Induced Chilling Tolerance Research Articles

Combining molecular docking and experimental approaches to uncover how Ca2+/PpCaM1-PpCAMTA3 regulated PpLCD2 expression and hydrogen sulfide production contributing to chilling tolerance in peach fruit

Hydrogen sulfide (H2S) and calcium ions (Ca2+) are implicated in various processes in fruit response to cold. L-cysteine desulfhydrase (LCD) produces H2S using L-cysteine as a substrate, but the exact role of Ca2+ signaling in LCD-mediated H2S synthesis to induce chilling tolerance in peach fruit remains unclear. Here, transcriptome analysis revealed that most differentially expressed genes associated with Ca2+ signaling after H2S treatment function in calcium ion binding and calmodulin (CaM) binding. CaM-binding transcription activator (CAMTA) is a class of CaM-binding proteins and CaM-CAMTA may be a master regulator of fruit response to cold. Further investigation implied that PpCAMTA3 positively regulated PpLCD2 transcription by binding to the CG-box motif via multiple interactions. Three PpCaM genes were identified, in which PpCaM1 interaction with PpCAMTA3 probably occurred through hydrogen bonding with the third IQ domain. Each dumbbell-shaped structure of PpCaM1 contained two EF-hand domains that bound two calcium ions, and the interaction of PpCaM1 and PpCAMTA3 was Ca2+-dependent, enhancing PpCAMTA3-mediated PpLCD2 transcriptional activation. Exogenous H2S further increased intracellular Ca2+ concentrations and PpCaM expression, which resulted in a higher PpLCD2 expression and H2S synthesis, contributing to chilling tolerance in peach fruit. These findings indicated that the Ca2+/PpCaM1-PpCAMTA3 module regulated H2S production in peach fruit under cold stress, thus shedding light on the mechanisms of peach fruit response to cold stress.

Postharvest quality evaluation on the hot water-dipped Zingiber officinale rhizomes stored at low-temperature storage

Storing ginger at chilling temperature will reduce its postharvest quality as they are prone to chilling injury (CI). Therefore, a study on hot-water dip treatment in alleviating CI in 'Bentong' ginger rhizome on physical and chemical properties was conducted. Fresh ginger rhizomes were harvested in the 9th month after planting. The fresh and cleaned rhizomes were hot-water treated at 45°C for 0, 5, 10 and 15 mins before being packed in a box and stored at 5°C for 0, 8 and 16 days. There was a significant interaction effect between dipping and storage durations on the physical and chemical properties of the rhizome. Exposed rhizome for 5, 10 and 15 mins was observed to maintain the ho and L* of the rhizome after storage at 5°C. The decreases in h° from yellow to slightly brown also indicated rhizome browning. Rhizome held at 45°C for 5 mins managed to reduce browning as compared to other durations. In addition, dipping for 15 mins resulted in a significant increase in total phenolic content, total flavonoid content and 6-gingerols. While 6-shogaols was maintained at 45°C for 5 mins. Preconditioning by the hot-water treatment could induce chilling tolerance upon storage at chilling temperature.

Improved chilling tolerance in glasshouse-grown potted sweet basil by end-of-production, short-duration supplementary far red light.

Sweet basil is a popular culinary herb used in many cuisines around the world and is widely grown commercially for retail as a live potted plant. However, basil is easily damaged by temperatures below 12 °C meaning plants must be transported from the grower to the retailer in a warm transport chain, adding considerable commercial cost in temperate countries. Improvement of chilling tolerance has been demonstrated in post-harvest crops such as tomato fruits and, indeed, fresh cut basil, by manipulation of the red:far red ratio of light provided to plants throughout the photoperiod and for a significant duration of the growing process in controlled environment chambers. We tested the effectiveness of periodic short-duration end-of-production supplementary far red light treatments designed for use with basil plants grown in a large scale commercial glasshouse for the live potted basil market. Four days of periodic, midday supplementary far red light given at end of production induced robust tolerance to 24 h of 4 °C cold treatment, resulting in greatly reduced visual damage, and reduced physiological markers of chilling injury including electrolyte leakage and reactive oxygen species accumulation. Antioxidant levels were also maintained at higher levels in live potted basil following this cold treatment. RNAseq-based analysis of gene expression changes associated with this response pointed to increased conversion of starch to soluble raffinose family oligosaccharide sugars; increased biosynthesis of anthocyanins and selected amino acids; inactivation of gibberellin signaling; and reduced expression of fatty acid desaturases, all previously associated with increased chilling tolerance in plants. Our findings offer an efficient, non-invasive approach to induce chilling tolerance in potted basil which is suitable for application in a large-scale commercial glasshouse.

