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Pivotal barrier properties of the hydrophobic plant cuticle covering aerial plant surfaces depend on its physicochemical composition. Among plant species and organs, compounds of this boundary layer between the plant interior and the environment vary considerably but cuticle-related studies comparing different organs from the same plant species are still scarce. Thus, this study focused on the cuticle profiles of Physalis peruviana, Physalis ixocarpa, Alkekengi officinarum, and Nicandra physalodes species. Inflated fruiting calyces enveloping fruitsmake Physalis, Alkekengi, and Nicandra highly recognizable genera among the Solanoideae subfamily. Although the inflation of fruiting calyces is well discussed in the literature still little is known about their post- floral functionalities. Cuticular composition, surface structure, and barrier function were examined and compared in fully expanded amphistomatous leaves, ripe astomatous fruits, and fully inflated hypostomatous fruiting calyces. Species- and organ-specific abundances of non-glandular and glandular trichomes revealed high structural diversity, covering not only abaxial and adaxial leaf surfaces but also fruiting calyx surfaces, whereas fruits were glabrous. Cuticular waxes, which limit non-stomatal transpiration, ranged from <1 μg cm−2 on P. peruviana fruiting calyces and N. physalodes fruits to 22 μg cm−2 on P. peruviana fruits. Very-long-chain aliphatic compounds, notably n- alkanes, iso-, and anteiso-branched alkanes, alkanols, alkanoic acids, and alkyl esters, dominated the cuticular wax coverages (≥86%). Diversity of cuticular wax patterns rose from leaves to fruiting calyces and peaked in fruits. The polymeric cutin matrix providing the structural framework for cuticular waxes was determined to range from 81 μg cm−2 for N. physalodes to 571 μg cm−2 for A. officinarum fruits. Cuticular transpiration barriers were highly efficient, with water permeabilities being ≤5 × 10−5 m s−1. Only the cuticular water permeability of N. physalodes fruits was 10 × 10−5 m s−1 leading to their early desiccation and fruits that easily split, whereas P. peruviana, P. ixocarpa, and A. officinarum bore fleshy fruits for extended periods after maturation. Regarding the functional significance, fruiting calyces establish a physicochemical shield that reduces water loss and enables fruit maturation within a protective microclimate, and promotes different seed dispersal strategies among plant species investigated. [ABSTRACT FROM AUTHOR]

Plants prevent uncontrolled water loss by synthesizing, depositing and maintaining a hydrophobic layer over their primary aerial organs—the plant cuticle. Quercus coccifera L. can plastically respond to environmental conditions at the cuticular level. When exposed to hot summer conditions with high vapour-pressure deficit (VPD) and intense solar radiation (Mediterranean atmospheric conditions; MED), this plant species accumulates leaf cuticular waxes even over the stomata, thereby decreasing transpirational water loss. However, under mild summer conditions with moderate VPD and regular solar radiation (temperate atmospheric conditions; TEM), this effect is sharply reduced. Despite the ecophysiological importance of the cuticular waxes of Q. coccifera , the wax composition and its contribution to avoiding uncontrolled dehydration remain unknown. Thus, we determined several leaf traits for plants exposed to both MED and TEM conditions. Further, we qualitatively and quantitatively investigated the cuticular lipid composition by gas chromatography. Finally, we measured the minimum leaf conductance (gmin) as an indicator of the efficacy of the cuticular transpiration barrier. The MED leaves were smaller, stiffer and contained a higher load of cuticular lipids than TEM leaves. The amounts of leaf cutin and cuticular waxes of MED plants were 1.4 times and 2.6 times higher than that found for TEM plants, respectively. In detail, MED plants produced higher amounts of all compound classes of cuticular waxes, except for the equivalence of alkanoic acids. Although MED leaves contained higher cutin and cuticular wax loads, the gmin was not different between the two habitats. Our findings suggest that the qualitative accumulation of equivalent cuticular waxes might compensate for the higher wax amount of MED plants, thereby contributing equally to the efficacy of the cuticular transpirational barrier of Q. coccifera. In conclusion, we showed that atmospheric conditions profoundly affect the cuticular lipid composition of Q. coccifera leaves, but do not alter its transpiration barrier properties. [ABSTRACT FROM AUTHOR]

