Effect of nitric oxide on antioxidative response and proline metabolism in banana during cold storage

Effects of the Combined Treatment of Trans-2-Hexenal, Ascorbic Acid, and Dimethyl Dicarbonate on the Quality in Fresh-Cut Potatoes (Solanum tuberosum L.) during Storage

Fresh-cut potatoes (Solanum tuberosum L.) are susceptible to browning and microbial contamination during storage. In this study, the effects of trans-2-hexenal (E2H), ascorbic acid (VC), dimethyl dicarbonate (DMDC), and the combined treatment of E2H, VC, and DMDC on quality deterioration in fresh-cut potatoes were investigated. The response surface methodology (RSM) demonstrated that E2H, VC, and DMDC concentrations of 0.010%, 0.65%, and 240 mg/L, respectively, were the optimum conditions for fresh-cut potato preservation. Further analysis showed that the combined treatment of E2H, VC, and DMDC was the most effective method of reducing quality deterioration in potatoes compared to the control and individual treatments. Furthermore, the combined treatment of E2H, VC, and DMDC could decrease the accumulation of reactive oxygen species (ROS) via improving antioxidant enzyme activities. Meanwhile, energy-metabolism-related enzyme activities and glutamate decarboxylase (GAD) activity were enhanced, while γ-aminobutyric acid transaminase (GABA-T) activity was reduced via the combined treatment of E2H, VC, and DMDC, which contributed to maintaining high energy levels and GABA content in potatoes. These findings suggested that the combined treatment of E2H, VC, and DMDC could protect membrane integrity through enhancing antioxidant capacity, energy levels, and GABA content to maintain quality in fresh-cut potatoes.

Investigation of Melatonin Incorporated CMC-Gelatin Based Edible Coating on the Alleviation of Chilling Injury Induced Pericarp Browning in Longkong

Longkong (Aglaia dookkoo Griff.) fruit is prone to rapid pericarp browning and shortened shelf life (<7 days) under prolonged low-temperature storage. This study investigates the effect of an edible coating, comprising carboxymethyl cellulose (CMC) and gelatin in a fixed 3:1 ratio, integrated with various concentrations of melatonin (MT) (0.4, 0.8, and 1.2 mM/L) to mitigate chilling injury in longkong fruit. Coated longkong fruits were stored at 13 °C with 90% relative humidity for 18 days and underwent physicochemical evaluations every three days. Samples coated with CMC-Gel without MT and uncoated fruits were served as controls. The findings indicated that the CMC-Gel-MT coating significantly mitigated pericarp browning, chilling injury, weight loss, and respiration rate increase under extended cold storage conditions. High concentrations of MT (≥0.8 mM/L) in the coating notably inhibited the activities of cellular degrading enzymes such as lipoxygenase and phospholipase D. This inhibition contributed to reduced membrane permeability, lower reactive oxygen species accumulation (H2O2, OH-, O2-), and decreased malondialdehyde levels in the longkong pericarp. Furthermore, the CMC-Gel-MT coating increased the activity of phenylalanine ammonia lyase, leading to an enhancement in phenolic content. Consequently, it improved the fruit's ability to scavenge DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,20-azino-di-3-ethylbenzthiazoline sulfonic acid) radicals. Control samples exhibited high levels of pericarp browning-related enzymes (polyphenol oxidase, peroxidase), whereas CMC-Gel-MT-coated fruits, particularly at higher MT concentrations, showed significant reductions in those enzyme activities. In conclusion, incorporating high concentrations of MT in a CMC-Gel-based edible coating is a promising alternative for mitigating chilling injury in longkong fruit.

Assessment of proline function in higher plants under extreme temperatures

Climate change and abiotic stress factors are key players in crop losses worldwide. Among which, extreme temperatures (heat and cold) disturb plant growth and development, reduce productivity and, in severe cases, lead to plant death. Plants have developed numerous strategies to mitigate the detrimental impact of temperature stress. Exposure to stress leads to the accumulation of various metabolites, e.g. sugars, sugar alcohols, organic acids and amino acids. Plants accumulate the amino acid 'proline' in response to several abiotic stresses, including temperature stress. Proline abundance may result from de novo synthesis, hydrolysis of proteins, reduced utilization or degradation. Proline also leads to stress tolerance by maintaining the osmotic balance (still controversial), cell turgidity and indirectly modulating metabolism of reactive oxygen species. Furthermore, the crosstalk of proline with other osmoprotectants and signalling molecules, e.g. glycine betaine, abscisic acid, nitric oxide, hydrogen sulfide, soluble sugars, helps to strengthen protective mechanisms in stressful environments. Development of less temperature-responsive cultivars can be achieved by manipulating the biosynthesis of proline through genetic engineering. This review presents an overview of plant responses to extreme temperatures and an outline of proline metabolism under such temperatures. The exogenous application of proline as a protective molecule under extreme temperatures is also presented. Proline crosstalk and interaction with other molecules is also discussed. Finally, the potential of genetic engineering of proline-related genes is explained to develop 'temperature-smart' plants. In short, exogenous application of proline and genetic engineering of proline genes promise ways forward for developing 'temperature-smart' future crop plants.

Potassium fulvic acid alleviates salt stress of citrus by regulating rhizosphere microbial community, osmotic substances and enzyme activities

Salt stress damage to plants has been becoming a global concern for agriculture. The application of potassium fulvic acid (PFA) is a promising strategy to alleviate the damage to plants and improve soil quality. However, the study of PFA on plant growth and rhizosphere microbial community remains limited. In this study, microcosmic experiments were conducted to verify the effect of PFA on citrus. Trifoliate orange (Poncirus trifoliata), the most important citrus rootstock, was used to evaluate the effect of PFA on salt damage. The results showed that PFA significantly increased the contents of chlorophyll a, chlorophyll b and carotenoid by 30.09%, 17.55% and 27.43%, and effectively avoided the yellowing and scorching of leaves under salt stress. Based on the results of two-way ANOVA, the mitigation of salt stress on trifoliate seedlings primarily attributed to the enhancement of protective enzyme activities, K⁺/Na⁺ ratio and the contents of soluble sugar, soluble protein and proline. Moreover, PFA enhanced neutral protease (S-NPT), sucrase (S-SC) and urease (S-UE) of rhizosphere soil and improved soil nutrition status. The abundance of Bacillus, a kind of rhizosphere beneficial bacteria, was improved by PFA under salt stress, which was mainly associated with the increased activities of S-NPT, S-SC and S-UE. Overall, the application of PFA showed great potential for the alleviation of salt damage on citrus.