Abscisic Acid Mediates Salicylic Acid Induced Chilling Tolerance of Grafted Cucumber by Activating H2O2 Biosynthesis and Accumulation.

Grafting is widely applied to enhance the tolerance of some vegetables to biotic and abiotic stress. Salicylic acid (SA) is known to be involved in grafting-induced chilling tolerance in cucumber. Here, we revealed that grafting with pumpkin (Cucurbita moschata, Cm) as a rootstock improved chilling tolerance and increased the accumulation of SA, abscisic acid (ABA) and hydrogen peroxide (H2O2) in grafted cucumber (Cucumis sativus/Cucurbita moschata, Cs/Cm) leaves. Exogenous SA improved the chilling tolerance and increased the accumulation of ABA and H2O2 and the mRNA abundances of CBF1, COR47, NCED, and RBOH1. However, 2-aminoindan-2-phosphonic acid (AIP) and L-a-aminooxy-b-phenylpropionic acid (AOPP) (biosynthesis inhibitors of SA) reduced grafting-induced chilling tolerance, as well as the synthesis of ABA and H2O2, in cucumber leaves. ABA significantly increased endogenous H2O2 production and the resistance to chilling stress, as proven by the lower electrolyte leakage (EL) and chilling injury index (CI). However, application of the ABA biosynthesis inhibitors sodium tungstate (Na2WO4) and fluridone (Flu) abolished grafting or SA-induced H2O2 accumulation and chilling tolerance. SA-induced plant response to chilling stress was also eliminated by N,N'-dimethylthiourea (DMTU, an H2O2 scavenger). In addition, ABA-induced chilling tolerance was attenuated by DMTU and diphenyleneiodonium (DPI, an H2O2 inhibitor) chloride, but AIP and AOPP had little effect on the ABA-induced mitigation of chilling stress. Na2WO4 and Flu diminished grafting- or SA-induced H2O2 biosynthesis, but DMTU and DPI did not affect ABA production induced by SA under chilling stress. These results suggest that SA participated in grafting-induced chilling tolerance by stimulating the biosynthesis of ABA and H2O2. H2O2, as a downstream signaler of ABA, mediates SA-induced chilling tolerance in grafted cucumber plants.

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.

γ-Aminobutyric acid treatment induced chilling tolerance in postharvest kiwifruit (Actinidia chinensis cv. Hongyang) via regulating ascorbic acid metabolism

The effect of γ-Aminobutyric acid (GABA) treatment on ascorbic acid (AsA) metabolism and chilling injury in postharvest kiwifruit was studied. The results revealed that kiwifruit treated with GABA displayed higher chilling tolerance and better quality maintenance as compared to the controls. Higher AsA was observed in GABA-treated fruit which was beneficial to cell membrane protection and damage alleviation against chilling mediated oxidative stress. Gene expression analysis found the increased expression of AsA anabolic and regenerative genes and down-regulation of its catabolic genes together could contribute to the elevation of AsA levels in kiwifruit after GABA treatment. In addition, the transcripts of several candidate transcription factors such as bHLHs and HZ1 involved in AsA biosynthesis were also enhanced by GABA treatment. Collectively, our results indicated that GABA induced chilling tolerance in postharvest kiwifruit due to the higher AsA content by positively regulating ascorbate metabolic genes and candidate transcription factors.

