Structural features of reconstituted wheat wax films

Caprylic acid in Vitex mollis fruit and its inhibitory activity against a thiabendazole-resistant Colletotrichum gloeosporioides strain

BACKGROUND

Colletotrichum gloeosporioides causes anthracnose in a large number of crops. Synthetic fungicides are employed to prevent this disease, even though their effectiveness and safety is questionable. Thus, effective and innocuous antifungal compounds are proposed as natural alternatives against anthracnose. The hexane fraction of Vitex mollis pulp (HF-VM) reduces anthracnose incidence in papaya fruit; however, the active compounds and antifungal mechanism of HF-VM are unknown. The aims of this study were to characterize the activity of HF-VM sub-fractions (sHF₁ -sHF₇ ) against a thiabendazole-resistant Colletotrichum gloeosporioides strain, identify the chemical components and investigate the mechanism of the most active sub-fraction.

RESULTS

The sHF₃ showed the highest inhibitory activity against Colletotrichum gloeosporioides with a minimal inhibitory concentration (MIC) of 0.5 mg mL^-1 , whereas thiabendazole (TBZ) had a MIC value higher than 2 mg mL^-1 . The gas chromatography-mass spectrometry (GC-MS) analysis showed that the compounds in sHF₃ were methyl 4-decenoate, caprylic acid, and 24-methylencycloartanol. These compounds are rarely found in fruits and are reported for the first time on Vitex species. The purified 24-methylencycloartanol was inactive (MIC > 0.5 mg mL^-1 ). In contrast, the commercial standard of caprylic acid presented an elevated activity (MIC = 0.125 mg mL^-1 ), indicating that this compound is the main one responsible for the antifungal properties of sHF₃ . Furthermore, the sHF₃ inhibited the spore germination and induced membrane disruption in both the spore and mycelium of Colletotrichum gloeosporioides.

CONCLUSION

Vitex mollis fruit is a novel source of antifungal caprylic acid that could be employed as a marker to prepare standardized extracts with antifungal properties. © 2022 Society of Chemical Industry.

Contrasting impacts of mixed nonionic surfactant micelles on plant growth in the delivery of fungicide and herbicide

HYPOTHESIS

Nonionic alkyl ethoxylate surfactants are widely used in agrochemicals to facilitate the permeation of systemic herbicides and fungicides across the plant waxy film. Industrial grade surfactants are often highly mixed and how the mixing affects their interactions with pesticides and wax films remains largely unexplored. A better understanding could enable design of mixed nonionic surfactants for herbicides and fungicides to maximize their efficiency and reduce wastage whilst controlling their impact on plant wax films.

EXPERIMENT

In this study, nonionic surfactants with general structure n-oxyethylene glycol monododecyl ether (C₁₂E_n) were used to form surfactant mixtures with the same average ethoxylate numbers but different hydrophilic-lipophilic balance (HLB) values. Their mixed micellar systems were then used to solubilize a herbicide diuron (DN) and a fungicide cyprodinil (CP), followed by plant wax solubilization upon contact with wax films. These processes were monitored by ¹H NMR and SANS.

FINDING

Pesticide solubilization made surfactant micelles effectively more hydrophobic but subsequent wax dissolution caused pesticide release and the restoration of the micellar amphiphilicity. Nonionic surfactants with lower HLBs form larger nanoaggregates, show enhanced wettability, and have better ability to solubilize and permeate pesticides across the wax film, but may cause significant damage to plant growth. These observations help explain why herbicides applied on weeds would benefit from surfactants with lower HLB values while fungicides require surfactants with HLBs to balance between delivery efficiency and potential phytotoxicity risks.

Effects of different fermentation assisted enzyme treatments on the composition, microstructure and physicochemical properties of wheat straw used as a substitute for peat in nursery substrates

To solve the central problems caused by traditional composting treatments, such as long-time consumption and poor regulation effects, this study used three fermentation methods and four enzymes to develop rapid and directional regulation methods to convert wheat straw into a suitable substrate. The results showed that the mixed anaerobic method led to better pH (4.39-5.75) and EC values (1.27-1.89 mS/cm) in the straw substrates, while the aerobic method retained more nutrients and increased lignin and cellulose contents by 5.07-8.04% and 1.52-3.32%. The cellulase mixed with hemicellulase or laccase treatments all increased the crystallinity by 0.45-7.23%. The TG/DTG results showed that all treatments decreased the initial straw glass transition temperature, particularly when using the mixed anaerobic method, with decreases of 10.63-25.48 °C. Overall, mixed anaerobic fermentation and multiple enzymes, including cellulase, have been suggested as alternative biological modification methods for straw substrates.

