Postharvest Chilling Injury Research Articles

A comprehensive meta-analysis exploring potential of GABA for postharvest chilling injury mitigation in horticultural produce

γ-Aminobutyric acid (GABA) exhibits anti-chilling properties and significantly mitigates chilling stress in horticultural products. While numerous studies have explored the effects of GABA on fruits, vegetables, and flowers, uncertainties persist regarding the optimal GABA application method, concentration, and dipping duration for suppressing chilling injury (CI) symptoms. To address this gap, we conducted a comprehensive global meta-analysis comprising 157 evaluations from 19 research papers to assess the impact of GABA on horticultural goods. Our study revealed an overall substantial reduction in CI (-51.1 %) with GABA application compared to the control group. Furthermore, all relevant markers associated with the GABA shunt pathway, oxidative stress, antioxidant system (enzymatic and non-enzymatic), and lipid oxidation with the CI mechanism exhibited significance, except for GABA-En. Interestingly, dipping emerged as a more effective GABA application. Regarding horticultural commodities, GABA was found more effective in fruits (-54.65 %) followed by vegetables (-45.46 %) and flowers (-31.30 %). The regression analysis revealed that GABA concentrations exceeding 1 mM, 5 mM, and 15 mM were ineffective in mitigating CI in flowers, vegetables, and fruits, respectively. These results highlight the efficacy of the GABA dipping and dipping time, as well as, the precise GABA concentration in alleviating CI in flowers, vegetables, and fruits.

Ectopic overexpression of ShCBF1 and SlCBF1 in tomato suggests an alternative view of fruit responses to chilling stress postharvest.

Postharvest chilling injury (PCI) is a physiological disorder that often impairs tomato fruit ripening; this reduces fruit quality and shelf-life, and even accelerates spoilage at low temperatures. The CBF gene family confers cold tolerance in Arabidopsis thaliana, and constitutive overexpression of CBF in tomato increases vegetative chilling tolerance, in part by retarding growth, but, whether CBF increases PCI tolerance in fruit is unknown. We hypothesized that CBF1 overexpression (OE) would be induced in the cold and increase resistance to PCI. We induced high levels of CBF1 in fruit undergoing postharvest chilling by cloning it from S. lycopersicum and S. habrochaites, using the stress-inducible RD29A promoter. Harvested fruit were cold-stored (2.5°C) for up to three weeks, then rewarmed at 20°C for three days. Transgene upregulation was triggered during cold storage from 8.6- to 28.6-fold in SlCBF1-OE, and between 3.1- to 8.3-fold in ShCBF1-OE fruit, but developmental abnormalities in the absence of cold induction were visible. Remarkably, transgenic fruit displayed worsening of PCI symptoms, i.e., failure to ripen after rewarming, comparatively higher susceptibility to decay relative to wild-type (WT) fruit, lower total soluble solids, and the accumulation of volatile compounds responsible for off-odors. These symptoms correlated with CBF1 overexpression levels. Transcriptomic analysis revealed that the ripening and biotic and abiotic stress responses were altered in the cold-stored transgenic fruit. Seedlings grown from 'chilled' and 'non-chilled' WT fruit, in addition to 'non-chilled' transgenic fruit were also exposed to 0°C to test their photosynthetic response to chilling injury. Chilled WT seedlings adjusted their photosynthetic rates to reduce oxidative damage; 'non-chilled' WT seedlings did not. Photosynthetic parameters between transgenic seedlings were similar at 0°C, but SlCBF1-OE showed more severe photoinhibition than ShCBF1-OE, mirroring phenotypic observations. These results suggest that 1) CBF1 overexpression accelerated fruit deterioration in response to cold storage, and 2) Chilling acclimation in fructus can increase chilling tolerance in seedling progeny of WT tomato.

Is ATP a signaling regulator for postharvest chilling tolerance in fruits?

Low-temperature storage is used to extend the shelf life of fruits, but prolonged storage at temperatures below tolerable levels may cause postharvest chilling injury (PCI) in sensitive commodities. This review aims to highlight adenosine triphosphate (ATP) activation and the interplay of extracellular ATP (eATP) and intracellular ATP (iATP) in fruits and to find out its significance in mitigating PCI. Various pathways, such as the Embden-Meyerhof-Parnas pathway, the tricarboxylic acid cycle, the pentose phosphate pathway, the γ-aminobutyric acid shunt pathway, and the cytochrome pathway, are studied critically to elucidate their role in continuous ATP supply and maintaining the membrane fluidity and integrity. This review summarizes the treatments helpful in modulating energy metabolism in fruit. Additionally, this work provides insights into the energy status in attenuating chilling tolerance. Moreover, it states the potential of nicotinamide adenine dinucleotide in mitigating PCI. Furthermore, it discusses the role of eATP and its receptor DORN1 in mitigating chilling stress.

