Fruit Water Loss Research Articles

Nitric oxide fumigation maintains cantaloupe fruit quality by regulating the production of reactive oxygen species

Cantaloupe (Cucumis melo L.) is a major crop cultivated in Northwest China. However, with the extension of storage periods, cantaloupes are increasingly prone to post-ripening senescence, quality deterioration, rot, and other phenomena, which in turn seriously limit shelf life. During postharvest storage, the quality of cantaloupes is affected by a large increase in ROS in the fruit. Herein, the effects of exogenous NO fumigation treatment on the quality of Xizhoumi NO.17 cantaloupe were investigated, with a focus on ROS generation and removal. NO fumigation treatment effectively reduced the rate of cantaloupe decay, inhibited fruit water loss and better maintained fruit firmness and relative conductivity. NO treatment induced O2·– and H2O2 production during early storage (within 24 h), whereas their accumulation decreased during later storage. NOX activity and expression of related genes in the treatment group were higher than those in the control group during the early storage but lower during later storage. NO fumigation also induced the antioxidant capacity of enzymatic and non-enzymatic systems in cantaloupe and helped to inhibit the accumulation of ROS. Taken together, NO fumigation triggers H2O2 production via the NOX/SOD system, activating the antioxidant response of cantaloupe to overcome excessive ROS production in the late stage of storage, thus maintaining fruit quality.

Revealing the crucial role of cuticular wax components in postharvest water loss in passion fruit (Passiflora edulis Sims.)

Passion fruit (Passiflora edulis Sims.) is highly prone to water loss and shrinkage after harvesting. The fruit cuticle serves as a crucial barrier to prevent non-stomatal water loss. However, the impact of cuticle on water loss in passion fruit remains unclear. Therefore, the present study primarily focuses on the influence of the cuticle on postharvest water loss of passion fruit, specifically emphasizing the changes in cuticular wax components. Our results showed that both the thickness and content of cutin decreased during storage. The degradation of wax components exhibited a similar trend to fruit water loss. At the end of the storage, n-triacontane content was stored at 25 °C retained 2.8% of that at 7 °C. Follwed by stearic acid, palmitate, and so on, with amounts at 25 °C are 9.3% and 13.8% at 7 °C, respectively. Interestingly, the reduction of amides, erucamide and hexadecanamide lead to water loss in fruit. So far as we know, this is the first report demonstrating that cuticle amides influence water loss in fruit. This study provides new insights into the role of cuticle in the water loss of passion fruit.

Water Loss: A Postharvest Quality Marker in Apple Storage

AbstractApple fruit can be stored for long periods of time, especially with the use of controlled atmosphere storage, but like many fruits and vegetables are susceptible to water loss. Water loss can result in compromised appearance such as skin shriveling, as well as loss of firmness, and reduced saleable weight, which in turn affect the income of growers and other industry stakeholders. Preharvest factors that can influence water loss in apples during the postharvest period include climate, cultivar, fruit size, tree age, orchard practices, and harvest maturity. Postharvest factors such as the storage temperature, relative humidity, storage type, and duration can also affect water loss in apple fruit during storage. The mechanisms of cuticle biosynthesis in water permeance, the role of stomata and lenticels, microcracking, crosstalk with mechanical injuries, storage disorders, and decay incidence during the storage of apples are reviewed. Additionally, the review summarizes: preharvest and postharvest factors influencing water loss; recent management strategies including pre-cooling, cold storage, controlled atmospheres, packaging, and anti-senescence chemicals; the use of edible coatings, as well as other non-chemical approaches for modulating water loss and maintaining storage quality. The review also provides direction for the industry to manage this destructive problem in the postharvest supply chain of apple fruit.

Cuticular wax biosynthesis in blueberries (Vaccinium corymbosum L.): Transcript and metabolite changes during ripening and storage affect key fruit quality traits.