BACKGROUND: The barrier to diffusion of organic solutes across the plant cuticle is composed of waxes consisting of very long‐chain aliphatic (VLCA) and, to varying degrees, cyclic compounds like pentacyclic triterpenoids. The roles of both fractions in controlling cuticular penetration by organic solutes, e.g. the active ingredients (AI) of pesticides, are unknown to date. We studied the permeability of isolated leaf cuticular membranes from Garcinia xanthochymus and Prunus laurocerasus for lipophilic azoxystrobin and theobromine as model compounds for hydrophilic AIs. RESULTS: The wax of P. laurocerasus consists of VLCA (12%) and cyclic compounds (88%), whereas VLCAs make up 97% of the wax of G. xanthochymus. We show that treating isolated cuticles with methanol almost quantitatively releases the cyclic fraction while leaving the VLCA fraction essentially intact. All VLCAs were subsequently removed using chloroform. In both species, the permeance of the two model compounds did not change significantly after methanol treatment, whereas chloroform extraction had a large effect on organic solute permeability. CONCLUSION: The VLCA wax fraction makes up the permeability barrier for organic solutes, whereas cyclic compounds even in high amounts have a negligible role. This is of significance when optimizing the foliar uptake of pesticides. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

When the stomata are closed under drought, the only route for water loss from the leaf interior to the atmosphere is across the cuticle. Thus, the extent of cuticular transpiration in relation to the reservoirs of water in the plant and the water acquisition from the soil determines the fitness and survival of the plant. It is, therefore, widely assumed that the cuticular water permeability of plants regularly experiencing drought is comparatively low and, thus, adapted to the environment. To test this hypothesis, 382 measurements of cuticular permeability from 160 species were extracted from the literature published between 1996 and 2017. The data had been produced either by using isolated cuticles and astomatous leaf sides or by measuring the minimum leaf conductance under conditions assumed to induce maximum stomatal closure. The species were assigned to 11 life form groups. Except for two particular cases (epiphytes, and climbers and lianas), the cuticular permeabilities of all groups either did not differ significantly or the available data did not allow a statistical test. In conclusion, present knowledge either does not support the hypothesis that ecological adaptions of cuticular water permeability exist or the available data are insufficient to test it. [ABSTRACT FROM AUTHOR]

The water permeability of the leaves of three deciduous plants (Acer campestre, Fagus sylvatica, Quercus petraea) and two evergreen plants (Hedera helix, Ilex aquifolium) was analysed in order to assess its role as a mechanism of drought resistance. Cuticular permeances were determined by measurement of the water loss through adaxial, astomatous leaf surfaces. Minimum conductances after complete stomatal closure were obtained by leaf drying curves. The comparison of the water permeabilities determined with these two experimental systems revealed good agreement in the case of Acer, Fagus, Quercus, and Ilex. For Hedera the minimum conductance was 3‐fold higher than the cuticular permeance indicating a significant contribution of residual stomatal transpiration. The leaf water potential was measured as a function of water content and analysed by pressure–volume curves. The influence of water potential as a component of the driving force for transpirational water loss was assessed in order to identify modifications of the cuticular barrier by the leaf water content. The ecophysiological meaning of the water relations parameters describing transpiration under drought conditions (cuticular transpiration, minimum transpiration, residual stomatal transpiration, effect of leaf water content on transpiration) and the water relations parameters derived from pressure–volume curves (osmotic potential at full saturation, turgor loss point, bulk modulus of elasticity) are discussed with regard to adaptations for drought resistance. [ABSTRACT FROM PUBLISHER]

