Chitosan treatment reduces softening and chilling injury in cold-stored Hami melon by regulating starch and sucrose metabolism

Cold-stored Hami melon is susceptible to chilling injury, resulting in quality deterioration and reduced sales. Pre-storage treatment with chitosan reduces fruit softening and chilling injury in melon; however, the underlying mechanism remains unclear. In this study, Gold Queen Hami melons were treated with 1.5% chitosan solution for 10 min before cold storage at 3°C and then the effect of chitosan was examined on fruit firmness, weight loss, chilling injury, soluble solid content (SSC), pectin, and soluble sugar contents of melon fruit. Also, the enzyme activities and gene expressions related to fruit softening and starch and sucrose metabolism were investigated. Chitosan treatment reduced the fruit softening and chilling injury, maintained the high levels of starch and sucrose contents, and regulated the enzyme activities and gene expressions related to starch and sucrose metabolism. Fruit firmness was significantly positively correlated with sucrose and starch contents. Altogether, we uncovered the potential mechanism of chitosan coating mitigating melon softening and chilling injury through the regulation of starch and sucrose metabolism.

The Regulatory Mechanisms and Control Technologies of Chilling Injury and Fungal Diseases of Postharvest Loquat Fruit

Loquat is a popular fruit widely cultivated all over the world. It is rich in minerals and carotenoids and has high commercial value. At room temperature, loquat fruit is impressionable to water and nutritional losses, physical damage, and microbial decay, resulting in a short postharvest life. Low-temperature storage is routinely used to prolong the shelf life of loquat fruit; however, cold storage can also lead to lignification of flesh tissue, which is one of the major symptoms of chilling injury (CI), reducing the quality and economic value of the fruit. In addition, fruit decay caused by microbial infection is another important reason for postharvest losses of loquat. To reduce quality deterioration and optimize the postharvest storage strategies of loquat fruit, considerable progress has been made in the physiological and molecular biological studies of CI, microbial decay, and preservation technologies of loquat fruit during the postharvest phase in recent decades. This review summarizes the current research progress and provides a reference for the improvement of loquat fruit quality.

γ-Aminobutyric acid treatment induced chilling tolerance in postharvest peach fruit by upregulating ascorbic acid and glutathione contents at the molecular level

Peach fruit was treated with 5 mM γ-aminobutyric acid (GABA) to further investigate the mechanism by which GABA induced chilling tolerance. Here, we found that GABA not only inhibited the occurrence of chilling injury in peach fruit during cold storage but also maintained fruit quality. Most of the ascorbic acid (AsA) and glutathione (GSH) biosynthetic genes were up-regulated by GABA treatment, and their levels were increased accordingly, thus reducing chilling damage in treated peaches. Meanwhile, the increased transcript of genes in the AsA-GSH cycle by GABA treatment was also related to the induced tolerance against chilling. GABA treatment also increased the expression levels of several candidate ERF transcription factors involved in AsA and GSH biosynthesis. In conclusion, our study found that GABA reduced chilling injury in peach fruit during cold storage due to the higher AsA and GSH contents by positively regulating their modifying genes and candidate transcription factors.

Quality of Goji Berry Fruit (Lycium barbarum L.) Stored at Different Temperatures

Goji berries are widely known for their outstanding nutritional and medicinal properties; they are usually found in the market as dried fruit or as juice because the fruit has a short shelf-life, and little information is available about its postharvest behavior at low temperatures. This study aimed to determine the storage performance of goji berry fruit by evaluating physicochemical, and sensorial attributes during storage at three different temperatures (0, 5, and 7 °C) for 12 days in a range that has not been extensively studied before. In addition, fruit respiration and ethylene production rates were also measured at the three temperatures. Fruit stored at 0 °C showed the lowest respiration rate and ethylene production (5.8 mg CO₂ kg^-1h^-1 and 0.7 µg C₂H₄ kg^-1h^-1, respectively); however, at this temperature, the incidence and severity of pitting and electrolytic leakage were the highest. In contrast, 5 °C was found to be the best storage temperature for goji berry fruit; the fruit appeared fresh and healthy, had the highest scores during sensory analysis with an acceptable general impression, and had the lowest amount of damage attributable to chilling injury, with 17.1% fruit presenting with shriveling, 12.5% pitting, 6.7% mold, and 35% electrolytic leakage on day 9 of storage. Storage of goji berries at 7 °C resulted in the lowest marketability and the highest incidence of decay. Significant differences were also found in the phytochemical attributes, vitamin C content, soluble solid content (SSC), titratable acidity (TA), SSC/TA ratio, total polyphenol content, 2,2-diphenylpicrylhydrazy (DPPH), and anthocyanin content. This study revealed that a storage temperature of 5 °C for 9 days is recommended to maintain the quality of fresh goji berry. Thus, broadening the existing knowledge of the postharvest behavior of fresh goji berries; our results can help improve the commercial life of goji berries and ensure high-quality attributes throughout distribution.