In fruits, cuticular waxes affect fruit quality traits such as surface color at harvest and water loss during postharvest storage. This study investigated the transcriptional regulation of cuticular wax deposition in northern highbush blueberries (Vaccinium corymbosum L.) in relation to fruit water loss and surface color during ripening and postharvest storage, as well as the effects of abscisic acid (ABA)-mediated changes in cuticular wax deposition on these fruit quality traits. Total cuticular wax content (μg∙cm-2) decreased during fruit ripening and increased during postharvest storage. Transcriptome analysis revealed a transcript network for cuticular wax deposition in blueberries. Particularly, five OSC-Likes were identified as putative genes for triterpene alcohol production, with OSC-Like1 and OSC-Like2 encoding mixed amyrin synthases, OSC-Like3 encoding a lupeol synthase, and OSC-Like4 and OSC-Like5 encoding cycloartenol synthases. The expression of three CYP716A-like genes correlated to the accumulation of two triterpene acids oleanolic acid and ursolic acid, the major wax compounds in blueberries. Exogenous ABA application induced the expression of triterpenoid biosynthetic genes and the accumulation of β-amyrin and oleanolic acid, as well as increased the ratio of oleanolic acid to ursolic acid. These changes were associated with reduced fruit water loss. The content of β-diketones was also increased by ABA application, and this increase was associated with increased fruit lightness (measured as L* using CIELAB Color Space by a colorimeter). This study provided key insights on the molecular basis of cuticular wax deposition and its implications on fruit quality traits in blueberries.

SlCNR regulates postharvest water loss and wax accumulation in tomato fruit and directly represses the transcription of very-long-chain (VLC) alkane biosynthesis-related genes SlCER1-2 and SlCER6

Cuticular waxes play a crucial role in the control of quality and storability of fruit and many transcription factors (TFs) contribute to fruit wax accumulation and affect the postharvest water loss. The tomato SBP-box protein Colorless Non-Ripening (SlCNR) is commonly investigated as a TF regulating fruit ripening, and its regulation role in mediating postharvest water loss remains to be unknown. Here, we found that fruit of SlCNR knockout (KO) mutants (KO-SlCNR#16 and KO-SlCNR#23) generated by CRISPR/Cas9 editing system exhibited decreased postharvest water loss, while fruit of the SlCNR-overexpressing (OE-SlCNR#21 and OE-SlCNR#24) displayed increased water loss compared to the wild type (WT). The overall wax accumulation increased by 17–30% in fruit of SlCNR KO mutants and decreased by 26–42% in OE-SlCNR#21 and OE-SlCNR#24, accompanied by the change of major components of waxes, such as n-alkanes, triterpenoids, and primary alcohol. RNA-seq analysis showed that the expression of numerous genes involved in wax biosynthesis were up-regulated in fruit of KO-SlCNR#23, including SlCER1–2, which encodes one part of the VLC alkane formation complex, and SlCER6, which encodes a β-ketoacyl-coenzyme A synthase. Furthermore, we proved that SlCNR directly represses the transcription of wax biosynthetic genes SlCER1–2 and SlCER6 in vivo and in vitro, thereby negatively regulating wax accumulation. These findings expand our understanding in the genetic regulatory mechanisms governing ripe tomato fruit wax accumulation and present SlCNR as a novel target of wax accumulation and postharvest water loss.

1-Methylcyclopropene reduces postharvest water loss by modulating cuticle formation in tomato fruit

Water loss during fruit postharvest is influenced by both internal and external determinants. Although 1-MCP is extensively employed to prolong fruit storage life and retain quality by minimizing water loss, its influence on water loss rate remains underexplored. This research investigated the effect of 1-MCP on tomato fruit (Solanum lycopersicum cv. Micro-tom) at 5 days post-breaker stage with intact pedicels. The tomatoes were exposed to a 3-day fumigation with 1 μL L−1 1-MCP, followed by evaluations on fruit water loss, cuticle wax and cutin composition, and related gene expression. Our findings demonstrate that 1-MCP notably postponed fruit water loss and curbed ethylene production. It also modified cuticle wax biosynthesis by elevating specific alkanes (heptacosane, octacosane, nonacosane, triacontane, hentriacontane, dotriacontane, tritriacontane, tetratriacontane, and total alkanes), and 13-docosen-1-ol while diminishing triterpenoids and sterols. For cutin composition, 1-MCP increased the content of hexadecanedioic acid, 9,10-dihydroxyoctadecanoic acid, 9,10-dihydroxyoctadecanedioic acid, and 9,10,18-trihydroxyoctadecanoic acid. At the transcript level, 1-MCP upregulated the expression of SlCER2-Like1, SlCER3, SlCYP77A1, SlCYP77A2, and SlHTH, but downregulated the expression of SlLACS4. This study elucidates potential mechanisms underlying 1-MCP regulated water permeability during fruit postharvest.