The behaviour of (semi‐)volatile organic compounds at the interface between the leaf surface and the atmosphere was investigated by finite‐element numerical simulation. Three model systems with increasing complexity and closeness to the real situation were studied. The three‐dimensional model systems were translated into appropriate grid structures and diffusive and convective transport in the leaf/atmosphere interface was simulated. Fenpropimorph (cis‐4‐[3‐(4‐tert‐butylphenyl)‐2‐methylpropyl]‐2,6‐dimethylmorpholine) and Kresoxim‐methyl ((E)‐methyl‐2‐methoxyimino‐2‐[2‐(o‐tolyloxy‐methyl)phenyl] acetate) were used as model compounds. The simulation showed that under still and convective conditions the vapours emitted by a point source rapidly form stationary envelopes around the leaves. Vapour concentrations within these unstirred layers depend on the vapour pressure of the compound in question and on its affinity to the lipoid surface layers of the leaf (cuticular waxes, cutin). The rules deduced from the numerical simulation of organic vapour behaviour in the leaf/atmosphere interface are expected to help in assessing how (semi‐)volatile plant products (e.g. hormones, pheromones, secondary metabolites) and xenobiotics (e.g. pesticides, pollutants) perform on plant surfaces. [ABSTRACT FROM PUBLISHER]

The cuticle is the major barrier against uncontrolled water loss from leaves, fruits and other primary parts of higher plants. More than 100 mean values for water permeabilities determined with isolated leaf and fruit cuticles from 61 plant species are compiled and discussed in relation to plant organ, natural habitat and morphology. The maximum barrier properties of plant cuticles exceed that of synthetic polymeric films of equal thickness. Cuticular water permeability is not correlated to the thickness of the cuticle or to wax coverage. Relationships between cuticular permeability, wax composition and physical properties of the cuticle are evaluated. Cuticular permeability to water increases on the average by a factor of 2 when leaf surface temperature is raised from 15 °C to 35 °C. Organic compounds of anthropogenic and biogenic origin may enhance cuticular permeability. The pathway taken by water across the cuticular transport barrier is reviewed. The conclusion from this discussion is that the bulk of water diffuses as single molecules across a lipophilic barrier while a minor fraction travels along polar pores. Open questions concerning the mechanistic understanding of the plant cuticular transport barrier and the role the plant cuticle plays in ensuring the survival and reproductive success of an individual plant are indicated. [ABSTRACT FROM AUTHOR]

A method for measurement of non‐electrolyte transport through enzymatically isolated cuticles of Ficus elastica Roxb. var. decora is presented. Permeance coefficients and hold‐up times are determined under steady‐state conditions. The transport system consists of two small reservoirs separated by the cuticle. The compounds tested (4‐nitrophenol and pentachlorophenol) differ widely in lipid solubility and enable a critical evaluation of the apparatus used. The sorption capacity of the cuticle for lipophilic compounds is related to their cuticle/water partition coefficients. The problems of unstirred layers and of membrane integrity are discussed. The permeances measured ranged from 10−11 to 10−5 m s−1, the hold‐up times from 50 s to 22 h. [ABSTRACT FROM AUTHOR]

Treating the outer surfaces of isolated cuticles of Seville orange (Citrus aurantium L.) and pear (Pyrus communis L. cv. Bartlett) leaves with a number of nonionic (polyoxyethylene) surfactants increased their permeability to water by factors ranging from 4.1 to 14.7 and from 7.2 to 152.4, respectively. However, sodium dodecylsulphate, an anionic surfactant, had little effect on water permeability. In both species the major aliphatic constituents were n-alkanes, 1-alkanols and n-alkyl esters. None of the surfactant treatments altered the amounts or composition of waxes in the cuticles used for transport measurements. The reasons for the apparent absence of solubilization or dissolution of cuticular waxes by nonionic surfactants are discussed and a hypothesis is presented for the mechanism by which activator adjuvants may increase the permeability of plant cuticles. [ABSTRACT FROM AUTHOR]