Ameliorative effect of melatonin against storage chilling injury in pomegranate husk and arils through promoting the antioxidant system

Pomegranate is a tropical and subtropical fruit sensitive to chilling injury during its cold storage, leading to quantitative and qualitative losses, as well as reduced economic value. Recently, melatonin has been considered as an environmentally friendly treatment to maintain the postharvest quality of horticultural products. In this study, the effect of melatonin treatment on chilling tolerance, postharvest quality and antioxidant system of pomegranate fruit was investigated during storage at 4 °C for 120 days. According to the results, pH, titratable acidity and the total soluble solids of the fruit were not influenced by applying melatonin. However, melatonin treatment at 100 μM dramatically improved chilling tolerance in the pomegranate fruit by reducing electrolyte leakage and increasing the total phenol content, as well as the antioxidant potential. Melatonin significantly reduced polyphenol oxidase (PPO) activity and increased the activity of phenyl alanine amylase (PAL), catalase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD) enzymes in the husk and arils of the pomegranate fruit during storage. In addition, melatonin inhibited H2O2 accumulation in the pomegranate fruits. Therefore, our data suggest that melatonin might be useful in improving the postharvest quality and inducing chilling tolerance in pomegranates during the cold storage.

Changes in Morphology, Metabolism and Composition of Cuticular Wax in Zucchini Fruit During Postharvest Cold Storage.

Cuticle composition is an important economic trait in agriculture, as it is the first protective barrier of the plant against environmental conditions. The main goal of this work was to study the role of the cuticular wax in maintaining the postharvest quality of zucchini fruit, by comparing two commercial varieties with contrasting behavior against low temperatures; the cold-tolerant variety ‘Natura’, and the cold-sensitive ‘Sinatra’, as well as ‘Sinatra’ fruit with induced-chilling tolerance through a preconditioning treatment (15°C for 48 h). The freshly-harvested ‘Natura’ fruit had a well-detectable cuticle with a significant lower permeability and a subset of 15 up-regulated cuticle-related genes. SEM showed that zucchini epicuticular waxes mainly consisted of round-shaped crystals and clusters of them, and areas with more dense crystal deposition were found in fruit of ‘Natura’ and of preconditioned ‘Sinatra’. The cuticular wax load per surface was higher in ‘Natura’ than in ‘Sinatra’ fruit at harvest and after 14 days at 4°C. In addition, total cuticular wax load only increased in ‘Natura’ and preconditioned ‘Sinatra’ fruit with cold storage. With respect to the chemical composition of the waxes, the most abundant components were alkanes, in both ‘Natura’ and ‘Sinatra’, with similar values at harvest. The total alkane content only increased in ‘Natura’ fruit and in the preconditioned ‘Sinatra’ fruit after cold storage, whereas the amount of total acids decreased, with the lowest values observed in the fruit that showed less chilling injury (CI) and weight loss. Two esters were detected, and their content also decreased with the storage in both varieties, with a greater reduction observed in the cold-tolerant variety in response to low temperature. Gene expression analysis showed significant differences between varieties, especially in CpCER1-like and CpCER3-like genes, involved in alkane production, as well as in the transcription factors CpWIN1-like and CpFUL1-like, associated with cuticle development and epidermal wax accumulation in other species. These results suggest an important role of the alkane biosynthetic pathway and cuticle morphology in maintaining the postharvest quality of zucchini fruit during the storage at low temperatures.

Antioxidant enzymatic changes in bell pepper fruit associated with chilling injury tolerance induced by hot water.

Green bell pepper is highly susceptible to low temperature. The activation of the enzymatic antioxidant system plays a determining role in tolerance to chilling injury (CI). Immersion in hot water for short time previous to storage at low temperature induces tolerance to this disorder. However, there is a lack of information about the induction of chilling tolerance in bell pepper by hot water and its relationship with the enzymatic antioxidant system. We evaluated the effect of three immersion times (T, 1-, 2-, 3-min) in hot water (HW, 53°C) on the reduction of CI in bell pepper and its relationship with the enzymatic antioxidant system during storage at 5°C and 21°C. The use of hot water for 1-, 2- or 3-min reduced the decay and CI indexes, maintained quality parameters, ascorbic acid, and total phenolics content. The storage at 5°C by itself activated the enzymatic antioxidant system. The use of HWT 1-, 2-, and 3-min helped to increase this effect, especially by HWT2 . PRACTICAL APPLICATIONS: The application of a treatment with hot water for short times in fruit sensitive to chilling injury is undoubtedly a viable alternative to increase their tolerance and commercialization. In this study, the application of a hot water treatment for 1-, 2- or 3-min in bell pepper reduced the deterioration and susceptibility to chilling injury and stimulated the enzymatic antioxidant system. In this sense, agricultural producers can take advantage of this treatment to prolong the storage period of the fruit maintaining its quality and improving its commercialization.