Investigation on epidermal structure and water migration of postharvest passion fruit during storage.

Passion fruit is a tropical fruit that has plenty of fruit fragrance. During storage, passion fruit quickly loses water, resulting in its poor quality. Researching the mechanism of water loss contributes to prolonging the storage time. In this study, passion fruit was stored at 7 or 25°C to analyze the relationship between epidermal structure and water migration. The epidermal wax and structure of passion fruit began to show signs of destruction from the middle stage (day 8) during storage. The mobility of free water was decreased at 7°C and increased at 25°C in passion fruit from the middle stage of storage (day 8). The migration rate of free water in passion fruit stored at 7°C was lower than that at 25°C. The mobility of immobile water was weaker in the late storage period but that of bound water changed barely. These results showed that the migration of free, immobile, and bound water had a connection with the epidermal structure. Incomplete epidermal structure promoted water loss in passion fruit, with the most pronounced loss of free water. PRACTICAL APPLICATION: Maintaining the epidermal structure of passion fruit well can decrease the water loss ratio. Passion fruit stored at low temperatures could better sustain the integrity of epidermal wax and structure; it was able to change the water migration rate in the epidermis of passion fruit, which was conducive to maintaining the water content.

Effects of Deficit Irrigation and Anti-Stressors on Water Productivity, and Fruit Quality at Harvest and Stored ‘Murcott’ Mandarin

A two-year experiment using ‘Murcott’ mandarin (Citrus reticulata) was conducted under deficit irrigation (DI) strategies with an anti-stressor application and then stored. The three DI regimes were 70% crop evapotranspiration (70% ETC), 85% ETc, and full irrigation (100% ETc). Anti-stressor treatments consisted of a foliar application of either sodium nitroprusside (SNP), selenium nanoparticles (NanoSe), microalgae (Spirulina platensis), or a non-treated control. Mean water productivity values were highest for trees at 70% ETc and 85% ETc when they were sprayed with microalgae, which was 42% and 51% greater, respectively, compared to control trees at 100% ETc, but only 6.5% and 13% greater, respectively, compared to trees sprayed with microalgae at 100% ETc. Trees sprayed with microalgae at 100% ETc or 85% ETc had the highest and second-highest fruit yields. The percentage of fruit water loss after 15 d storage at either 1.5 °C + 90% RH or 16 ± 2 °C + 60–65% RH was reduced at all DI regimes when trees were sprayed with an anti-stressor compared to control trees at the same DI regime. Trees sprayed with 150 μmol L−1 SNP had the only fruit peel that maintained the carotenoid content after cold storage. In general, trees sprayed with SNP were most successful at each DI regime for reduced Malondialdehyde (MDA), but after 15 d of cold storage, only trees sprayed with 150 μmol L−1 SNP at 85% ETc or 100% ETc and/or trees sprayed with NanoSe at 70% ETc had fruit that maintained low MDA content. Catalase and peroxidase enzyme activities and proline content were enhanced when trees were sprayed with 150 μmol L−1 SNP during DI strategies. This study demonstrates the effectiveness of deficit irrigation combined with anti-stressor applications to improve water productivity, fruit yields, and post-storage quality of ‘Murcott’ mandarin trees. These findings offer valuable insights into sustainable citrus production under limited water resources.

Cuticular Wax Triterpenes Maintain Storage Quality of Blueberries by Reducing Water Loss.

Cuticular wax contributes to maintaining postharvest storage quality against fruit water loss and softening. Triterpenoids, such as oleanolic acid (OA) and ursolic acid (UA), are the main components in blueberry cuticular wax, but their role in water migration during the storage of blueberries remains to be determined. Here, we examined the relationship between the content of OA and UA and the storage quality of blueberry fruit (25 °C). The results revealed that the UA content during eight-day postharvest storage ranged from 58 to 77 μg cm-2, which was negatively related to weight loss. Additionally, we investigated the effect of exogenous OA and UA on water migration in the blueberry fruit during storage at room temperature; the weight loss was significantly lower (by 22%) with UA treatment than in the control fruit. Our findings indicate that OA and UA effectively affect water migration in blueberry fruit during postharvest storage, which could contribute to improving postharvest preservation techniques.