Barrier properties of the hydrophobic plant cuticle depend on its physicochemical composition. The cuticular compounds vary considerably among plant species but also among organs and tissues of the same plant and throughout developmental stages. As yet, these intraspecific modifications at the cuticular wax and cutin level are only rarely examined. Attempting to further elucidate cuticle profiles, we analysed the adaxial and abaxial surfaces of the sclerophyllous leaf and three developmental stages of the drupe fruit of Prunus laurocerasus , an evergreen model plant native to temperate regions. According to gas chromatographic analyses, the cuticular waxes contained primarily pentacyclic triterpenoids dominated by ursolic acid, whereas the cutin biopolyester mainly consisted of 9/10,ω-dihydroxy hexadecanoic acid. Distinct organ- and side-specific patterns were found for cuticular lipid loads, compositions and carbon chain length distributions. Compositional variations led to different structural and functional barrier properties of the plant cuticle, which were investigated further microscopically, infrared spectroscopically and gravimetrically. The minimum water conductance was highlighted at 1 × 10−5 m s−1 for the perennial, hypostomatous P. laurocerasus leaf and at 8 × 10−5 m s−1 for the few-month-living, stomatous fruit suggesting organ-specific cuticular barrier demands. • The cuticle of the evergreen shrub P. laurocerasus displays a high phenotypic plasticity. • Organ-specific patterns of cuticular wax compound classes were detected. • Side-specific shifts were found for carbon chain lengths in leaf cuticular waxes. • Minimum water conductance differed considerably between organs of the same plant. • Temperature-dependent minimum conductance and cuticular permeability were compared. [ABSTRACT FROM AUTHOR]

The cuticle is a heterogeneous extracellular layer, whose composition varies between plant species, cultivars and organs. Specific structural and compositional characteristics indicate the domesticated apple ( Malus domestica Borkh.) as a suitable non-model plant system for comprehensive analyses of the cuticularization of epidermal cell walls. Our findings focused on the cuticular deposition of apple fruits, offering a continuous, thick and robust but also lenticel-containing experimental system for functional studies. In detail, the cuticular wax and cutin composition and the water permeance of apple fruits were comparatively analyzed in two cultivars, which also demonstrates the cultivar-specific plasticity of cuticle formation. Despite significant differences in cuticle thickness and weight, fruits of the early and late season apple cultivars ‘Prima’ and ‘Florina’ accumulated on average 95 μg cm −2 cuticular waxes mainly consisting of pentacyclic triterpenoids like ursolic acid (≥70%). The average chain length of the aliphatic wax fraction of ‘Florina’ and ‘Prima’ was about 29.1. The cutin matrix averaged 995 μg cm −2 dominated by hydroxylated hexadecanoic and octadecanoic acid monomers (mixed C 16 /C 18 type). Although the hydrophobic cuticle is the main barrier in limiting transpirational water loss across the outermost plant surface, chemical differences between both cultivars were not related to the water permeance. ‘Prima’ and ‘Florina’ fruit surfaces had an average permeance for water of 5 × 10 −5 m s −1 . It is hypothesized that compositional differences such as a higher amount of alkanoic acids, primary alkanols and alkanals in the cuticular wax mixture and modifications in the cutin matrix in the late season cultivar ‘Florina’ compared to early season cultivar ‘Prima’ represent cultivar-specific patterns in cuticle formation of apple fruits. [ABSTRACT FROM AUTHOR]

Abstract: Cuticular waxes are known to play a pivotal role in limiting transpirational water loss across primary plant surfaces. The astomatous tomato fruit is an ideal model system that permits the functional characterization of intact cuticular membranes and therefore allows direct correlation of their permeance for water with their qualitative and quantitative composition. The recessive positional sterile (ps) mutation, which occurred spontaneously in tomato (Solanum lycopersicum L.), is characterized by floral organ fusion and positional sterility. Because of a striking phenotypical similarity with the lecer6 wax mutant of tomato, which is defective in very-long-chain fatty acid elongation, ps mutant fruits were analyzed for their cuticular wax and cutin composition. We also examined their cuticular permeance for water following the developmental course of fruit ripening. Wild type and ps mutant fruits showed considerable differences in their cuticular permeance for water, while exhibiting similar quantitative wax accumulation. The ps mutant fruits showed a five- to eightfold increase in water loss per unit time and surface area when compared to the corresponding wild type fruits. The cuticular waxes of ps mutant fruits were characterized by an almost complete absence of n-alkanes and aldehydes, with a concomitant increase in triterpenoids and sterol derivatives. We also noted the occurrence of alkyl esters not present in the wild type. Quantitative and qualitative cutin monomer composition remained largely unaffected. The significant differences in the cuticular wax composition of ps mutant fruits induced a distinct increase of cuticular water permeance. The fruit wax compositional phenotype indicates the ps mutation is responsible for effectively blocking the decarbonylation pathway of wax biosynthesis in epidermal cells of tomato fruits. [Copyright &y& Elsevier]