Changes In Wax Composition Research Articles

Changes in wax composition but not amount enhance cuticular transpiration.

This study focuses on the role of the qualitative leaf wax composition in modulating the cuticular water loss using a Populus × canescens cer6 mutant line, which accumulates C34-C46 wax ester dimers and is reduced in wax monomers >C24. The two literature-based hypotheses to be tested were the importance of the amount of wax esters and the weighted mean carbon chain length in restricting cuticular water loss. The main results were acquired by chemical analysis of cuticular wax and gravimetric cuticular transpiration measurements. Besides additional physiological measurements, the leaf surface properties were characterised by scanning electron microscopy and spectrophotometric light reflectance quantification. Mutation of the CER6 gene resulted in striking changes in qualitative wax composition but not quantitative wax amount. Based on the strong accumulation of dimeric wax esters, the relative proportion of esters increased to >90%, and the weighted mean carbon chain length increased by >6 carbon atoms. These qualitative alterations were found to increase the cuticular transpiration of leaves by twofold. Our results do not support the hypotheses that enhanced amounts of wax esters or increased weighted mean carbon chain lengths of waxes lead to reduced cuticular transpiration.

Characterization of the Epidermis and Cuticle of the Cashew Pseudofruit during Its Development and Maturation

The epidermis and cuticle play an important role in reducing dehydration and protecting the cashew pseudofruit in both the production environment and the postharvest stage. This study analyzes the alterations on the epidermis and cuticle of CCP 76 cashew pseudofruits harvested in five developmental and maturation stages (S1, S2, S3, S4, and S5). The epidermis and cuticle of the samples were analyzed under light microscopy (LM) (quantitative analysis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The epidermal cells at S3 reached maximum outer periclinal wall thickness, which reduced during ripening (S4 and S5), while the cuticle increased in thickness during the same period. These changes coincided with the rapid initial growth of the cashew pseudofruit when the epidermis and cuticle need to accompany the expansion of internal tissues. At the ultrastructural level, lipid material is transported via vesicles through the cell wall to the cuticle, increasing its thickness. Epicuticular waxes, previously deposited as plates and globules, began to develop an amorphous shape during maturation. This process possibly occurs due to changes in wax composition that can be related to the development of greasiness on the fruit skin. These findings provide a better understanding of cashew pseudofruit skin, which will aid future studies and strategies to preserve quality during the postharvest stage.

WOOLLY, interacting with MYB transcription factor MYB31, regulates cuticular wax biosynthesis by modulating CER6 expression in tomato.

Cuticular waxes play a crucial role not only in plant defense against biotic and abiotic stresses, but also in the quality and storability of fruits, such as the tomato (Solanum lycopersicum). Although the biosynthetic pathways of waxes have been extensively characterized, the regulatory mechanisms underlying wax biosynthesis in tomato remain largely unclear. Here, we show that Woolly (Wo), a multicellular trichome regulator, is involved in modulating wax biosynthesis in tomato. Wo enhances the expression of the wax biosynthetic genes SlCER6, SlKCR1, and SlPAS2, and the wax transporter gene SlLTP, and thereby promotes wax accumulation. Furthermore, Wo directly binds to the L1-box in the promoter of SlCER6, an essential element of the very-long-chain fatty acid elongase complex. Intriguingly, overexpression (OE) or knock-down of SlMYB31, an MYB transcription factor that physically interacts with Wo in vivo and in vitro, produces marked changes in wax composition, and whereas Wo knock-down inhibits wax accumulation in SlMYB31-OE lines, SlMYB31 knock-down inhibits wax accumulation in Wo-OE lines, implying that these two genes function in the same pathway. Lastly, SlCER6 expression is induced by abscisic acid in a manner that is partially dependent on Wo. These results demonstrate that Wo and SlMYB31 cooperatively control tomato cuticular wax biosynthesis by regulating the expression of SlCER6.

Recognition at the leaf surface.

Recognition at the leaf surface.