Impact of chilling injury on global trade in tropical products

Abstract International trade in fresh products is dominated by products capable of long-term refrigerated storage, allowing marketing flexibility. For tropical products, postharvest chilling injury (PCI) is a barrier to long-term storage that limits trade by exacerbating the already-challenging requirements to minimise physical or biotic damage to products. In this review, the practical consequences of PCI in terms of international trade are described. Options for choosing to grow more resistant varieties or to predict the chilling injury risk of batches of fresh products can reduce overall losses by allowing better-informed sequencing of product marketing. Recent advances in technologies that reduce PCI risk or predict its severity, some of which can be used before harvest, are reviewed. At a more fundamental level, there is a growing number of excellent reviews on the potential for gene editing to alleviate postharvest chilling injury in tropical fruits and vegetables. Most are focused on research into ways to alleviate the consequences of chilling injury: i.e. oxidative stress arising from membrane dysfunction. A few recent reports show that reducing membrane dysfunction itself is possible, for example by increasing desaturation of membrane lipids, but this approach comes with a new and predictable problem: increased preharvest susceptibility to heat stress. Refined suggestions for strategies that could produce durable improvements in product quality hold the potential for significant increases in global trade with resulting economic benefits, particularly for developing countries.

Melatonin: A biomolecule for mitigating postharvest chilling injury in fruits and vegetables

AbstractThe best strategy to extend the shelf life of fresh horticultural produce is to keep it at a low temperature. However, storing fruits and vegetables at a temperature lower than their recommended storage temperature and above the freezing point for a prolonged time leads to the development of chilling injury (CI). Melatonin (MT) being a versatile biological signal has been reported to possess antioxidant properties that aid in mediating stress response and extending the postharvest storage life of horticultural crops. Among CI‐induced mechanisms, MT substantially reduces oxidative stress by elevating the reactive oxygen species scavenging and triggering the phenol accumulation in association with 2, 2‐diphenyl‐1 picryl hydrazyl scavenging activity. Besides, MT increases intracellular energy by maintaining a proper ratio of unsaturated to saturated fatty acid and improving cellular fluidity. Additionally, MT regulates arginine metabolism by maintaining the γ‐aminobutyric acid synthesis. Furthermore, MT encodes the mitogen‐activated protein kinases, and calcium‐dependent protein kinases cascade and acclimate to cold stress by activating C‐repeat binding factors and helps in maintaining postharvest quality. This review reports the recent progress of MT‐induced physiological, biochemical, and molecular mechanisms for enhancing chilling tolerance, which can elevate the marketability and earnings from postharvest horticultural crops.

1-Methylcyclopropene Alleviates Postharvest Chilling Injury of Snap Beans by Enhancing Antioxidant Defense System.

Chilling injury is a major disorder affecting the quality of tropical and subtropical vegetables during low temperature storage. Snap bean (Phaseolus vulgaris L.) is sensitive to chilling injury. The main purpose of the present study is to investigate the alleviating effects of 1-methylcyclopropene (1-MCP) on chilling injury of snap bean. In addition, the related mechanisms were also detected from the perspective of the changes of antioxidant defense system. Snap beans were exposed to different volume fractions of 1-MCP. After 24 h of treatment, snap beans were stored at 4 °C for up to 14 days. Chilling injury index, electrolyte leakage, titratable acidity and total soluble solids were determined. Contents of chlorophyll, ascorbic acid and malondialdehyde were assessed. The total antioxidant capacity, Fe(II) ion chelating capacity, scavenging capacities on free radicals and activities of antioxidant enzymes were detected. Total phenol content and activities of related metabolic enzymes were also determined. 1-MCP treatment reduced chilling injury index, electrolyte leakage rate and malondialdehyde content of snap beans. The amounts of total soluble solids, titratable acid, ascorbic acid and total chlorophyll in 1-MCP-treated snap beans were significantly higher than those of control. The snap beans treated with 1-MCP showed stronger total antioxidant capacity and metal chelating activity. The 1-MCP treatment enhanced scavenging effects of snap beans on superoxide, hydroxyl and 1,1-diphenyl-2-trinitrophenylhydrazine radicals. The activities of peroxidase, ascorbate peroxidase, superoxide dismutase and catalase in 1-MCP-treated group were higher than of control. The treatment also enhanced the accumulation of phenolic compounds in snap beans by regulating the activities of phenol-metabolizing enzymes such as shikimate dehydrogenase, phenylalanine ammonia lyase enzyme, cinnamic acid 4-hydroxylase and polyphenol oxidase. In conclusion, with the mechanism that involves the activation of enzymatic and non-enzymatic antioxidant systems, 1-MCP has the ability to avoid chilling injury of snap bean. This study gives insights into whether 1-MCP can regulate postharvest cold resistance in vegetables by enhancing the enzymatic antioxidant system and inducing the accumulation of non-enzymatic antioxidants. Considering the results, 1-MCP treatment could be an effective method to alleviate postharvest chilling injury of snap beans during low temperature storage.