Handling, Reproducing and Cryopreserving Five European Sea Urchins (Echinodermata, Klein, 1778) for Biodiversity Conservation Purposes

In this work, five local sea urchin species found in European waters were studied. Four were regular species: Sphaerechinus granularis, Psammechinus miliaris, Echinus esculentus (Linnaeus, 1758) and the edible sea urchin Paracentrotus lividus; and one was an irregular species, Echinocardium cordatum. These five species of sea urchins have been studied regarding their fertility, toxicity of cryoprotecting agents, cryopreservation of different cell types and chilling injury. The baseline fertility is similar in P. lividus, P. miliaris and S. granularis. Nonetheless, the sperm:egg ratio, contact time and development of the fertilization envelope would need to be studied further on a case-by-case basis. Sperm can be maintained inactively in the gonad (4 °C), and oocytes also maintain quality in sea water (4 °C), even after 72 h. Sperm was cryopreserved for four species with some post-thaw intra specific variability, and embryo cryopreservation was only possible for S. granularis. Overall, this study provided a wider vision of the biology and reproduction of these species that will help us develop tools for their biodiversity conservation through cryopreservation.

A Synergistic Effect Based on the Combination of Melatonin with 1-Methylcyclopropene as a New Strategy to Increase Chilling Tolerance and General Quality in Zucchini Fruit

Zucchini fruit are highly sensitive to low temperatures leading to significant peel depressions, increasing weight loss and making them impossible to be commercialized. In this study the effect on the reduction of chilling injury (CI) assaying different postharvest treatments to cv. Cronos was evaluated. We have compared the application of substances such as 1-methylcyclopropene (1-MCP) with the application of a natural origin compound as melatonin (MT), both with demonstrated activity against CI in different vegetal products. The effects of MT (1 mM) by dipping treatment of 1 h and 1-MCP (2400 ppb) have been evaluated on zucchini fruit during 15 days of storage at 4 °C plus 2 days at 20 °C. Treatments applied independently improved some fruit quality parameters in comparison with control fruit but were not able to manage CI even though they mitigated the impact on several parameters. However, when these two separated strategies were combined, zucchini cold tolerance increased with a synergic trend. This synergic effect affected in general all parameters but specially CI, being also the only lot in which zucchini fruit were most effectively preserved. This is the first evidence in which a clear positive effect on zucchini chilling tolerance has been obtained combining these two different strategies. In this sense, the combined effect of 1-MCP and MT could be a suitable tool to reach high quality standards and increasing shelf life under suboptimal temperatures.

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.

Advances in chilling injury of postharvest fruit and vegetable: Extracellular ATP aspects

Due to the global use of cold chain, the development of postharvest technology to reduce chilling injury (CI) in postharvest fruits and vegetables during storage and transport is needed urgently. Considerable evidence shows that maintaining intracellular adenosine triphosphate (iATP) in harvested fruits and vegetables is beneficial to inhibiting CI occurrence. Extracellular ATP (eATP) is a damage-associated signal molecule and plays an important role in CI of postharvest fruits and vegetables through its receptor and subsequent signal transduction under low-temperature stress. The development of new aptasensors for the simultaneous determination of eATP level allows for better understanding of the roles of eATP in a myriad of responses mediated by low-temperature stress in relation to the chilling tolerance of postharvest fruits and vegetables. The multiple biological functions of eATP and its receptors in postharvest fruits and vegetables were attributed to interactions with reactive oxygen species (ROS) and nitric oxide (NO) in coordination with phytohormones and other signaling molecules via downstream physiological activities. The complicated interconnection among eATP in relation to its receptors, eATP/iATP homeostasis, ROS, NO, and heat shock proteins triggered by eATP recognition has been emphasized. This paper reviews recent advances in the beneficial effects of energy handling, outlines the production and homeostasis of eATP, discusses the possible mechanism of eATP and its receptors in chilling tolerance, and provides future research directions for CI in postharvest fruits and vegetables during low-temperature storage.

