Physiological and Genetic Properties of Tomato Fruits from 2 Cultivars Differing in Chilling Tolerance at Cold Storage

Tomato SlMAPK3 Modulates Cold Resistance by Regulating the Synthesis of Raffinose and the Expression of SlWRKY46

Mitogen-activated protein kinase (MAPK) cascades and raffinose have been observed to increase in plants exposed to cold. However, it remains elusive whether and how MAPK regulates raffinose synthesis under cold stress. Here, overexpression of SlMAPK3 promoted the accumulation of galactinol and raffinose under cold stress, while CRISPR/Cas9-mediated mutants showed the opposite results. Moreover, SlMAPK3 promoted the expression of SlWRKY46 at low temperatures and interacted with SlWRKY46 protein. Overexpression of SlWRKY46 enhanced cold resistance. Furthermore, SlWRKY46 directly bound to the promoter of SlGols1 to enhance its expression and promoted the accumulation of raffinose. Virus-induced gene-silencing (VIGS)-mediated knockdown of SlGols1 remarkably elevated cold sensitivity and reduced raffinose content. Meanwhile, exogenous supplementation of raffinose could improve the cold tolerance of tomato plants. Thus, our data indicates that SlMAPK3 modulates cold resistance by regulating raffinose content and SlWRKY46 expression. SlWRKY46 also promotes the accumulation of raffinose by inducing the expression of SlGols1.

Melatonin-induced plant adaptation to cadmium stress involves enhanced phytochelatin synthesis and nutrient homeostasis in Solanum lycopersicum L

Cadmium (Cd) pollution is an increasingly serious problem in crop production. Although significant progress has been made to comprehend the molecular mechanism of phytochelatins (PCs)-mediated Cd detoxification, the information on the hormonal regulation of PCs is very fragmentary. In the present study, we constructed TRV-COMT, TRV-PCS, and TRV-COMT-PCS plants to further assess the function of CAFFEIC ACID O-METHYLTRANSFERASE (COMT) and PHYTOCHELATIN SYNTHASE (PCS) in melatonin-induced regulation of plant resistance to Cd stress in tomato. Cd stress significantly decreased chlorophyll content and CO₂ assimilation rate, but increased Cd, H₂O₂ and MDA accumulation in the shoot, most profoundly in PCs deficient TRV-PCS and TRV-COMT-PCS plants. Notably, Cd stress and exogenous melatonin treatment significantly increased endogenous melatonin and PC contents in non-silenced plants. Results also explored that melatonin could alleviate oxidative stress and enhance antioxidant capacity and redox homeostasis by conserving improved GSH:GSSG and ASA:DHA ratios. Moreover, melatonin improves osmotic balance and nutrient absorption by regulating the synthesis of PCs. This study unveiled a crucial mechanism of melatonin-regulated PC synthesis, persuaded Cd stress tolerance and nutrient balance in tomato, which may have potential implications for the enhancement of plant resistance to toxic heavy metal stress.

Postharvest fruit quality of tomatoes influenced by an ethylene signaling component during long-term cold storage

Ethylene production is essential for improving cold resistance of postharvest tomatoes. However, the role of ethylene signaling pathway in maintaining fruit quality during long-term cold storage remains poorly understood. Here, we demonstrated that a partial loss of function in ethylene signaling by mutation of Ethylene Response Factor 2 (SlERF2), worsened fruit quality during cold storage, as determined by visual characterization, and physiological analyses of membrane damage and reactive oxygen species metabolism. In addition, the transcriptions of genes related to abscisic acid (ABA) biosynthesis and signaling were also altered by SlERF2 gene in response to cold storage. Furthermore, mutation of SlERF2 gene compromised cold-induced expression of genes in the C-repeat/dehydration-responsive binding factor (CBF) signaling pathway. Therefore, it's concluded that an ethylene signaling component, SlERF2 contributed to the regulations of ABA biosynthesis and signaling, as well as CBF cold signaling pathway, ultimately affecting the fruit quality during long-term cold storage of tomatoes.

SlMAPK3 Positively Regulates the Ethylene Production of Postharvest Tomato Fruits and Is Involved in Ethylene-Mediated Cold Tolerance

Mitogen-activated protein kinase (MAPK) cascades and ethylene are crucial for plant growth, development, and stress responses, but their potential mechanisms in cold resistance remain unclear. We revealed that SlMAPK3 transcript levels were dramatically induced by cold treatment in an ethylene-dependent manner. Under cold stress, the proline content of SlMAPK3-overexpression fruit was 96.5 and 115.9% higher than that of wild-type fruit (WT), respectively, while the ion leakage was 37.3 and 32.5% lower than that of WT. RNA sequencing revealed that overexpression of SlMAPK3 caused upregulation of genes that are enriched in the ethylene-activated signaling pathway (GO:0009873), cold signaling pathway (GO:0009409), and heat signaling pathway (GO:0009408). RT-qPCR demonstrated that the expression levels of SlACS2, SlACS4, SlSAHH, SlCBF1, SlDREB, SlGolS1, and SlHSP17.7 in the OE.MAPK3 fruits were consistent with the RNA sequencing results. Meanwhile, the knockout of SlMAPK3 reduced the ethylene content, ACC content, and ACS activity. Moreover, the knockout of SlMAPK3 reduced the positive effect of ethylene in cold stress, while suppressing the expression of SlICE1 and SlCBF1. In conclusion, our study demonstrated a novel mechanism by which SlMAPK3 positively regulates the ethylene production of postharvest tomato fruits and is involved in ethylene-mediated cold tolerance.

Metabolite Profiling Reveals the Effect of Cold Storage on Primary Metabolism in Nectarine Varieties with Contrasting Mealiness

Chilling injury is a physiological disorder caused by cold storage in peaches and nectarines. The main symptom of chilling injury is mealiness/wooliness, described as a lack of juice in fruit flesh. In this work, we studied two nectarine varieties (Andes Nec-2 and Andes Nec-3) with contrasting susceptibility to mealiness after cold storage. A non-targeted metabolomic analysis was conducted by GC-MS to understand if changes in metabolite abundance are associated with nectarine mealiness induced by cold storage. Multivariate analyses indicated that in unripe nectarines, cold storage promoted a higher accumulation of amino acids in both varieties. Interestingly, for ripe nectarines, cold storage induced an accumulation of fewer amino acids in both varieties and showed an increased abundance of sugars and organic acids. A pathway reconstruction of primary metabolism revealed that in ripe nectarines, cold storage disrupted metabolite abundance in sugar metabolism and the TCA cycle, leading to a differential accumulation of amino acids, organic acids, and sugars in mealy and juicy nectarines.