Dangler for Accelerated Dehydration: A Novel System for Assessing the Impacts of Relative Humidity on Fruit Water Loss During Cold Storage of Blueberries

Blueberries are prone to dehydration during storage. Firmness is one of the most critical quality attributes associated with this period, with the loss of water from the fruit representing the most significant limitation for the fresh market. Therefore, one of the great challenges is maintaining the quality characteristics of the fruit in shipments by sea, which can take up to 60 days when sent from the southern hemisphere to the northern hemisphere. The random arrangement of each fruit within a packaging unit (different proportions of the stem scar and cuticular surface exposed to the environment) represents an essential source of variation in the prediction of softening during the storage period. A special device, referred to as a dangler for accelerated dehydration (DAD), was designed to expose nearly the entire fruit surface to the environment and determine the impact of factors such as relative humidity and the role of the stem scar and cuticle on fruit water loss. Consequently, to evaluate the ability of DADs to find differences in fruit dehydration, blueberries sampled at early, peak, and late harvest dates were placed in DADs and exposed to three controlled levels of relative humidity (30%, 65%, and 96% relative humidity; 1.2 ± 0.7 °C) for 10 days. Berries within the DADs were untreated, immersed in hexane for 5 seconds to remove bloom, painted with quick-drying nail polish on the pedicel end to seal the stem scar or immersed in hexane for 5 seconds, and painted with quick-drying nail polish on the pedicel end. At each harvest, fruit weight loss was significantly affected by the fruit and RH treatments, as well as the interaction between them. A regression analysis of the control treatment indicated that water loss at lower relative humidities occurred faster in fruit from the first harvest. The results reveal that DADs can be used to characterize preharvest and postharvest stimuli at an individual level and within a short time (10 days).

β-1,3-GLUCANASE10 regulates tomato development and disease resistance by modulating callose deposition.

β-1,3-Glucanases are considered key regulators responsible for the degradation of callose in plants, yet little is known about the role and mode of action of their encoding genes in tomato (Solanum lycopersicum). In the present study, we identified the β-1,3-glucanase encoding gene β-1,3-GLUCANASE10 (SlBG10) and revealed its regulation in tomato pollen and fruit development, seed production, and disease resistance by modulating callose deposition. Compared to wild-type or SlBG10 overexpressing (SlBG10-OE) lines, knockout of SlBG10 caused pollen arrest and failure to set fruit with reduced male rather than female fecundity. Further analyses showed that SlBG10-knockout promoted callose deposition in anther at the tetrad-to-microspore stages, resulting in pollen abortion and male sterility. Moreover, loss-of-function SlBG10 delayed degradation of endosperm cell wall calloses during cellularization and impeded early seed development. We also uncovered that Botrytis cinerea infection induces SlBG10 expression in wild-type tomato, and the knockout lines showed increased callose accumulation in fruit pericarps, reduced susceptibility to B. cinerea and enhanced antioxidant capacity to maintain tomato fruit quality. However, expression of genes encoding cell wall hydrolases decreased in SlBG10-knockout tomatoes and thus led to an increase in pericarp epidermal thickness, enhancement in fruit firmness, reduction of fruit water loss and extension of tomato shelf life. These findings not only expand our understanding of the involvement of β-1,3-glucanases as callose regulators in multiple developmental processes and pathogen resistance, but also provide additional insight into the manipulation of multi-agronomic traits for targeted tomato breeding.

A Review of Storage Temperature Recommendations for Apples and Pears.

