Wax Platelets Research Articles

The dominant white color trait of the melon fruit rind is associated with epicuticular wax accumulation.

Microscopic analyses and chemical profiling demonstrate that the white rind phenotype in melon fruit is associated with the accumulation of n-alkanes, fatty alcohols, aldehydes and wax esters. Serving as an indicator of quality, the rind (or external) color of fruit directly affects consumer choice. A fruit's color is influenced by factors such as the levels of pigments and deposited epicuticular waxes. The latter produces a white-grayish coating often referred to as "wax bloom". Previous reports have suggested that some melon (Cucumis melo L.) accessions may produce wax blooms, where a dominant white rind color trait was genetically mapped to a major locus on chromosome 7 and suggested to be inherited as a single gene named Wi. We here provide the first direct evidence of the contribution of epicuticular waxes to the dominant white rind trait in melon fruit. Our light and electron microscopy and gas chromatography-mass spectrometry (GC-MS) comparative analysis of melon accessions with white or green rinds reveals that the rind of melon fruit is rich in epicuticular waxes. These waxes are composed of various biochemical classes, including fatty acids, fatty alcohols, aldehydes, fatty amides, n-alkanes, tocopherols, triterpenoids, and wax esters. We show that the dominant white rind phenotype in melon fruit is associated with increased accumulation of n-alkanes, fatty alcohols, aldehydes and wax esters, which are linked with the deposition of crystal-like wax platelets on their surfaces. Together, this study broadens the understanding of natural variation in an important quality trait of melon fruit and promotes the future identification of the causative gene for the dominant white rind trait.

Design of a biomimetic, small-scale artificial leaf surface for the study of environmental interactions.

The cuticle with its superimposed epicuticular waxes represents the barrier of all aboveground parts of higher plant primary tissues. Epicuticular waxes have multiple effects on the interaction of plants with their living and non-living environment, whereby their shape, dimension, arrangement, and chemical composition play significant roles. Here, the ability of self-assembly of wax after isolation from the leaves was used to develop a small-scale wax-coated artificial leaf surface with the chemical composition and wettability of wheat (Triticum aestivum) leaves. By thermal evaporation of extracted plant waxes and adjustment of the evaporated wax amounts, the wettability and chemical character of the microstructure of the surface of wheat leaves were transferred onto a technical surface. For the use of these artificial leaves as a test system for biotic (e.g., germination of fungal pathogens) and non-biotic (e.g., applied surfactants) interactions on natural leaf surfaces, the chemical composition and the wetting behavior should be the same in both. Therefore, the morphology, chemistry, and wetting properties of natural and artificial surfaces with recrystallized wax structures were analyzed by scanning electron microscopy, gas chromatography–mass spectrometry, and by the determination of water contact angles, contact angle hysteresis, and tilting angles. Wheat leaves of different ages were covered exclusively with wax platelets. The extracted wheat wax was composed of alcohols, aldehydes, esters, and acids. The main component was 1-octacosanol. The waxes recrystallized as three-dimensional structures on the artificial surfaces. The three tested wetting parameters resembled the ones of the natural surface, providing an artificial surface with the chemical information of epicuticular waxes and the wetting properties of a natural leaf surface.

Interaction of surfactants with barley leaf surfaces: time-dependent recovery of contact angles is due to foliar uptake of surfactants