Enhancement of cucumber resistance under salt stress by 2, 4-epibrassinolide lactones

This study investigated the effects of exogenous 2, 4-epibrassinolide lactone (EBR) on the growth, photosynthetic pigments, antioxidant defense system, ion homeostasis, MAPK cascade and key genes of SOS signaling pathway of cucumber seedlings under salt stress using cucumber "Xinchun 4" as the test material. The experiment was set up with four treatments: foliar spraying of distilled water (CK), 50 mmol.L^-1 NaCl (NaCl), 50 mmol.L^-1 NaCl+foliar spray of 0.02 μmol.L^-1 EBR (EBR+NaCl), and 50 mmol.L^-1 NaCl+foliar spray of 24 μmol.L^-1 Brassinazole (BRZ) (BRZ+NaCl). The results showed that EBR+NaCl treatment significantly increased plant height, above-ground fresh weight, total root length, total root surface area, average rhizome and photosynthetic pigment content compared to NaCl treatment. Meanwhile, compared with NaCl treatment, EBR+NaCl treatment significantly increased superoxide dismutase, catalase and ascorbate peroxidase (SOD, CAT and APX) activities, significantly promoted the accumulation of osmoregulatory substances (soluble sugars and proline), and thus effectively reduced malondialdehyde (MDA) content and relative electrical conductivity of cucumber leaves. Exogenous spraying of EBR also significantly reduced Na⁺/K⁺ under NaCl stress, effectively alleviating the toxic effects of Na⁺ ions. In addition, exogenous EBR induced the up-regulated expression of CsMAPK3, CsMAPK4, CsMAPK6 and CsMAPK9 genes in the MAPK cascade signaling pathway and CsSOS1, CsSOS2 and CsSOS3 genes in the SOS signaling pathway to enhance salt tolerance in cucumber under NaCl stress. Therefore, exogenous spraying EBR may effectively reduce the damage of salt stress on cucumber seedlings by improving antioxidant capacity, maintaining ion homeostasis and activating salt-tolerant related signaling pathways, which might promote the growth of cucumber seedlings and the establishment of root system morphology. This study provides a reference for EBR to improve the salt tolerance of cucumber.

Chilling injury of tomato fruit was alleviated under low-temperature storage by silencing Sly-miR171e with short tandem target mimic technology

In this study, the role of Sly-miR171e on post-harvest cold tolerance of tomato fruit was researched. The results showed that overexpression of Sly-miR171e (miR171e-OE) promoted postharvest chilling injury (CI) of tomato fruit at the mature red (MR) and mature green (MG) stage. Contrasted with the wild type (WT) and miR171e-OE fruit, the knockdown of Sly-miR171e (miR171e-STTM) showed a lower CI index, lower hydrogen peroxide (H2O2) content, and higher fruit firmness after harvest. In the fruit of miR171e-STTM, the expression level of GRAS24, CBF1, GA2ox1, and COR, and the GA3 content were ascended, while the expression levels of GA20ox1 and GA3ox1 were descended. The research demonstrated that CI in tomato fruit was alleviated at low temperature storage by silencing Sly-miR171e with short tandem target mimic (STTM) technology. Furthermore, it also provided helpful information for genetic modification of miR171e and control of CI in the postharvest fruit.

The effect of ascorbic acid and bio fertilizers on basil under drought stress

Evaluate the effect of ascorbic acid application and coexistence of Mycorrhiza fungus and Azospirillium on basil (Ocimum basilicum L.) under drought stress. This experiment was performed as a split factorial in a randomized complete block design with three replications in the crop year 2017-2018 in Shahriar, Iran. In this experiment, irrigation was the main factor in three levels, including drought stress based on 40-70-100 mm from the evaporation pan of class A. Biofertilizer including growth-promoting bacteria (Azospirillium) and mycorrhiza fungus in four levels, including a(Non-consumption) B (Seeds of growth-promoting bacteria (Azospirillium)) C (Consumption of mycorrhiza fungus as seeds) D (Concomitant use of growth-promoting bacteria Azospirillium with mycorrhiza fungi as seeds) and ascorbic acid in two levels of foliar application, including A (Absence Application of ascorbic acid) and B (Application of ascorbic acid (two days after irrigation treatment)) was considered as a factorial factor. The results showed that the highest biological yield was obtained in drought stress of 40 mm and application of biological fertilizers in the form of mycorrhiza application with an average of 3307.1 kg/ha, which was about 70% more than 100 mm evaporation stress and no application of biological fertilizer. The use of ascorbic acid under drought stress conditions improved by 10%, the essential oil using ascorbic acid evaporated under drought stress conditions of 100 mm. As a general conclusion, the use of ascorbic acid and Mycorrhiza + Azospirillium biological fertilizer improved the quantitative and qualitative characteristics of basil under drought stress.

Foliar Application of Salicylic Acid at Different Phenological Stages of Peach Fruit CV. 'Flordaking' Improves Harvest Quality and Reduces Chilling Injury during Low Temperature Storage

Peaches are well-liked amongst the stone fruits in Pakistan. The peach industry faces significant losses, from harvesting to marketing. The objective of this study was to investigate the effectiveness of foliar sprays of salicylic acid (SA) on the fruit quality of peaches (cv. 'Flordaking') at the harvest and postharvest life or stages. Different concentrations of SA (control, 1, 2 and 3 mM) were sprayed on the plants at three growth stages of fruit, i.e., the cell division, cell enlargement and pit-hardening stages. In general, all the SA treatments improved the fruit quality at harvest and maintained higher levels of flesh firmness, titratable acidity and ascorbic acid during storage. However, fruit weight loss, soluble solid contents, membrane leakage, chilling injury, color development, disease and decay incidence and the climacteric peak of ethylene were lowered by SA treatment after six weeks of low-temperature storage. SA at a 3-mM concentration was proven to be the most effective in maintaining the quality for a longer period of time during low-temperature storage. Based on the results, it can be concluded that the application of SA at fruit development stages can improve the harvest quality and storability of 'Flordaking' peaches.