Physiological and Transcriptome Analyses of CaCl2 Treatment to Alleviate Chilling Injury in Pineapple

The post-harvest ripening of pineapples can be effectively postponed by refrigerated storage. Nevertheless, internal browning (IB) frequently appears in pineapples after refrigerated storage during the course of the shelf life at room temperature, which is known as chilling injury (CI). In this study, the chilling injury of pineapple fruit was induced by a low temperature (6 °C) and transferred to normal-temperature storage; the best concentration of 50 μmol/L of CaCl₂ was selected by the IB appearance and electrical conductivity. Fruit quality, reactive oxygen species (ROS), antioxidants, and transcription factors were investigated. The physiological data results indicated that pineapples treated with 50 μmol/L of CaCl₂ maintained fruit quality, decreased reactive oxygen species (ROS), and enhanced the antioxidant activity of fruits, alleviating internal browning (IB) symptoms in pineapple fruit. The expressions of related genes were also consistent with the physiological changes by the transcriptome data analysis. In addition, we focused on some related metabolic pathways, including phenylpropanoid biosynthesis, MAPK pathway, plant hormone, plant-pathogen interaction, tricarboxylic acid cycle (TAC), and fatty acid biosynthesis. We performed integrative analyses of transcriptome data combined with a series of physiology and experimental analyses on the internal browning of pineapples, which will be of great significance to extending the shelf life of pineapples through molecular biology in the future.

The CaMYB340 transcription factor induces chilling injury in post-harvest bell pepper by inhibiting fatty acid desaturation

Bell pepper (Capsicum annuum L.) is a tradable and desirable crop; however, its perishable nature requires low-temperature handling. Paradoxically, cold causes chilling injury (CI) and post-harvest waste. Current knowledge about CI in pepper is limited. The mechanism of CI is multi-faceted; therefore, we focused on fatty acid (FA) desaturation. We identified an upstream nuclear transcription factor (TF), CaMYB340, belonging to the R2R3 MYB subfamily, that negatively regulates FA desaturation and CaCBF3 expression and whose gene and protein expression is induced by low temperature (4°C). Specifically, McrBC treatment and bisulfite sequencing PCR indicate that exposure to cold triggers DNA methylation on one of the CHH sites in the CaMYB340 promoter. This epigenetic event at least partly contributes to the upregulation of CaMYB340 transcript levels. Increased expression of CaMYB340 results in the formation of protein complexes with CabHLH93 and CaMYB1R1, which in turn downregulate the expression of downstream genes. For peppers held at low temperature, transient overexpression of CaMYB340 reduced unsaturated FA content and membrane fluidity, resulting in cold-induced poor peel texture. Transient CaMYB340 silencing increased FA desaturation and lowered electrolyte leakage, enhancing cold tolerance in CaMYB340 knockdown fruits. Overall, these results underscore the intricacy of transcriptional networks in plants and highlight the role of CaMYB340 in CI occurrence in pepper fruits.

Hydrogen Sulfide Mitigates Chilling Injury of Postharvest Banana Fruits by Regulating γ-Aminobutyric Acid Shunt Pathway and Ascorbate-Glutathione Cycle

This study aimed to determine the effect of hydrogen sulfide on chilling injury (CI) of banana (Musa spp.) during cold storage (7°C). It was observed that hydrogen sulfide application (2 mmol L^-1) markedly reduced the CI index and showed significantly higher chlorophyll contents, along with suppressed chlorophyll peroxidase and chlorophyllase enzyme activity. The treated banana fruits exhibited substantially higher peel lightness (L*), along with significantly a lower browning degree and soluble quinone content. The treated bananas had substantially a higher endogenous hydrogen sulfide content and higher activity of its biosynthesis-associated enzymes such as D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD), along with significantly lower ion leakage, lipid peroxidation, hydrogen peroxide, and superoxide anion concentrations. Hydrogen sulfide-treated banana fruits showed an increased proline content and proline metabolism-associated enzymes including ornithine aminotransferase (OAT), Δ¹-pyrroline-5-carboxylate synthetase (P5CS), and proline dehydrogenase (PDH). In the same way, hydrogen sulfide-fumigated banana fruits accumulated higher endogenous γ-aminobutyric acid (GABA) due to enhanced activity of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) enzymes. The hydrogen sulfide-treated fruits exhibited higher total phenolics owing to lower polyphenol oxidase (PPO) and peroxidase (POD) activity and stimulated phenylalanine ammonia lyase (PAL). The treated banana exhibited higher ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and superoxide dismutase (SOD) activity, along with higher glutathione (GSH) and ascorbic acid (AsA) concentrations and a significantly lower dehydroascorbic acid (DHA) content. In conclusion, hydrogen sulfide treatment could be utilized for CI alleviation of banana fruits during cold storage.