Melatonin treatment induces chilling tolerance by regulating the contents of polyamine, γ-aminobutyric acid, and proline in cucumber fruit

The mechanism of melatonin (MT) induced chilling tolerance in harvested cucumber fruit was investigated at commercial maturity. In this study, cucumber fruits were treated with 100 µmol L–1 MT at 4°C and 90% relative humidity for 15 d of storage. In comparison with the control, cucumber treatment with MT resulted in reduced chilling injury (CI), decreased electrolyte leakage and enhanced firmness. The fruits treated with MT showed higher chlorophyll contents in storage conditions with suppressed chlorophyllase enzyme activity. MT treatment increased arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) enzyme activities. Moreover, enhanced expression of the Cucumis sativus ADC (CsADC) and C. sativus ODC (CsODC) genes resulted in the accumulation of polyamine contents. Similarly, proline levels exhibited higher levels among treated fruits. Meanwhile, the proline synthesizing enzymes △1-pyrroline-5-carboxylate syntheses (P5CS) and ornithine aminotransferase (OAT) were significantly increased, while a catabolic enzyme of proline dehydrogenase (PDH) activity was inhibited by treatment. In addition, MT induced expression of C. sativus OAT (CsOAT) and C. sativus P5CS (CsP5CS) genes. Cucumber fruits treated with MT also exhibited higher γ-aminobutyric acid (GABA) content by enhanced GABA transaminase (GABA-T) and glutamate decarboxylase (GAD) enzyme activities and a higher C. sativus GAD (CsGAD) gene expression. To sum up, the results show that MT treatment enhanced chilling tolerance, which was associated with the regulation of polyamines, as well as proline and γ-aminobutyric acid.

Effects of chilling acclimation and methyl jasmonate on sugar metabolism in tomato fruits during cold storage

Chilling acclimation and methyl jasmonate (MeJA) treatments are effective ways to alleviate chilling injury (CI) in postharvest fruit and vegetables. Soluble sugars can be used as an important energy substance, as well as an osmotic adjustment substance, participating in various stress responses in plants. However, the regulation mechanism of chilling acclimation and MeJA treatments on sugar metabolism remains unclear during the fruit response to chilling stress. In this study, tomato fruits were used to study the regulation of sugar metabolism during chilling resistance induced by 0.05 mM MeJA and 2 °C chilling acclimation treatments for 12 h and recovering at 25 °C for 6 h before being stored at 2 °C for up to 20 days. The results showed that both 2 °C and MeJA significantly induced chilling tolerance in tomato fruit, which was reflected by the decreased CI and malondialdehyde content, as well as the increased fruit color change and total antioxidant capacity. In addition, we found that 2 °C and MeJA promoted starch degradation and sucrose accumulation, but inhibited the increase of glucose and fructose contents. MeJA and 2 °C treatments enhanced the transcription levels of genes encoding amylase (AM), sucrose phosphate synthase (SPS), sucrose synthase (SuS) and neutral invertase (NI), while decreased the transcription level of gene encoding acid invertase (AI) during most of the storage periods. Further correlation analysis suggested that the chilling resistance of three groups of fruit was closely associated with sucrose content (r=−0.824 in control, r=−0.964 in 2 °C-treated fruit and r=−0.838 in MeJA-treated fruit); and the sucrose content of the fruit was positively correlated with SlSPS3 (r=0.681 in control, r=0.947 in 2 °C-treated fruit and r=0.889 in MeJA-treated fruit) and negatively correlated with SlAI (r=−0.954 in control, r=−0.921 in 2 °C-treated fruit and r=−0.637 in MeJA-treated fruit). In addition, in 2 °C-treated fruit, sucrose content was also correlated with the expression of a-AM (r=0.723), while in MeJA-treated fruit sucrose content was correlated with β-AM (r=0.694). These results suggested that 2 °C and MeJA treatments were both effective measures for enhancing the chilling resistance of tomato fruit by regulating sugar metabolism.