Tomato calmodulin-like protein SlCML37 is a calcium (Ca2+) sensor that interacts with proteasome maturation factor SlUMP1 and plays a role in tomato fruit chilling stress tolerance

Calmodulin-like proteins (CMLs), as well as their targets, play significant roles in various key developmental and stress responses in the plant. In tomato (Solanum lycopersicum), there are at least 52 CML genes in its genome. However, most of their functions are not well known, especially in response to cold stress. Here, we investigated SlCML37 biochemical and structural characteristics, including a typical α-helical secondary structure and exposing its hydrophobic regions after binding to Ca²⁺. Then we certificated that SlCML37 protein could physically interact with SlUMP1 by using yeast two-hybrid, bimolecular florescence complementation (BiFC) and GST pull-down assays. Further analysis showed that SlCML37-transgenic tomato fruit conferred significantly improved tolerance to chilling stress. This study indicates a possible role of calmodulin-like protein-mediated proteasome assemble in the regulation of plant cold response.

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

Research background

Low 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 approach

Phenylalanine 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 conclusions

Phenylalanine 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 contribution

In 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.

VvBAP1, a Grape C2 Domain Protein, Plays a Positive Regulatory Role Under Heat Stress

Temperature is considered one of the critical factors directly influencing grapevine during the three primary growth and development stages: sprout, flowering, and fruit-coloring, which is strongly correlated to the yield and quality of the grape. The grapevine is frequently exposed to high-temperature conditions that are detrimental to growth. However, the mechanisms of the heat stress response and adaptation in grapevine are not adequately studied. The Arabidopsis copine gene AtBON1 encodes a highly conserved protein containing two C2 domains at the amino terminus, participation in cell death regulation and defense responses. Previously, we showed that a BON1 association protein from the grapevine, VvBAP1, plays a positive role in cold tolerance. Similarly, the involvement of VvBAP1 in the resistance to heat stress was also found in the present study. The results indicated VvBAP1 was significantly induced by high temperature, and the elevated expression of VvBAP1 was significantly higher in the resistant cultivars than the sensitive cultivars under heat stress. Seed germination and phenotypic analysis results indicated that overexpression of VvBAP1 improved Arabidopsis thermoresistance. Compared with the wild type, the chlorophyll content and net photosynthetic rate in VvBAP1 overexpressing Arabidopsis plants were markedly increased under heat stress. At high temperatures, overexpression of VvBAP1 also enhanced antioxidant enzyme activity as well as their corresponding gene transcription levels, to reduce the accumulation of reactive oxygen species and lipid peroxidation. Besides, the transcriptional activities of HSP70, HSP101, HSFA2, and HSFB1 in VvBAP1 overexpressing Arabidopsis plants were significantly up-regulated compare to the wild type. In summary, we propose that VvBAP1 may play a potential important role in enhanced grapevine thermoresistance, primarily through the enhancement of antioxidant enzyme activity and promoted heat stress response genes expression.

Increased Precipitation Shapes Relationship between Biochemical and Functional Traits of Stipa glareosa in Grass-Dominated Rather than Shrub-Dominated Community in a Desert Steppe

Understanding the effects of precipitation variations on plant biochemical and functional traits is crucial to predict plant adaptation to future climate changes. The dominant species, Stipa glareosa, plays an important role in maintaining the structure and function of plant communities in the desert steppe, Inner Mongolia. However, little is known about how altered precipitation affects biochemical and functional traits of S. glareosa in different communities in the desert steppe. Here, we examined the responses of biochemical and functional traits of S. glareosa in shrub- and grass-dominated communities to experimentally increased precipitation (control, +20%, +40%, and +60%). We found that +40% and +60% increased plant height and leaf dry matter content (LDMC) and decreased specific leaf area (SLA) of S. glareosa in grass community. For biochemical traits in grass community, +60% decreased the contents of protein and chlorophyll b (Cb), while +40% increased the relative electrical conductivity and superoxide dismutase. Additionally, +20% increased LDMC and malondialaenyde, and decreased SLA and protein in shrub community. Chlorophyll a, Cb, carotenoids, protein and superoxide dismutase in the grass community differed with shrub community, while +60% caused differences in SLA, LDMC, leaf carbon content, malondialaenyde and peroxidase between two communities. The positive or negative linear patterns were observed between different functional and biochemical traits in grass- rather than shrub-community. Soil water content explained changes in some biochemical traits in the grass community, but not for functional traits. These results suggest that increased precipitation can affect functional traits of S. glareosa in the grass community by altering biochemical traits caused by soil water content. The biochemical and functional traits of S. glareosa were more sensitive to extreme precipitation in grass- than shrub-community in the desert steppe. Our study highlights the important differences in adaptive strategies of S. glareosa in different plant communities at the same site to precipitation changes.

A Combination of Melatonin and Ethanol Treatment Improves Postharvest Quality in Bitter Melon Fruit

Central composite design (CCD), utilized with three independent variables, verified that the optimal treatment conditions in bitter melon fruit were melatonin (MT) concentration of 120 µmol L−1, ethanol concentration of 6%, and immersing time of 10 min. Under optimal conditions, the experimental values of firmness, chilling injury (CI) index, and weight loss were shown as 27.81 N, 65.625%, and 0.815%, respectively. Moreover, the combined effect of MT and ethanol on CI and physiological quality in postharvest bitter melon fruit stored at 4 °C was investigated. It was found that the combined treatment contributed to the reduced CI symptoms and inhibited ion leakage and malondialdehyde (MDA) accumulation. Moreover, higher levels of chlorophyll, total soluble solids (TSSs), soluble sugar, soluble protein, and ascorbic acid (AsA) were observed in comparison with the control group. Furthermore, the synthesis of total phenols and flavonoids in bitter melon was greatly promoted. Therefore, the combination of MT and ethanol could have the potential for alleviating CI and maintaining postharvest quality for the duration of cold storage.

Transcriptomic Profiling of Young Cotyledons Response to Chilling Stress in Two Contrasting Cotton (Gossypium hirsutum L.) Genotypes at the Seedling Stage

Young cotyledons of cotton seedlings are most susceptible to chilling stress. To gain insight into the potential mechanism of cold tolerance of young cotton cotyledons, we conducted physiological and comparative transcriptome analysis of two varieties with contrasting phenotypes. The evaluation of chilling injury of young cotyledons among 74 cotton varieties revealed that H559 was the most tolerant and YM21 was the most sensitive. The physiological analysis found that the ROS scavenging ability was lower, and cell membrane damage was more severe in the cotyledons of YM21 than that of H559 under chilling stress. RNA-seq analysis identified a total of 44,998 expressed genes and 19,982 differentially expressed genes (DEGs) in young cotyledons of the two varieties under chilling stress. Weighted gene coexpression network analysis (WGCNA) of all DEGs revealed four significant modules with close correlation with specific samples. The GO-term enrichment analysis found that lots of genes in H559-specific modules were involved in plant resistance to abiotic stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that pathways such as plant hormone signal transduction, MAPK signaling, and plant–pathogen interaction were related to chilling stress response. A total of 574 transcription factors and 936 hub genes in these modules were identified. Twenty hub genes were selected for qRT-PCR verification, revealing the reliability and accuracy of transcriptome data. These findings will lay a foundation for future research on the molecular mechanism of cold tolerance in cotyledons of cotton.

