliar application is the uptake of the nutrient into the symplast for metabolization by the plant. Our aim was to determine the subcellular distribution of foliar-applied P in leaves, the translocation of this element within the whole plant, and its impact on the ion status of P-deficient maize plants within the first 48 h of treatment. Maize plants with P deficiency were sprayed with 200 mM KH2PO4. After 6, 24, and 48 h, the 5th leaf of each plant was harvested for the isolation of apoplastic washing fluid, cell sap, and vascular bundle sap and for the examination of transporter gene expression. The remaining tissues were divided into 4th leaf, older and younger shoots, and root for total P determination. No accumulation of foliar-applied P was measured in the apoplast. P was mostly taken up into the cytosol within the first 6 h and was associated with increased mRNA levels of PHT1 transporters. A strong tendency towards rapid translocation into the younger shoot and an increase in NO3- uptake or a decrease in organic acid translocation were observed. The apoplast seems to exert no effect on the uptake of foliar-applied P into the epidermal and mesophyll cells of intact leaves. Instead, the plant responds with the rapid translocation of P and changes in ion status to generate further growth. The effect of the absorbed foliar-applied P is assumed to be a rapid process with no transient storage in the leaf apoplast.

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.

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.

Identifying the pathways for foliar water uptake in beech (Fagus sylvatica L.): a major role for trichomes.

Foliar water uptake (FWU), the direct uptake of water into leaves, is a global phenomenon, having been observed in an increasing number of plant species. Despite the growing recognition of its functional relevance, our understanding of how FWU occurs and which foliar surface structures are implicated, is limited. In the present study, fluorescent and ionic tracers, as well as microcomputed tomography, were used to assess potential pathways for water entry in leaves of beech, a widely distributed tree species from European temperate regions. Although none of the tracers entered the leaf through the stomatal pores, small amounts of silver precipitation were observed in some epidermal cells, indicating moderate cuticular uptake. Trichomes, however, were shown to absorb and redistribute considerable amounts of ionic and fluorescent tracers. Moreover, microcomputed tomography indicated that 72% of empty trichomes refilled during leaf surface wetting and microscopic investigations revealed that trichomes do not have a cuticle but are covered with a pectin-rich cell wall layer. Taken together, our findings demonstrate that foliar trichomes, which exhibit strong hygroscopic properties as a result of their structural and chemical design, constitute a major FWU pathway in beech.

Impacts of foliar exposure to multi-walled carbon nanotubes on physiological and molecular traits of Salvia verticillata L., as a medicinal plant.

Owing to the growing applications of the multi-walled carbon nanotubes (MWCNTs) in the communications and energy industries, they have attracted increasing attention for their effects on the environment and plants. Therefore, we investigated the impact of foliar exposure to MWCNTs on the oxidative stress responses in the Salvia verticillata as a medicinal plant. Furthermore, we evaluated the possible correlations between gene expression and activity of the key enzymes in the phenolic acids biosynthesis pathways and their accumulation in the treated leaves. The leaves of two-month-old plants were sprayed with different concentrations (0-1000 mg L-1) of MWCNTs. Raman's data and Transmission Electron Microscopy images have confirmed the absorption of MWCNTs via epidermal cells layer into the parenchymal cells of the exposed leaves. The results showed that exposure to MWCNTs led to a decrease in the photosynthetic pigments and increases in the oxidative stress indices (enzymatic and non-enzymatic antioxidants) in the leaves with a dose-dependent manner. The content of rosmarinic acid as a main phenolic acid was increased in the MWCNTs-exposed leaves to 50 and 1000 mg L-1, nearly four times relative to the control. Unlike with other examined enzymes, a positive correlation was deduced between the activity and gene expression patterns of the rosmarinic acid synthase with the rosmarinic acid accumulation in the treatments. Overall, MWCNTs at the low concentrations could promote the production of the pharmaceutical metabolites by the changes in the ROS generation. However, at the higher concentrations, MWCNTs were toxic and induced the oxidative damages in S. verticillata.

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.

Nonstereoselective foliar absorption and translocation of cycloxaprid, a novel chiral neonicotinoid, in Chinese cabbage.

Exploring traditional neonicotinoid pesticides substitutes has become one of the global scientific attentions because of their hazardous environmental impacts. Cycloxaprid (CYC) is considered to be a promising candidate alternative. But the environmental behaviors and fate of CYC in different planting system remain poorly understood. The accumulation of 14C-labeled CYC stereoisomers within different parts of Chinese cabbage (Brassica chinensis L.) was investigated, with a particular focus on the foliar absorption, translocation and stereoselectivity of CYC, during a laboratory trial. In general, the stereoisomers 14C-5R,8S-CYC and 14C-5S,8R-CYC, their metabolites, as well as the breakdown and reaction products can be transferred in both acropetal and basipetal directions. Most of the two stereoisomers absorbed by plants remained in the treated leaves, whereas a small amount was distributed to the roots. The amount of 14C in the stalks varied among the experimental time points. At 192 h after treatment (HAT), the detected radioactivity of both 14C-5R,8S-CYC and 14C-5S,8R-CYC in the leaves above the treated leaf (LATL) was higher than that in the leaves below the treated leaf (LBTL). However, the stereoisomers of CYC underwent nonstereoselective absorption and translocation in this trial. This information implies that racemic CYC and its metabolites should be a main research focus. Thus, the obtained results provide implications for a more accurate prediction about the risk assessment of CYC, which will be helpful for guiding its rational use as well as securing the ecological environment safety and human health.

