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Broccoli heads usually age by yellowing or producing an off-flavor after harvesting and during storage under improper conditions. However, the reasons for the off-flavor are complex, and the factors affecting the development of this characteristic is unclear. This study aimed to investigate the relationship between off-flavor compounds and differentially expressed proteins in a controlled O2/CO2 atmosphere using headspace GC–MS fingerprinting and an iTRAQ-based quantitative proteomic approach. Results demonstrated that a suitably controlled O2/CO2 atmosphere increased the energy production efficiency, improved stress resistance, and markedly extended the shelf life of broccoli heads. However, treatment with an excessively high CO2 proportion promoted glycolysis and fermentation, reduced energy generation efficiency, altered sulfur-component metabolism, and promoted the accumulation of an offensive odor in broccoli heads. This study provides a foundation for understanding the metabolic mechanisms responsible for off-flavor and highlights potential control measures under high CO2 conditions.

To investigate the impact of ethylene in regulating wax synthesis-related gene expression and the consequent fruit quality changes during cold storage, four key apple wax synthesis genes from ‘Starkrimson’ apple, MdCER4, MdCER6, MdWSD1 and MdMAH1, were identified, and their expression levels in response to treatments with ethephon and 1-methylcyclopropene (1-MCP) during cold storage were studied. The fruit quality changes in these two treatments were also determined during cold storage. The results showed that ethephon increased cuticular wax density, accelerated wax crystal melting and fruit senescence during cold storage of ‘Starkrimson’ apple, while 1-MCP delayed these processes. The results also showed that ethephon increased the expression levels of MdCER6 (a key gene in very long chain fatty acids synthesis), MdCER4 and MdWSD1 (two key genes in the alcohol-forming pathway of wax synthesis), while 1-MCP decreased their expression. In addition, neither ethephon nor 1-MCP regularly regulated the expression of MdMAH1, a key gene in the final step of the alkane-forming pathway of wax synthesis. Therefore, it was concluded that ethylene altered fruit cuticular wax composition and crystal morphology via MdCER6 and the subsequent alcohol-forming pathway, thus affecting the fruit quality to some extent during ‘Starkrimson’ apple fruit cold storage.

Wounding stress induces phenolic accumulation in pitaya fruit (Hylocereus undatus). This study aimed to elucidate the possible molecular mechanism underlying the wound-induced phenolic biosynthesis in fresh-cut pitaya fruit based on transcriptomic and bioinformatic analysis. Wounding stress induced the activation of metabolic pathways associated with phenolic biosynthesis, including secondary metabolism such as phenylpropanoid pathway and flavonoid pathway, signaling molecules metabolism such as ethylene, reactive oxygen species and jasmonic acid, and primary metabolism such as glycolysis, pentose phosphate pathway and shikimate pathway. Moreover, weighted gene coexpression network analysis and evolutionary relationship analysis revealed that 1 HuMYB, 3 HubHLHs, 7 HuAP2-EREBPs could be identified as putative transcription factors participating in the regulation of wound-induced phenolic biosynthesis in pitaya fruit. These findings validated previous study that wounding stress induces the conversion of hexose pool to supply essential carbon skeletons for the phenolic accumulation in fresh-cut pitaya fruit in transcriptional level and provide important and useful genetic information for further studies on the functions of transcription factors in wounding response in pitaya fruit.

To investigate ethylene effects on fruit cuticular wax during cold storage, apple fruit (Malus domestica Borkh. c.v. Starkrimson) were treated with 500 mg L−1 ethephon and 1 μL L−1 1-methylcyclopropene (1-MCP), and the composition and contents of the cuticular wax were analyzed at 20 d intervals during cold storage. The results showed that the prevailing cuticular wax components were acids, 1-alcohols and n-alkanes. Ethephon accelerated fruit senescence, positively regulated total wax quantity and its alcohol, olefin, alkane, and acid constituents during cold storage, especially 1-pentacosanol, 1-octacosanol, α-farnesane, n-octacosanoic acid, stearyl acid butyl ester, stearic acid hexyl ester and n-tetradecanal, while 1-MCP inhibited these processes. It can be concluded that ethylene altered the fruit cuticular wax contents and constituents, which may alter the subsequent postharvest qualities of the fruit and the susceptibility of the fruit to disorders during cold storage.