Cold storage reveals distinct metabolic perturbations in processing and non-processing cultivars of potato (Solanum tuberosum L.)

Cold-induced sweetening (CIS) causes considerable losses to the potato processing industry wherein the selection of potato genotypes using biochemical information has found to be advantageous. Here, ¹H NMR spectroscopy was performed to identify metabolic perturbations from tubers of five potato cultivars (Atlantic, Frito Lay-1533, Kufri Jyoti, Kufri Pukhraj, and PU1) differing in their CIS ability and processing characteristics at harvest and after cold storage (4 °C). Thirty-nine water-soluble metabolites were detected wherein significantly affected metabolites after cold storage were categorized into sugars, sugar alcohols, amino acids, and organic acids. Multivariate statistical analysis indicated significant differences in the metabolic profiles among the potato cultivars. Pathway enrichment analysis revealed that carbohydrates, amino acids, and organic acids are the key players in CIS. Interestingly, one of the processing cultivars, FL-1533, exhibited a unique combination of metabolites represented by low levels of glucose, fructose, and asparagine accompanied by high citrate levels. Conversely, non-processing cultivars (Kufri Pukhraj and Kufri Jyoti) showed elevated glucose, fructose, and malate levels. Our results indicate that metabolites such as glucose, fructose, sucrose, asparagine, glutamine, citrate, malate, proline, 4-aminobutyrate can be potentially utilized for the prediction, selection, and development of potato cultivars for long-term storage, nutritional, as well as processing attributes.

Postharvest melatonin treatment reduces chilling injury in sapota fruit

BACKGROUND

Sapota is a popular tropical fruit characterized by a very short postharvest life. Low-temperature storage prolongs postharvest life of sapota fruit, but chilling injury symptoms can develop if the storage temperature is less than 14 °C. There have been no reports on the effects of postharvest melatonin application on the development of chilling injury in sapota fruit during cold storage. The objective of this study was to investigate the effects of different concentrations of postharvest melatonin application (0, 30, 60 and 90 μmol L^-1 ) during cold storage (8 °C) for up to 30 days with an additional 1-day shelf life at ambient temperature.

RESULTS

All melatonin treatments reduced chilling injury symptoms, reduced electrolyte leakage, malondialdehyde (MDA) content, H₂ O₂ and superoxide anion (O₂ ^- ), and increased proline content and the activity of superoxide dismutase (SOD), catalase (CAT) and γ-aminobutyric acid (GABA), and reduced the activities of phospholipase D (PLD) and lipoxygenase (LOX) compared to the control.

CONCLUSION

Postharvest melatonin treatment could be a useful strategy for reducing chilling injury during cold storage and transport of sapota fruit. The results indicate that melatonin reduces chilling injury of sapota fruit through maintaining membrane integrity, SOD and CAT activities, and reducing PLD and LOX activities. © 2019 Society of Chemical Industry.

The membrane lipid metabolism in horticultural products suffering chilling injury

Horticultural commodities suffer chilling injury following exposure to extremely low temperatures, which results in visible symptoms and considerable quality loss. Therefore, it is of significance to understand the mechanism of this physiological disorder and to develop effective strategies to control it. Chilling stress causes alteration in structure and function of the plasma membrane, which is assumed to be the primary event in response to cold stress. During this process, the membrane lipid metabolism plays a pivotal role in membrane fluidity and stability. In this review, we summarized the possible roles of membrane lipid metabolism in the development of chilling injury, having the potential for developing effective strategies to alleviate chilling injury in horticultural products under refrigerated storage in practice.

Transcriptome analysis of postharvest blueberries (Vaccinium corymbosum 'Duke') in response to cold stress

BACKGROUND

Blueberry (Vaccinium spp.) is a small berry with high economic value. Although cold storage can extend the storage time of blueberry to more than 60 days, it leads to chilling injury (CI) displaying as pedicle pits; and the samples of 0 °C-30 days was the critical point of CI. However, little is known about the mechanism and the molecular basis response to cold stress in blueberry have not been explained definitely. To comprehensively reveal the CI mechanisms in response to cold stress, we performed high-throughput RNA Seq analysis to investigate the gene regulation network in 0d (control) and 30d chilled blueberry. At the same time, the pitting and decay rate, electrolyte leakage (EL), malondialdehyde (MDA) proline content and GSH content were measured.

RESULTS

Two cDNA libraries from 0d (control) and 30d chilled samples were constructed and sequenced, generating a total of 35,060 unigenes with an N50 length of 1348 bp. Of these, 1852 were differentially expressed, with 1167 upregulated and 685 downregulated. Forty-five cold-induced transcription factor (TF) families containing 1023 TFs were identified. The DEGs indicated biological processes such as stress responses; cell wall metabolism; abscisic acid, gibberellin, membrane lipid, energy metabolism, cellular components, and molecular functions were significantly responsed to cold storage. The transcriptional level of 40 DEGs were verified by qRT-PCR.

CONCLUSIONS

The postharvest cold storage leads serious CI in blueberry, which substantially decreases the quality, storability and consumer acceptance. The MDA content, proline content, EL increased and the GSH content decreased in this chilled process. The biological processes such as stress responses, hormone metabolic processes were significantly affected by CI. Overall, the results obtained here are valuable for preventing CI under cold storage and could help to perfect the lack of the genetic information of non-model plant species.

Effect of foliar application with sodium selenate on selenium biofortification and fruit quality maintenance of 'Starking Delicious' apple during storage

BACKGROUND

Selenium (Se) is an essential micronutrient due to its anticarsinogenic properties and positive influence on human immune system. Fortification of some fruits based on their rates of consumption and availability all year round appears to be an effective way to supplement Se in the human diet. In this study the possibility of augmenting Se content in 'Starking Delicious' apple fruit during two growing seasons was investigated. In 2016, the impact of 0, 0.5, 1 and 1.5 mg Se L^-1 by foliar application on Se accumulation and fruit ripening as well as quality attributes was investigated. In 2017, the effects of 1.5 mg Se L^-1 foliar application on fruit Se content and changes in the antioxidant system and storability were studied with a 30-day interval during 6 months storage at 0 ± 1 °C.