Postharvest chitosan-arginine nanoparticles application ameliorates chilling injury in plum fruit during cold storage by enhancing ROS scavenging system activity

BACKGROUND

Plum (Prunus domestica L.) has a short shelf-life period due to its high respiration rate and is sensitive to low storage temperatures, which can lead to the appearance of chilling injury symptoms. In this investigation, we applied new coating treatments based on chitosan (CTS) and arginine (Arg) to plum fruit (cv. 'Stanley').

RESULTS

Fruit were treated with distilled water (control), Arg at 0.25 and 0.5 mM, CTS at 1% (w/v) or Arg-coated CTS nanoparticles (CTS-Arg NPs) at 0.5 and 1% (w/v), and then stored at 1 °C for days. The application of CTS-Arg NPs at 0.5% attenuated chilling injury, which was accompanied by accumulation of proline, reduced levels of electrolyte leakage and malondialdehyde, as well as suppressed the activity of polyphenol oxidase. Plums coated with CTS-Arg NPs (0.5%) showed higher accumulation of phenols, flavonoids and anthocyanins, due to the higher activity of phenylalanine ammonia-lyase, which in turn resulted in higher DPPH scavenging capacity. In addition, CTS-Arg NPs (0.5%) treatment delayed plum weight loss and retained fruit firmness and ascorbic acid content in comparison to control fruit. Furthermore, plums treated with CTS-Arg NPs exhibited lower H₂O₂ accumulation than control fruit due to higher activity of antioxidant enzymes, including CAT, POD, APX and SOD.

CONCLUSIONS

The present findings show that CTS-Arg NPs (0.5%) were the most effective treatment in delaying chilling injury and prolonging the shelf life of plum fruit.

Arbuscular mycorrhizal fungi enhanced rice proline metabolism under low temperature with nitric oxide involvement

Arbuscular mycorrhizal fungi (AMF) are known to improve plant stress tolerance by regulating proline accumulation, and nitric oxide (NO) plays an important signaling role in proline metabolism. Environmental nitrogen (N) affects AMF colonization and its contribution to host plants resistance to stress conditions. However, the relationship between proline metabolism and NO in mycorrhizal rice and the effect of N application on symbiont proline metabolism under low temperature have not been established. Pot culture experiments with different temperature, N and exogenous NO donor treatments were conducted with non-mycorrhizal and mycorrhizal rice. The results showed that AMF enhanced rice proline accumulation under low-temperature stress and decreased glutamate (Glu) and ornithine (Orn) concentrations significantly. In comparison with non-mycorrhizal rice, AMF colonization significantly decreased the Glu concentration, but had little effect on the Orn concentration under low-temperature stress, accompanied by increasing expression of OsP5CS2, OsOAT and OsProDH1. Exogenous application of NO increased proline concentration both under normal and low temperature, which exhibited a higher increase in mycorrhizal rice. NO also triggered the expression of key genes in the Glu and Orn pathways of proline synthesis as well as proline degradation. Higher N application decreased the AMF colonization, and AMF showed greater promotion of proline metabolism at low N levels under low temperature stress by regulating the Glu synthetic pathway. Meanwhile, AMF increased rice nitrate reductase (NR) and nitric oxide synthase (NOS) activities and then enhanced NO accumulation under low N levels. Consequently, it could be hypothesized that one of the mechanisms by which AMF improves plant resistance to low-temperature stress is the accumulation of proline via enhancement of the Glu and Orn synthetic pathways, with the involvement of the signaling molecule NO. However, the contribution of AMF to rice proline accumulation under low-temperature stress was attenuated by high N application.

Role of Nitric Oxide in Postharvest Senescence of Fruits

Nitric oxide (NO) acts as a gaseous signalling molecule and is considered to be a key regulator in the postharvest storage of fruits. Postharvest senescence is one of the most serious threats affecting the usage and economic value of fruits. Most recent studies have found that exogenous NO application can effectively improve the quality and prolong the shelf life of fruit postharvest by inhibiting postharvest diseases and alleviating chilling injury. Understanding the roles of NO is essential to elucidating how NO activates the appropriate set of responses to postharvest senescence. Here, we concluded that exogenous NO treatment alleviated senescence in postharvest fruit and attributed this to the following factors: (1) ethylene biosynthesis, (2) the antioxidant system, (3) polyamine metabolism and γ-aminobutyric acid (GABA) shunting, (4) cell wall metabolism, (5) sugar metabolism, (6) energy metabolism, (7) the CRT/DRE-binding factor (CBF) pathway and (8) S-nitrosylation. Moreover, crosstalk between NO and hydrogen sulfide (H₂S), hydrogen peroxide (H₂O₂), oxalic acid (OA), arginine (Arg), GATA or plant hormone abscisic acid (ABA), melatonin (MT), and methyl jasmonate (MeJA), along with the regulation of key genes, were found to be very important in responses to postharvest senescence. In this study, we focus on the recent knowledge concerning the alleviative effect of NO on postharvest senescence, covering ethylene biosynthesis, the antioxidant system and related gene and protein expression.