Aliphatic extractive effects on acetic acid catalysis of typical agricultural residues to xylo-oligosaccharide and enzymatic hydrolyzability of cellulose

BACKGROUND

Xylo-oligosaccharide is the spotlight of functional sugar that improves the economic benefits of lignocellulose biorefinery. Acetic acid acidolysis technology provides a promising application for xylo-oligosaccharide commercial production, but it is restricted by the aliphatic (wax-like) compounds, which cover the outer and inner surfaces of plants.

RESULTS

We removed aliphatic compounds by extraction with two organic solvents. The benzene-ethanol extraction increased the yield of acidolyzed xylo-oligosaccharides of corncob, sugarcane bagasse, wheat straw, and poplar sawdust by 14.79, 21.05, 16.68, and 7.26% while ethanol extraction increased it by 11.88, 17.43, 1.26, and 13.64%, respectively.

CONCLUSION

The single ethanol extraction was safer, more environmentally friendly, and more cost-effective than benzene-ethanol solvent. In short, organic solvent extraction provided a promising auxiliary method for the selective acidolysis of herbaceous xylan to xylo-oligosaccharides, while it had minimal impact on woody poplar.

What happens when pesticides are solubilised in binary ionic/zwitterionic-nonionic mixed micelles?

HYPOTHESIS

Surfactants have been widely used as adjuvants in agri-sprays to enhance the solubility of pesticides in foliar spray deposits and their mobility through leaf cuticles. Previously, we have characterised pesticide solubilisation in nonionic surfactant micelles, but what happens when pesticides become solubilised in anionic, cationic and zwitterionic and their mixtures with nonionic surfactants remain poorly characterised.

EXPERIMENTS

To facilitate characterisations by SANS and NMR, we used nonionic surfactant hexaethylene glycol monododecyl ether (C₁₂E₆), anionic sodium dodecylsulphate (SDS), cationic dodecyltrimethylammonium bromide (DTAB) and zwitterionic dodecylphosphocholine (C₁₂PC) as model adjuvant systems to solubilise 3 pesticides, Cyprodinil (CP), Azoxystrobin (AZ) and Difenoconazole (DF), representing different structural features. The investigation focused on the influence of solubilisates in driving changes to the micellar nanostructures in the absence or presence of electrolytes. NMR and NOESY were applied to investigate the solubility and location of each pesticide in the micelles. SANS was used to reveal subtle changes to the micellar structures due to pesticide solubilisation with and without electrolytes.

FINDINGS

Unlike nonionic surfactants, the ionic and zwitterionic surfactant micellar structures remain unchanged upon pesticide solubilisation. Electrolytes slightly elongate the ionic surfactant micelles but have no effect on nonionic and zwitterionic surfactants. Pesticide solubilisation could alter the structures of the binary mixtures of ionic/zwitterionic and ionic/nonionic micelles by causing elongation, shell shrinkage and dehydration, with the exact alteration being determined by the molar ratio in the mixture.

How does substrate hydrophobicity affect the morphological features of reconstituted wax films and their interactions with nonionic surfactant and pesticide?

HYPOTHESIS

Surfactants are widely used in agri-sprays to improve pesticide efficiency, but the mechanism underlying their interactions with the surface wax film on plants remains poorly understood. To facilitate physical characterisations, we have reconstituted wheat cuticular wax films onto an optically flat silicon substrate with and without octadecyltrimethoxysilane modification to control surface hydrophobicity.

EXPERIMENTS

Imaging techniques including scanning electron microscopy (SEM) unravelled morphological features of the reconstituted wax films similar to those on leaves, showing little impact from the different substrates used. Neutron reflection (NR) established that reconstituted wax films were comprised of an underlying wax film decorated with top surface wax protrusions, a common feature irrespective of substrate hydrophobicity and highly consistent with what was observed from natural wax films. NR measurements, with the help of isotopic H/D substitutions to modify the scattering contributions of the wax and solvent, revealed different wax regimes within the wax films, illustrating the impact of surface hydrophilicity on the nanostructures within the wax films.

FINDINGS

It was observed from both spectroscopic ellipsometry and NR measurements that wax films formed on the hydrophobic substrate were more robust and durable against attack by nonionic surfactant C₁₂E₆ solubilised with pesticide Cyprodinil (CP) than films coated on the bare hydrophilic silica. Thus, the former could be a more feasible model for studying the wax-surfactant-pesticide interactions.