RESULTS

Foliar application of Se significantly increased both leaf and fruit Se concentration. The increase in Se content enhanced the flesh firmness, titrable acidity, and soluble solid content of the fruit. The activities of antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) were markedly amplified by Se treatments as compared to the control, resulting in lower superoxide anion radical (O₂ ^-• ) and hydrogen peroxide (H₂ O₂ ) contents, correspondingly higher membrane integrity as revealed by lower ion leakage and malondialdehyde accumulation and the fruit with lower water core.

CONCLUSION

Application of Se was efficient in increasing fruit Se content and nutraceutical properties, retarding the flesh firmness reduction, and postponing fruit ripening resulting from lower ethylene biosynthesis rate, thereby positively affecting apple fruit quality and storability. © 2019 Society of Chemical Industry.

Knockout of SlMAPK3 enhances tolerance to heat stress involving ROS homeostasis in tomato plants

BACKGROUND

High temperature is a major environmental stress that limits plant growth and agriculture productivity. Mitogen-activated protein kinases (MAPKs) are highly conserved serine and threonine protein kinases that participate in response to diverse environmental stresses in plants. A total of 16 putative SlMAPK genes are identified in tomato, and SlMAPK3 is one of the most extensively studied SlMAPKs. However, the role of SlMAPK3 in response to heat stress is not clearly understood in tomato plants. In this study, we performed functional analysis of SlMAPK3 for its possible role in response to heat stress.

RESULTS

qRT-PCR analyses revealed that SlMAPK3 relative expression was depressed by heat stress. Here, wild-type (WT) tomato plants and CRISPR/Cas9-mediated slmapk3 mutant lines (L8 and L13) were used to investigate the function of SlMAPK3 in response to heat stress. Compared with WT plants, slmapk3 mutants exhibited less severe wilting and less membrane damage, showed lower reactive oxygen species (ROS) contents, and presented higher both activities and transcript levels of antioxidant enzymes, as well as elevated expressions of genes encoding heat stress transcription factors (HSFs) and heat shock proteins (HSPs).

CONCLUSIONS

CRISPR/Cas9-mediated slmapk3 mutants exhibited more tolerance to heat stress than WT plants, suggesting that SlMAPK3 was a negative regulator of thermotolerance. Moreover, antioxidant enzymes and HSPs/HSFs genes expression were involved in SlMAPK3-mediated heat stress response in tomato plants.

Integrative analysis of postharvest chilling injury in cherry tomato fruit reveals contrapuntal spatio-temporal responses to ripening and cold stress

Postharvest chilling injury (PCI) reduces fruit quality and shelf-life in tomato (Solanum lycopersicum L.). PCI has been traditionally studied in the pericarp, however its development is likely heterogeneous in different fruit tissues. To gain insight into PCI's spatio-temporal development, we used postharvest biomarkers e.g. respiration and ethylene rates, ion leakage etc., to confirm the occurrence of PCI, and compared these data with molecular (gene expression), biophysical (MRI data) and biochemical parameters (Malondialdehyde (MDA) and starch content) from the pericarp or columella. Tissues were stored at control (12.5 °C) or PCI-inducing temperatures (2.5 or 5 °C) followed by rewarming at 20 °C. MRI and ion leakage revealed that cold irreversibly impairs ripening-associated membrane liquefaction; MRI also showed that the internal and external fruit tissues responded differently to cold. MDA and especially starch contents, were affected by chilling in a tissue-specific manner. The expression of the six genes studied: ACO1 and ACS2 (ripening), CBF1 (cold response), DHN, AOX1a and LoxB (stress-related) showed non-overlapping temporal and spatially-specific responses. Overall, the data highlighted the interconnectedness of fruit cold response and ripening, and showed how cold stress reconfigures the latter. They further underscored that multidimensional spatial and temporal biological studies are needed to develop effective solutions to PCI.

Transcriptional and physiological analyses of short-term Iron deficiency response in apple seedlings provide insight into the regulation involved in photosynthesis

Background

Iron (Fe) is an essential micronutrient for plants. Utilization of Fe deficiency-tolerant rootstock is an effective strategy to prevent Fe deficiency problems in fruit trees production. Malus halliana is an apple rootstock that is resistant to Fe deficiency; however, few molecular studies have been conducted on M. halliana.

Results

To evaluate short-term molecular response of M. halliana leaves under Fe deficiency condition, RNA sequencing (RNA-Seq) analyses were conducted at 0 (T1), 0.5 (T2) and 3 d (T3) after Fe-deficiency stress, and the timepoints were determined with a preliminary physiological experiment. In all, 6907, 5328, and 3593 differentially expressed genes (DEGs) were identified in pairs of T2 vs. T1, T3 vs. T1, and T3 vs. T2. Several of the enriched DEGs were related to heme binding, Fe ion binding, thylakoid membranes, photosystem II, photosynthesis-antenna protein, porphyrin and chlorophyll metabolism and carotenoid biosynthesis under Fe deficiency, which suggests that Fe deficiency mainly affects the photosynthesis of M. halliana. Additionally, we found that Fe deficiency induced significant down-regulation in genes involved in photosynthesis at T2 when seedlings were treated with Fe-deficient solution for 0.5 d, indicating that there was a rapid response of M. halliana to Fe deficiency. A strong up-regulation of photosynthesis genes was detected at T3, which suggested that M. halliana was able to recover photosynthesis after prolonged Fe starvation. A similar expression pattern was found in pigment regulation, including genes for coding chlorophyllide a oxygenase (CAO), β-carotene hydroxylase (β-OHase), zeaxanthin epoxidase (ZEP) and 9-cis-epoxycarotenoid dioxygenase (NCED). Our results suggest that pigment regulation plays an important role in the Fe deficiency response. In addition, we verified sixteen genes related to photosynthesis-antenna protein, porphyrin and chlorophyll metabolism and carotenoid biosynthesis pathways using quantitative real-time PCR (qRT-PCR) to ensure the accuracy of transcriptome data. Photosynthetic parameters, Chl fluorescence parameters and the activity of Chlase were also determined.

Conclusions

This study broadly characterizes a molecular mechanism in which pigment and photosynthesis-related regulations play indispensable roles in the response of M. halliana to short-term Fe deficiency and provides a basis for future analyses of the key genes involved in the tolerance of Fe deficiency.

