Structural changes in needle epicuticular waxes of Balkan Abies species in relation to natural weathering

The production of superhydrophobic coatings inspired by the surface of plant leaves is a challenging goal. Such coatings hold a bright technological future in niche markets of the aeronautical, space, naval, building, automobile, and biomedical sectors. This work is focused on the adaxial (top) and abaxial (bottom) surfaces of the leaflet of the Ceratonia silique L. (carob), a high-commercial-value Mediterranean tree cultivated in many regions of the world. The adaxial and abaxial surfaces feature hydrophobic and superhydrophobic behaviors, respectively. Their chemical composition is very simple: monopalmitin ester and palmitic acid are protuberant in the epicuticular and intracuticular wax layers of the adaxial surface, respectively, whereas 1-octacosanol dominates in the abaxial wax layers. In both surfaces, epicuticular wax is organized along a randomly oriented and intricate network of nanometer-thick and micrometer-long plates, whose density and degree of interconnection are significantly higher in the abaxial surface. The measured tilting angles for the abaxial surface (12-70°) reveal unusual variable density and water adhesion of the nanostructured plate-based texture. Optical measurements demonstrate that light reflectance/absorbance of the glaucous abaxial surface is significantly higher/lower than that of the nonglaucous adaxial surface. In both surfaces, diffuse reflectance is dominant, and the absorbance is weakly dependent on the light incidence angle. We show that the highly dense nanostructured platelike texture of the epicuticular abaxial layer of the C. siliqua leaflet works as a sophisticated light and water management system: it reflects solar radiation diffusely to lower the surface temperature, and it has superhydrophobic character to keep the surface dry. Such attributes enable efficient gas exchange (photosynthesis and respiration), transpiration, and evaporation. To mimic for the first time the abaxial surface, a templation approach was adopted using poly(dimethylsiloxane) (PDMS)/poly(methylphenylsiloxane) (PMPS) positive/negative replicas and a soft polymer/siloxane negative replica produced by the sol-gel process. Because high topographical variations of the biotemplate and wax adhesion to the biohybrid film affected the replication quality, the reproduction of the wax texture via the synthesis of 1-octacosanol-grafted siloxane-based hybrid materials is proposed as a suitable route to duplicate the abaxial surface with high fidelity. The natural chemical/physical strategy adopted by the C. siliqua leaflet to face the harsh Mediterranean climate is a powerful source of bioinspiration for the development of diffuse reflecting and superhydrophobic material systems with foreseen applications as dual-functional antiglare and water-repelling coatings.

Plant surface characteristics were repeatedly shown to play a pivotal role in plant-pathogen interactions. The abaxial leaf surface of perennial ryegrass (Lolium perenne) is extremely glossy and wettable compared to the glaucous and more hydrophobic adaxial surface. Earlier investigations have demonstrated that the abaxial leaf surface was rarely infected by powdery mildew (Blumeria graminis), even when the adaxial surface was densely colonized. This led to the assumption that components of the abaxial epicuticular leaf wax might contribute to the observed impairment of growth and development of B. graminis conidia on abaxial surfaces of L. perenne. To re-assess this hypothesis, we analyzed abundance and chemical composition of L. perenne ab- and adaxial epicuticular wax fractions. While the adaxial epicuticular waxes were dominated by primary alcohols and esters, the abaxial fraction was mainly composed of n-alkanes and aldehydes. However, the major germination and differentiation inducing compound, the C26-aldehyde n-hexacosanal, was not present in the abaxial epicuticular waxes. Spiking of isolated abaxial epicuticular Lolium waxes with synthetically produced n-hexacosanal allowed reconstituting germination and differentiation rates of B. graminis in an in vitro germination assay using wax-coated glass slides. Hence, the absence of the C26-aldehyde from the abaxial surface in combination with a distinctly reduced surface hydrophobicity appears to be primarily responsible for the failure of normal germling development of B. graminis on the abaxial leaf surfaces of L. perenne.

The evergreen conifer Cedrus libani A.Rich. İs frost- and drought-tolerant and of economic and ecological importance. It has valuable timber and thus has promising potential for cultivation within and outside its natural distribution. Our aim was to determine the morphological and physiological characteristics of C. Libani needle leaves with respect to epicuticular waxes, photosynthetic assimilation rates, and needle age. The study was conducted in the Cedar Research Forest near Elmalı, Antalya (SW Turkey) at 1650 m a.s.l. An equation to calculate needle surface area from needle length was created (R2 = 0.96) for adult cedar needles. The form factor for total needle surface area to projected needle surface area was 3.248. The epicuticular wax morphology using scanning electron microscopy showed that the rhomboidal needles of C. Libani possess a dense and intact network of tubular wax crystals, which is common in the family Pinaceae. Wax crystals were found on all sites of the needles and were especially dominant on epistomatal cavities. Wax degradation started in 1-year-old needles and increased with advancing age. The degree of wax degradation gave no indication of significant stress or damage at the study site (e.g., air pollution, extreme drought events). Gas exchange properties were derived from light response and A/ci curves measured in situ in 1-year-old and 2-year-old needles of mature C. Libani trees. Compared to 1-year-old needles, net carbon assimilation rates decreased by about 25% in 2-year-old needles. Assimilation rates and respiration rates were comparable with other conifers, showing no signs of significant stress with needle age. The aging of needles affected both the epicuticular wax structures and the photosynthetic performance. It remains to be clarified to what degree wax degradation influences the decrease of photosynthesis in cedar needles.