Abnormal chilling injury of postharvest papaya is associated with the antioxidant response

Generally, the lower the temperature and/or the longer the duration of low temperature, the more serious chilling injury (CI) symptom appears in fruit. However, our previous study showed that the higher storage temperature (6°C) resulted in a more serious CI in papaya fruit compared to that stored at 1°C, which could be viewed as an abnormal CI behavior. This study investigated the antioxidant responses that existed in abnormal CI behavior of papaya fruit. Compared to 6°C, antioxidant enzyme activities of papaya fruit which was stored at 1°C were maintained at a higher level while the circulatory metabolism of the ascorbate-glutathione cycle (AsA-GSH) was more vigorous in papaya fruit, as indicated by higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR) activities and higher AsA and GSH levels, which could reduce the superoxide anion (·O₂ ^- ) production rate and the hydrogen peroxide (H₂ O₂ ) content. Suppressed reactive oxygen species (ROS) generation in papaya fruit at 1°C resulted in reduced membrane permeability and malondialdehyde (MDA) accumulation when compared to that at 6°C, thus the development of CI was restricted during storage at 1°C. This study deepened the understanding of differential antioxidant responses during cold storage at 1°C and 6°C in papaya fruit and provided a theoretical basis for further study on the mechanism of the abnormal CI behavior in papaya fruit. PRACTICAL APPLICATIONS: Low-temperature storage is one of the most effective methods to preserve fruit and vegetable products. While, inappropriate low temperature could induce CI, and the damage caused by CI is often more serious than estimated. Therefore, it is necessary to study the physiological and biochemical characteristics of different postharvest fruits and vegetables to prolong storage period, improve storage quality and reduce the loss of products. This study analyzed the antioxidant reaction in abnormal CI behavior of papaya, which could contribute to the further study on the mechanism of CI in papaya fruit and provide theoretical basis for the development of preservation technology of papaya fruit.

Cell wall stabilization and calcium absorption on mango fruit treated with a quarantine hot water treatment combined with calcium salts and stored at chilling temperature

Hot water treatment (HT) induces chilling injury (CI) tolerance in mango, but prolonged exposure to HT causes softening. In this sense, calcium salts stabilize the cell wall. Nevertheless, there is little information on the effect of HT combined with calcium salts (HT-Ca) on calcium absorption and cell wall stability during storage of mango at CI temperature. We evaluated the effect of quarantine HT in combination with calcium chloride (CaCl₂ ), calcium citrate (CaCit), or calcium lactate (CaLac) on calcium absorption, CI tolerance, and cell wall stabilization. HT and HT-CaCl₂ had the lowest CI development. HT increased firmness loss and electrolyte leakage, and HT-Ca counteracted this effect. Overall, HT-Ca treatments had a similar effect on the cell wall degrading enzymes. HT-CaCl₂ was the best treatment and did not present alterations on the epicuticular wax as observed on HT. HT-CaCl₂ is a useful technology to stabilize cell wall and preserve mango during chilling storage. PRACTICAL APPLICATIONS: The addition of calcium salts in an established hot water quarantine procedure for mango exportation represents a viable alternative to counteract the negative effects of this thermal treatment upon cell microstructure, maintaining its positive effect of tolerance to chilling injury. In this sense, mango producers and packers can use a HT-CaCl₂ treatment to reduce the presence of chilling injury and extent the fruit shelf life and improve its commercialization. Furthermore, technical and infrastructure changes are not necessary for the packaging chain.

Eggplant grafting on a cold-tolerant rootstock reduces fruit chilling susceptibility and improves antioxidant stability during storage

BACKGROUND

Vegetable grafting has been increasingly evaluated to improve preharvest tolerance to biotic and abiotic stresses. However, very few studies have identified rootstock-scion combinations able to improve fruit shelf life and reduce the susceptibility to postharvest disorders. Herein, a purple eggplant scion (cv. Monarca) was grafted onto a cold-tolerant hybrid Solanum rootstock ('Java') and the changes in growth, quality, postharvest chilling tolerance, and antioxidant stability were evaluated.

