cuticular wax
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Cuticular wax covering the surface of fleshy fruit is closely related to fruit glossiness, development, and post-harvest storage quality. However, the information about formation characteristics and molecular mechanisms of cuticular wax in grape berry is limited. In this study, crystal morphology, chemical composition, and gene expression of cuticular wax in grape berry were comprehensively investigated. Morphological analysis revealed high density of irregular lamellar crystal structures, which were correlated with the glaucous appearances of grape berry. Compositional analysis showed that the dominant wax compounds were triterpenoids, while the most diverse were alkanes. The amounts of triterpenoids declined sharply after véraison, while those of other compounds maintained nearly constant throughout the berry development. The amounts of each wax compounds varied among different cultivars and showed no correlation with berry skin colors. Moreover, the expression profiles of related genes were in accordance with the accumulation of wax compounds. Further investigation revealed the contribution of cuticular wax to the water preservation capacity during storage. These findings not only facilitate a better understanding of the characteristics of cuticular wax, but also shed light on the molecular basis of wax biosynthesis in grape.

Cuticle composition is an important economic trait in agriculture, as it is the first protective barrier of the plant against environmental conditions. The main goal of this work was to study the role of the cuticular wax in maintaining the postharvest quality of zucchini fruit, by comparing two commercial varieties with contrasting behavior against low temperatures; the cold-tolerant variety ‘Natura’, and the cold-sensitive ‘Sinatra’, as well as ‘Sinatra’ fruit with induced-chilling tolerance through a preconditioning treatment (15°C for 48 h). The freshly-harvested ‘Natura’ fruit had a well-detectable cuticle with a significant lower permeability and a subset of 15 up-regulated cuticle-related genes. SEM showed that zucchini epicuticular waxes mainly consisted of round-shaped crystals and clusters of them, and areas with more dense crystal deposition were found in fruit of ‘Natura’ and of preconditioned ‘Sinatra’. The cuticular wax load per surface was higher in ‘Natura’ than in ‘Sinatra’ fruit at harvest and after 14 days at 4°C. In addition, total cuticular wax load only increased in ‘Natura’ and preconditioned ‘Sinatra’ fruit with cold storage. With respect to the chemical composition of the waxes, the most abundant components were alkanes, in both ‘Natura’ and ‘Sinatra’, with similar values at harvest. The total alkane content only increased in ‘Natura’ fruit and in the preconditioned ‘Sinatra’ fruit after cold storage, whereas the amount of total acids decreased, with the lowest values observed in the fruit that showed less chilling injury (CI) and weight loss. Two esters were detected, and their content also decreased with the storage in both varieties, with a greater reduction observed in the cold-tolerant variety in response to low temperature. Gene expression analysis showed significant differences between varieties, especially in CpCER1-like and CpCER3-like genes, involved in alkane production, as well as in the transcription factors CpWIN1-like and CpFUL1-like, associated with cuticle development and epidermal wax accumulation in other species. These results suggest an important role of the alkane biosynthetic pathway and cuticle morphology in maintaining the postharvest quality of zucchini fruit during the storage at low temperatures.

Abstract Alcohol- and alkane-forming pathways in cuticular wax biosynthesis are well characterized in Arabidopsis. However, potential interactions between the two pathways remain unclear. Our study revealed that mutation of CER4, the key gene in the alcohol-forming pathway, also led to a deficiency in alkane-forming pathway in distal stems. To trace the connection between these two pathways, we characterized two homologs of fatty alcohol oxidase (FAO), FAO3 and FAO4b, which were highly expressed in distal stems and localized to the endoplasmic reticulum. The amounts of waxes from the alkane-forming pathway were significantly decreased in stems of fao4b, and much lower in fao3 fao4b, indicative of an overlapping function for both proteins in wax synthesis. Additionally, overexpression of FAO3 and FAO4b in Arabidopsis resulted in a dramatic reduction of primary alcohols and significant increase of aldehydes and related waxes. Moreover, expressing FAO3 or FAO4b led to significantly decreased amounts of C18 - C26 alcohols in yeast co-expressing CER4 and FAR1. Collectively, these findings demonstrate that FAO3 and FAO4b are functionally redundant in suppression of primary alcohols accumulation and contribution to aldehyde production, which provides a missing and long sought-after link between the two pathways in wax biosynthesis.