Changes in chemical wax composition of three different apple (Malus domestica Borkh.) cultivars during storage

Abstract The effects of year, picking date and storage conditions on the chemical composition of the wax layer of three apple cultivars (‘Jonagold’, ‘Jonagored’ and ‘Elstar’) were investigated by means of GCMS and multivariate statistical techniques. Wax of apples with different surface characteristics also differed in chemical composition. Controlled atmosphere (CA) storage and subsequent shelf life affected wax properties and caused changes in the chemical composition, especially during shelf life. The changes in wax composition of ‘Elstar’, however, were smaller than those in ‘Jonagold’ and ‘Jonagored’, possibly associated with lower diffusion resistance and more limited structural changes of ‘Elstar’ wax. Longer CA storage periods accelerated the changes in wax composition during subsequent shelf life. The components responsible for the changes were mainly the alkane and ester fractions. The secondary alcohol nonacosan-10-ol was particularly important in explaining the changes in wax composition of ‘Jonagold’ during shelf life and its presence could be linked with greater development of greasiness.

Geochemical monitoring of waxes and asphaltenes in oils produced during the transition from primary to secondary water flood recovery

Results are presented on changes in the content and composition of waxes and asphaltenes of oil produced during the transition from primary to secondary recovery following water flooding. Oil samples have been collected for a period of about three years from one well in Prairie Gem field in central Oklahoma. Wax and asphaltene fractions have been isolated from the produced oils and analyzed, qualitatively and quantitatively, by high temperature gas chromatography. The results demonstrate significant variations in the asphaltene and wax content of the oil produced during the transition period from primary to secondary water flood recovery, ranging from 0.7 to 5 wt%, and 11 to 33 wt%, respectively. Moreover, these variations are found to be accompanied by changes in wax composition and to precede specific production events. The oil produced a month before the response of the well to water flooding indicated an enhanced concentration of nC 22–C 35 alkanes in the wax. The following episode of wax plugging in well equipment was preceded by increased amounts of asphaltenes and high molecular weight (nC 35–C 50) alkanes in the wax of produced oils. Changes in the asphaltene and wax compositions are discussed in terms of processes displacing weakly adsorbed organic material from the pore spaces of the reservoir under increased reservoir pressure and flowing fluid volumes related to water flooding.

The influence of UV-B radiation on the physicochemical nature of tobacco (Nicotiana tabacumL.) leaf surfaces

Relationships between leaf wettability and surface physicochemical characteristics were examined in two genotypes of tobacco (Nicotiana tabacum L. cv. Samsun) grown under controlled conditions at three different levels of biologically effective ultraviolet-B (UV-BBE; 280–320 nm) radiation; 0 (control), 4.54 and 5.66 kJ m–2d–1. Leaf wettability, assessed by measuring leaf-water droplet contact angles, was positively correlated with epicuticular wax chemical composition and trichome density, but not the amount of wax on the surface of leaves. Tobacco wax comprised a mixture of C19–C33 n-alkanes (59%) with homologues containing an odd number of carbon atoms predominating, C28–C32 br-alkanes (38%), and a small quantity (3%) of free Cl6–C18 fatty acids. Significant effects of UV-B radiation upon wax production and chemical composition were restricted to the adaxial surface of leaves. Enhanced UV-B radiation reduced the quantity of epicuticular wax in the more sensitive genotype [GR32-3], assessed from effects on dry matter accumulation, partitioning and changes in leaf morphology, and resulted in marked changes in wax composition and homologue distributions in both genotypes. UV-B-induced increases in branching, and shifts toward the synthesis of shorter-chain homologues provided evidence for a fundamental effect of UV-B radiation on wax biosynthesis, with the observed effects consistent with a highly specific and direct effect of UV-B radiation on microsomal-based elongases in the epidermis. UV-B radiation also reduced the density of trichomes on the adaxial leaf surface, whilst increasing the number of trichomes on the abaxial leaf surface. Changes in wax composition and trichome density induced by UV-B radiation were associated with increases in leaf surface wettability which were particularly pronounced on the adaxial surface. The subtle, though possibly far-reaching, physiological consequences of such UV-B-induced changes in surface wettability are discussed in the light of other recent findings.