RESULTS

Eggplant grafting enhanced plant vigor and fruit growth rate, decreasing the time from set to harvest by 10-15%. Grafted eggplants had a thinner shape and lighter pulp color than the control. The rootstock-scion combination tested showed lower respiration (~60%), dry matter (~15-20%), and phenolic compounds contents (~15-20%) than eggplants from non-grafted plants. Grafting markedly improved fruit performance during postharvest storage. Remarkably, grafted eggplants showed much higher tolerance to chilling injury than the control did, evidenced by a reduction of surface scalds along with decreased softening and pulp browning. The trend in antioxidants found at harvest time was reversed after cold storage due to enhanced stability (20% and 100% for pulp and peel respectively) in fruit from grafted plants.

CONCLUSION

Purple eggplant (cv. Monarca) grafting onto 'Java' hybrid rootstock modulated fruit growth, quality at harvest, and increased fruit chilling injury tolerance during storage. Grafting may be a bona fide strategy to induce phenotypic traits able to improve vegetable postharvest performance. © 2021 Society of Chemical Industry.

PpCBF6 Is Involved in Phytosulfokine α-Retarded Chilling Injury by Suppressing the Expression of PpLOX5 in Peach Fruit

The involvement of PpCBF6 in phytosulfokine α (PSKα)-ameliorated chilling injury (CI) by suppressing the expression of lipoxygenase 5 (LOX5) in peach fruit was revealed. The peaches were immersed in distilled water and PSKα solution. PSKα application inhibited the progression of CI index and weight loss, and the reduction of firmness and total soluble solids content in peaches. The endogenous PSKα accumulation and gene expression of PSK receptor 1 (PSKR1) and PSKR2 were up regulated by PSKα application. The superoxide anion (O2 -) production rate, hydrogen peroxide (H2O2) production and reactive oxygen species (ROS) content decreased by PSKα application. Furthermore, PSKα application reduced the gene expression of 12 PpLOXs and LOX activity. The gene expression of 6 PpCBFs was enhanced by PSKα application. Importantly, after PSKα application, among 12 PpLOXs, the decrease in gene expression of PpLOX5 was the lowest, and among 6 PpCBFs, the increase in gene expression of PpCBF6 was the highest. Further results suggested that PpCBF6 bound to the C-repeat/dehydration responsive element (CRT/DRE) motif in PpLOX5 promoter, and repressed its transcription. Thus, PpCBF6 was involved in the PSKα-retarded CI by inhibiting the expression of PpLOX5 in peaches.

Lack of Blue Light Regulation of Antioxidants and Chilling Tolerance in Basil

Blue light, measuring from 400 to 500 nm, is generally assumed to increase the content of antioxidants in plants independent of the species. Blue light stimulates the biosynthesis of phenolic compounds such as flavonoids and their subclass anthocyanins from the phenylpropanoid pathway. Flavonoids, anthocyanins, and phenolic acids are strong reactive oxygen species (ROS) scavengers and may lessen the symptoms of abiotic stresses such as chilling. We tested the hypothesis that a high percentage of blue light induces the accumulation of antioxidants and that this effect depends on the photosynthetic photon flux density (PPFD, 400-700 nm). The effect may be more pronounced at a lower PPFD. We investigated the changes in primary and secondary metabolites of basil in response to the percentage of blue light (9, 33, 65, and 100%) applied either as a 5-day End-Of-Production (EOP) treatment or continuous throughout the growth cycle in the green cv. Dolly. We also studied if the response to the percentage of blue light (9 or 90%) was dependent on the total PPFD (100 or 300 μmol m-2 s-1 PPFD) when applied as a 5-day EOP treatment in the green cv. Dolly and the purple cv. Rosie. For both green and purple basil, it was found that the percentage of blue light had little effect on the levels of antioxidants (rosmarinic acid, total ascorbic acid, total flavonoids, and total anthocyanins) at harvest and no interactive effect with PPFD was found. Antioxidants generally decreased during postharvest storage, wherein the decrease was more pronounced at 4 than at 12°C. Chilling injury, as judged from a decrease in F v /F m values and from the occurrence of black necrotic areas, was not affected by the percentage of blue light. Particularly, chilling tolerance in the purple cultivar was increased in plants grown under higher PPFD. This may be related to the increased levels of soluble sugar and starch in leaves from high PPFD treated plants.