It has been demonstrated that Agaricus bisporus (J.E. Kange) Imbach fruit body exerts enhanced postharvest quality retention when treated with 100 μmol L −1 exogenous methyl jasmonate (MeJA) vapor. In this study, fruit bodies of A. bisporus were treated with 100 μmol L −1 MeJA vapor or the combination of 100 μmol L −1 MeJA and 20 μmol L −1 N ω -hydroxy-nor- l -arginine (nor-NOHA, an inhibitor of arginase), respectively, before they were stored for 21 d at 4 °C. Our data showed that treatment with MeJA alone indeed induced the increased transcription and activity of arginase whereas this effect was largely inhibited by pretreatment with nor-NOHA. In correspondence to this observation, nor-NOHA suppressed the ability of MeJA to decrease open caps and to down-regulate malondialdehyde (MDA) production and polyphenol oxidase (PPO) and lipoxygenase (LOX) activities. Biochemical analysis further demonstrated that nor-NOHA counteracted the MeJA in stimulating antioxidant enzyme activities of catalase (CAT) and superoxide dismutase (SOD) and accumulating total phenolics and flavonoids. In addition, the effect of MeJA in slowing the decline rate of soluble protein and total sugar contents was also partially impaired by nor-NOHA. Taken together, our findings firmly showed that arginase acts as an important regulatory factor in maintaining the MeJA-induced mushroom quality retention during postharvest storage.

Chilling injury (CI) is a major limiting factor in the retention of the postharvest quality of chilling-sensitive vegetables and fruit stored at low temperatures. The enhanced chilling tolerance induced by methyl jasmonate (MeJA) treatment might be related to the polyamines biosynthesis. However, the molecular mechanism of polyamines biosynthesis induced by MeJA is far from clear. Here, we found that the application of 0.05 mmol L−1 MeJA enhanced the activities of arginase, arginine decarboxylase and ornithine decarboxylase, as well as the transcripts of SlARG1, SlARG2, SlADC and SlODC, promoted the accumulations of polyamines and further inhibited CI development. In addition, polyamines induced by MeJA were strongly positively correlated with the SlMYC2 expression level. Moreover, MeJA-induced polyamines biosynthesis was largely inhibited due to the silencing of SlMYC2. The (SlMYC2-silenced + MeJA)-treated fruit possessed higher incidence and index of CI than the MeJA-treated fruit. Combining these findings with results of the principal component analysis, we concluded that SlMYC2 is involved in MeJA-induced chilling tolerance in postharvest tomato fruit by regulating polyamines biosynthesis. Furthermore, the electrophoretic mobility shift and dual-luciferase reporter assays indicated that SlMYC2 could activate the transcription of SlARG1, SlARG2, SlADC and SlODC by binding directly to G/E-box elements in their promoters. From the findings, it was revealed that the targeted up-regulation of SlARG1, SlARG2, SlADC and SlODC by SlMYC2 is involved in MeJA-induced polyamines biosynthesis, which enhances chilling tolerance in tomato fruit.

In this study, the impacts of Arginine (Arg) on strawberry fruit quality and postharvest decay caused by fungi, as well as on the nitric oxide synthase (NOS) pathway of strawberry fruit, were considered. Strawberry fruits were first treated with 0, 0.5, 1, 5, and 10 mM Arg solution, and the result showed that treatment with 1 mM Arg was the best in inhibiting fruit decay and maintaining fruit quality, which is indicated by firmness, titratable acid, soluble solid content and respiration rate. To investigate the action mechanism of Arg and determine whether NOS is involved in the process, strawberry fruits were further treated with 1 mM Arg and 0.2 mM Nω-nitro-L-arginine (L-NNA), a specific inhibitor of NOS, before storage at 20 ± 1 °C. In addition to reducing the decay incidence (DIC) and the decay index (DI), 1 mM Arg triggered NO accumulation, resulting from higher NOS activity, which is associated with a higher vitamin C, anthocyanin and total phenolic content, as well as the activities of the antioxidant enzymes - superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) - which are associated with a lower malondialdehyde (MDA) content. Moreover, the expression level of the pathogenesis-related protein1 (FaPR1) and the activities of the defense enzymes - phenylalanine ammonialyase (PAL), chitinase (CHI), β-1,3-glucanase (GLU) and polyphenol oxidase (PPO) – were higher in the Arg-treated fruits. However, such effects of 1 mM Arg treatment on strawberry fruits were almost reversed by the simultaneous addition of 0.2 mM L-NNA, leading to severer fruit decay. In addition, correlation analysis showed that Arg treatment significantly improved the correlation of NO with the activities of GLU (R2 = 0.72*), CHI (R2 = 0.85**), PAL (R2 = 0.67*) and APX (R2 = 0.72*). These findings indicated that Arg treatment might be a useful technique to improve quality and delay postharvest decay in strawberry fruit, and the NOS pathway played an important role in this process.