Hydraulic redistribution of foliar absorbed water causes turgor-driven growth in mangrove seedlings.

Although foliar water uptake (FWU) has been shown in mature Avicennia marina trees, the importance for its seedlings remains largely unknown. A series of experiments were therefore performed using artificial rainfall events in a greenhouse environment to assess the ecological implications of FWU in A. marina seedlings. One-hour artificial rainfall events resulted in an increased leaf water potential, a reversed sap flow, and a rapid diameter increment signifying a turgor-driven growth of up to 30.1 ± 5.4 µm. Furthermore, the application of an artificial rainfall event with deuterated water showed that the amount of water absorbed by the leaves and transported to the stem was directly and univocally correlated to the observed growth spurts. The observations in this process-based study show that FWU is an important water acquisition mechanism under certain circumstances and might be of ecological importance for the establishment of A. marina seedlings. Distribution of mangrove trees might hence be more significantly disturbed by climate change-driven changes in rainfall patterns than previously assumed.

Surface Properties and Permeability to Calcium Chloride of Fagus sylvatica and Quercus petraea Leaves of Different Canopy Heights.

Plant surfaces have a considerable degree of chemical and physical variability also in relation to different environmental conditions, organs and state of development. The potential changes on plant surface properties in association with environmental variations have been little explored so far. Using two model tree species (i.e., Quercus petraea, sessile oak and Fagus sylvatica, beech) growing in 'Montejo de la Sierra Forest,' we examined various traits of the abaxial and adaxial surface of leaves of both species collected at a height of approximately 15 m (top canopy), versus 3.5-5.5 m for beech and sessile oak, lower canopy leaves. Leaf surface ultra-structure was analyzed by scanning and transmission electron microscopy, and the surface free energy and related parameter were estimated after measuring drops of 3 liquids with different degrees of polarity and apolarity. The permeability of the adaxial and abaxial surface of top and bottom canopy leaves to CaCl2 was estimated by depositing 2 drops of 3-4 µl per cm2 and comparing the concentration of Ca in leaf tissues 24 h after treatment, and also Ca and Cl concentrations in the washing liquid. Higher Ca concentrations were recorded after the application of CaCl2 drops onto the veins and adaxial blade of top canopy beech leaves, while no significant evidence for foliar Ca absorption was gained with sessile oak leaves. Surprisingly, high amounts of Cl were recovered after washing untreated, top canopy beach and sessile oak leaves with deionised water, a phenomenon which was not traced to occur on lower canopy leaves of both species. It is concluded that the surface of the two species analyzed is heterogeneous in nature and may have areas favoring the absorption of water and solutes as observed for the veins of beech leaves.

Development and assessment of a simple ecological model (TRIPS) for forests contaminated by radiocesium fallout.

The management of vast forested zones contaminated by radiocesium (rCs) following the Chernobyl and Fukushima fallout is of great social and economic concern in affected areas and requires appropriate dynamic models as predictive or questioning tools. Generally, the existing radio-ecological models need less fragmented data and more ecological realism in their quantitative description of the rCs cycling processes. The model TRIPS ("Transfer of Radionuclide In Perennial vegetation Systems") developed in this study privileged an integrated approach which makes the best use of mass balance studies and available explicit experimental data for Scots pine stands. A main challenge was the differentiation and calibration of foliar absorption as well as root uptake in order to well represent the rCs biocycling. The general dynamics of rCs partitioning was simulated with a relatively good precision against an independent series of observed values. In our scenario the rCs biological cycling enters a steady-state about 15 years after the atmospheric deposits. At that time, the simulations showed an equivalent contribution of foliage and root uptake to the tree contamination. But the root uptake seems not sufficient to compensate the activity decline in the tree. The initial foliar uptake and subsequent internal transfers were confirmed to have a great possible impact on the phasing of tree contamination. An extra finding concerns the roots system acting as a buffer in the early period. The TRIPS model is particularly useful in cases where site-specific integrated datasets are available, but it could also be used with adequate caution to generic sites. This development paves the way for simplification or integration of new modules, as well as for a larger number of other applications for the Chernobyl or Fukushima forests once the appropriate data become available. According to the sensitivity analysis that involves in particular reliable estimates of net foliar uptake as well as root uptake not disconnected from rCs exchange reactions in soil.