An exploration of the range of expert opinions on the optimum storage temperature for apples and pears in RA (refrigerated air), CA (controlled atmosphere), and DCA (dynamic controlled atmosphere) is provided, based on the accumulated postharvest data from the last 20 years. Apple cultivars have been divided into two storage temperature groups (0 to 1 °C and >1 °C), based on chilling sensitivity. Increasingly, gradual cooling, rather than rapid cooling, is recommended for apple cultivars, especially for chilling-sensitive cultivars. European pear cultivars are held at storage temperatures close to or just below 0 °C since they are not chilling-sensitive, and most cultivars require a cold temperature to induce ethylene production and ripening, especially if picked early for long-term storage. Asian pears apparently have higher temperature requirements in CA, compared with European pears. The temperature recommendations for RA and CA storage differ in some apple and European pear cultivars. In such cases, the CA recommendation is, on average, approximately 0.9 °C higher for apple cultivars and approximately 0.5 °C higher for pear cultivars, compared with RA. Research evidence suggests that some apple and pear cultivars can be stored at higher temperatures in DCA than in CA, and if the ethylene inhibitor, 1-methylcyclopropene (1-MCP), is applied in CA and/or DCA, leading to possible energy savings and quality benefits. A cool growing season may increase postharvest disorders, depending on cultivar and region. The store or packinghouse manager may choose to mitigate potential postharvest problems by maintaining the storage temperature at or above the temperature listed here and/or using stepwise (gradual) cooling. The storage temperature can affect the humidity and vapour pressure deficit (driving force) in the storage room. Altering the vapour pressure deficit controls the water loss in stored fruit, which can affect various quality parameters and the occurrence of several storage disorders.

High-Relative-Humidity Storage Reduces the Chilling Injury Symptoms of Red Sweet Peppers in the Breaker Stage

Water loss, interwoven with other factors, is identified as the cause of chilling injury to sweet peppers. The breaker stage is the most vulnerable of all maturity stages. The purpose of this study was to see if increasing the storage relative humidity (RH) reduces the chilling injury and to compare its effect on breaker-stage fruits to red-ripe fruits at a normal RH. The fruits were stored at 5 °C with a RH of 98 ± 2% and 70 ± 6% for high and low RH, respectively. After 15 days of cold storage, the fruits were moved to ambient conditions for 3–5 days for chilling injury symptoms to appear. The results showed that high RH storage reduced fruit water loss by 4–4.5% compared to low RH storage, resulting in fewer chilling injury symptoms regardless of fruit maturity stage. Due to the increased RH, cell membrane damage indicators such as electrolyte leakage, MDA, respiration, and ethylene production rates were shown to be reduced, while brix and color were well maintained, indicating reduced or stopped senescence. Furthermore, DPPH antioxidant activity and vitamin C were retained and optimized. The microbiological analyses also showed that a high RH may not promote the growth of microorganisms as quickly as may have been thought. Finally, the findings of this study indicate that breaker-stage peppers stored at a high RH may be less susceptible to chilling injury than red-ripe peppers stored at a low RH.

CsERF003, CsMYB7 and CsMYB102 promote cuticular wax accumulation by upregulating CsKCS2 at fruit ripening in Citrus sinensis

Cuticular wax is a hydrophobic protective layer covering the surface of citrus fruit, which plays an important role in preventing fruit water loss and improving fruit appearance quality. Our previous study has demonstrated that CsKCS2 is highly expressed at fruit ripening and involved in fruit cuticular wax synthesis in Citrus sinensis. However, the upstream regulators of CsKCS2 and the transcription factors regulating fruit cuticular wax synthesis at ripening remain unclear. Here, we performed a gene co-expression analysis with the published transcriptomic data of five developmental stages of Citrus sinensis fruit. The results showed that the gene expression trend of the blue module was synchronized with the accumulation pattern of fruit cuticular wax during fruit development and ripening. Further dual luciferase assay suggested that the promoter of CsKCS2 could be activated by CsERF003, CsMYB7 and CsMYB102 in the blue module. Moreover, ectopic expression in Arabidopsis revealed that CsERF003, CsMYB7 and CsMYB102 could increase cuticular wax content in leaves by upregulating the expression of wax-related genes (such as KCS, CER1, CER3 and CER4). Our results provide new insights into the transcriptional regulation of fruit cuticular wax synthesis, and important information for the mining of regulatory factors involved in cuticular wax synthesis in Citrus sinensis fruit.