Electronic supplementary material

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Metabolic Responses to Low Temperature of Three Peach Fruit Cultivars Differently Sensitive to Cold Storage

Refrigerated storage is widely applied in order to maintain peach quality but it can also induce chilling injuries (CIs) such as flesh browning and bleeding, and mealiness. Peach fruit from three cultivars ('Red Haven', RH, 'Regina di Londa', RL, and 'Flaminia', FL) were stored for 4 weeks under low temperatures (0.5 and 5.5°C). GC-MS was employed to study changes in both metabolome and volatilome induced by cold storage in the mesocarp. CIs were assessed both at the end of each week of storage and after subsequent shelf-life (SL) at 20°C. Flesh browning and mealiness appeared to be more related to 5.5°C storage, while flesh bleeding revealed high incidence following 0.5°C storage. Compared to RL and FL, RH showed a marked lower incidence of CIs. Multivariate statistical analyses indicate that RH peaches indeed differ from RL and FL in particular when considering data from samples collected at the end of the cold storage. Common and divergent responses have been identified in terms of metabolic responses to the applied low temperatures. In all three cultivars raffinose, glucose-6P, fucose, xylose, sorbitol, GABA, epicatechin, catechin, and putrescine markedly increased during cold storage, while citramalic, glucuronic, mucic and shikimic acids decreased. Among volatile organic compounds (VOCs), aldehydes and alcohols generally accumulated more under low temperature conditions while esters and lactones evolved during subsequent SL. The main cultivar differences developed after cold storage during SL although some common responses (e.g., an increased production of ethyl acetate) were observed. The lower levels of flesh browning and bleeding displayed by RH peaches were related to compounds with antioxidant activity, or acting as osmotic protectants and membrane stabilizer. Indeed, RH showed higher levels of amino acids and urea, together with a marked increase in putrescine, sorbitol, maltitol, myoinositol and sucrose detected during storage and SL.

Interaction of 24-epibrassinolide and salicylic acid regulates pigment contents, antioxidative defense responses, and gene expression in Brassica juncea L. seedlings under Pb stress

Lead (Pb) is considered one the most hazardous pollutant, and its accumulation in soil and plants is of prime concern. To understand the role of plant hormones in combating heavy metal stress, the present study was planned to assess the interactive effects of 24-epibrassinolide (EBL) (10^-7 M) and salicylic acid (SA) (1 mM) in regulating growth, pigment contents, antioxidative defense response, and gene expression in Brassica juncea L. seedlings exposed to different concentrations of Pb metal (0.25, 0.50, and 0.75 mM). Reduction in root and shoot lengths, chlorophyll and carotenoid content, and non-enzymatic antioxidants like glutathione, ascorbic acid, and tocopherol in response to Pb toxicity was observed. The enzymatic antioxidants such as guaiacol peroxidase (POD), ascorbate peroxidase (APOX), glutathione peroxidase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate redductase (MDHAR), glutathione-S-transferease (GST), and glutathione peroxidase (GPOX) were lowered in response to Pb treatments. Other antioxidative enzymes including superoxide dismutase (SOD), catalase (CAT), and polyphenol oxidase (PPO) enhanced under metal stress. Co-application of EBL + SA to 0.75 mM Pb-treated seedlings resulted in improvement of root and shoot lengths, chlorophyll, and carotenoid contents. Similarly, glutathione, ascorbic acid, and tocopherol contents were also elevated. Enzymatic antioxidants were also significantly enhanced in response to pre-sowing combined treatment of both hormones. Gene expression analysis suggested elevation in expression of CAT, POD, GR, DHAR, and GST genes by application of EBL. Our results reveal that Pb metal toxicity caused adverse impact on B. juncea L. seedlings, but pre-soaking treatment with EBL and SA individually and in combination help seedlings to counter the ill effects of Pb by improving growth, contents of pigment, and modulation of antioxidative defense system. The combined application of EBL and SA was found to be more effective in ameliorating Pb stress as compared to their individual treatments.

Reduced Drought Tolerance by CRISPR/Cas9-Mediated SlMAPK3 Mutagenesis in Tomato Plants

Drought stress is one of the most destructive environmental factors that affect tomato plants adversely. Mitogen-activated protein kinases (MAPKs) are important signaling molecules that respond to drought stress. In this study, SlMAPK3 was induced by drought stress, and the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system was utilized to generate slmapk3 mutants. Two independent T1 transgenic lines and wild-type (WT) tomato plants were used for analysis of drought tolerance. Compared with WT plants, slmapk3 mutants exhibited more severe wilting symptom, higher hydrogen peroxide content, lower antioxidant enzymes activities, and suffered more membrane damage under drought stress. Furthermore, knockout of SlMAPK3 led to up- or down-regulated expressions of drought stress-responsive genes including SlLOX, SlGST, and SlDREB. The results suggest that SlMAPK3 is involved in drought response in tomato plants by protecting cell membranes from oxidative damage and modulating transcription of stress-related genes.

Deciphering the Role of CBF/DREB Transcription Factors and Dehydrins in Maintaining the Quality of Table Grapes cv. Autumn Royal Treated with High CO2 Levels and Stored at 0°C

C-repeat/dehydration-responsive element binding factors (CBF/DREB) are transcription factors which play a role in improving plant cold stress resistance and recognize the DRE/CRT element in the promoter of a set of cold regulated genes. Dehydrins (DHNs) are proteins that accumulate in plants in response to cold stress, which present, in some cases, CBF/DREB recognition sequences in their promoters and are activated by members of this transcription factor family. The application of a 3-day gaseous treatment with 20 kPa CO2 at 0°C to table grapes cv. Autumn Royal maintained the quality of the bunches during postharvest storage at 0°C, reducing weight loss and rachis browning. In order to determine the role of CBF/DREB genes in the beneficial effect of the gaseous treatment by regulating DHNs, we have analyzed the gene expression pattern of three VviDREBA1s (VviDREBA1-1, VviDREBA1-6, and VviDREBA1-7) as well as three VviDHNs (VviDHN1a, VviDHN2, and VviDHN4), in both alternative splicing forms. Results showed that the differences in VviDREBA1s expression were tissue and atmosphere composition dependent, although the application of high levels of CO2 caused a greater increase of VviDREBA1-1 in the skin, VviDREBA1-6 in the pulp and VviDREBA1-7 in the skin and pulp. Likewise, the application of high levels of CO2 regulated the retention of introns in the transcripts of the dehydrins studied in the different tissues analyzed. The DHNs promoter analysis showed that VviDHN2 presented the cis-acting DRE and CRT elements, whereas VviDHN1a presented only the DRE motif. Our electrophoretic mobility shift assays (EMSA) showed that VviDREBA1-1 was the only transcription factor that had in vitro binding capacity to the CRT element of the VviDHN2 promoter region, indicating that the transcriptional regulation of VviDHN1a and VviDHN4 would be carried out by activating other independent routes of these transcription factors. Our results suggest that the application of high CO2 levels to maintain table grape quality during storage at 0°C, leads to an activation of CBF/DREBs transcription factors. Among these factors, VviDREBA1-1 seems to participate in the transcriptional activation of VviDHN2 via CRT binding, with the unspliced form of this DHN being activated by high CO2 levels in all the tissues analyzed.