Main conclusionTime-dependent contact angle measurements of pure water on barley leaf surfaces allow quantifying the kinetics of surfactant diffusion into the leaf.Barley leaf surfaces were sprayed with three different aqueous concentrations (0.1, 1.0 and 10%) of a monodisperse (tetraethylene glycol monododecyl ether) and a polydisperse alcohol ethoxylate (BrijL4). After 10 min, the surfactant solutions on the leaf surfaces were dry leading to surfactant coverages of 1, 10 and 63 µg cm−2, respectively. The highest surfactant coverage (63 µg cm−2) affected leaf physiology (photosynthesis and water loss) rapidly and irreversibly and leaves were dying within 2–6 h. These effects on leaf physiology did not occur with the lower surfactant coverages (1 and 10 µg cm−2). Directly after spraying of 0.1 and 1.0% surfactant solution and complete drying (10 min), leaf surfaces were fully wettable for pure water and contact angles were 0°. Within 60 min (0.1% surfactant) and 6 h (1.0% surfactant), leaf surfaces were non-wettable again and contact angles of pure water were identical to control leaves. Scanning electron microscopy investigations directly performed after surfactant spraying and drying indicated that leaf surface wax crystallites were partially or fully covered by surfactants. Wax platelets with unaltered microstructure were fully visible again within 2 to 6 h after treatment with 0.1% surfactant solutions. Gas chromatographic analysis showed that surfactant amounts on leaf surfaces continuously disappeared over time. Our results indicate that surfactants, applied at realistic coverages between 1 and 10 µg cm−2 to barley leaf surfaces, leading to total wetting (contact angles of 0°) of leaf surfaces, are rapidly taken up by the leaves. As a consequence, leaf surface non-wettability is fully reappearing. An irreversible damage of the leaf surface fine structure leading to enhanced wetting and increased foliar transpiration seems highly unlikely at low surfactant coverages of 1 µg cm−2.

OsGL1-1/WSL2 遺伝子はワックス結晶を形成することでイネ葉のガスフィルム維持を制御する

OsGL1-1/WSL2 遺伝子はワックス結晶を形成することでイネ葉のガスフィルム維持を制御する

Potential of ozonated-air (OA) application to reduce the weight and volume loss in fresh figs (Ficus carica L.)

This study investigated the effect of ozonated air (OA) on weight loss, volume reduction (shriveling), and skin firmness on fresh figs and monitored the changes in the epidermis of OA-treated fruits within 14 d of storage at 4 °C and 65 % RH. In Phase 1 of the study, fresh Kadota figs at two different maturity levels, commercial-ripe and tree-ripe, were exposed to OA for up to 11 h at room temperature to find the optimum parameters for ozone treatment. The 3-h OA-treated (15 ppm) fig samples showed 10 % less weight loss, 16 % less shrivel, had a better appearance, showed fewer brown spots, and had less fungal growth than the control. In Phase 2, Kadota and Black Mission figs were treated with OA (15 ppm for 3 h) and their aging parameters were evaluated. The Mission figs in the control group showed the highest rate of weight loss (25.8 %) and volume reduction (32.5 %). Kadota figs had the lowest weight loss (18.8 %) and volume reduction (9.8 %) in 14 d. Due to the oxidation, the OA treatment resulted in a considerable decrease in skin firmness in both Kadota and Mission figs; however, the skin firmness increased in the Kadota samples on Day 7. The recovery of Kadota epidermises continued at a very slow rate until Day 14. However, Mission samples did not show any firmness increase on Day 7. Scanning electron microscopy showed the differences between the control and the OA-treated Kadota and Mission figs. Ozone treatment affected the epidermis of figs, specifically the stomata and epicuticular wax crystals, resulting in stomata blockage or deformation, and irregular shapes in the wax platelets. Although the fruit epidermis was affected by OA treatment, the self-assembly properties of the epicuticular wax layer helped the fruit to recover from the oxidative damage caused by ozone by Day 7. Small microcracks and cell wall disassembly were observed on the fruit surface after 14 d of cold storage; they were very noticeable in the control samples and resulted in considerable water loss and weight loss, decreased shelf life, and significant fungal infection. This study showed that OA treatment of fresh figs can be used to minimize the volume and weight loss and improve the overall quality of fresh figs.

Anatomical Remarks of Some Species of Silene and Bufonia (Caryophyllaceae), Endemic to Sinai, Egypt

ANATOMICAL features of stem and leaf have been studied on four endemic species collected from St. Catherine area, S. Sinai, Egypt. viz. Silene leucophylla Boiss., S. oreosinaica, S. schimperiana and Bufonia multiceps which is provided for the first time. Comparative study was conducted using both light microscope (LM) and scanning electron microscopy (SEM), based on the anatomical structure of the leaf and stem. Druses were found abundantly in both leaf and stem tissue in studied Silene taxa, absent in Bufonia multiceps. Stomata were mostly diacytic or both diacytic and anomocytic were also recorded. Surface view of epidermal cells were straight or undulated. Epicuticular wax platelets have been observed on epidermal and guard cells of S. schimperiana and S. leucophylla. The leaf epidermal and stem anatomical characters were found distinct in each species. Artificial key was provided for the identification of the studied species.