Mineral Nutrients, Physiological Disorders, Postharvest Water Loss, and PR Gene Expression in Bell Pepper (Capsicum annuum L.) Fruit under Shade Nets

Abstract Shade nets can be an effective technology for producing bell pepper (Capsicum annuum L.) under hot climatic conditions. However, the effects of shading on fruit quality are still unclear. The objectives were to evaluate the effects of shade level on fruit mineral nutrient content, physiological disorders, and postharvest water loss. Trials were conducted in the spring–summer of 2016, 2017, and 2018 in Tifton, Georgia, USA, following a randomized complete block design with five shade levels: 0% (open field), 30%, 47%, 63%, and 80%. Shading increased the bell pepper fruit dimensions (length, diameter, and weight) in 2016 and mineral nutrient content in 2017. Fruit sunscald incidence decreased with increasing shade level, while blossom-end rot showed inconsistent responses. Postharvest fruit water loss and transpiration rates were highest in fruits from the unshaded treatment in 2016; there were no differences in fruit water loss among the shade levels. NONEXPRESSOR OF PATHOGENESIS-RELATED 1 (NPR1) and PATHOGENESIS-RELATED 1 (PR1) genes expressed more than 1.5-fold and 10-fold, respectively, at 47% shade level compared to 80%, though not significantly. Therefore, plants grown under shading had fruit with greater size, increased mineral nutrient content, and reduced sunscald incidence compared with the unshaded control.

QTL analysis reveals reduction of fruit water loss by NAC042 through regulation of cuticular wax synthesis in citrus fruit

Postharvest water loss is a critical factor that determines the quality and shelf life of fresh fruit. Cuticular wax constitutes a key barrier to reduce fruit water loss. Our previous study has shown that HJ (Citrus reticulata) has a significantly higher postharvest water loss rate than ZK (Poncirus trifoliata). Here, we investigated the fruit water loss rate of the HJ × ZK F1 pseudo-testcross population in 2016 and 2019. QTL mapping for fruit water loss rate was performed by high-density genetic map and bulk segregant analysis, and QTL9 was identified to be associated with fruit water loss. The expression of NAC042 from QTL9 in ZK was 170-fold that in HJ. Heterologous expression in Arabidopsis showed that NAC042 could reduce the water loss of leaves by increasing the cuticular wax content (especially alkanes). Further expression analysis revealed that NAC042 could enhance the expression of many wax-related genes in Arabidopsis leaves, including AtKCS1, AtKCS2, AtKCS9, AtKCS20, AtCER1 and AtCER3. Therefore, NAC042 might be involved in fruit cuticular wax synthesis to reduce fruit water loss. The findings provide new insights into the regulation of cuticular wax and fruit water loss as well as valuable information for breeding of citrus with better storability.

C24 and C26 aldehydes are potential natural additives of coating for citrus water retention

Water loss is a key factor for the postharvest senescence of fruit. It has been reported that natural cuticular wax at high concentrations has better performance than commercial coating in water retention of fruit, which can prevent postharvest water loss without the accumulation of off-flavor. Here, we analyzed the correlation between epicuticular wax and postharvest water loss with 75 citrus varieties from a natural population. The water loss rate of the fruit was little influenced by the wax microstructure (stomata and wax crystal morphology), but strongly affected by epicuticular wax components. Further, C24 and C26 aliphatic aldehydes showed the greatest impact on fruit water loss rate, whose correlation coefficients reached –0.63 and –0.67, respectively. These two substances could significantly reduce the fruit water loss rate, indicating that they are potential natural additives to be used in the coating for citrus fruit water retention.

Chemical Composition of Cuticle and Barrier Properties to Transpiration in the Fruit of Clausena lansium (Lour.) Skeels.

The plant cuticle, as a lipid membrane covering aerial plant surfaces, functions primarily against uncontrolled water loss. Herein, the cuticle chemical composition and the transpiration of wampee fruit (Clausena lansium (Lour.) Skeels) at the green, turning, and yellow stages in cultivars of “Jixin” and “Tianhuangpi” were comprehensively studied. The coverage of wax and cutin monomers per unit of fruit surface area at the green stage was lower in “Jixin” than in “Tianhuangpi” and increased gradually during development. Cutin monomers accumulated ranging from 22.5 μg cm−2 (green) to 52.5 μg cm−2 (turning) in “Jixin” and from 36.5 μg cm−2 (green) to 81.7 μg cm−2 (yellow) in “Tianhuangpi.” The total composition of waxes ranged between 6.0 μg cm−2 (green) and 11.1 μg cm−2 (turning) in “Jixin,” while they increased from 7.4 μg cm−2 (green) to 16.7 μg cm−2 (yellow) in “Tianhuangpi.” Cutin monomers were dominated by ω-, mid-dihydroxy fatty acids (over 40%), followed by multiple monomers of α,ω-dicarboxylic acids with or without added groups, α-monocarboxylic acids with or without ω- or mid-chain hydroxy or mid-epoxy groups, primary alcohols, and phenolics. The very-long-chain (VLC) aliphatic pattern of cuticular waxes was prominently composed of n-alkanes (ranging from 21.4% to 39.3% of total wax content), fatty acids, primary alcohols, and aldehydes. The cyclic waxes were dominated by triterpenoids (between 23.9 and 51.2%), sterols, and phenolics. Water loss in wampee fruit exhibited linear changes over time, indicating an overall monofunctional barrier to transpiration. Permeance for water in wampee fruit was higher at the green stage than at the yellow stage in both “Jixin” and “Tianhuangpi,” which showed a negative correlation with the changes of VLC n-alkanes. The results showed the cuticular chemicals, including cutin monomers and waxes, in wampee fruit and further indicated the potential contributions of the cuticular chemical composition to the physiological functions in fruits.