SlMAPK1/2/3 and Antioxidant Enzymes Are Associated with H2O2-Induced Chilling Tolerance in Tomato Plants

Hydrogen peroxide (H₂O₂) acts as a signaling molecule in response to cold stress. Mitogen-activated protein kinases (MAPKs) and C-repeat/dehydration-responsive factor (CBF) play important roles in cold response regulation. To investigate the roles of MAPKs and CBF in H₂O₂-induced chilling tolerance, tomato (Solanum lycopersicum cv. Ailsa Craig) plants were treated with 1 mM H₂O₂ before chilling treatment. The results showed that H₂O₂ treatment protected subcellular structure, increased concentrations of abscisic acid (ABA), zeatin riboside (ZR), and methyl jasmonate (MeJA), but decreased the concentration of gibberellic acid (GA₃). Furthermore, 1 mM H₂O₂ treatment enhanced the activities of antioxidant enzymes. Meanwhile, relative expressions of SlMAPK1/2/3 and SlCBF1 in H₂O₂-treated plants were higher than those in the control. Our findings suggest that H₂O₂ treatment might enhance the chilling tolerance of tomato plants by activating SlMAPK1/2/3 and SlCBF1 gene expression and by regulating phytohormone concentrations and antioxidant enzyme activities.

Effect of Exogenous Nitro Oxide on Chilling Tolerance, Polyamine, Proline, and γ-Aminobutyric Acid in Bamboo Shoots (Phyllostachys praecox f. prevernalis)

The effects of exogenous nitro oxide (NO) on chilling resistance and the metabolism of polyamine, proline, and γ-aminobutyric acid of bamboo shoots were investigated. Bamboo shoots were dipped in 0.07 mM sodium nitroprusside (SNP) and stored at 1 °C for 56 days. During the storage, the development of chilling injury of SNP treated bamboo shoots was inhibited with decreased accumulation of malonaldehyde and electrical leakage. At the end of storage, the chilling injury incidence of treated bamboo shoots decreased by 37.9% while their malonaldehyde content and electrical leakage were 8.8% and 18.6% lower than that of the control, respectively. Interestingly, the endogenous NO, polyamines, γ-aminobutyric acid, and proline contents of treated bamboo shoot also significantly increased. Consistently, the metabolisms of these nitrogenous compounds were stimulated in treated bamboo shoots, according to their higher (20.2%-49.8%) related enzyme activities, including nitric oxide synthase, arginine decarboxylase, ornithine decarboxylase, glutamate decarboxylase, orn-δ-aminotransferase, and Δ1-pyrroline-5-carboxylate synthetase. The results indicated that the SNP treatment enhanced chilling tolerance of bamboo shoots, which might associate with the activated metabolism of polyamines, γ-aminobutyric acid, and proline. SNP treatment might be an alternative technology to avoid chill injury during cold storage of bamboo shoots.

SRNAome and degradome sequencing analysis reveals specific regulation of sRNA in response to chilling injury in tomato fruit

Plant genomes encode diverse small RNA classes that function in distinct gene-silencing pathways. To elucidate the intricate regulation of microRNAs (miRNAs) and endogenous small-interfering RNAs (siRNAs) in response to chilling injury in tomato fruit, the deep sequencing and bioinformatic methods were combined to decipher the small RNAs landscape in the control and chilling-injured groups. Except for the known miRNAs and ta-siRNAs, 85 novel miRNAs and 5 ta-siRNAs members belonging to 3 TAS families (TAS5, TAS9 and TAS10) were identified, 34 putative phased small RNAs and 740 cis/trans-natural antisense small-interfering RNAs (nat-siRNAs) were also found in our results which enriched the tomato small RNAs repository. A large number of genes targeted by those miRNAs and siRNAs were predicted to be involved in the chilling injury responsive process and five of them were verified via degradome sequencing. Based on the above results, a regulatory model that comprehensively reveals the relationships between the small RNAs and their targets was set up. This work provides a foundation for further study of the regulation of miRNAs and siRNAs in the plant in response to chilling injury.

Salicylic-Acid-Induced Chilling- and Oxidative-Stress Tolerance in Relation to Gibberellin Homeostasis, C-Repeat/Dehydration-Responsive Element Binding Factor Pathway, and Antioxidant Enzyme Systems in Cold-Stored Tomato Fruit

Effects of salicylic acid (SA) on gibberellin (GA) homeostasis, C-repeat/dehydration-responsive element binding factor (CBF) pathway, and antioxidant enzyme systems linked to chilling- and oxidative-stress tolerance in tomato fruit were investigated. Mature green tomatoes (Solanum lycopersicum L. cv. Moneymaker) were treated with 0, 0.5, and 1 mM SA solution for 15 min before storage at 4 °C for 28 days. In comparison to 0 or 0.5 mM SA, 1 mM SA significantly decreased the chilling injury (CI) index in tomato fruit. In the SA-treated fruit, the upregulation of GA biosynthetic gene (GA3ox1) expression was followed by gibberellic acid (GA₃) surge and DELLA protein degradation. CBF1 participated in the SA-modulated tolerance and stimulated the expression of GA catabolic gene (GA2ox1). Furthermore, 1 mM SA enhanced activities of antioxidant enzymes and, thus, reduced reactive oxygen species accumulation. Our findings suggest that SA might protect tomato fruit from CI and oxidative damage through regulating GA metabolism, CBF1 gene expression, and antioxidant enzyme activities.

Contribution of polyamines metabolism and GABA shunt to chilling tolerance induced by nitric oxide in cold-stored banana fruit

Effect of exogenous nitric oxide (NO) on polyamines (PAs) catabolism, γ-aminobutyric acid (GABA) shunt, proline accumulation and chilling injury of banana fruit under cold storage was investigated. Banana fruit treated with NO sustained lower chilling injury index than the control. Notably elevated nitric oxide synthetase activity and endogenous NO level were observed in NO-treated banana fruit. PAs contents in treated fruit were significantly higher than control fruit, due to the elevated activities of arginine decarboxylase and ornithine decarboxylase. NO treatment increased the activities of diamine oxidase, polyamine oxidase and glutamate decarboxylase, while reduced GABA transaminase activity to lower levels compared with control fruit, which resulted the accumulation of GABA. Besides, NO treatment upregulated proline content and significantly enhanced the ornithine aminotransferase activity. These results indicated that the chilling tolerance induced by NO treatment might be ascribed to the enhanced catabolism of PAs, GABA and proline.