Postharvest Treatment with Abscisic Acid Alleviates Chilling Injury in Zucchini Fruit by Regulating Phenolic Metabolism and Non-Enzymatic Antioxidant System.

Reports show that phytohormone abscisic acid (ABA) is involved in reducing zucchini postharvest chilling injury. During the storage of harvested fruit at low temperatures, chilling injury symptoms were associated with cell damage through the production of reactive oxygen species. In this work, we have studied the importance of different non-enzymatic antioxidants on tolerance to cold stress in zucchini fruit treated with ABA. The application of ABA increases the antioxidant capacity of zucchini fruit during storage through the accumulation of ascorbate, carotenoids and polyphenolic compounds. The quantification of specific phenols was performed by UPLC/MS-MS, observing that exogenous ABA mainly activated the production of flavonoids. The rise in all these non-enzymatic antioxidants due to ABA correlates with a reduction in oxidative stress in treated fruit during cold stress. The results showed that the ABA mainly induces antioxidant metabolism during the first day of exposure to low temperatures, and this response is key to avoiding the occurrence of chilling injury. This work suggests an important protective role of non-enzymatic antioxidants and polyphenolic metabolism in the prevention of chilling injury in zucchini fruit.

Non-thermal effects of microwave irradiation alleviates postharvest chilling injury of peach fruit by retarding phenolic accumulation and enhancing membrane stability

Postharvest chilling injury (CI) of fruit, including peaches, is a huge challenge to horticultural product preservation. Microwave irradiation can be used as a physiological regulator due to the thermal effects; however, its non-thermal effects on the CI of postharvest fruit remain unclear. Thus, the physiological attributes and metabolisms involving phenolics, fatty acids, and sugars were compared between ‘Zhongtao No.9’ peaches treated with microwave irradiation at 45.5 W for different durations and control. Microwave treatment especially at 45.5 W for 7 min without inducing thermal effects could significantly inhibit internal browning caused by CI, concomitant with reduced total phenolic content. Moreover, the maintenance of membrane stability was indicated by a boosted double bond index, which may be attributed to the inhibition of membrane lipid degradation, and sucrose accumulation. In summary, the non-thermal effects of microwave irradiation contribute to CI alleviation through restraining phenolic content and maintaining membrane stability in peach fruit.

Radiação e condições de temperatura pré colheita determinam a suscetibilidade dos frutos do tomate a danos causados pelo frio pós-colheita

ABSTRACT The aim of this work was to improve the understanding about the relationship between solar radiation and temperature exposure during crop and tomato fruit susceptibility to postharvest chilling injury. Two preharvest treatments were applied: direct sunlight exposed plants (Ex) and shaded plants (Sh). After harvest, fruit were stored at 10⁰C and 4⁰C for ten days. Then, fruit were removed from the chambers and stored at room temperature for four days. Several determinations were carried out: total mineral and calcium content, fruit quality and postharvest parameters, ions leakage and thiobarbituric acid reactive species content and chilling injury index (CII). Ex fruit had higher values of chilling injury index than the Sh fruit, and at the same time, fruit under 4⁰C storage treatment presented a more marked damage than those stored at 10⁰C, demonstrating that accumulated radiation in the field, as a result of a higher solar radiation exposure, is a critical factor affecting postharvest chilling injury susceptibility. The lower calcium content in the Ex fruit could be one of the causes of their response to chilling.