Exogenous gibberellin treatment improves fruit quality in self-pollinated apple

Although a few apple (Malus × ×domestica) varieties are self-compatible, little is known about the differences in fruit quality between self- and cross-pollinated apple. In our current study, we compared the fruit quality of self-pollinated apple plants (cultivar ‘Hanfu’) in self-pollination or cross-pollinated by another cultivar ‘Qinguan’. Analysis of fruit quality revealed substantial differences in the external qualities between self- and cross-pollinated apple fruit, but not in the internal qualities. Fruits harvested from self-pollinated ‘Hanfu’ were smaller and more asymmetrical than those harvested from the cross-pollinated plants. We developed a mathematical model describing how seed number and distribution affect fruit growth. According to this model, the fewer the seeds, the greater the force released from the seeds and the more asymmetrical the fruit. Detection of endogenous hormone and the associated gene expression revealed that gibberellin (GA) levels and GA transporter gene expression on the seedless side were significantly lower than those on the seeded side. Analysis of fruit pectin methylesterase activity and demethylated pectin levels indicated that the lack of GA limits fruit cell wall extension. Additionally, spraying the self-pollinating plants with gibberellic acid increased the fruit weight and lowered the proportion of asymmetrical fruit, recovering the exterior fruit quality to that of the cross-pollinated fruit. Furthermore, exogenous GA treatment increased the wax layer thickness and reduced the fruit water loss rate, leading to a dramatic improvement in fruit storage capacity. Therefore, exogenous GA treatment could be used to ensure regular fruit production of self-pollinated ‘Hanfu’.

CitWRKY28 and CitNAC029 promote the synthesis of cuticular wax by activating CitKCS gene expression in citrus fruit.

CitWRKY28 and CitNAC029 are involved in cuticular wax synthesis as indicated by the comparative analysis of fruit aliphatic wax content between Citrus reticulata and Citrus trifoliata and gene co-expression analysis. Cuticular wax covers the fruit surface, playing important roles in reduction of fruit water loss and resistance to pathogen invasion. However, there is limited research on the synthesis and transcriptional regulation of cuticular wax in citrus fruit. In this study, we characterized the variations of aliphatic wax in HJ (Citrus reticulata) and ZK (Citrus trifoliata) from young fruit to mature fruit, as well as performed transcriptome sequencing on 27 samples at different fruit developmental stages. The results revealed that the ZK fruit always had a higher aliphatic wax content than the HJ fruit during development. qRT-PCR analysis demonstrated that two KCS genes, CitKCS1 and CitKCS12, had the most significant difference in expression between HJ and ZK. Furthermore, a heterologous expression assay in Arabidopsis indicated that CitKCS1 and CitKCS12 are involved in cuticular wax synthesis. Subsequently, gene co-expression network analysis screened CitWRKY28 and CitNAC029. Dual luciferase and EMSA assays indicated that CitWRKY28 might bind to the promoter of CitKCS1 and CitKCS12 and CitNAC029 might bind to that of CitKCS1 to activate their expression. Moreover, CitWRKY28 and CitNAC029 could promote the accumulation of cuticular wax in Arabidopsis leaves. Our findings provide new insights into the synthesis and regulation of cuticular wax and valuable information for further mining of wax-related genes in citrus fruit.