Electrowetting on Langmuir-Blodgett films from epicuticular wax

Langmuir and Langmuir-Blodgett (LB) films were fabricated from epicuticular wax, that had been extracted from Vitis vinifera. For Langmuir films, the influence of subphase temperature on their structure was examined, whereas for LB films, the surface morphology at various temperatures and the effect of the layer number on electrowetting were investigated. Isotherms of surface pressure revealed no well-defined phase transition or collapse on Langmuir films at 22 °C, whereas Brewster angle microscopy showed that even before starting the compression procedure, there are platelets of epicuticular wax floating on the subphase. Those platelets give rise to the Langmuir films of epicuticular wax during compression. In contrast, for higher temperatures (40 °C and 50 °C), a well-defined phase transition was found – without epicuticular wax platelets, with a behavior close to those found in typical fatty acids. For LB films, atomic force microscopy images indicated a decreasing of roughness as a function of the subphase temperature as a result of greater organization of the epicuticular wax film. A significant modulation of about 20 ° (under applied voltage range of 0 to 100 V) was demonstrated of the electrowetting on LB films, which did not depend on the LB layer number. Our results suggest that epicuticular wax LB films have the potential for being applied in electrowetting-based devices. Furthermore, the Langmuir-Blodgett technique is feasible to fabricate films with various compositions focusing on the electrowetting.

Disordered wax platelets on Tradescantia pallida leaves create golden shine.

Plants have various strategies to protect themselves from harmful light. An example of such a protective mechanism is the growth of epicuticular nanostructures, such as a layer of hair or wax crystals. Most nanostructures are optimised to screen UV radiation, as UV light is particularly damaging for cellular tissue. We find that, contrary to the commonly found UV reflectance, the epicuticular wax crystals on Tradescantia leaves reflect strongly in the higher visible wavelength regime. Thus, they give the leaves a golden shine. We characterize the optical appearance of Tradescantia pallida 'purpurea' leaves by angularly resolved spectroscopy and compare the results to finite difference time domain simulations. We find that it is the disordered assembly of the wax platelets that is the crucial parameter to obtain the observed reflected intensity increase for higher wavelengths.

Apple peel morphology and attachment of Listeria innocua through aqueous environment as shown by scanning electron microscopy

The industrial apple packing process begins with submerging the harvested or stored apples into the water dump tank and carrying them by water flumes through various washing steps before drying and packing. Constant introduction of organic matter and water recirculation introduces the risk of apples being cross-contaminated with pathogenic bacteria such as Listeria monocytogenes. This study investigated the relationship between the apple peel microstructure and attachment of bacteria in an aqueous environment. Whole fresh apples of three varieties (viz., Gala, Golden Delicious, and Granny Smith) were inoculated with L. innocua, a surrogate strain of L. monocytogenes, by submerging the apples into the inoculum solution containing ∼106 CFU/mL level. Apples were carefully turned around in the inoculum for 10 min simulating industrial dump tank and fumes conditions. Attachment of L. innocua, to different apple peel sections, was demonstrated using scanning electron microscopy (SEM). Textural characteristics varied considerably among apple varieties. Generally, the apple peel was covered with an amorphous layer of wax, disrupted by microcracks, lenticels, and occasionally overlaid with various types of epicuticular wax platelets. Listeria innocua attached primarily to the apple peel in the stem bowl and calyx sections, embedding in the microcracks, lenticels and on the surface of the trichomes. Bacteria were difficult to locate on the smooth peel surface in the equatorial section of the apples. Results provide valuable information on Listeria attachment on apples which can be used in developing new intervention methods of microbial decontamination.