Preparation and characterization of epicuticular wax films

Dipping films from epicuticular wax (EW) were prepared as model systems of epicuticular wax films found in plants. In these films, the growth uniformity, surface morphology, and hydrophobicity were examined. It was observed growth uniformity (linear growth) only from the fifth layer onwards because of the influence of substrate. The surface morphology of the films was found to be composed of pores formed by aggregates of EW molecules, both with a fractal form. An increase in the number of film layers resulted in the increase of the number of pores up to a maximum value followed by a decrease. Such increase was assigned to the growth of aggregates whereas the decrease was explained by the increase of pore sizes, because during the growth of the aggregates, the small pores are replaced by the large pores. Hydrophobicity increased with the number of layers, which was associated with the increase of irregularities on the surface caused by the pores and aggregates. In addition, it was observed that the number of pores increased with temperature. This was explained by the increase in the mobility of EW molecules, which led to a larger amount of EW molecules deposited. Based on our results and the advantages offered by dipping films – including the control of thickness and structure – this type of film is feasible as a model for studies of cuticular water transport in plants.

Structural Features of Reconstituted Cuticular Wax Films upon Interaction with Nonionic Surfactant C12E6

The interaction of nonionic surfactant hexaethylene glycol monododecyl ether (C₁₂E₆) with a reconstituted cuticular wheat wax film has been investigated by spectroscopic ellipsometry and neutron reflection (NR) to help understand the role of the leaf wax barrier during pesticide uptake, focusing on the mimicry of the actions adjuvants impose on the physical integrity and transport of the cuticular wax films against surfactant concentration. As the C₁₂E₆ concentration was increased up to the critical micelle concentration (CMC = 0.067 mM), an increasing amount of surfactant mass was deposited onto the wax film. Alongside surface adsorption, C₁₂E₆ was also observed to penetrate the wax film, which is evident from the NR measurements using fully protonated and chain-deuterated surfactants. Furthermore, surfactant action upon the model wax film was found to be physically reversible below the CMC, as water rinsing could readily remove the adsorbed surfactant, leaving the wax film in its original state. Above the CMC, the detergency action of the surfactant became dominant, and a significant proportion of the wax film was removed, causing structural damage. The results thus reveal that both water and C₁₂E₆ could easily penetrate the wax film throughout the concentration range measured, indicating a clear pathway for the transport of active ingredients while the removal of the wax components above the CMC must have enhanced the transport process. As the partial removal of the wax film could also expose the underlying cutaneous substrate to the environment and undermine the plant's health, this study has a broad implication to the roles of surfactants in crop care.

Recent upgrades of the neutron reflectometer D17 at ILL

The vertical sample-plane reflectometer D17 at the Institut Laue–Langevin in Grenoble, France, has undergone several major upgrades since its commissioning, which are summarized in this article. The three major improvements are (i) a new focusing guide, increasing the usable flux on the sample by a factor of 2.5; (ii) a new beam polarizer and new spin flippers, allowing for the use of polarized neutrons in time-of-flight mode; and (iii) a new detector with a particularly uniform response under homogeneous exposure, improved stability and state-of-the-art detector electronics. The combination of these factors has paved the road to new possibilities in fast kinetic measurements, magnetism and off-specular scattering. Examples and scientific references for the new capabilities are presented.

Alleviatory effects of silicon on the foliar micromorphology and anatomy of rice (Oryza sativa L.) seedlings under simulated acid rain

Silicon (Si) is a macroelement in plants. The biological effects and mitigation mechanisms of silicon under environmental stress have become hot topics. The main objectives of this study were to elucidate the roles of Si in alleviating the effects on the phenotype, micromorphology and anatomy of the leaves of rice seedlings under acid rain stress. The results indicated that the combined or single effects of Si and simulated acid rain (SAR) stress on rice roots depended on the concentration of Si and the intensity of the SAR stress. The combined or single effects of the moderate concentration of Si (2.0 mM) and light SAR (pH 4.0) enhanced the growth of the rice leaves and the development of the mesophyll cells, and the combined effects were stronger than those of the single treatments. The high concentration of Si (4.0 mM) and severe SAR (pH 3.0 or 2.0) exerted deleterious effects. The incorporation of Si (2.0 or 4.0 mM) into SAR at pH values of 3.0 or 2.0 promoted rice leaf growth, decreased necrosis spots, maintained the structure and function of the mesophyll cells, increased the epicuticular wax content and wart-like protuberance (WP) density, and improved the stomatal characteristics of the leaves of rice seedlings more than the SAR only treatments. The alleviatory effects observed with a moderate concentration of Si (2.0 mM) were better than the effects obtained with the high concentration of Si (4.0 mM). The alleviatory effects were due to the enhancement of the mechanical barriers in the leaf epidermis.