Comparative study of pyrochar and hydrochar on peanut seedling growth in a coastal salt-affected soil of Yellow River Delta, China

Biochar (i.e., pyrochar and hydrochar) application is a promising strategy to improve soil quality and productivity. However, the comparison of biochars with different carbonization methods and feedstocks for the plant growth in the coastal salt-affected soil remains limited. In this study, a 30-day microcosmic experiment was conducted to compare the effects of pyrochars and hydrochars derived from reed straw (RPC and RHC) and cow manure (CPC and CHC) on the peanut (Arachis hypogaea L.) seedling growth in a coastal salt-affected soil of Yellow River Delta, China. The results showed that RPC, CHC and CPC significantly elevated fresh shoot weight by 67.77%-89.37%, whereas the RHC amendment showed little effect. The malondialdehyde contents in peanut seedling leaves were significantly declined by 25.28%-35.51% with pyrochar and hydrochar amendments, which might be associated with the enhanced proline contents and K/Na ratios. The stimulation of certain phytohormones (i.e., indole-3-acetic acid, zeatin riboside, gibberellic acid 3) in peanut seedlings with pyrochar and hydrochar amendments might be attributed to the growth enhancement. RPC, CPC and CHC improved the soil properties and fertility such as cation-exchange capacity (CEC), total nitrogen, and available potassium and water holding capacity (WHC) of the coastal salt-affected soil. However, RHC not only significantly decreased soil CEC and WHC, but also increased soil exchangeable sodium percentage. The abundances of soil beneficial bacteria, such as f_Gemmatimonadacea, Sphingomonas, Blastococcus and Lysobacter were enhanced by RPC, CHC and CPC amendments, which were mainly associated with the increased WHC and CEC. Fungal community was less sensitive to pyrochar and hydrochar amendments than bacterial community according to the relative abundance and diversity, and beneficial fungi, such as Oidiodendron and Sarocladium were enriched in the CHC soil. Overall, the application of RPC, CHC and CPC showed greater potentials for the enhancement of peanut growth in a coastal salt-affected soil.

Application of Glycine betaine coated chitosan nanoparticles alleviate chilling injury and maintain quality of plum (Prunus domestica L.) fruit

The use of edible coatings can lead to significant extension of the postharvest life of fresh horticultural products through the regulation of water and gaseous exchange during storage. In this regard, nano-engineered materials are of great interest to design novel and multifunctional edible coatings and are increasingly employed. Chitosan and glycine betaine have been reported to enhance fruit tolerance to chilling stress during cold storage. The current study applied new coating treatments to plum (Prunus domestica L. cv. 'Stanley') fruit at maturity stage in a completely randomized factorial design with three replicates. Plums were treated with distilled water (control), glycine betaine (GB) at 2.5 and 5 mM, chitosan (CTS) at 1% (w/v) or glycine betaine-coated chitosan nanoparticles (CTS-GB NPs) at 0.5 and 1% (w/v) and stored at 1 °C for up to 40 days. The application of CTS-GB NPs (0.5% w/v) was the most effective treatment and induced lower electrolyte leakage, MDA and H₂O₂ content, and significantly alleviated chilling injury. Furthermore, this treatment remarkably increased the activity of PAL enzyme, resulting in higher levels of phenolics, flavonoids and anthocyanins content, and enhanced DPPH scavenging capacity. In addition, CTS-GB NPs treatment increased endogenous GB (9.25 mg g^-1 DW) and proline (1929.29 μg g^-1 FW) accumulation leading to higher activity of CAT, POD, SOD and APX enzymes. Based on the obtained results, the commercial application of CTS-GB NPs could effectively reduce chilling injury, preserve nutritional quality, and prolong the storage potential and shelf life of plum fruit.

Combination of salicylic acid and ultrasonication for alleviating chilling injury symptoms of longkong

Objectives

Chilling injury is a prominent physiological disorder in longkong fruit pericarp when stored under 13 °C for a prolonged period. This study aimed to investigate the effects of individual salicylic acid (SA) and ultrasonication (US) treatments and of the combination salicylic acid and ultrasonication (SA-US) on alleviating the chilling injury symptoms in longkong fruit pericarp when in prolonged cold storage.

Materials and methods

SA (1 mmol/L) and US (40 kHz, 10 min at 90% amplitude, 350 W) were used as individual and combined (SA-US) treatments to control the chilling injury in longkong pericarp. The various quality measures were checked every 2 days in longkong for up to 18 days of cold storage (13 °C, 90% relative humidity).

Results

The results revealed that the control fruits treated with water exhibited severe chilling injury symptoms followed in rank order by US, SA, and SA-US cases. Treatments such as US and SA alone were more effective in controlling chilling injuries than control, while only minimal significant differences were noticed between them. On the other hand, the longkong pericarp treated with the SA-US combination had significantly increased antioxidant enzyme (superoxide dismutase and catalase) activities and decreased levels of membrane lytic (phospholipase D and lipoxygenase) enzymes and browning-inducing enzymes (phenylalanine ammonia lyase and polyphenol oxidase). Consequently, in the longkong pericarp, the chilling injury index, electrolytic leakage, respiration rate, weight loss, firmness, malondialdehyde content, changes in unsaturated and saturated fatty acid contents, and reactive oxygen species were significantly controlled by this treatment.

Conclusions

The present study concludes that longkong fruit treatment with a combination of US and SA is an excellent alternative for controlling the chilling injury symptoms and extending the shelf-life.

A novel phase change coolant promoted quality attributes and glutamate accumulation in postharvest shiitake mushrooms involved in energy metabolism

Cold chain transportation is an important link in postharvest logistics of agricultural products. In current study, we developed a novel water-based phase change coolant (PCC), which showed longer effectiveness in maintaining low temperature condition compared with ice, and applied in preserving the postharvest mushrooms. The results showed that the novel PCC effectively inhibited water loss, as well as maintained quality attributes including firmness, color, phenolics, flavonoids, and thus prolonged the shelf-life of mushrooms. Low temperature condition created by the novel PCC treatment maintained high level of energy charge by activating the activities of SDH, CCO, H⁺-ATPase and Ca²⁺-ATPase, resulting in the delay of postharvest senescence. In addition, sufficient energy supply decreased the consumption of glutamate as carbon skeleton by inhibiting GDH activity, improved glutamate accumulation, and therefore maintained sensory properties as a result. Thus, the novel PCC might be an excellent substitute for ice in cold chain transportation of mushrooms.