Rice leaf hydrophobicity and gas films are conferred by a wax synthesis gene (LGF1) and contribute to flood tolerance.

Floods impede gas (O2 and CO2 ) exchange between plants and the environment. A mechanism to enhance plant gas exchange under water comprises gas films on hydrophobic leaves, but the genetic regulation of this mechanism is unknown. We used a rice mutant (dripping wet leaf 7, drp7) which does not retain gas films on leaves, and its wild-type (Kinmaze), in gene discovery for this trait. Gene complementation was tested in transgenic lines. Functional properties of leaves as related to gas film retention and underwater photosynthesis were evaluated. Leaf Gas Film 1 (LGF1) was identified as the gene determining leaf gas films. LGF1 regulates C30 primary alcohol synthesis, which is necessary for abundant epicuticular wax platelets, leaf hydrophobicity and gas films on submerged leaves. This trait enhanced underwater photosynthesis 8.2-fold and contributes to submergence tolerance. Gene function was verified by a complementation test of LGF1 expressed in the drp7 mutant background, which restored C30 primary alcohol synthesis, wax platelet abundance, leaf hydrophobicity, gas film retention, and underwater photosynthesis. The discovery of LGF1 provides an opportunity to better understand variation amongst rice genotypes for gas film retention ability and to target various alleles in breeding for improved submergence tolerance for yield stability in flood-prone areas.

Changes in cuticle compositions and crystal structure of ‘Bingtang’ sweet orange fruits (Citrus sinensis) during storage

ABSTRACTChanges in composition and structure of orange cuticle during storage at 4°C or 25°C for 40 days were investigated. The total epicuticular wax content of fruits increased during storage at 4°C for 30 days and then decreased as storage time prolonged to 40 days, while it increased continuously at 25°C for 40 days. The total intracuticular wax content of fruits increased to 9.70 μg cm−2 stored at 4°C for 10 days and then decreased to 6.74 μg cm−2 for 40 days. The total intracuticular wax content of fruits was decreased to 5.17 μg cm−2 stored at 25°C for 10 days and then increased to 10.06 μg cm−2 for 30 days. Fatty acids were the most abundant component of the epicuticular wax and terpenoids were restricted to the intracuticular wax. Terpenoids were restricted to the intracuticular wax, and their amounts in the fruit stored at 4°C increased continuously during the first 20 days of storage at 4°C and then decreased as storage time increased up to 40 days. Although significant changes were found in the contents of the cutin monomer, their proportions did not change significantly during storage at 4°C or 25°C. Size of wax platelets crystals wax increased during storage of fruits at 4°C up to 30 days; however, the crystals were degraded and decreased as storage prolonged to 40 days. Furthermore, the shape of the fruit cuticle surface wax crystals changed from flattened platelets to small granulelike after storage at 25°C for 20–40 days. The obtained results provide detailed information about the changes in orange cuticle occur during storage at varying temperatures, which may help in preserving the quality of citrus fruits during storage.

Microstructure of Soft Scald in ‘Honeycrisp’ Apples

Soft scald is an apple (Malus ×domestica Borkh.) fruit disorder that appears in response to cold storage after about 2–8 weeks. It appears as a ribbon of dark tissue on the peel of the fruit, with occasional browning into the flesh. Several apple cultivars are susceptible to it, including Honeycrisp. The objectives of this study were to examine the cellular microstructure of fruit exhibiting soft scald and determine if any aspect of the peel microstructure at harvest could be indicative of future soft scald incidence. Light and electron microscopy were used to examine the peel microstructure of ‘Honeycrisp’ fruit that were unaffected or affected by soft scald. Tissue with soft scald had brown pigmented epidermal and hypodermal cells, whereas unaffected fruit peel epidermal cells were unpigmented. Cuticular wax of unaffected peel had upright wax platelets or clumps of wax, but peel surfaces with soft scald exhibited flattened granules and were more fragile than that of unaffected fruit. Epidermal cells of fruit with soft scald were more disorganized than that of unaffected fruit. Light microscopy was used to examine peels of ‘Honeycrisp’ fruit from four growing locations and fruit from a ‘Honeycrisp’ breeding population at harvest. ‘Honeycrisp’ and ‘Honeycrisp’ progeny fruit were also stored at 0 °C for 8 weeks and scored for soft scald incidence. Cross-sections of unaffected peel of stored ‘Honeycrisp’ fruit looked similar to that of freshly harvested fruit. No significant correlations were found between soft scald incidence and measured microstructural attributes of ‘Honeycrisp’ fruit at harvest, suggesting that peel microstructure cannot be used to predict possible soft scald incidence after storage.