Influence of cryopreservation on the antioxidative activity of in vitro cultivated Hypericum species

Antioxidative activity of two in vitro cultivated Hypericum species – H. rumeliacum Boiss. and H. tetrapterum Fr. – was estimated after cryopreservation. Both species were successfully regenerated after a cryopreservation procedure performed by the vitrification method. H. tetrapterum did not manifest any significant oxidative stress-induced changes caused by low-temperature treatment. Conversely, a decrease in green pigments' content of H. rumeliacum was measured, particularly pronounced in chlorophyll b, which was accompanied by an increase of carotenoids in the regenerated plants.

A strong increase of malone dialdehyde and H₂O₂ levels in H. rumeliacum tissues was detected. Superoxide dismutase activity was enhanced by 170%, as well as the catalase activity, which was 220% above the control. The same trend was observed in H. tetrapterum, although less pronounced – 143% increase of superoxide dismutase and 112% of catalase.

Cryopreservation did not influence the phenol content in the examined plants, but it led to an increase of flavonoid content, especially in H. tetrapterum, by 237%. Total antioxidant activity in regenerated H. tetrapterum varied around the control level, but it was increased in H. rumeliacum. The free proline content in H. tetrapterum remained almost unaffected after freezing, as opposed to H. rumeliacum, where a strong increase of proline content (208% above the control) occurred. An electrolyte leakage from the cells of H. rumeliacum regenerated after cryopreservation was also registered, albeit not significant.

A bulk segregant gene expression analysis of a peach population reveals components of the underlying mechanism of the fruit cold response

Peach fruits subjected for long periods of cold storage are primed to develop chilling injury once fruits are shelf ripened at room temperature. Very little is known about the molecular changes occurring in fruits during cold exposure. To get some insight into this process a transcript profiling analyses was performed on fruits from a PopDG population segregating for chilling injury CI responses. A bulked segregant gene expression analysis based on groups of fruits showing extreme CI responses indicated that the transcriptome of peach fruits was modified already during cold storage consistently with eventual CI development. Most peach cold-responsive genes have orthologs in Arabidopsis that participate in cold acclimation and other stresses responses, while some of them showed expression patterns that differs in fruits according to their susceptibility to develop mealiness. Members of ICE1, CBF1/3 and HOS9 regulons seem to have a prominent role in differential cold responses between low and high sensitive fruits. In high sensitive fruits, an alternative cold response program is detected. This program is probably associated with dehydration/osmotic stress and regulated by ABA, auxins and ethylene. In addition, the observation that tolerant siblings showed a series of genes encoding for stress protective activities with higher expression both at harvest and during cold treatment, suggests that preprogrammed mechanisms could shape fruit ability to tolerate postharvest cold-induced stress. A number of genes differentially expressed were validated and extended to individual genotypes by medium-throughput RT-qPCR. Analyses presented here provide a global view of the responses of peach fruits to cold storage and highlights new peach genes that probably play important roles in the tolerance/sensitivity to cold storage. Our results provide a roadmap for further experiments and would help to develop new postharvest protocols and gene directed breeding strategies to better cope with chilling injury.

Deciphering the metabolic pathways influencing heat and cold responses during post-harvest physiology of peach fruit

Peaches are highly perishable and deteriorate quickly at ambient temperature. Cold storage is commonly used to prevent fruit decay; however, it affects fruit quality causing physiological disorders collectively termed 'chilling injury' (CI). To prevent or ameliorate CI, heat treatment is often applied prior to cold storage. In the present work, metabolic profiling was performed to determine the metabolic dynamics associated with the induction of acquired CI tolerance in response to heat shock. 'Dixiland' peach fruits exposed to 39 °C, cold stored, or after a combined treatment of heat and cold, were compared with fruits ripening at 20 °C. Dramatic changes in the levels of compatible solutes such as galactinol and raffinose were observed, while amino acid precursors of the phenylpropanoid pathway were also modified due to the stress treatments, as was the polyamine putrescine. The observed responses towards temperature stress in peaches are composed of both common and specific response mechanisms to heat and cold, but also of more general adaptive responses that confer strategic advantages in adverse conditions such as biotic stresses. The identification of such key metabolites, which prime the fruit to cope with different stress situations, will likely greatly accelerate the design and the improvement of plant breeding programs.

Alleviating effects of exogenous Gamma-aminobutiric acid on tomato seedling under chilling stress

Low temperature during germination and early seedling growth is one of the most significant limiting factors in the productivity of plants. Tomato seedling germination is sensitive to chilling stress. Gamma-aminobutyric acid (GABA), as a non-protein amino acid, involved in various stress tolerances in plants. In this study, 5-day old tomato seedlings were exposed to chilling stress (2 ± 0.05 °C for 48 h) and then the effects of 0, 100, 250, 500 and 750 μmolL(-1) concentrations of GABA on electrolyte leakage, proline and malondialdehyde (MDA) content were investigated. The resultS showed that the antioxidant enzyme activity, electrolyte leakage, MDA and proline content were significantly reduced by GABA treatments. However under chilling stress seedlings treated with GABA exhibited significantly higher sugar and proline contents as compared to un-treated seedlings. These results suggest that GABA treatment protects tomato seedlings from chilling stress by enhancing some antioxidant enzymes activity and reducing MDA content which results in maintaining membrane integrity.

Mitigation of postharvest chilling injury in tomato fruit by prohexadione calcium

Storage of tomato (Solanum lycopersicum) as originally tropical fruit is limited by the risk of chilling injury (CI). To develop an effective technique to reduce CI, the effects of treatment with 0, 50 and 100 μM prohexadione-calcium (Pro-Ca) on CI, electrolyte leakage (EL), malondialdehyde (MDA) and proline contents, and activities of phospholipase D (PLD) and lipoxygenase (LOX), were investigated in tomato fruit stored at 1°C for 21 days. Treatment with Pro-Ca, without significant difference between two applied concentrations, significantly mitigated chilling injury. Also, Pro-Ca treatment maintained lower levels of EL and MDA content, higher level of proline content and inhibited the increases in PLD and LOX activities compared with the control fruit. These results suggest that Pro-Ca might mitigate CI by inhibiting PLD and LOX activities and by enhancing membrane integrity.