Exogenous hydrogen peroxide induces chilling tolerance in Phalaenopsis seedlings through glutathione-related antioxidant system

Phalaenopsis is the most economically important flower crops wildly but hardly tolerated to low-temperature stress. Hydrogen peroxide (H2O2), a reactive oxygen species was participated in many chilling-response processes. In this study, the efficiency and mechanism of chilling tolerance induced by transient oxidative shock with H2O2 pretreatment were investigated. Phalaenopsis seedlings demonstrated chilling injury when the ambient temperature was at 6°C or lower. Transient oxidative shock by pretreatment with 50 mM H2O2 induced chilling tolerance. This pretreatment reduced the leaf electrolyte leakage (EL) from 64.1% to 28.3% of plants cultivated at 6°C for 6 days. Increasing the frequency of H2O2 pretreatment from 1 to 3 times strengthened the protective efficiency; however, an H2O2 concentration of ≥100 mM caused abnormal leaf morphology such as curl and necrosis. Time-course analysis findings indicated that chilled seedlings pretreated with H2O2 had lower EL and malondialdehyde (MDA) content but higher chlorophyll content and better photosynthetic performance, including a higher assimilation rate, maximum quantum yield of photosynthetic system II (Fv/Fm), quantum yield of electron transport (ɸPSII), photochemical quenching (qP), and electron transport rates. The results also demonstrated that pretreatment with 50 mM exogenous H2O2 did not alter the endogenous H2O2 level only a minor elevation of approximately 2 μmol•g−1 was noted. Under low temperature suffering, activity of catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were increased with fluctuant changes, but CAT and APX inhibited in the low level by H2O2 pretreatments. In addition, the significantly high GR activity was reduced the glutathione-to-oxidized glutathione ratio, with peaks occurring at 4-8 h and on day 2 during chilling. Taken together, the findings indicate that exogenous H2O2 induced chilling tolerance in Phalaenopsis seedlings, and the process may be involved the glutathione-related oxidant defense system.

Role of AOX in low-temperature conditioning induced chilling tolerance in sweetpotato roots

Chilling injury is a significant postharvest physiological disorder in sweetpotatoes during storage. This study investigated the role of alternative oxidase (AOX) in low-temperature conditioning (LTC) induced chilling tolerance in sweetpotato storage roots. Roots were pre-treated with a LTC treatment (12°C for 5 days) or with salicylhydroxamic acid (SHAM, AOX inhibitor) combined with LTC, followed by storage at 4°C for 35 days. Results showed that LTC pre-treatment significantly lowered root chilling injury symptoms, suppressed malondialdehyde levels and the accumulation of reactive oxygen species. However, SHAM reduced the impact triggered by LTC and resulted in lower antioxidant enzyme activities and free proline content, reduced glutathione and adenosine triphosphate contents compared with LTC alone. The results from gene expression analysis showed that LTC-induced higher transcript level of IbAOX1a and IbAOX1b during storage at 4°C. However, SHAM suppressed the effect of LTC. SHAM treatment not only reduced AOX activity but also resulted in a lower AOX transcript and protein abundance, which might contribute to the lower AOX activity observed in the SHAM treated roots. These results suggest that AOX participates in LTC-induced chilling tolerance of sweetpotato storage roots.

Transcriptomic analysis reveals a role of phenylpropanoid pathway in the enhancement of chilling tolerance by pre-storage cold acclimation in cucumber fruit

Cucumber fruits are susceptible to chilling injury, which can cause severe quality losses. In this study, pre-storage cold acclimation (PsCA, 10°C for 72 h) significantly induced chilling tolerance in cucumber fruits. To gain insight into the induction mechanisms of PsCA, comparative transcriptome analysis of fruit samples at 0 h, 12 h and 72 h during cold treatments were conducted. High-throughput transcriptome sequences were de novo assembled into 24878 unique transcripts. A total of 10164 differentially expressed genes (DEGs) were identified during cold stress, and 6205 DEGs were identified during cold acclimation, and 7976 DEGs were identified in cold acclimation compared to cold stress. Large numbers of DEGs were commonly detected between cold stress and cold acclimation, suggesting that these DEGs are related to cold response. Twelve DEGs were selected for qRT-PCR validation, and confirmed the credibility and accuracy of transcriptome data. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of DEGs indicated that biological processes or pathways such as plant hormone signal transduction, carbon metabolism, and biosynthesis of amino acids were commonly affected by cold stress and acclimation treatments when compared to fruits just harvested. However, compared with cold stress, cold acclimation-affected DEGs were most enriched in phenylpropanoid pathway. Moreover, PsCA upregulated the expression of six DEGs in phenylpropanoid pathway in cold-stored cucumbers. These results suggest that phenylpropanoid pathway may play a role in PsCA-enhanced chilling tolerance. These findings provide novel insights into understand the induction mechanisms underlying PsCA-induced chilling tolerance in cold-stored cucumbers.