Identification of COR413 Gene Family in Peach and Its Expression in Low Temperature and LTC Treatment at Postharvest

Peach were susceptible to chilling injury during low temperature (0 o C) storage at postharvest, and LTC (Low temperature conditioning) treatment could reduce chilling injury such as of H 2 O 2  production and fruit browning. In order to study the function of peach COR413  in the regulation of postharvest chilling injury in peach ‘Beijing No. 9’, four COR413 gene family members were identified based on the peach genome database, namely  PpCOR1 ~ PpCOR4 . Phylogenetic analysis showed that the four PpCORs could be clustered into two subfamilies. PpCOR1 ~ PpCOR3  belonged to the first subfamily, and most of the members in this subfamily were located in plasma membrane. PpCOR4  belongs to the second subfamily, and its members are mainly located in thylakoid membrane. The cis-acting elements analysis of PpCORs  promoter showed that PpCOR3  contained abundant abiotic stress responsive and hormone responsive elements such as jasmonate and abscisic acid. The results of gene expression showed that PpCOR3 was induced by low temperature while LTC treatment could repress the induction of PpCOR3  by low temperature. Interestingly, the expression of PpCOR3  was positively correlated with the change of H 2 O 2  content in peach, which indicated that PpCOR 3 was involved in the regulation of postharvest chilling injury in peach fruit. This result provides a theoretical basis for the study of postharvest storage and quality maintenance of peach fruit as well as the breeding of cold resistant peach varieties.

Genome-wide identification of the CDPK gene family reveals the CDPK-RBOH pathway potential involved in improving chilling tolerance in peach fruit

Calcium-dependent protein kinase (CDPK), as an essential calcium receptor, plays a major role in the perception and decoding of intracellular calcium signaling in plant development and stress responses. Here, the CDPK gene family was analyzed at the genome-wide level in peach. This study identified 17 PpCDPK gene members from the peach genome, and systematically investigated phylogenetic relationships, conserved motifs, exon-intron structures, chromosome distribution, and cis-acting elements of each PpCDPK gene using bioinformatics. Furthermore, the expression levels of most PpCDPK genes were significantly changed under the CaCl2, EBR, GB, cold shock, hot water treatments, and various temperatures in the cold storage of peach fruits. RNA-seq data showed that PpCDPK2, PpCDPK7, PpCDPK10, and PpCDPK13 were related to postharvest chilling stress in peach. The interaction network of PpCDPK7 protein showed that the interaction between PpCDPK7 and PpRBOH may be the intersectional point of Ca2+ and ROS signal transmission during cold storage of peach fruits. These systematic analyses are helpful to further characterize the regulation of PpCDPKs and CDPK-RBOH mediated signal cascades in postharvest chilling injury in peach fruit.

Alleviation of postharvest chilling injury in sweet pepper using Salicylic acid foliar spraying incorporated with caraway oil coating under cold storage.

The decrease in the postharvest quality of sweet peppers in terms of the physiological disorders resulting from cold storage (<7–10°C) results in the significant economic losses. The ability of pre-harvest foliar spraying of Salicylic acid (SA) (1.5 and 3 mM) and the postharvest caraway (Carum carvi) oil coating (0.3% and 0.6%) on chilling injury (CI) and the quality of stored sweet pepper at 4 ± 2°C for 60 d followed by an additional 2 d at 20°C were investigated. The antifungal activity of caraway oil (0.15%, 0.3%, and 0.6%) on Botrytis cinerea mycelia in in vitro showed that the maximum percentage of inhibition was equal to 95% in the medium with 0.6% of this oil. The CI of sweet pepper was significantly reduced by increasing SA, and caraway oil concentrations compared to the control, especially the lowest CI (14.36%), were obtained at 3 mM SA and 0.6% caraway oil treatment. The results showed a significant delay in the changes of weight loss (79.43%), firmness (30%), pH (6%), total soluble solids (TSS) (17%), titratable acidity (TA) (32%), and color surface characteristics and capsaicin content (5%) compared to control fruits at 3 mM SA and 0.6% caraway oil concentrations. Results indicated that the decrease in CI was related to a decrease in electrolyte leakage, malondialdehyde (MDA) content, total phenolic production, decay incidence, and an increase in the activity of antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD). Thus, the incorporation of SA (3 mM) and caraway oil (0.6%) to reduce the CI of stored sweet pepper at low temperature can be considered a practical solution to improve the quality and marketability of this product.