Effects of changes in leaf properties mediated by methyl jasmonate (MeJA) on foliar absorption of Zn, Mn and Fe.

Background and Aims: Foliar fertilization to overcome nutritional deficiencies is becoming increasingly widespread. However, the processes of foliar nutrient absorption and translocation are poorly understood. The present study aimed to investigate how cuticular leaf properties affect the absorption of foliar-applied nutrients in leaf tissues. Methods: Given that methyl jasmonate (MeJA) can cause alterations in leaf properties, we applied 1 mm MeJA to sunflower (Helianthus annuus), tomato (Solanum lycopersicum) and soybean (Glycine max) to assess changes in leaf properties. Using traditionally analytical approaches and synchrotron-based X-ray fluorescence microscopy, the effects of these changes on the absorption and translocation of foliar-applied Zn, Mn and Fe were examined. Key Results: The changes in leaf properties caused by the application of MeJA increased foliar absorption of Zn, Mn and Fe up to 3- to 5-fold in sunflower but decreased it by 0·5- to 0·9-fold in tomato, with no effect in soybean. These changes in the foliar absorption of nutrients could not be explained by changes in overall trichome density, which increased in both sunflower (86%) and tomato (76%) (with no change in soybean). Similarly, the changes could be not attributed to changes in stomatal density or cuticle composition, given that these properties remained constant. Rather, the changes in the foliar absorption of Zn, Mn and Fe were related to the thickness of the cuticle and epidermal cell wall. Finally, the subsequent translocation of the absorbed nutrients within the leaf tissues was limited (<1·3mm) irrespective of treatment. Conclusions: The present study highlights the potential importance of the combined thickness of the cuticle and epidermal cell wall in the absorption of foliar-applied nutrients. This information will assist in increasing the efficacy of foliar fertilization.

Stereoselective uptake and distribution of the chiral neonicotinoid insecticide, Paichongding, in Chinese pak choi (Brassica campestris ssp. chinenesis).

Neonicotinoid chiral insecticidal Paichongding is a promising substitute for the widely used imidacloprid. Four stereoisomers of Paichongding, 5R,7R, 5S,7S, 5S,7R and 5R,7S, were employed in both foliage and roots of Chinese pak choi to investigate their stereoselective uptake and distribution in pak choi. Results showed that after foliar application, no stereoselective absorption into pak-choi plants was observed among the enantiomers. Total absorptions were 35.40% of the applied amount for 5R,7R, 36.66% for 5S,7S, 36.80% for 5S,7R and 38.20% for 5R,7S at 96 HAT. The translocation of the four absorbed stereoisomers within pak choi occurred both acropetally and basipetally and the transport of (14)C from enantiomers 5R,7R and 5S,7S were significantly higher than for 5R,7S and 5S,7R. Significant stereoselective translocation inside plants was observed between Paichongding epimers. Total root uptake reached 16.49-19.85% for 5R,7R and 5S,7S, and 24.57-28.82% for 5S,7R and 5R,7S at 144 HAT. Both enantioselective and diastereoselective root uptake into pak-choi occurred between the four stereoisomers. The 5R,7S and 5S,7R enantiomers were more readily uptaken by the roots than 5R,7R and 5S,7S and accumulated in the edible leaves. These results will help to develop an understanding of Paichongding using only the target-active enantiomer of pesticides.

Enantioselective uptake and translocation of a novel chiral neonicotinoid insecticide cycloxaprid in Youdonger (Brassica campestris subsp. Chinensis).

For a novel potential commercial chiral pesticide, an independent study on the fate characteristics and residues of each stereoisomer is essential if the application rates for the pesticide and human exposure are to be reduced. The absorption and translocation behavior of a chiral insecticide, cycloxaprid, in plants treated by root immersion and blade smearing was studied using (14)C-labeling tracer techniques. With the root treatment, total absorption of (1R;8S)-cycloxaprid (RS) (12.39%) was much greater than that of (1S;8R)-cycloxaprid (SR) (3.31%) at 192 h after treatment (HAT). The mass concentrations (RS/SR) of cycloxaprid in the roots, cotyledons, leaf 1, leaf 2, and leaf 3 were 37.0/16.8, 8.3/2.8, 11.7/6.5, 5.1/4.8, and 8.0/4.7 mg kg(-1) (fresh weight), respectively, at 192 HAT at an initial concentration 1.6 mg kg(-1). With the foliar application treatment, no significant difference was observed between the total absorption of RS (3.11%) and SR (4.03%) at the end of the treatment. Both acropetal and basipetal transport of absorbed (14)C occurred and more than 71.83% of absorbed RS and 82.42% of SR remained in the treated leaf. Stereoselective absorption was observed during root uptake but not during foliar absorption.