Leaf gas film retention during submergence of 14 cultivars of wheat (Triticum aestivum).

Flooding of fields after sudden rainfall events can result in crops being completely submerged. Some terrestrial plants, including wheat (Triticum aestivum L.), possess superhydrophobic leaf surfaces that retain a thin gas film when submerged, and the gas films enhance gas exchange with the floodwater. However, the leaves lose their hydrophobicity during submergence, and the gas films subsequently disappear. We tested gas film retention time of 14 different wheat cultivars and found that wheat could retain the gas films for a minimum of 2 days, whereas the wild wetland grass Glyceria fluitans (L.) R.Br. had thicker gas films and could retain its gas films for a minimum of 4 days. Scanning electron microscopy showed that the wheat cultivars and G. fluitans possessed high densities of epicuticular wax platelets, which could explain their superhydrophobicity. However, G. fluitans also had papillae that contributed to higher hydrophobicity during the initial submergence and could explain why G. fluitans retained gas films for a longer period of time. The loss of gas films was associated with the leaves being covered by an unidentified substance. We suggest that leaf gas film is a relevant trait to use as a selection criterion to improve the flood tolerance of crops that become temporarily submerged.

The interactions between surfactants and the epicuticular wax on soybean or weed leaves: Maximal crop protection with minimal wax solubilization

Abstract Surfactants are commonly added to aqueous herbicide formulations to reduce the surface tension, facilitating their application. In the present study the interaction between the surface of freshly harvested soybean leaves and pure water, solutions of cationic (CTAB), anionic (SDS) and uncharged (ethoxylated sorbitan monolaurate 20 EO – ESM20) surfactants and a commercial herbicide formulation (CF) was investigated by means of contact angle measurements and scanning electron microscopy (SEM). The wettability and the hysteresis in the contact angle values determined for soybean leaves were the largest for the surfactant with the highest critical micelle concentration. The epicuticular wax on soybean leaves presented rosette-like clusters of platelets, as observed by SEM. After interaction with the surfactants or CF, most of the wax platelet rosettes disappeared from the surface, indicating that the epicuticular wax was dissolved by the surfactant. The wax contained long hydrocarbon and long chain esters, as qualitatively analyzed by gas-chromatography coupled with mass spectroscopy. The wax extracted from soybean leaves presented no significant biocidal activity against Micrococcus luteus, Staphylococcus aureus or Escherichia coli . Its protective role against pathogens depends solely on the tridimensional arrangement on the surface, which impairs the physical attachment of microorganisms to the surface. For comparison, the wettability and morphology of Eleusine indica , a common weed, was investigated. The weed leaves presented smooth surfaces and a much lower contact angle values. Therefore, surfactants should be added to the herbicide formulations with the compromise to protect the crop adequately and to minimize the solubilization of protective epicuticular wax layer on soybean leaves.

Surface hydrophobicity of slippery zones in the pitchers of two Nepenthes species and a hybrid.