Low temperature conditioning improves American eggplant (Solanum melongena L.) storage compatibility

ABSTRACT Low-temperature conditioning (LTC) has been reported to effectively control post-harvest chilling injury (CI). Conspicuously, it has not been widely adopted by the industry. This is in part related to an incomplete understanding of the factors governing the treatment's efficacy and consistency along genotypes and maturities. Herein, we evaluated the effect of fruit type (striped and purple) and harvest maturity (baby and large) on the effectiveness of LTC (10°C for 2 days) to control eggplant CI. Purple eggplants showed a strong increase in chilling susceptibility between the baby and large maturity stages. In contrast, striped fruit evidenced no major changes in chilling susceptibility along maturation. Susceptible purple large eggplants benefited far more from LTC than baby fruit. Prestorage LTC not only controlled surface scaled development but also decreased pulp softening and browning. In addition, it substantially improved phenolic antioxidants, anthocyanin, and chlorogenic acid retention during storage at 4°C. Overall, results show, for the first time, that the efficacy of LTC in eggplant is deeply affected by the fruit's genotype and maturity. Low-temperature conditioning may be a valuable tool to improve the storage compatibility of commercial eggplant batches having different chilling injury sensitivity.

Knockdown of Sly-miR164a by short tandem target mimic (STTM) enhanced postharvest chilling tolerance of tomato fruit under low temperature storage

The function of Sly-miR164a on postharvest chilling tolerance of tomato fruit was investigated. In the present results, compared with the wild type (WT) fruit in the red and green maturity stage, overexpression of Sly-miR164a (miR164a-OE) promoted postharvest chilling injury (CI) of tomato fruit. Compared with the WT and miR164a-OE fruit, the postharvest CI index of tomato fruit of knockdown of Sly-miR164a (STTM 164a) by short tandem target mimic (STTM) was decreased, the content of hydrogen peroxide (H2O2) was reduced, and the fruit firmness was increased. In STTM 164a fruit, the relative expression levels of NAC1, NAM3, GOB, CBF1, COR, NCDE1, and NCDE2 were increased, the ABA content was enhanced, and the relative expression levels of CYP707A1 and CYP707A2 were decreased. The present study indicated that the knockdown of Sly-miR164a enhanced the postharvest chilling tolerance of tomato fruit during low temperature storage, and provided valuable information for genetically modifying miR164a and controlling postharvest CI of fruit.

Transcriptome and genome analysis to identify C2H2 genes participating in low-temperature conditioning-alleviated postharvest chilling injury of peach fruit

Abstract Objectives This work intended to identify candidate C2H2 genes participating in low-temperature conditioning (LTC)-alleviated postharvest chilling injury of peach fruit. Materials and Methods For LTC treatment, fruit were pre-stored at 10 °C for 5 d and then transferred to 0 °C storage. Fruit firmness was measured by a hardness tester. H2O2 content was determined by luminosity measurement model using a multifunctional enzyme labeler. Identification of C2H2 family members was performed by HMMSCAN according to peach genome. The cis-acting element of gene promoters was analyzed using the Plant CARE website. Weighted gene coexpression network analysis (WGCNA) was performed by the WGCNA package in the BMK Cloud platform. Results LTC treatment decreased flesh browning rate and H2O2 production of ‘Beijing No. 9’ peach. Transcription factor identification of differentially expressed genes in 0 °C and the LTC treatment indicated that peach C2H2 participated in the regulation of chilling injury. A total of 47 C2H2 genes were identified based on peach genome. Real-time quantitative polymerase chain reaction (qRT-PCR), phylogenetic analysis and promoter cis-acting element analysis revealed that ZFP21 was involved in the regulation of LTC-alleviated chilling injury in peach. WGCNA and dual luciferase assay suggested that ZFP21 participated in LTC-alleviated chilling injury by downregulating the expression of reactive oxygen species-related genes Rboh. Conclusions Our investigation, based on genome and RNA-seq, revealed that ZFP21 was involved in LTC treatment-alleviated chilling injury of peach fruit. This work is useful for the identification of peach cold tolerance-related genes and the study of C2H2 family in peach.