Impact of chitosan in combination with potassium sorbate treatment on chilling injury and quality attributes of pomegranate fruit during cold storage

The impact of chitosan (CH) and potassium sorbate (PS) on quality attributes of pomegranate fruits (cv. Malas e Saveh) was evaluated during 90 days of storage at 4°C and 85%-90% relative humidity. The CH as well as the combined treatments (CH + PS) were effective in decreasing the chilling injury (CI) symptoms, electrolyte leakage, and malondialdehyde contents of fruit peel. Furthermore, CH, PS, and CH + PS treatments enhanced the activity of DPPH radical scavenging, and antioxidant enzymes of arils, and preserved the ascorbic acid content at high levels during the storage period. Fruits treated with CH1% + PS10% and CH2% + PS10% exhibited the lowest decay incidence and weight loss. Higher content of arils' phenols, flavonoids, and anthocyanin was observed in treated-fruits as a result of more activity of phenylalanine ammonia-lyase (PAL) and low activity of polyphenol oxidase (PPO). Consequently, CH + PS showed positive effects on the storage life of pomegranate fruits in terms of CI, decay incidence, and also nutritional values. PRACTICAL APPLICATIONS: Enhancement of chilling tolerance of pomegranate fruits during cold storage condition is a crucial issue. Application of CH coating alone or in combination with potassium sorbate could decrease the CI symptoms and preserved peel cell membrane integrity by maintaining electrolyte leakage (EL) and malondialdehyde in lower levels. Also, these treatments prevent weight loss and decay incidence in peel, and increase the activity of phenylpropanoid pathway and antioxidant systems in arils. All in all, usage of CH edible coating (2%) plus PS (10%) illustrated high efficiency in alleviating CI, decay incidence, and preserving nutritional quality of pomegranate fruits.

Fruit quality and major metabolites in cold-stored 'Wonhwang' Asian pears are differentially affected by fruit size

BACKGROUND

The size of 'Wonhwang' Asian pear fruit may affect fruit quality and physiological disorders differentially during distribution. Thus, this study aimed to evaluate the effect of fruit size on fruit physiological attributes and metabolic responses in terms of soluble carbohydrates and free amino acids in different-sized 'Wonhwang' Asian pears during cold storage and shelf life.

RESULTS

The rate of weight loss and the severity of fruit shriveling were higher in small fruit than in large fruit, while the severity of decay was lower during shelf life. Lightness and chroma values were lower in the cortex and core tissues of large fruit than small fruit, but hue angle values were higher in large fruit compared to small fruit. Glucose and fructose were higher in large fruit than in small fruit but sucrose and sorbitol were lower during shelf life after cold storage. The levels of most free amino acids were higher in large fruit than in small fruit, and only γ-aminobutyric acid (GABA) level was lower in large fruit.

CONCLUSION

These results indicate that fruit physiological and metabolic responses are differentially affected by fruit size during cold storage and shelf life. © 2020 Society of Chemical Industry.

Combining salicylic acid and trisodium phosphate alleviates chilling injury in bell pepper (Capsicum annuum L.) through enhancing fatty-acid desaturation efficiency and water retention

Chilling injury (CI) restricts the quality and shelf life of bell pepper fruits; reducing these CI-induced detrimental effects is therefore of high economic and agricultural relevance. Here, we investigated the effects of trisodium phosphate (TSP), salicylic acid (SA), and TSP + SA treatments on pepper fruits under cold stress at 4 °C for 25 d. Combined TSP + SA treatment performed an optimal effect. Specifically, TSP + SA treatment enhanced fatty-acid desaturation efficiency, as indicated by the increased expression of key fatty acid desaturase genes, and higher content of unsaturated fatty acids. Meanwhile, TSP + SA treatment inhibited the CI-induced membrane damage, manifested as lower electrolyte leakage and malondialdehyde content. Furthermore, low field-nuclear magnetic resonance and proline content also revealed that TSP + SA treatment mitigated CI through enhancing water retention in pepper fruits. Collectively, our results may shed new light on optimizing the low-temperature storage conditions of post-harvest peppers.

Melatonin Enhances Cold Tolerance by Regulating Energy and Proline Metabolism in Litchi Fruit

Melatonin (MLT) is a vital signaling molecule that regulates multiple physiological processes in higher plants. In the current study, the role of MLT in regulating chilling tolerance and its possible mechanisms in litchi fruit during storage at ambient temperatures after its removal from refrigeration was investigated. The results show that the application of MLT (400 μM, dipping for 20 min) to 'Baitangying' litchi fruit effectively delayed the development of chilling injury (CI) while inhibiting pericarp discoloration, as indicated by higher chromacity values (L*, a*, b*) and anthocyanin levels. MLT treatment suppressed the enhancements of the relative electrical conductivity (REC) and malondialdehyde (MDA) content, which might contribute to the maintenance of membrane integrity in litchi fruit. MLT treatment slowed the decline in cellular energy level, as evidenced by higher adenosine triphosphate (ATP) content and a higher energy charge (EC), which might be ascribed to the increased activities of enzymes associated with energy metabolism including H⁺-ATPase, Ca²⁺-ATPase, succinate dehydrogenase (SDH), and cytochrome C oxidase (CCO). In addition, MLT treatment resulted in enhanced proline accumulation, which was likely a consequence of the increased activities of ornithine-δ-aminotransferase (OAT) and Δ¹-pyrroline-5-carboxylate synthase (P5CS) and the suppressed activity of proline dehydrogenase (PDH). These results suggest that the enhanced chilling tolerance of litchi fruit after MLT treatment might involve the regulation of energy and proline metabolism.

Role of phospholipase C in banana in response to anthracnose infection

Phospholipase C (PLC) plays an important role in plant immunity, and anthracnose caused by the Colletotrichum species is a common postharvest disease of the banana fruit. This study aims to evaluate the role of PLC in anthrax resistance in banana. The experimental group of banana samples was treated with a banana anthracnose conidia suspension, and the control group was treated with distilled water. After inoculation, the groups were sprayed with ethephon, and indicators, such as hardness and conductivity changes; PLC activity, 1,2-diacylglycerol (DAG) and phosphatidic acid (PA)content; and MaPLC-1and MaPLC-2 expression levels, were assessed at 0, 3, 6, 9, 12, and 15 days. Moreover, the expression levels of MaPLC-1 and MaPLC-2 were detected in various tissues. The hardness of banana fruits in the experimental group decreased faster than that in the control group. Furthermore, the conductivity was higher in the experimental group than in the control group. Regarding PLC activity, DAG, and PA content, bananas in the experimental group showed higher activities than those in the control group. Moreover, relatively higher expression of PLC mRNA was detected in anthracnose-inoculated tissues. The evaluation of MaPLC-1 and MaPLC-2 expression levels showed that the mature peel had the highest MaPLC-1 expression level. However, the MaPLC-2 gene was expressed at relatively low levels in the fruit and at relatively high levels in the flower organs. PLC might play a role in fruit ripening in response to anthracnose resistance.