Abstract Localization of cuticular wax (CW) on the leaf epidermis and its interaction with physiological mechanisms of three edible aroids, Alocasia, Colocasia, and Xanthosoma, were assessed. Scanning electron microscopy depicted the occurrence of CW in the leaf tissues, which was higher in Colocasia (10.61 mg dm-2) and Xanthosoma (11.36 mg dm-2) than in Alocasia (1.36 mg dm-2). Higher CW in Colocasia and Xanthosoma strengthened leaf epidermis and improved the physiological processes compared to Alocasia. CW acted as a protecting barrier against deleterious solar radiation in terms of sun protection factor (SPF). The glossy appearance of wax crystals in the Alocasia leaf cuticles resulted in higher SPF. The occurrence of CW was directly related to leaf chlorophyll stability, moisture retention ability, and cellular membrane integrity in the leaf tissues. Colocasia exhibited superhydrophobic properties with higher static contact angle (CA) >150o than hydrophobic Xanthosoma, and Alocasia with CA ranged between 99.0o to 128.7o. Colocasia CW highly influenced the qualitative and protective mechanisms of the leaf. Aroids are the cheapest sources of edible CW among the terrestrial plants, which could be used in food, agricultural and industrial applications.

Plant epidermal wax helps protect plants from adverse environmental conditions, maintains the function of tissues and organs, and ensures normal plant development. However, the constituents of epidermal wax and the regulatory mechanism of their biosynthesis in wheat have not been fully understood. Wheat varieties with different wax content, Jinmai47 and Jinmai84, were selected to comparatively analyze their waxy components and genetic characteristics, using a combination of lipidomic, transcriptomic, and BSA-Wheat 660K chip analysis. Through lipidomic analysis, 1287 lipid molecules were identified representing 31 lipid subclasses. Among these, Diacylglycerols (DG), (O-acyl)-ω-hydroxy fatty acids (OAHFA), wax ester (WE), Triacylglycerols (TG), and Monoradylglycerols (MG) accounted for 96.4% of the total lipids in Jinmai84 and 94.5% in Jinmai47. DG, OAHFA, and WE were higher in Jinmai84 than in Jinmai47 with the content of OAHFA 2.88-fold greater and DG 1.66-fold greater. Transcriptome sequence and bioinformatics analysis revealed 63 differentially expressed genes related to wax biosynthesis. Differentially expressed genes (DEGs) were found to be involved with the OAHFA, DG, and MG of synthesis pathways, which enriched the wax metabolism pathway. Non-glaucous and glaucous bulks from a mapping population were used to identify single nucleotide polymorphisms (SNP) via 660K chip analysis. Two loci centered on chromosomes 2D and 4B were detected and the locus on 4B is likely novel. These data improve understanding of complex lipid metabolism for cuticular wax biosynthesis in wheat and lay the foundation for future detailed investigation of mechanisms regulating wax metabolism.

Abstract Key message We identified two poplar clones of the same species as highly comparable, yet clones of two further species of the same genus to be distinctly different regarding multiple morphological and ecophysiological traits. Abstract Leaf morphology, wax composition, and residual (cuticular) transpiration of four poplar clones (two clones of the hybrid species P. × canescens, P. trichocarpa, and P. euphratica) were monitored from the beginning to end of the growing season 2020. A pronounced epicuticular wax coverage was found only with P. euphratica. As the most prominent substance classes of cuticular wax primary alcohols, alkanes and esters were identified with P. × canescens and P. trichocarpa, whereas esters and alkanes were completely lacking in P. euphratica. Wax amounts were slightly decreasing during the season and significantly lower wax amounts were found for newly formed leaves in summer compared to leaves of the same age formed in spring. Residual (cuticular) transpiration was about five to tenfold lower for P. × canescens compared with the two other poplar species. Interestingly, with three of the four investigated species, newly formed leaves in summer had lower wax coverages and lower rates of residual (cuticular) transpiration compared to leaves of exactly the same age formed in spring. Our findings were especially surprising with P. euphratica, representing the only one of the four investigated poplar species naturally growing in very dry and hot climates in Central Asia. Instead of developing very low rates of residual (cuticular) transpiration, it seems to be of major advantage for P. euphratica to develop a pronounced epicuticular wax bloom efficiently reflecting light.