To investigate the hydrophobicity of slippery zones, static contact angle measurement and microstructure observation of slippery surfaces from two Nepenthes species and a hybrid were conducted. Marginally different static contact angles were observed, as the smallest (133.83°) and greatest (143.63°) values were recorded for the N. alata and N. miranda respectively, and the median value (140.40°) was presented for the N. khasiana. The slippery zones under investigation exhibited rather similar surface morphologies, but different structural dimensions. These findings probably suggest that the geometrical dimensions of surface architecture exert primary effects on differences in the hydrophobicity of the slippery zone. Based on the Wenzel and Cassie-Baxter equations, models were proposed to analyze the manner in which geometrical dimensions affect the hydrophobicity of the slippery surfaces. The results of our analysis demonstrated that the different structural dimensions of lunate cells and wax platelets make the slippery zones present different real area of the rough surface and thereby generate somewhat distinguishable hydrophobicity. The results support a supplementary interpretation of surface hydrophobicity in plant leaves, and provide a theoretical foundation for developing bioinspired materials with hydrophobic properties and self-cleaning abilities.

Epicuticular wax on cherry laurel (Prunus laurocerasus) leaves does not constitute the cuticular transpiration barrier

Main conclusionEpicuticular wax of cherry laurel does not contribute to the formation of the cuticular transpiration barrier, which must be established by intracuticular wax.Barrier properties of cuticles are established by cuticular wax deposited on the outer surface of the cuticle (epicuticular wax) and in the cutin polymer (intracuticular wax). It is still an open question to what extent epi- and/or intracuticular waxes contribute to the formation of the transpiration barrier. Epicuticular wax was mechanically removed from the surfaces of isolated cuticles and intact leaf disks of cherry laurel (Prunus laurocerasus L.) by stripping with different polymers (collodion, cellulose acetate and gum arabic). Scanning electron microscopy showed that two consecutive treatments with all three polymers were sufficient to completely remove epicuticular wax since wax platelets disappeared and cuticle surfaces appeared smooth. Waxes in consecutive polymer strips and wax remaining in the cuticle after treatment with the polymers were determined by gas chromatography. This confirmed that two treatments of the polymers were sufficient for selectively removing epicuticular wax. Water permeability of isolated cuticles and cuticles covering intact leaf disks was measured using 3H-labelled water before and after selectively removing epicuticular wax. Cellulose acetate and its solvent acetone led to a significant increase of cuticular permeability, indicating that the organic solvent acetone affected the cuticular transpiration barrier. However, permeability did not change after two subsequent treatments with collodion and gum arabic or after treatment with the corresponding solvents (diethyl ether:ethanol or water). Thus, in the case of P. laurocerasus the epicuticular wax does not significantly contribute to the formation of the cuticular transpiration barrier, which evidently must be established by the intracuticular wax.

Morphological, Histological and Ultrastructural Changes in Fruit Epidermis of Apple Malus Domestica cv. Ligol (Rosaceae) at Fruit Set, Maturity and Storage

Abstract Fruit quality is closely related to the structure of the fruit peel, especially the epidermis and cuticle which form a barrier between its internal and external environments. This study used light, scanning and transmission elec-tron microscopy to examine changes in the epidermal structures of fruits of the Polish apple cultivar Malus domestica Borkh. cv. Ligol at three maturity stages. The single-layered epidermis was covered with cuticle and crystalline wax platelets. In the fruit set stage the fruit surface exhibited numerous nonglandular trichomes, stomata, microcracks and crystalline wax platelets. The surface of fruits at harvest and after 6-month controlled-atmosphere storage exhibited lenticels and horizontally or vertically oriented wax platelets. During fruit devel-opment there was an increase in epidermal cuticle thickness and a reduction in epidermal cell convexity and number of lenticels. After the storage period fruit weight declined, microcracks deepened and widened, and cuticular waxes accumulated. The cuticle was made up of two layers, lamellar and reticulate. In successive fruit development stages the width of the lamellar layer increased considerably. In the fruit set and harvest maturity stages the epidermal cells contained numerous mitochondria and plastids with starch grains. After the storage period there were fewer amyloplasts and the cell vacuoles contained flocculent residue and dark deposits.

