Surfactant softening of plant leaf cuticle model wax – A Differential Scanning Calorimetry (DSC) and Quartz Crystal Microbalance with Dissipation (QCM-D) study

Light-dimerization telechelic alginate-based amphiphiles reinforced Pickering emulsion for 3D printing

Functional Pickering emulsions that depend on the interparticle interactions hold promise for building template materials. A novel coumarin-grafting alginate-based amphiphilic telechelic macromolecules (ATMs) undergoing photo-dimerization enhanced particle-particle interactions and changed the self-assembly behavior in solutions. The influence of self-organization of polymeric particles on the droplet size, microtopography, interfacial adsorption and viscoelasticity of Pickering emulsions were further determined by multi-scale methodology. Results showed that stronger attractive interparticle interactions of ATMs (post-UV) endowed Pickering emulsion with small droplet size (16.8 μm), low interfacial tension (9.31 mN/m), thick interfacial film, high interfacial viscoelasticity and adsorption mass, and well stability. The high yield stress, outstanding extrudability (n₁ < 1), high structure maintainability, and well shape retention ability, makes them ideal inks for direct 3D printing without any additions. The ATMs provides an increased capacity to produce stable Pickering emulsions with tailoring their interfacial performances and, providing a platform for fabricating and developing alginate-based Pickering emulsion-templated materials.

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.

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.

Storage of orchid pollinia with varying lipid thermal fingerprints

Orchid pollinia have the potential to make a valuable contribution to current techniques of germplasm storage and assisted reproduction, yet information regarding their preservation and their ability to remain viable over time is currently limited. Dactylorhiza fuchsii and Disa uniflora were used as models for investigating potential techniques for storing orchid pollinia. Initially, freshly harvested pollinia of Dact. fuchsii were incubated at 25 °C and 100% RH (relative humidity) for up to 7 days and germinated in vitro. For pollinia from both species, moisture sorption isotherms were constructed and thermal fingerprints generated using differential scanning calorimetry (DSC). Pollinia were stored at three temperatures (5, - 18 and - 196 °C) after equilibration at four different RHs (5, 33, 50 and 75%) and germinated. The isotherms and DSC results varied between species. Compared with D. uniflora, pollinia of Dact. fuchsii consistently equilibrated at higher moisture content (MC) for each RH, had less detectable lipids by DSC and had shorter lifespans, remaining viable after 3-4 months only at - 20 and - 196 °C and at low RH (5 and 33%). Both species' pollinia stored well at - 20 °C and - 196 °C, although there was some evidence of a small loss of viability under cryopreservation. In conclusion, pollen of these two species can be stored successfully for at least 3-4 months, and to maximize the pre-storage quality, it is recommended that fresh pollen is collected from flowers just prior to anthesis.

A revised model of fungicide translaminar activity

Translaminar redistribution is valuable for fungicide activity but difficult to measure and predict. The translaminar activity of 38 fungicides active against cucumber powdery mildew was measured experimentally and used to develop a QSAR (Quantitative structure-activity relationship) model of translaminar movement from calculated parameters. Over 300 physiochemical parameters generated from energy-minimized 3D structures were considered and one-parameter, two-parameter, and five-parameter models were developed. The one-parameter lipophilicity model explained 39% of variability in translaminar activity in the full dataset but none of the variability in the small succinate dehydrogenase inhibitor (SDHI) set. Adding a polar surface area parameter to the lipophilicity parameter improved predictability to 52% and explained over 70% of the variability in the SDHI class. The expanded model with five physiochemical parameters explained more than 80% of the variability in overall translaminar redistribution. The three additional parameters were correlated with molecular size and reactivity. The models were validated with a Leave-One-Out method that showed excellent robustness (r²adj = 0.83, q² = 0.79, p < .0001) for the five-parameter model. Because the models require only calculated parameters from a 3D chemical structure, they could enable the design or selection of compounds likely to be translaminar.

Tristearin as a Model Cuticle for High-Throughput Screening of Agricultural Adjuvant Systems

The widely varied compositions and structures of plant cuticles create problems in the identification of suitable model systems for laboratory testing of adjuvants. We have compared the behavior of an extracted cuticle wax with tristearin, a well characterized crystalline triglyceride, which we propose as a model cuticle for ranking new adjuvant systems for their propensity to disrupt the cuticle barrier. The interaction of adjuvant products and their components with the extracted cuticle wax and tristearin was determined using differential scanning calorimetry and small angle X-ray scattering approaches. The interaction of the additive with tristearin caused a concentration-dependent change in the crystallite level, and correlated between the extracted wax and tristearin. Tristearin was subsequently used to compare the effectiveness of a range of adjuvant products and their major components. This approach has utility to quantify the effects of adjuvant components and enable more judicious selection of adjuvant candidates to progress to plant trials.

Understanding the kinetic mixing between liquid crystalline nanoparticles and agrochemical actives

The use of liquid crystalline nanoparticles as potential agrochemical delivery agents or adjuvant systems is gaining traction due to the possibility that the systems can enhance penetration of the active and increase adhesion of the formulation to the leaf, increasing overall efficacy and decreasing the harmful environmental impact. However the interaction between liquid crystalline nanoparticles and active products is not well understood. Using small angle X-ray scattering we investigated the structural changes that occur to liquid crystalline nanoparticles upon addition of three common herbicides, 2,4-D 2-ethylhexyl ester, bromoxynil octanoate and haloxyfop-p-methyl ester active agrochemicals in the form of emulsions. It was found that the hydrophobic herbicides induced structural changes to varying degrees when pre-mixed with liquid crystalline forming lipids (phytantriol and glycerol monooleate) and also during dynamic mixing as emulsions.

Agricultural adjuvants may impair leaf transpiration and photosynthetic activity

Adjuvants such as surfactants are commonly incorporated into agrochemical formulations to enhance the biological efficiency of foliar sprays by improving the wetting behavior of the spray and/or the penetration of the active ingredients into the leaf tissues. Penetration accelerating adjuvants are known to increase the cuticular permeability and may alter the cuticular barrier to water loss. However, none or very little emphasis has been given to the impacts of adjuvants on crop water balance or drought tolerance, a very important factor affecting crop performance under water scarcity. Two model crops with strongly varying leaf traits, kohlrabi (Brassica oleracea) and apple (Malus domestica) seedlings were grown in controlled environments. Three adjuvants with varying solubility in the cuticle, i.e. octanol-water partition coefficients (logKow) were selected: rapeseed methyl ester (RME) and the surfactants alkyl polyglycoside (APG) and polyoxyethylated tallow amine (POEA). The higher the logKow of the adjuvant, the stronger was the increase of minimum epidermal conductance (g_min, an essential parameter describing plant drought tolerance). However, such effects depended on the physio-chemical properties of the leaf surface. In comparison to kohlrabi, the adjuvant effects on g_min of apple leaves were relatively weak. The increase of g_min was associated with a decrease in contact angle and with an alteration of the wax microstructure. Furthermore, POEA affected photochemical efficiency of kohlrabi leaves. Some adjuvants could have a temporal influence on transpirational water loss and g_min. At repeated applications, they might alter the effective water use and possibly reduce drought tolerance of some horticultural crops.