EFFECTS OF SIMULATED ACID RAIN ON PRODUCTION, MORPHOLOGY AND COMPOSITION OF EPICUTICULAR WAX AND ON CUTICULAR MEMBRANE DEVELOPMENT

SummaryLeaves of Phaseolus vulgaris L., Vicia faba L., Pisum sativum L. and Brassica napus L. were exposed to simulated rain from emergence to full expansion at seven pHs between 5.6 and 2.6, applied at 2 mm h−1 in amounts and at intervals representative of ambient rain in southwestern England. Leaf expansion was unaffected by rain pH greater than 30 in V. faba, and pH 2–6 in the other species. Macroscopic foliar injury was induced at pH 3.4 in non‐wettable leaves of P. sativum and B. napus which had relatively large deposits of crystalline epicuticular wax, and at pH 3.0 in wettable leaves of P. vulgaris and V. faba which had small deposits of amorphous wax. Foliar injury was greatest in species with crystalline wax. Wax production was affected by simulated acid rain in all species and was often accompanied by changes in wax composition. Wax quantity was reduced on leaves of P. vulgaris exposed to rain at pH 4.6, while wax on leaves of P. sativum and B. napus had increased numbers of smaller plates and tubes, respectively, per unit area at pH 4.6. Leaves of B. napus, stripped of crystalline epicuticular wax at about 20% full expansion, regenerated less wax at pH 3.4 than at pH 5.6. The thickness of the cuticular membranes in leaves of P. vulgaris, V faba and P. sativum exposed to simulated acid rain at pH 4.2 decreased by 28 to 35 % compared with those exposed to pH 5.6 rain. Membrane ultrastructure was also altered in leaves of P. vulgaris. Taken together, these changes could have important consequences for leaf wettability, rainfall retention, foliar uptake of chemicals and host‐parasite interactions.

Wax synthesis in Brassica oleracea as modified by trichloroacetic acid and glossy mutations

Two different mutations in Brassica oleracea, gl 5 and gl 4 have been re-investigated using acetate-1- 14C labelling in an attempt to define more closely the nature of the genetic blocks to wax synthesis. It has been found that gl 5 is a mutation which blocks elongation in the Step C 28–C 30. The mutation gl 4 exhibits no elongation block and could be blocked in the decarboxylation Step C 30–C 29. 0·1 mM TCA supplied in the culture solution of cauliflower seedlings affected the leaf surface by producing a glossy appearance similar to that induced by gl 3 and gl 4. At this concentration growth was not inhibited and the appearance of the plants was normal except for the surface wax. The amount of surface wax produced was about 40% of that in untreated seedlings on a leaf area basis. Slight, but significant changes in wax composition were noted, mainly involving a reduction in C 30 acids and aldehydes, a slight reduction (33–29%) in alkane content, and a marked difference in chain length composition of the alkanes with C 27 increased relative to C 29. Over a range of concentrations from 0·1–1 mM, TCA inhibited incorporation of label from acetate-1- 14C into C 30 acids and aldehydes more than into C 28 at concentrations 0·4–0·8 mM while label tended to accumulate in C 24 and C 26 acids; thus elongation C 28–C 30 was especially sensitive to TCA. TCA also inhibited incorporation into primary alcohols and esters almost as much as into C 29 compounds. In spite of relatively specific effects on incorporation of label into longer chain lengths, the resulting block to C 30 synthesis is not sufficient to make much difference to the overall rate of C 29 synthesis. Both results of analysis of wax from whole plants and experiments with tissue slices in vitro indicated that the effect of TCA in reducing the glaucousness of the leaf surface is a combination of overall reduction of wax synthesis together with slight but significant changes in wax composition.