Antioxidant and Fatty Acid Changes in Pomegranate Peel With Induced Chilling Injury and Browning by Ethylene During Long Storage Times

Pomegranate (Punica granatum) is a non-climacteric fruit with a high antioxidant content in arils and peels, of which 92% are anthocyanins and tannins. However, it is susceptible to chilling injury (CI), a physiological disorder concentrated in the peel, which can affect the organoleptic quality of the fruit. To understand the effects of modified atmosphere and ethylene in responses to stress on the antioxidant quality of the fruit and composition of fatty acids in the peel under CI conditions, the exogenous ethylene treatments (0.5, 1.0, and 1.5 μg L^-1), 1-methylcyclopropene (1-MCP; 1 μl L^-1), modified atmosphere packaging (MAP: XTend™ bags), combined strategy MAP/1-MCP, and package in macroperforated bags (MPB-control treatment) were evaluated. The assay was performed in cold conditions (2 ± 1°C; 85% RH) to stimulate damage and was sampled for 120 days (+3 days at 20°C). During cold storage, CI symptoms began at 20 days in MPB and at 60 days for all treatments with exogenous ethylene; CI symptoms were delayed up to 120 days in MAP, 1-MCP, and the combined MAP/1-MCP treatment. Damage was concentrated in the peel. Ethylene and MPB-control treatments induced significant electrolyte leakage, lipid peroxidation, and oxidative damage. In contrast, MAP alone or in combination with 1-MCP successfully delayed CI symptoms. However, no significant differences were observed between treatments in fatty acid content, e.g., in the peel, oleic acid, linoleic acid, palmitic acid, but a significant loss was noted after 60 days of storage. Cold storage caused an increase in anthocyanin concentration in the peel and arils, increasing up to 12 times in the peel of the fruit treated with ethylene at the final stage of storage (120 days + 3 days at 20°C), with non-significant differences in the tannin content in the peel. During long-term cold storage of pomegranate, MAP and 1-MCP treatments delay and reduce the appearance of CI symptoms. This long cold storage induces an important decrease in the unsaturated/saturated fatty acid ratio, which is not reversed by any postharvest treatment. A higher unsaturated/saturated fatty acid ratio after 1-MCP treatments showed a protective effect in peel tissues. In addition, it was possible to increase the concentration of anthocyanins in the peel of cold-storage pomegranates treated with ethylene.

Genome-wide identification of heat shock transcription factors and potential role in regulation of antioxidant response under hot water and glycine betaine treatments in cold-stored peaches

BACKGROUND

Heat shock transcription factors (Hsfs) play pivotal roles in plant responses to stress. Although glycine betaine (GB) and hot water (HW) treatments are effective in reducing chilling injury (CI), little is known about the characterization of the Hsfs gene family and its potential roles in alleviating CI by regulating antioxidant systems in peach fruit.

RESULTS

In this study, 17 PpHsfs were identified in the peach genome and were investigated using bioinformatics, including chromosomal locations, phylogenetic relationships, gene structure, motifs, and promoter analyses. The expression patterns of PpHsfs under GB and HW treatments were also investigated. The PpHsfs showed different expression patterns in GB- and HW-treated fruit, and most of them were significantly up-regulated by both treatments, especially PpHsfA1a/b, PpHsfA2a, PpHsfA9a, and PpHsfB2a/b. Meanwhile, GB and HW treatments induced higher levels of gene expression and antioxidant enzyme activity of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) compared to the control, contributing to the inhibition of hydrogen peroxide (H₂ O₂ ) accumulation and superoxide anion (O₂ ^.- ) production. Moreover, the correlation analysis between PpHsfs and antioxidant-related genes showed that three PpAPXs were significantly correlated with ten PpHsfs, whereas PpCAT and PpSOD had no significant correlations with PpHsfs, which indicated that PpAPX might be regulated by PpHsfs.

CONCLUSIONS

The results indicated that GB and HW treatments induced different PpHsfs transcript levels to regulate the antioxidant gene expressions, which might be beneficial in inhibiting the accumulation of reactive oxygen species and protecting the integrity of cell structure, thus alleviating the development of CI in peach fruit during cold storage. © 2021 Society of Chemical Industry.

Reversible changes in galactolipid saturation level and head group composition are associated with tolerance to postharvest chilling in tomato fruit

BACKGROUND

Chilling injury (CI) is a physiological disorder that results in a limitation for cold storage (CS) of many fruits and vegetables. The low temperature-induced changes in the properties and composition of cell membranes are involved in the response to chilling temperature and in the mechanism of CI and tolerance.