Non-destructive detection of the wax bloom on European plum during post-harvest handling

Post-harvest handling may disturb the wax bloom of plum, blueberry or grape berry, which constitutes both an external visual (speckled fruit) as well as physiological fruit quality parameter (disturbing the water loss barrier) with the following results:(a)Destructive ESEM analysis showed the wax bloom of European plum to be caused by wax platelets, where the wax is largely re-distributed on handling rather than removed.(b)CIE L* values significantly (p<0.05) decreased from 37.3 to 28.1, indicating a darker plum surface after polishing. The a-value of the plum surfaces increased significantly from 2.35 to 2.86, whereas b-values decreased ca. 2.5-fold from −13.9 to −5.0 after polishing viz the plum surface became more red and less blue.(c)Luster levels (glossiness) detected non-destructively increased by almost 3-fold from 111 (SD+20) to 284 (SD+32) relative units.(d)Analysis of RGB images visualised the relative wax distribution over the fruit surface after polishing, as uneven with a more dense wax coverage at the fruit apex and less at the fruit equator, where the contacts by hand are most frequent.The changes in L and b values, and to a lesser extent in the a-value, luster levels and RGB image analysis may be used as a technical fruit quality parameter as determined non-destructively.

Comparative analysis of surface wax in mature fruits between Satsuma mandarin (Citrus unshiu) and ‘Newhall’ navel orange (Citrus sinensis) from the perspective of crystal morphology, chemical composition and key gene expression

Surface wax of mature Satsuma mandarin (Citrus unshiu) and ‘Newhall’ navel orange (Citrus sinensis) was analysed by crystal morphology, chemical composition, and gene expression levels. The epicuticular and total waxes of both citrus cultivars were mostly composed of aldehydes, alkanes, fatty acids and primary alcohols. The epicuticular wax accounted for 80% of the total wax in the Newhall fruits and was higher than that in the Satsuma fruits. Scanning electron microscopy showed that larger and more wax platelets were deposited on the surface of Newhall fruits than on the Satsuma fruits. Moreover, the expression levels of genes involved in the wax formation were consistent with the biochemical and crystal morphological analyses. These diversities of fruit wax between the two cultivars may contribute to the differences of fruit postharvest storage properties, which can provide important information for the production of synthetic wax for citrus fruits.

Cold quarantine responses of ‘Tarocco’ oranges to short hot water and thiabendazole postharvest dip treatments

This study investigated the effects of brief hot water and thiabendazole (TBZ) postharvest dip treatments on ultrastructural changes of fruit epicuticular wax (ECW), TBZ residues, decay development and quality traits of ‘Tarocco’ oranges [Citrus sinensis (L.) Osbek] subjected to cold quarantine, subsequent simulated transport and shelf-life. Commercially mature fruit were submerged in water at 20°C (control fruit) or TBZ at 1000mg/L and 20°C for 60s, or in hot water without or with TBZ at 300mg/L and 53, 56, or 59°C for 60, 30, and 15s respectively. Following treatments, fruit were stored for 3 weeks at 1°C (simulated quarantine conditions for fruit disinfestations against Mediterranean fruit fly, Medfly), followed by 4 days at 3°C (simulated long distance transport), and finally kept at 20°C for 3 days (shelf-life, SL). Scanning electron microscopy (SEM) analysis of ‘Tarocco’ orange surface showed that the typical wax platelets, lifting around edges of wax plates and areas free of epicuticular wax (ECW), that disappeared after hot water dips at 53–59°C for 60–15s, become visible again after storage for 21 days at 1°C (quarantine conditions), and changes involving the appearance of rough ultrastructure, presence large curled plates, fissured wax crusts, and areas with ECW deficiencies, became much more pronounced after shelf-life. These occurrences were related to the transient effect of hot water treatment in decay control. Conversely, treatments with 300mg/L TBZ 53°C for 60s or 56°C for 30s effectively reduced decay after quarantine. These treatments were as effective as standard treatment with 1000mg/L TBZ at 20°C and produced similar TBZ residue levels in fruit, without impairing fruit quality traits such as visual appearance, weight loss, compression test, sensory attributes, juice color parameters (a*, b*, h, L*, and Chroma), and juice chemical characteristics (soluble solids content, titratable acidity, ascorbic acid, glucose, sucrose, citric acid, total phenols, total anthocyanins, and total antioxidant activity).