Composition of the epicuticular and intracuticular wax layers on Kalanchoe daigremontiana (Hamet et Perr. de la Bathie) leaves

Epicuticular and intracuticular waxes from both adaxial and abaxial surfaces of the leaves of Kalanchoe daigremontiana were analyzed. All wax mixtures were found to contain approximately equal amounts of triterpenoids and very long chain fatty acid (VLCFA) derivatives. The triterpenoid fraction consisted of glutinol (8–19% of the total wax) and friedelin (4–9%), together with smaller amounts of glutanol, glutinol acetate, epifriedelanol, germanicol and β-amyrin. The VLCFA derivatives comprised C27–C35 alkanes (19–37% of the total wax), C32–C34 aldehydes (3–7%), C32 and C34 fatty acids (0.2–3%), C26–C36 primary alcohols (4–8%), and C42–C52 alkyl esters (2–9%). The wax layers were found to differ in triterpenoid amounts, with the intracuticular wax containing higher percentages of most triterpenoids than the epicuticular wax. Friedelin, the only triterpenoid ketone present, showed the opposite distribution with higher proportions in the epicuticular wax. VLCFA derivatives also accumulated to higher percentages in the epicuticular than in the intracuticular wax layer. Epicuticular wax crystals were observed on both the adaxial and abaxial leaf surfaces.

Discrimination between epicuticular and intracuticular wax in blackberry leaves: Ultrastructural and chemical evidence

Chemical Composition of the Epicuticular and Intracuticular Wax Layers on Adaxial Sides of Rosa canina Leaves

Epicuticular waxes of Salix species in relation to their overwintering survival and biomass productivity

Comparative Epidermal Ultrastructure of Cotton (Gossypium hirsutum L.) Leaf, Bract and Capsule Wall

Analysis of Epicuticular Phenolics of Prunus persica and Olea europaea Leaves: Evidence for the Chemical Origin of the UV-induced Blue Fluorescence of Stomata

Epicuticular waxes on the surface of plant leaves are important for the tolerance to abiotic stresses and plant–parasite interactions. In the onion (Allium cepa L.), the variation for the amounts and types of epicuticular waxes is significantly associated with less feeding damage by the insect Thrips tabaci (thrips). Epicuticular wax profiles are measured using used gas chromatography mass spectrometry (GCMS), which is a labor intensive and relatively expensive approach. Biochemical spectroscopy is a non-destructive tool for measurement and analysis of physiological and chemical features of plants. This study used GCMS and full-range biochemical spectroscopy to characterize epicuticular waxes on seven onion accessions with visually glossy (low wax), semi-glossy (intermediate wax), or waxy (copious wax) foliage, as well as a segregating family from the cross of glossy and waxy onions. In agreement with previous studies, GCMS revealed that the three main waxes on the leaves of a wild type waxy onion were the ketone hentriacontanone-16 (H16) and fatty alcohols octacosanol-1 (Oct) and triacontanol-1 (Tri). The glossy cultivar “Odourless Greenleaf” had a unique phenotype with essentially no H16 and Tri and higher amounts of Oct and the fatty alcohol hexacosanol-1 (Hex). Hyperspectral reflectance profiles were measured on leaves of the onion accessions and segregating family, and partial least-squares regression (PLSR) was utilized to generate a spectral coefficient for every wavelength and prediction models for the amounts of the three major wax components. PLSR predictions were robust with independent validation coefficients of determination at 0.72, 0.70, and 0.42 for H16, Oct, and Tri, respectively. The predicted amounts of H16, Oct, and Tri are the result of an additive effect of multiple spectral features of different intensities. The variation of reflectance for H16, Oct, and Tri revealed unique spectral features at 2259 nm, 645 nm, and 730 nm, respectively. Reflectance spectroscopy successfully revealed a major quantitative trait locus (QTL) for amounts of H16, Oct, and Tri in the segregating family, agreeing with previous genetic studies. This study demonstrates that hyperspectral signatures can be used for non-destructive measurement of major waxes on onion leaves as a basis for rapid plant assessment in support of developing thrips-resistant onions.