RESULTS

We compared the changes in the lipid composition by gas chromatography-mass spectrometry before, immediately after CS, as well as during a 3-day subsequent period, of tomato fruits with different chilling-sensitivity: Micro-Tom (tolerant) and Minitomato (susceptible). The changes in linolenic acid content, double bond index and digalactosyldiacylglycerol/monogalactosyldiacylglycerol ratio (DGDG/MGDG) showed membrane fluidity adjustment, depending on the temperature. By a database search, we identified 18 membrane-bound fatty acid desaturase (FAD) genes and five DGDG synthases (DGD) genes that phylogenetically clustered into four and two subfamilies, respectively. The FAD and DGD genes were differentially expressed in response to CS, as determined by quantitative reverse transcriptase-polymerase chain reaction analysis.

CONCLUSION

The data strongly suggest that reversion of CS-induced changes during the recovery period is important for the proper function of the membrane and tolerance to postharvest CI in tomato fruit. © 2021 Society of Chemical Industry.

[Identification of laccase gene family members in peach and its relationship with chilling induced browning]

The laccase (PpLAC) gene family members in peach fruit were identified and the relationship between their expression pattern and chilling induced browning were investigated. The study was performed using two varieties of peaches with different chilling tolerance, treated with or without exogenous γ-aminobutyric acid (GABA) during cold storage. Twenty-six genes were screened from the peach fruit genome. These genes were distributed on 6 chromosomes and each contained 5-7 exons. The PpLAC gene family members shared relatively similar gene structure and conserved motifs, and they were classified into 7 subgroups based on the cluster analysis. Transcriptome sequencing revealed that the expression levels of PpLAC7 and PpLAC9 exhibited an increasing pattern under low temperature storage, and displayed a similar trend with the browning index of peach fruit. Notably, GABA treatment reduced the degree of browning and inhibited the expression of PpLAC7 and PpLAC9. These results suggested that PpLAC7 and PpLAC9 might be involved in the browning of peach fruit during cold storage.

Additional Blue LED during Cultivation Induces Cold Tolerance in Tomato Fruit but Only to an Optimum

Simple Summary

LED lighting is increasingly applied to increase yield and quality of greenhouse produced crops, especially tomatoes. Tomatoes cannot be stored at cold temperatures due to chilling injury that manifests as quick quality deterioration during shelf life. The aim of this study is to investigate whether additional blue LED lighting can mitigate the negative effects of cold storage for ‘Foundation’ tomatoes. We applied three treatments, 0, 12 or 24% additional blue light during cultivation, and investigated quality attributes at harvest, after cold storage and subsequent shelf-life. We observed that red harvested tomatoes cultivated with 12% additional blue light acquired cold tolerance. Interestingly, these tomatoes were slightly less red colored at harvest and showed a faster loss of red color during cold storage. The measured red color is closely related to the lycopene concentration. We hypothesize that lycopene, a known antioxidant, present in 12% additional blue cultivated tomatoes mitigates chilling injury. Other antioxidants present in tomatoes were only affected by the ripeness at harvest and were therefore not involved in the acquired cold tolerance. The cultivation of tomatoes using additional blue LED is an attractive way to produce tomatoes that can withstand long transport at cold temperatures at the expense of a slightly less red tomato at the consumer.

Abstract

Tomato is a chilling-sensitive fruit. The aim of this study is to examine the role of preharvest blue LED lighting (BL) to induce cold tolerance in ‘Foundation’ tomatoes. Blue and red supplemental LED light was applied to achieve either 0, 12 or 24% additional BL (0B, 12B and 24B). Mature green (MG) or red (R) tomatoes were harvested and cold stored at 4 °C for 0, 5, 10, 15 and 20 d, and then stored for 20 d at 20 °C (shelf life). Chilling injury (CI) indices, color and firmness, hydrogen peroxide, malondialdehyde, ascorbic acid and catalase activity were characterized. At harvest, R tomatoes cultivated at 12B were firmer and showed less coloration compared to fruit of other treatments. These fruits also showed higher loss of red color during cold storage and lower CI symptoms during shelf-life. MG tomatoes cultivated at 12B showed delayed coloring (non-chilled) and decreased weight loss (long cold stored) during shelf life compared to fruit in the other treatments. No effects of light treatments, both for MG and R tomatoes, were observed for the selected antioxidant capacity indicators. Improved cold tolerance for R tomatoes cultivated at 12B points to lycopene having higher scavenging activity at lower concentrations to mitigate chilling injury.