IP3 mediates NO-enhanced chilling tolerance in postharvest kiwifruit

The function of inositol 1,4,5-trisphosphate (IP3) in nitric oxide (NO)-induced chilling tolerance in postharvest kiwifruit was revealed. The fruit were treated using sodium nitroprusside (SNP; exogenous NO donor) and neomycin (IP3 inhibitor). Data demonstrated that compared with the control, chilling injury (CI) index and firmness decreased and increased upon SNP treatment in kiwifruit. SNP treatment enhanced phosphoinositide-specific phospholipase C (PI-PLC) activity, and consequently induced IP3 production. Moreover, SNP treatment down regulated malondialdehyde (MDA) content and electrolyte leakage as well as the activity and gene expression of lipoxygenase (LOX) in kiwifruit. In addition, the gene expression of transcription factors, including C-repeat binding factor1 (CBF1), WRKY1 and NAC5 was induced by SNP treatment. The above effects induced upon SNP treatment were inhibited by neomycin treatment. Neomycin treatment alone also led to the increase in CI index, MDA content and electrolyte leakage as well as the activity and gene expression of LOX, and the decrease in firmness, PI-PLC activity and IP3 production and gene expression of CBF1, WRKY1 and NAC5. Thus, IP3 mediated the alleviation of membrane damage, and the induction of CBF1, WRKY1 and NAC5 by SNP, thereby delaying CI in kiwifruit.

Hydrogen sulfide is required for salicylic acid-induced chilling tolerance of cucumber seedlings.

Salicylic acid (SA) and hydrogen sulfide (H2S) have been proved to be multifunctional signal molecules to participate in the response of plants to abiotic stresses. However, it is still unclear whether there is interaction between SA and H2S in response to chilling intensity of cucumber seedlings. Here, we found SA was sensitive to chilling intensity. Under normal condition, NaHS (H2S donor) or removing endogenous H2S with hypotaurine (HT, a specific scavenger of H2S) and DL-propargylglycine (PAG, a specific inhibitor of H2S) has no effect on endogenous SA level; however, SA induced endogenous H2S content and activated the activities and mRNA level of L-/D-cysteine desulfhydrase (L-/D-CD), and inhibiting endogenous SA with paclobutrazol (PAC) or 2-aminoindan-2-phosphonic acid (AIP) blocked this effect, implying H2S may play a role after SA signal. Further studies showed that both SA and NaHS notably alleviated chilling injury, which was evidenced by lower electrolyte leakage (EL), MDA content, and ROS accumulation, compared with H2O treatment. Of note, SA and H2S improved the activities and mRNA level of antioxidant enzymes (SOD, POD, CAT, APX, and GR) as well as the contents of AsA and GSH. Additionally, the chilling-response genes (ICE, CBF1, and COR) were obviously upregulated by exogenous SA and NaHS. However, the positive effect of SA on chilling tolerance was inhibited by HT, whereas PAC or AIP did not affect NaHS-induced chilling tolerance. Taken together, the data reveals that H2S acts as a downstream signal of SA-induced chilling tolerance of cucumber via modulating antioxidant system and chilling-response genes.

Effect of hot water treatment on chilling injury and lignification of cold-stored fresh areca nut (Areca catechu L.).

Fresh areca nut is widely favored by consumers in South and Southeast Asia. However, postharvest areca nut perished quickly and was vulnerable to chilling injury (CI) and lignification during traditional cold storage. In order to alleviate this situation, hot water treatment was applied to investigate its effect on CI and lignification of fresh areca nut during cold storage at 13°C. Areca nuts were submersed in hot water at 45°C (HW45) and 50°C (HW50) for short-term 5min compared to fruit submersed in water at 20°C (CT), then stored at 13°C with 90% humidity for 60days. CI, malondialdehyde (MDA), electrolyte leakage (EL), lignin and total phenolic content, related enzymes including phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD) and peroxidase activity (POD) were examined. Results indicated that two HW treatments both induced chilling tolerance and delayed lignification of areca nut to varying degrees during cold storage compared with the CT. Among which, HW45 treated-areca nuts had the lowest CI, MDA content and EL while maintaining the highest total phenolic content. Moreover, no significant effects were found between HW45 and HW50 on tissue lignification, but they both effectively blocked lignin accumulation by inhibiting PAL, CAD and POD activities compared with the CT. The present study provided a safe physical method to mitigate CI and delay tissue lignification in cold-stored areca nut.