Metabolic responses and their correlations with phytochelatins in Amaranthus hypochondriacus under cadmium stress

Phytochelatins (PCs) play a vital role in the tolerance and enrichment of cadmium (Cd) in higher plants by chelating with Cd²⁺. The aim of this study was to perform a full-scale metabolomics analysis of metabolic responses highly correlated with PCs generation. These metabolites and metabolic pathways were expected to promote PCs generation and further optimize Cd absorption in plants. In the current study, Amaranthus hypochondriacus, a potential species for phytoremediation, was first adopted to investigate physiological responses to Cd stress via LCMS/MS-based metabolomics and the HPLC based determination of thiol compounds. The results showed that the leaves of A. hypochondriacus under high Cd stress accumulated 40 times the amount of Cd compared to the leaves of the plants not under Cd stress and had an increased content of three types of PCs. Metabolomics qualitatively identified 12084 substances in total, among which 41 were significantly different metabolites (SDMs) between the two groups and involved in 7 metabolic pathways. Among the SDMs, 12 metabolites were highly linearly correlated with PCs involved in three pathways (Val, Leu and Ile biosynthesis; Ala, Asp and Glu metabolism; and Arg and Pro metabolism). These results provide an innovative method to promote PCs synthesis for the restoration of Cd-contaminated-soil.

Nitric oxide and hydrogen sulfide in plants: which comes first?

Nitric oxide (NO) is a signal molecule regarded as being involved in myriad functions in plants under physiological, pathogenic, and adverse environmental conditions. Hydrogen sulfide (H2S) has also recently been recognized as a new gasotransmitter with a diverse range of functions similar to those of NO. Depending on their respective concentrations, both these molecules act synergistically or antagonistically as signals or damage promoters in plants. Nevertheless, available evidence shows that the complex biological connections between NO and H2S involve multiple pathways and depend on the plant organ and species, as well as on experimental conditions. Cysteine-based redox switches are prone to reversible modification; proteomic and biochemical analyses have demonstrated that certain target proteins undergo post-translational modifications such as S-nitrosation, caused by NO, and persulfidation, caused by H2S, both of which affect functionality. This review provides a comprehensive update on NO and H2S in physiological processes (seed germination, root development, stomatal movement, leaf senescence, and fruit ripening) and under adverse environmental conditions. Existing data suggest that H2S acts upstream or downstream of the NO signaling cascade, depending on processes such as stomatal closure or in response to abiotic stress, respectively.

Nitric oxide-dependent regulation of sweet pepper fruit ripening

Ripening is a complex physiological process that involves changes in reactive nitrogen and oxygen species that govern the shelf-life and quality of fruits. Nitric oxide (NO)-dependent changes in the sweet pepper fruit transcriptome were determined by treating fruits at the initial breaking point stage with NO gas. Fruits were also harvested at the immature (green) and ripe (red) stages. Fruit ripening in the absence of NO resulted in changes in the abundance of 8805 transcripts whose function could be identified. Among these, functional clusters associated with reactive oxygen/nitrogen species and lipid metabolism were significantly modified. NO treatment resulted in the differential expression of 498 genes framed within these functional categories. Biochemical analysis revealed that NO treatment resulted in changes in fatty acid profiling, glutathione and proline contents, and the extent of lipid peroxidation, as well as increases in the activity of ascorbate peroxidase and lipoxygenase. These data provide supporting evidence for the crucial role of NO in the ripening of pepper fruit.

The Role of IP3 in NO-Enhanced Chilling Tolerance in Peach Fruit

The role of inositol 1,4,5-trisphosphate (IP3) in nitric oxide (NO)-reduced chilling injury (CI) in peach fruit was investigated. The fruit were immersed in sodium nitroprusside (SNP) (NO donor) and neomycin (IP3 inhibitor). Results showed that chilling tolerance was enhanced upon exogenous SNP in postharvest peach fruit. Further, GABA accumulation was stimulated by SNP. The increase in protein expression and activity for enzymes in GABA biosynthesis, including glutamate decarboxylase (GAD), polyamine oxidase (PAO), and amino aldehyde dehydrogenase (AMADH), upon SNP treatment was also observed. Also, the up-regulation of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine d-aminotransferase (OAT) and the down-regulation of proline dehydrogenase (PDH) were induced by SNP treatment, thereby accelating proline production. Additionally, SNP treatment elevated protein expression and activity of alternative oxidase (AOX). The above effects induced upon SNP were partly weakened by neomycin. Therefore, IP3 mediated NO-activated GABA and proline accumulation as well as AOX, thus inducing chilling tolerance in postharvest peach fruit.

Effect of eugenol fumigation treatment on chilling injury and CBF gene expression in eggplant fruit during cold storage

The effect of eugenol (EUG) on chilling injury (CI) to eggplant fruit (Solanum melongena L.) was investigated. Eggplant fruit were pre-treated with 25 μL/L EUG, and then stored at 4 °C for 12 days. Results showed that EUG fumigation treatment effectively retarded the CI development, reduced pulp browning, weight loss, and malondialdehyde (MDA) content, and sustained soluble solids content (SSC) and proline content. Moreover, the activities of polyphenol oxidase (PPO) and peroxidase (POD) were inhibited by EUG. C-repeat/dehydration-responsive element binding factors (CBF) genes are transcription factors playing a critical role in cold acclimation. To illuminate the molecular regulation of EUG on chilling tolerance in eggplant fruit, a 1151 bp SmCBF gene was identified and the effect of EUG on SmCBF expression was determined by RT-qPCR. EUG resulted in a higher SmCBF expression. These findings suggested that EUG treatment had potential effect on alleviating CI in eggplant fruit.