Abscisic acid alleviates chilling injury in cold-stored peach fruit by regulating ethylene and hydrogen peroxide metabolism

Peach (Prunus persica (L.) Batsch) is susceptible to chilling injury under improper low-temperature storage (2°C-5°C). Previous research has shown that abscisic acid (ABA) alleviates chilling injury in fruits and vegetables, but the potential mechanism is still unclear. To explore its effectiveness and potential mechanism in alleviating chilling injury during cold storage, exogenous ABA was applied to peach fruit by immersion in 100 μmol L^-1 solutions for 10 min. In our experiment, ABA alleviated chilling injury by reducing hydrogen peroxide (H₂O₂) content and ethylene production. In addition, ABA inhibited the expression of the ethylene synthesis-related genes PpACO1 and PpEIN2. At the same time, ABA activated the antioxidant enzymatic pathway and the ascorbate-glutathione (AsA-GSH) cycle, the transcript abundance encoding genes related to antioxidant enzyme activities also changed correspondingly. The results suggested that ABA alleviated chilling injury by scavenging excessive H₂O₂ by promoting antioxidant enzymes and the AsA-GSH pathway.

Changes of Morphology, Chemical Compositions, and the Biosynthesis Regulations of Cuticle in Response to Chilling Injury of Banana Fruit During Storage

The plant cuticle covers almost all the outermost surface of aerial plant organs, which play a primary function in limiting water loss and responding to the environmental interactions. Banana fruit is susceptible to thermal changes with chilling injury below 13°C and green ripening over 25°C. Herein, the changes of surface morphology, chemical compositions of cuticle, and the relative expression of cuticle biosynthesis genes in banana fruit under low-temperature storage were investigated. Banana fruit exhibited chilling injury rapidly with browned peel appearance stored at 4°C for 6 days. The surface altered apparently from the clear plateau with micro-crystals to smooth appearance. As compared to normal ones, the overall coverage of the main cuticle pattern of waxes and cutin monomers increased about 22% and 35%, respectively, in browned banana stored under low temperature at 6 days. Fatty acids (C₁₆-C₁₈) and ω-OH, mid-chain-epoxy fatty acids (C₁₈) dominated cutin monomers. The monomers of fatty acids, the low abundant ω, mid-chain-diOH fatty acids, and 2-hydroxy fatty acids increased remarkably under low temperature. The cuticular waxes were dominated by fatty acids (> C₁₉), n-alkanes, and triterpenoids; and the fatty acids and aldehydes were shifted to increase accompanied by the chilling injury. Furthermore, RNA-seq highlighted 111 cuticle-related genes involved in fatty acid elongation, biosynthesis of very-long-chain (VLC) aliphatics, triterpenoids, and cutin monomers, and lipid-transfer proteins were significantly differentially regulated by low temperature in banana. Results obtained indicate that the cuticle covering on the fruit surface was also involved to respond to the chilling injury of banana fruit after harvest. These findings provide useful insights to link the cuticle on the basis of morphology, chemical composition changes, and their biosynthesis regulations in response to the thermal stress of fruit during storage.

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.

Antioxidative Responses to Pre-Storage Hot Water Treatment of Red Sweet Pepper (Capsicum annuum L.) Fruit during Cold Storage

The effects of hot water treatments on antioxidant responses in red sweet pepper (Capsicum annuum L.) fruit during cold storage were investigated. Red sweet pepper fruits were treated with hot water at 55 °C for 1 (HWT-1 min), 3 (HWT-3 min), and 5 min (HWT-5 min) and stored at 10 °C for 4 weeks. The results indicated that HWT-1 min fruit showed less development of chilling injury (CI), electrolyte leakage, and weight loss. Excessive hot water treatment (3 and 5 min) caused cellular damage. Moreover, HWT-1 min slowed the production of hydrogen peroxide and malondialdehyde and promoted the ascorbate and glutathione contents for the duration of cold storage as compared to HWT-3 min, HWT-5 min, and control. HWT-1 min enhanced the ascorbate-glutathione cycle associated with ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase, but it was less effective in simulating catalase activity. Thus, HWT-1 min could induce CI tolerance in red sweet pepper fruit by activating the ascorbate-glutathione cycle via the increased activity of related enzymes and the enhanced antioxidant level.