Integrative transcriptomic and metabolomic alterations unravel the effect of melatonin on mitigating postharvest chilling injury upon plum (cv.Friar) fruit

Plum fruit often suffer severe chilling injury (CI) during storage. Plum (Prunus salicina Lindl. cv. Friar) fruit were treated with melatonin at various concentrations and stored at 0 ℃ for 6 w and additional 3 d of shelf-life at 23 ℃. Observations revealed that the treatment with 1.0 mmol L−1 melatonin mitigated CI of the fruit by reducing flesh-reddening and ‘ethylene burst’. The melatonin treatment also suppressed fruit softening and maintained energy status. Results from UPLC-MS assay showed that several individual phenolic compounds involved in the biosynthesis of flavonoids and anthocyanins, especially, the red pigment of cyanidin-3-O-glucoside, were stimulated by cold stress and its removal, but the stimulation was effectively inhibited by melatonin treatment, and thereby flesh-reddening was alleviated. Results from RNA-sequencing unraveled that cold stress and its removal altered transcriptomic profiling of the plum fruit, but the melatonin treatment hindered the transcription of genes related to the anthocyanin biosynthesis. Correlation analysis indicated that seven MYBs were positively correlated with anthocyanin biosynthesis, which were generally down-regulated in the melatonin-treated plums. The integrative analysis of transcriptomic and metabolic alterations revealed differentially but delicately coordinated inhibition of postharvest physiological metabolisms of ‘Friar’ plums by melatonin in response to cold stress.

Alleviation of Postharvest Chilling Injury of Carambola Fruit by γ-aminobutyric Acid: Physiological, Biochemical, and Structural Characterization.

Chilling injury is a physiological disorder affecting the quality of carambola fruit. In the present study, the effect of exogenous γ-aminobutyric acid (GABA) on CI development in carambola fruit during storage at 4°C for 15 days was investigated. The results showed that 2.5-mM GABA reduced CI index, maintained pericarp lightness, and decreased the electrolyte leakage (EL) and malondialdehyde content (MDA) while increased the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) enzyme activities. Endogenous GABA content was significantly higher in the treated fruit than in the control fruit during the whole storage. Besides, the treatment promoted the accumulation of proline and ascorbic acid (AsA) under chilling stress. Compared to the control, GABA-treated fruit exhibited a higher activity of phenylalanine ammonia-lyase (PAL) and total phenolic compounds, and a lower activity of polyphenol oxidase (PPO). In addition, the Safranin O/fast green staining revealed via microscopic images that the GABA treatment reduced the cell walls degradation of carambola fruit. Moreover, the results displayed a lower activity of phospholipase D (PLD) and lipoxygenase (LOX) enzymes, which coincided with a higher content of oleic acid (C18:1), linoleic acid (C18:2n6), and α-linolenic acid (C18:3n3) after 15 days of treatment, leading to the maintenance of the integrity and prevention of the membrane of the rapid softening of carambola fruit. The findings of the present work showed particularly new insights into the crosstalk between GABA and fatty acids. GABA might preserve the pericarp of carambola fruit by increasing the content of the unsaturated fatty acid (UFA) γ-linolenic acid and reducing the saturated fatty acid (SFA) such as caproic acid (C6:0), caprylic acid (C8:0), myristic acid (C14:0), and palmitic acid (C16:0) progressively. GABA can be used as an appropriate postharvest technology for improving the quality of carambola fruit during low-temperature storage.

DNA hypermethylation associated with the development of temperature-dependent postharvest chilling injury in peach fruit

Peach fruit is often subjected to postharvest chilling injury (CI) during long-term cold storage and the degree of CI is related to the storage temperature. Analysis of the data on softening, ethylene production and internal browning (IB) showed that CI occurred in fruit stored at or below 12 °C. Impairment of ethylene production and softening was greater in fruit stored at 0 and 5 °C and was consistent with lower expression of related critical genes. Lower malondialdehyde and hydrogen peroxide contents and enhanced hydroxyl radical contents were observed in fruit stored at 0 and 5 °C. These changes were associated with higher transcript levels of polyphenol oxidases and peroxidase, but lower expression levels of lipoxygenase, superoxide dismutase and catalase. To investigate whether DNA methylation is involved in the CI development in peach fruit, single-base resolution DNA methylome and transcriptome analysis was carried out. The DNA methylation level was higher in CI fruit and a close positive correlation was observed between the methylation level and IB index. Furthermore, for most genes involved in softening, ethylene biosynthesis and signal transduction, IB and reactive oxygen species metabolism, the expression level was found to be well correlated with low temperature-induced DNA hyper- or hypo-methylation in promoter, genebody or downstream regions. It was concluded that changes in DNA methylation in different genomic regions regulate CI associated gene expression and contribute to the development of temperature-dependent CI in postharvest peach fruit.