The amounts and types of epicuticular waxes on onion ( Allium cepa ) leaves affect the severity of feeding damage by onion thrips ( Thrips tabaci ), a serious insect pest of onion. Onion plants with light green leaves are referred to as “glossy” and accumulate less epicuticular wax relative to the blue–green (“waxy”) foliage of wild-type onion. The onion cultivar Odourless Greenleaf (OGL) has visually glossy foliage, shows resistance to thrips feeding damage, and has the unique profile of accumulating waxes with 28 or fewer carbons. Plants of glossy OGL were crossed with the glossy inbred B9885 and waxy inbred lines DH2107, DH066619, and B8667. Hybrid progenies from glossy OGL by waxy plants had waxy foliage, indicating recessiveness of the glossy OGL phenotype relative to the waxy phenotype. Hybrids from the cross of glossy OGL with glossy B9885 were also waxy, revealing different genetic bases for the glossy phenotype in these two onions. Hybrid plants were self-pollinated and segregations in F 2 families from OGL × waxy crosses fit the expected 3:1 ratio for the single locus at which the homozygous recessive genotype conditions glossy foliage. Segregations in F 2 families from crosses of glossy 9885 × glossy OGL fit the 9:7 ratio, supporting two independently segregating loci, where the recessive genotype at either locus conditions the glossy phenotype. Amounts and types of epicuticular waxes on leaves of F 2 progenies from crosses of OGL × waxy B8667 and glossy B9885 × OGL were determined using gas chromatography-mass spectrometry. Single-nucleotide polymorphisms were genotyped and genetic maps were constructed. The visually glossy phenotype from OGL and its unique profile of epicuticular waxes were conditioned by one locus on chromosome 6, for which we propose the name gl ogl . Onion populations such as OGL with unique epicuticular wax profiles will be important germplasms for the development of onion cultivars that suffer less feeding damage from onion thrips compared with waxy onion.

Three-dimensional surface topography of the needle stomatal complexes of Pinus rigida and its hybrid species by complementary microscopy

To examine the leaf epidermal microstructure of three genera (Scopolia s.s., Anisodus, AtroPanthe, including Przewalskia as an outgroup) in the genera Scopolia Jacq. s.l., leaves of 10 species (37 specimens) were investigated by the light microscopy (LM) and scanning electron microscopy (SEM). The stomata of studied taxa were 'amphistomatic type' and the size (guard cell) range was . The size of stomata is slightly differed from between the taxa; the smallest size of stomata were found in the monotypic genus, Przewalskia (), on the other hand the largest one was found in Anisodus carniolicoides (). The stomatal complex was mostly anomocytic (in Scopolia s.s., Anisodus taxa : A. luridus, A. carniolicoides, A. acutangulus) and sometimes anisocytic (in Anisodus tanguticus, Przewalskia, Atropanthe). The stomata is mostly crescent in shape, but rarely circular, especially in Przewalskia tangutica. The shapes of epidermal cells are similar in both adaxial and abaxial sides, and mostly undulate/sinuate polygonal anticlinal wall, but rarely arched in Przewalskia tangutica. The epicuticular wax was not well developed in most studied taxa, except Anisodus tanguticus which is well developed cuticular striae around the stomatal complex. The elongate-headed glandular trichomes were found in Scopolia s.s. and Przewalskia. While the taxa of Anisodus and Atropanthe have not any trichomes (i. e., glabrous), except Anisodus luridus, which has simple or sometimes branched (dendritic- type) non-glandular trichome. Finally, the systematic and ecological significance of the leaf micromorphological features (stomata complex, trichome, etc.) in identification and elucidation of Scopolia s.l. including Przewalskia, especially between or within the genera including among the species is also discussed.

Epicuticular wax forms an outer coating on the aerial surfaces of many crop plants and is implicated in tolerance to several environmental stresses including drought. Advances in knowledge of biosynthesis and secretion of these leaf surface waxes could lead to improvements in crop‐stress tolerance. To study the genetics of epicuticular wax deposition, we screened for bloomless (bm) and sparse‐bloom (h) mutants with reduced glaucousness of abaxial sheath surfaces within chemically mutagenized populations of Sorghum bicolor (L.) Moench. We screened over 3974 segregating M2 head rows with over 160,000 plants and identified 38 putative recessive epicuticular wax mutant alleles. We grouped 31 of these into allelic groups associated with one existing and 18 new epicuticular wax loci. The overall epicuticular wax mutation frequency was 0.88%. In addition, analysis of the mutant segregation frequencies within the M2 rows allowed us to calculate the existence of five target meristem cells in a dormant (M0) seed embryo. The high epicuticular wax mutation rate and identification of 19 epicuticular wax loci indicate the presence of a complex genetic system of epicuticular wax production in sorghum as has been shown in other species. The new bloomless and sparse‐bloom mutants identified here have a wide range of phenotypes and constitute a valuable resource for studies of the genetics and biosynthesis of epicuticular waxes and their effects on tolerance to environmental stresses such as drought.