Broccoli is prone to adopting fermentation under inappropriate conditions, especially high−CO2 atmospheres. In this study, broccoli stalks were soaked in 0.4 % reduced glutathione (GSH) for 3 h, before being maintained in 50 % O2 + 50 % CO2 or 30 % O2 + 70 % CO2 controlled atmosphere. We compared the samples with control broccoli heads soaked in distilled water and maintained in normal atmospheric conditions. Broccoli heads from all treatments were stored at 10 ± 1 °C with 90–95 % relative humidity. Under O2/CO2 conditions, GSH pre-soaking of broccoli stimulated the ascorbate–glutathione (AsA–GSH) cycle, elevated nicotinamide adenine dinucleotide (NAD+) levels, improved the antioxidant capacity, enhanced the activities of respiratory metabolism enzymes, led to a higher adenosine triphosphate (ATP) status, and efficiently inhibited the accumulation of ethanol and acetaldehyde produced by fermentation, compared with control broccoli. Thus, GSH pre-soaking competitively inhibited fermentation by increasing NAD+ levels by promoting the AsA–GSH cycle and electron transfer chain (ETC) pathway. In conclusion, this study provides a potential technology to prevent the occurrence of fermentation in postharvest product.

Treatment of tomato ( Solanum lycopersicum L. cv. Messina) fruit with hot air (HA) at 38 °C enhanced the transcript levels of LeARG1 and LeARG2 , the two genes encoding arginase, and arginase activity. The strongest induction of LeARG1 and LeARG2 transcripts was observed after fruit treated with 38 °C HA for 12 h, which also effectively alleviated chilling injury (CI) of tomato fruit, manifested as decreased CI index, electrolyte leakage and malondialdehyde content during cold storage. To investigate the potential role of arginase in HA-induced chilling tolerance, fruit were treated with HA, or arginase inhibitor Nω-hydroxy-nor- l -arginine (nor-NOHA) combined with HA and then stored at 2 °C for up to 28 d. The results showed that HA-induced arginase activity was strongly inhibited by pretreatment with nor-NOHA and the reduction of CI by HA was nearly abolished by the arginase inhibitor. In addition, HA treatment increased activities of superoxide dismutase, catalase and ascorbate peroxidase, inhibited peroxidase activities, and promoted the accumulation of arginine, proline and putrescine. These effects were partially counteracted by nor-NOHA except that arginine and putrescine accumulation was unaffected. Our results indicate that arginase induction may be partly involved in HA-induced chilling tolerance in tomato fruit, possibly by a mechanism involving activation of antioxidant enzymes and an increase in proline levels.

Freshly harvested tomato fruit were pretreated with 0.2 mM arginine at −35 kPa for 0.5 min and then stored at 2 °C for 28 d to investigate the effect of exogenous arginine treatment on endogenous arginine catabolism in relation to chilling injury (CI). Arginine treatment reduced the CI index of fruit and enhanced accumulation of polyamines, especially putrescine, and proline, which resulted from the increased activities of the catabolic enzymes arginase, arginine decarboxylase, ornithine decarboxylase and ornithine δ-aminotransferase at most sampling times. Nitric oxide synthase activity was also increased by arginine treatment, which at least partly contributed to the increased nitric oxide concentration. These results revealed that the reduction in CI by exogenous arginine may be due to the accumulation of putrescine, proline and nitric oxide induced by activating the different pathways of endogenous arginine catabolism.

The influence of methyl jasmonate (MeJA) on levels of gene transcripts, enzyme activities and metabolites related to arginine catabolism and chilling injury (CI) was studied in cherry tomato (Solanum lycopersicum L. cv. Messina) fruit stored at 2 °C for 21 days. The CI index of fruit pretreated with 0.05 mM MeJA vapor for 12 h at 20 °C was reduced compared with that of untreated fruit. The reduction was associated with up-regulated arginine catabolism. The mRNA levels and activities of arginase, arginine decarboxylase (ADC) and ornithine aminotransferase (OAT) in treated fruit were higher than in control fruit, while those of ornithine decarboxylase (ODC) increased transiently in response to MeJA treatment during the early days of cold storage. Free putrescine (Put) and proline accumulated in MeJA-treated fruit, while levels of other arginine-related amino acids were affected by MeJA. Spermidine (Spd) and spermine (Spm) contents remained unchanged in response to MeJA treatment over most of the storage time. The results indicate that MeJA becomes involved in coordinated catabolism of arginine, and helps to improve chilling tolerance in cherry tomato fruit.