Accumulation of tocopherols and transcriptional regulation of their biosynthesis during cold storage of mandarin fruit

Tocopherols are plant-derived isoprenoids with potent antioxidant activity, which have been implicated in the tolerance of plants to different stresses. However, tocopherol accumulation and biosynthesis in fruit, and their potential implication in postharvest chilling injury (CI), has been scarcely studied. Therefore, in this work, we have investigated tocopherol accumulation and biosynthesis in the peel of mandarin fruit of three cultivars with contrasting susceptibility to CI during storage at 2 °C (‘Fortune’>‘Nova’> ‘Nadorcott’). α- and γ-tocopherol were the isoforms detected in the flavedo of the fruit, and a direct relationship between tocopherols content and CI-tolerance was found, since CI-tolerant fruit accumulated the highest tocopherol content whereas CI-sensitive fruit the lowest. Moreover, the transcriptional profiling of 14 genes related to the specific steps of tocopherol biosynthesis, and to their precursor’s synthesis, were analyzed. Upstream genes DXS1 and DXS2 (1-deoxy-d-xylulose-5-phosphate synthase) and GGDR (geranylgeranyl diphosphate reductase), involved in the supply of phytyl pyrophosphate, and the VTE3 (2-methyl-6-phytyl-1,4-benzoquinol methyltransferase) isoforms appear to be key for the differences in total tocopherol content among the cultivars at harvest. During cold storage, most genes involved in the precursors supply were up-regulated, whereas genes of the tocopherol-core pathway were in general repressed. Changes in VTE4 during cold storage may account for the differences in γ-tocopherol among cultivars. Collectively, results suggest that the concentration of tocopherols at harvest may play a function in the natural tolerance of mandarin fruit to CI, and that changes in the expression of genes during storage appear to be cold-regulated responses, rather than involved in CI tolerance.

Phenylalanine Alleviates Postharvest Chilling Injury of Plum Fruit by Modulating Antioxidant System and Enhancing the Accumulation of Phenolic Compound

SUMMARYResearch backgroundLow temperature storage causes chilling injury in plum (Prunus domestica L.) fruits. Consequently, any treatments with beneficial effects against these symptoms would achieve attention. For this purpose, phenylalanine treatments were applied on ‘Stanley’ plum fruits. The main purpose of the present study is to investigate the influence of the exogenous application of phenylalanine on fruit quality, chilling tolerance, and antioxidant capacity of ‘Stanley’ plums during cold storage.Experimental approachPhenylalanine at different concentrations was applied on ‘Stanley’ plums. Following phenylalanine application, plums were cold stored. Chilling injury, antioxidant capacity, electrolyte leakage, malondialdehyde, proline and internal contents of anthocyanin, flavonoids, phenols, ascorbic acid and some antioxidant enzymes were assessed.Results and conclusionsPhenylalanine treatment significantly alleviated chilling injury in plum fruits by enhancing antioxidant capacity and increasing the activity of phenylalanine ammonia lyase enzyme (PAL). Phenylalanine-treated fruits had higher mass fractions of ascorbic acid, anthocyanins, flavonoids and phenols, as well as a higher total antioxidant activity than the control fruits during low temperature storage. Phenylalanine at 7.5 mM was the most effective treatment in enhancing the activity of PAL, the accumulation of phenolic compounds and in reducing the severity of chilling injury. Treatments delayed mass loss and maintained fruit firmness. In addition, the application of 7.5 mM phenylalanine improved the activities of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase), decreased the accumulation of hydrogen peroxide, and increased the endogenous content of proline. Moreover, phenylalanine maintained membrane integrity, manifested by a reduced electrolyte leakage and malondialdehyde accumulation.Novelty and scientific contributionIn the current study, chilling injury had a positive correlation with the activities of PAL and antioxidant enzymes. However, negative correlations were observed between the chilling injury and ascorbic acid mass fraction, and antioxidant capacity. Considering the results, phenylalanine treatment could be an encouraging approach to alleviate the severity of chilling injury and thus preserve nutritional quality of plums during low temperature storage.