Exogenous progesterone treatment alleviates chilling injury in postharvest banana fruit associated with induction of alternative oxidase and antioxidant defense

The effects of exogenous progesterone (PROG) on chilling injury (CI) in postharvest banana fruit were investigated. Concentration screening tests showed that 10^-5 mol/l PROG was most effective in reducing CI in banana fruit stored for 25 d at 5 ± 1 °C, but did not markly increase PROG content of pulps. This PROG treatment significantly reduced the electrolyte leakage, levels of malondialdehyde, O₂^- production rate and H₂O₂ contents in banana compared with control fruit. The PROG treatment caused an early induction of alternative oxidase (AOX) at the transcript and protein level to reduce the generation of O₂^- and H₂O₂. PROG treatment also enhanced the transcript levels and activities of antioxidant enzymes and maintained higher levels of reduced glutathione and ascorbic acid than the control fruit. These results suggested that PROG attenuating CI in banana fruit may be attributed to the induction of AOX and the improvement of enzyme and non-enzymatic antioxidant defenses.

Phomopsis longanae Chi-Induced Change in ROS Metabolism and Its Relation to Pericarp Browning and Disease Development of Harvested Longan Fruit

Phomopsis longanae Chi is a major pathogenic fungus that infects harvested longan fruit. This study aimed to investigate the effects of P. longanae on reactive oxygen species (ROS) metabolism and its relation to the pericarp browning and disease development of harvested longan fruit during storage at 28°C and 90% relative humidity. Results showed that compared to the control longans, P. longanae-inoculated longans displayed higher indexes of pericarp browning and fruit disease, higher O2 -. generation rate, higher accumulation of malondialdehyde (MDA), lower contents of glutathione (GSH) and ascorbic acid (AsA), lower 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability and reducing power in pericarp. In addition, P. longanae-infected longans exhibited higher activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) in the first 2 days of storage, and lower activities of SOD, CAT, and APX during storage day 2-5 than those in the control longans. These findings indicated that pericarp browning and disease development of P. longanae-infected longan fruit might be the result of the reducing ROS scavenging ability and the increasing O2 -. generation rate, which might lead to the peroxidation of membrane lipid, the loss of compartmentalization in longan pericarp cells, and subsequently cause polyphenol oxidase (PPO) and peroxidase (POD) to contact with phenolic substrates which result in enzymatic browning of longan pericarp, as well as cause the decrease of disease resistance to P. longanae and stimulate disease development of harvested longan fruit.

Tyrosine nitration of cytosolic peroxidase is probably triggered as a long distance signaling response in sunflower seedling cotyledons subjected to salt stress

Present work focuses on tissue and concentration-dependent effect of nitric oxide (NO) on the modulation of cytosolic peroxidase (POD; EC 1.11.1.7) activity in 2-day old etiolated sunflower (Helianthus annuus L.) seedlings. Exogenously supplied NO (in the form of sodium nitroprusside [SNP] or diethylenetriamine NONOate [DETA]; 125 to 500 μM) results in noteworthy enhancement in seedling growth in a concentration dependent manner irrespective of salt-stress and differentially affects POD activity in 2-day old seedling cotyledons. Elevated NO availability leads to an increase in the specific activity of POD in a concentration-dependent manner within 48 hrs as a rapid signaling response. Purification of POD protein using immunoprecipitation technique has shown that cotyledons derived from salt stressed seedlings exhibit a higher extent of tyrosine nitration of POD as compared to the control seedlings. Out of the four tyrosine residues found in the amino acid sequence of POD, the one at position 100 has been predicted to undergo nitration. Thus, a probable NO-POD crosstalk is evident in sunflower seedling cotyledons accompanying salt stress.

Regulation of gaseous signaling molecules on proline metabolism in plants

Proline accumulation plays an important role in the response and adaptation of plants to abiotic stress. Gaseous signaling molecules such as nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S) are involved in complicated events of cell signaling. However, the regulatory mechanisms of gaseous signaling molecules on proline synthesis and degradation are still unclear. This review summarized the biosynthesis and degradation of proline. The role of gaseous signaling molecules and their cross-talk on proline metabolic regulation in plants was discussed along with the future perspectives.

Molecular insights into the functional role of nitric oxide (NO) as a signal for plant responses in chickpea

The molecular mechanisms and targets of nitric oxide (NO) are not fully known in plants. Our study reports the first large-scale quantitative proteomic analysis of NO donor responsive proteins in chickpea. Dose response studies carried out using NO donors, sodium nitroprusside (SNP), diethylamine NONOate (DETA) and S-nitrosoglutathione (GSNO) in chickpea genotype ICCV1882, revealed a dose dependent positive impact on seed germination and seedling growth. SNP at 0.1mM concentration proved to be most appropriate following confirmation using four different chickpea genotypes. while SNP treatment enhanced the percentage of germination, chlorophyll and nitrogen contents in chickpea, addition of NO scavenger, cPTIO reverted its impact under abiotic stresses. Proteome profiling revealed 172 downregulated and 76 upregulated proteins, of which majority were involved in metabolic processes (118) by virtue of their catalytic (145) and binding (106) activity. A few crucial proteins such as S-adenosylmethionine synthase, dehydroascorbate reductase, pyruvate kinase fragment, 1-aminocyclopropane-1-carboxylic acid oxidase, 1-pyrroline-5-carboxylate synthetase were less abundant whereas Bowman-Birk type protease inhibitor, non-specific lipid transfer protein, chalcone synthase, ribulose-1-5-bisphosphate carboxylase oxygenase large subunit, PSII D2 protein were highly abundant in SNP treated samples. This study highlights the protein networks for a better understanding of possible NO induced regulatory mechanisms in plants.

Physiological, molecular and ultrastructural analyses during ripening and over-ripening of banana (Musa spp., AAA group, Cavendish sub-group) fruit suggest characteristics of programmed cell death

BACKGROUND

Programmed cell death (PCD) is a part of plant development that has been studied for petal senescence and vegetative tissue but has not been thoroughly investigated for fleshy fruits. The purpose of this research was to examine ripening and over-ripening in banana fruit to determine if there were processes in common to previously described PCD.

RESULTS

Loss of cellular integrity (over 40%) and development of senescence related dark spot (SRDS) occurred after day 8 in banana peel. Nuclease and protease activity in the peel increased during ripening starting from day 2, and decreased during over-ripening. The highest activity was for proteases and nucleases with apparent molecular weights of 86 kDa and 27 kDa, respectively. Images of SRDS showed shrinkage of the upper layers of cells, visually suggesting cell death. Decrease of electron dense areas was evident in TEM micrographs of nuclei.