Exogenous Ascorbic Acid Induced Chilling Tolerance in Tomato Plants Through Modulating Metabolism, Osmolytes, Antioxidants, and Transcriptional Regulation of Catalase and Heat Shock Proteins.

Chilling, a sort of cold stress, is a typical abiotic ecological stress that impacts the development as well as the growth of crops. The present study was carried to investigate the role of ascorbic acid root priming in enhancing tolerance of tomato seedlings against acute chilling stress. The treatments included untreated control, ascorbic acid-treated plants (AsA; 0.5 mM), acute chilling-stressed plants (4 °C), and chilling stressed seedlings treated by ascorbic acid. Exposure to acute chilling stress reduced growth in terms of length, fresh and dry biomass, pigment synthesis, and photosynthesis. AsA was effective in mitigating the injurious effects of chilling stress to significant levels when supplied at 0.5 mM concentrations. AsA priming reduced the chilling mediated oxidative damage by lowering the electrolyte leakage, lipid peroxidation, and hydrogen peroxide. Moreover, up regulating the activity of enzymatic components of the antioxidant system. Further, 0.5 mM AsA proved beneficial in enhancing ions uptake in normal and chilling stressed seedlings. At the gene expression level, AsA significantly lowered the expression level of CAT and heat shock protein genes. Therefore, we theorize that the implementation of exogenous AsA treatment reduced the negative effects of severe chilling stress on tomato.

The Mediation of NO-Enhanced Chilling Tolerance by GSK-3 in Postharvest Peach Fruit

The role of glycogen synthase kinase-3 (GSK-3) in nitric oxide (NO)-enhanced chilling tolerance in postharvest peach fruit was investigated. The fruits were immersed in sodium nitroprusside (SNP; exogenous NO donor) and bikinin (GSK-3 inhibitor). Results showed that the chilling injury (CI) index declined following the exposure of the peach fruit to exogenous SNP. SNP treatment also induced GSK-3 expression. Furthermore, SNP treatment reduced malondialdehyde (MDA) content and electrolyte leakage in the peach fruit. In addition, SNP treatment induced the increase in alternative oxidase (AOX) activity and the upregulation of the gene expression of 18.1-kDa class I heat shock protein (HSP), WRKY2, and C-repeat binding factor (CBF). The effects of SNP treatment were partly weakened by the addition of bikinin. These findings indicate that GSK-3 mediated the reduction of MDA content and electrolyte leakage and the activation of AOX, 18.1-kDa class I HSP, WRKY2, and CBF by NO, thereby inducing chilling tolerance in peach fruit.

The Role of Glycogen Synthase Kinase-3 in Gibberellic Acid-Induced Chilling Tolerance and Defense Response in Postharvest Peach Fruit

The induction of chilling tolerance and defense response by glycogen synthase kinase-3 (GSK-3) under gibberellic acid (GA3) treatment in peach fruit was explored at 4 °C up to 28 days. The fruits were treated with exogenous GA3 and bikinin (GSK-3 inhibitor). Results showed that exogenous GA3 alleviated chilling injury, and upregulated endogenous GA3 content in peach fruit. Furthermore, GSK-3 expression was activated by exogenous GA3 treatment. GA3 also upregulated gene expression of superoxide dismutase, peroxidase, catalase, glutathione reductase, glutathione S-transferase, and ascorbate peroxidase. Additionally, GA3 enhanced gene and protein expression of small ubiquitin-like modifier and gene expression of methionine sulfoxide reductase, and weakened gene expression of lipoxygenase and phospholipase D. These above impacts stimulated by exogenous GA3 were blocked by the addition of bikinin. Overall, GSK-3 was involved in stimulation of chilling tolerance and defense response under GA3 treatment in postharvest peach fruit.