CONCLUSION

This study shows for the first time that ripening and over-ripening of banana peel share physiological and molecular processes previously described in plant PCD. SRDS could represent a morphotype of PCD that characterizes a structural and biochemical failure in the upper layers of the peel, thereafter spreading to lower and adjacent layers of cells. © 2017 Society of Chemical Industry.

Prediction of banana color and firmness using a novel wavelengths selection method of hyperspectral imaging

This study investigated the feasibility of using hyperspectral imaging for determining banana color (L^∗, a^∗ and b^∗) and firmness as well as classifying ripe and unripe samples. The hyperspectral images at wavelengths 380-1023nm were acquired. Partial least squares (PLS) models were built to predict color and firmness. Two-wavelength combination method λ_i-λ_jλ_i+λ_j,λ_i²-λ_j²λ_i²+λ_j²,λ_iλ_jandλ_i-λ_j was used to identify the effective wavelengths. Based on the selected wavelengths, PLS models obtained good results with the coefficient of determination in prediction (R_p²) of 0.795 for L^∗, 0.972 for a^∗, 0.773 for b^∗ and 0.760 for firmness. The corresponding residual predictive deviation (RPD) values were 2.234, 6.098, 2.119 and 2.062, respectively. The classification results of ripe and unripe samples were excellent in two different principal components spaces (PC1+PC2 and PC1+PC3). It indicated hyperspectral imaging can be used to non-destructively determine banana color and firmness as well as classify ripe and unripe samples.

Hyperspectral Imaging for Predicting the Internal Quality of Kiwifruits Based on Variable Selection Algorithms and Chemometric Models

We investigated the feasibility and potentiality of determining firmness, soluble solids content (SSC), and pH in kiwifruits using hyperspectral imaging, combined with variable selection methods and calibration models. The images were acquired by a push-broom hyperspectral reflectance imaging system covering two spectral ranges. Weighted regression coefficients (BW), successive projections algorithm (SPA) and genetic algorithm-partial least square (GAPLS) were compared and evaluated for the selection of effective wavelengths. Moreover, multiple linear regression (MLR), partial least squares regression and least squares support vector machine (LS-SVM) were developed to predict quality attributes quantitatively using effective wavelengths. The established models, particularly SPA-MLR, SPA-LS-SVM and GAPLS-LS-SVM, performed well. The SPA-MLR models for firmness (R _pre  = 0.9812, RPD = 5.17) and SSC (R _pre  = 0.9523, RPD = 3.26) at 380-1023 nm showed excellent performance, whereas GAPLS-LS-SVM was the optimal model at 874-1734 nm for predicting pH (R _pre  = 0.9070, RPD = 2.60). Image processing algorithms were developed to transfer the predictive model in every pixel to generate prediction maps that visualize the spatial distribution of firmness and SSC. Hence, the results clearly demonstrated that hyperspectral imaging has the potential as a fast and non-invasive method to predict the quality attributes of kiwifruits.

Involvement of WRKY Transcription Factors in Abscisic-Acid-Induced Cold Tolerance of Banana Fruit

Phytohormone abscisic acid (ABA) and plant-specific WRKY transcription factors (TFs) have been implicated to play important roles in various stress responses. The involvement of WRKY TFs in ABA-mediated cold tolerance of economical fruits, such as banana fruit, however remains largely unknown. Here, we reported that ABA application could induce expressions of ABA biosynthesis-related genes MaNCED1 and MaNCED2, increase endogenous ABA contents, and thereby enhance cold tolerance in banana fruit. Four banana fruit WRKY TFs, designated as MaWRKY31, MaWRKY33, MaWRKY60, and MaWRKY71, were identified and characterized. All four of these MaWRKYs were nuclear-localized and displayed transactivation activities. Their expressions were induced by ABA treatment during cold storage. More importantly, the gel mobility shift assay and transient expression analysis revealed that MaWRKY31, MaWRKY33, MaWRKY60, and MaWRKY71 directly bound to the W-box elements in MaNCED1 and MaNCED2 promoters and activated their expressions. Taken together, our findings demonstrate that banana fruit WRKY TFs are involved in ABA-induced cold tolerance by, at least in part, increasing ABA levels via directly activating NECD expressions.

Characteristics of Three Thioredoxin Genes and Their Role in Chilling Tolerance of Harvested Banana Fruit

Thioredoxins (Trxs) are small proteins with a conserved redox active site WCGPC and are involved in a wide range of cellular redox processes. However, little information on the role of Trx in regulating low-temperature stress of harvested fruit is available. In this study, three full-length Trx cDNAs, designated MaTrx6, MaTrx9 and MaTrx12, were cloned from banana (Musa acuminata) fruit. Phylogenetic analysis and protein sequence alignments showed that MaTrx6 was grouped to h2 type with a typical active site of WCGPC, whereas MaTrx9 and MaTrx12 were assigned to atypical cys his-rich Trxs (ACHT) and h3 type with atypical active sites of GCAGC and WCSPC, respectively. Subcellular localization indicated that MaTrx6 and MaTrx12 were located in the plasma membrane and cytoplasm, respectively, whereas MaTrx9 showed a dual cytoplasmic and chloroplast localization. Application of ethylene induced chilling tolerance of harvested banana fruit, whereas 1-MCP, an inhibitor of ethylene perception, aggravated the development of chilling injury. RT-qPCR analysis showed that expression of MaTrx12 was up-regulated and down-regulated in ethylene- and 1-MCP-treated banana fruit at low temperature, respectively. Furthermore, heterologous expression of MaTrx12 in cytoplasmic Trx-deficient Saccharomyces cerevisiae strain increased the viability of the strain under H₂O₂. These results suggest that MaTrx12 plays an important role in the chilling tolerance of harvested banana fruit, possibly by regulating redox homeostasis.

Exogenous Melatonin Treatment Increases Chilling Tolerance and Induces Defense Response in Harvested Peach Fruit during Cold Storage

The effect of exogenous melatonin on chilling injury in peach fruit after harvest was investigated. To explore the optimum concentration of melatonin for chilling tolerance induction, peach fruit were treated with 50, 100, or 200 μM melatonin for 120 min and then stored for 28 days at 4 °C. The results showed that application of melatonin at 100 μM was most effective in reducing chilling injury of peach fruit after harvest. Peaches treated with melatonin at this concentration displayed higher levels of extractable juice rate and total soluble solids than the non-treated peaches. In addition, melatonin treatment enhanced expression of PpADC, PpODC, and PpGAD and consequently increased polyamines and γ-aminobutyric acid (GABA) contents. Meanwhile, the upregulated transcripts of PpADC and PpODC and inhibited PpPDH expression resulted in the higher proline content in melatonin-treated fruit compared to the control fruit. Our results revealed that melatonin treatment may be a useful technique to alleviate chilling injury in cold-stored peach fruit. The chilling tolerance of harvested peaches induced by melatonin treatment is associated with higher levels of polyamine, GABA, and proline. These data provided here are the first protective evidence of exogenous melatonin in harvested horticultural products in response to direct chilling stress.

Effects of nitric oxide on mitochondrial oxidative defence in postharvest peach fruits

BACKGROUND

It has been confirmed that the accumulation of reactive oxygen species (ROS) in fruit can cause oxidative damage and nitric oxide (NO) can regulate the accumulation of ROS and the antioxidative defence of fruit. However, little is known about the roles of NO on the antioxidant system in mitochondria of fruit. In this study, Feicheng peach fruits were dipped with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) and NO solutions to explore the effects of NO on the membrane permeability transition and antioxidant system in mitochondria of peach fruit.

RESULTS

Treatment with 15 µmol L(-1) NO solution could delay the decrease of mitochondrial permeability transition and decrease the content of ROS in mitochondria. Besides, when the endogenous NO was scavenged by c-PTIO, the ROS in mitochondria increased greatly and superoxide dismutase activity decreased, while the content and activities of peroxidase and catalase changed slightly.

CONCLUSION

By delaying the decrease of mitochondrial permeability transition, 15 µmol L(-1) NO treatment could promote a more stable internal medium in mitochondria of Feicheng peach fruit. The increases in the activities of antioxidant enzymes in mitochondria caused by the remove of endogenous NO suggested that NO also plays an important role in the mitochondrial antioxidant system of Feicheng peach fruit.

Involvement of energy metabolism to chilling tolerance induced by hydrogen sulfide in cold-stored banana fruit

In this study, the effect of hydrogen sulfide (H2S) on energy metabolism in postharvest banana fruit under chilling stress was investigated. Banana fruit, fumigated with optimal concentration (0.5mM) of aqueous sodium hydrosulfide (NaHS) solution for 24h, were initially stored at 7°C for 14d and 20°C for another 6d. H2S treated banana fruit showed both higher value of firmness and Hue angle, as well as lower value of electrolyte leakage, malondialdehyde (MDA) content and ethylene production. These indicated slower development of chilling injury compared with the control. Decrease in adenosine triphosphate (ATP) and energy charge was not noticeable in H2S treated banana fruit. Moreover, the activity of H(+)-ATPase, Ca(2+)-ATPase, cytochrome C oxidase (CCO) and succinate dehydrogenase (SDH), associated with energy metabolism, were significantly enhanced by H2S treatment. Therefore, it can be deduced that H2S can potentially alleviate chilling development in banana fruit by increasing enzymes activities, involved in energy metabolism, to maintain energy charge.

Mechanisms of nitric oxide crosstalk with reactive oxygen species scavenging enzymes during abiotic stress tolerance in plants

Nitric oxide (NO) acts in a concentration and redox-dependent manner to counteract oxidative stress either by directly acting as an antioxidant through scavenging reactive oxygen species (ROS), such as superoxide anions (O(2)(-)*), to form peroxynitrite (ONOO(-)) or by acting as a signaling molecule, thereby altering gene expression. NO can interact with different metal centres in proteins, such as heme-iron, zinc-sulfur clusters, iron-sulfur clusters, and copper, resulting in the formation of a stable metal-nitrosyl complex or production of varied biochemical signals, which ultimately leads to modification of protein structure/function. The thiols (ferrous iron-thiol complex and nitrosothiols) are also involved in the metabolism and mobilization of NO. Thiols bind to NO and transport it to the site of action whereas nitrosothiols release NO after intercellular diffusion and uptake into the target cells. S-nitrosoglutathione (GSNO) also has the ability to transnitrosylate proteins. It is an NO˙ reservoir and a long-distance signaling molecule. Tyrosine nitration of proteins has been suggested as a biomarker of nitrosative stress as it can lead to either activation or inhibition of target proteins. The exact molecular mechanism(s) by which exogenous and endogenously generated NO (or reactive nitrogen species) modulate the induction of various genes affecting redox homeostasis, are being extensively investigated currently by various research groups. Present review provides an in-depth analysis of the mechanisms by which NO interacts with and modulates the activity of various ROS scavenging enzymes, particularly accompanying ROS generation in plants in response to varied abiotic stress.

Effect of Poly(γ-glutamic acid) on the Physiological Responses and Calcium Signaling of Rape Seedlings (Brassica napus L.) under Cold Stress

Cold stress adversely affects plant growth and development. Poly(γ-glutamic acid) (γ-PGA) is a potential plant growth regulator that may be an effective cryoprotectant that prevents crops from damage during cold weather. In this study, the effects of γ-PGA on the physiological responses of rape seedlings subject to cold stress were investigated using hydroponic experiments. We determined that the malondialdehyde content was decreased by 33.4% and the proline content was increased by 62.5% by γ-PGA after 144 h under cold stress. Antioxidant enzymes activities were also evidently enhanced after treatment with γ-PGA. These responses counteracted increases in the fresh weight and chlorophyll content of rape seedlings, which increased by 24.5 and 50.9%, respectively, after 144 h, which meant that growth inhibition caused by cold was mitigated by γ-PGA. Our results also showed that γ-PGA also regulated Ca(2+) concentrations in the cytoplasm and calcium-dependent protein kinases, which are associated with cold resistance. In conclusion, we suggest that the Ca(2+)/CPKs signal pathway is involved in the γ-PGA-mediated enhancement of cold resistance in rape seedlings.