Chitosan Augments Tetramycin against Soft Rot in Kiwifruit and Enhances Its Improvement for Kiwifruit Growth, Quality and Aroma.

In this study, the co-application of chitosan and tetramycin against kiwifruit soft rot and its effects on the disease resistance, growth, quality and aroma of kiwifruit were investigated. The results show that chitosan could effectively enhance tetramycin against soft rot of kiwifruit with the field control efficacy of 85.33% for spraying chitosan 100 time + 0.3% tetramycin AS 5000-time dilution liquid, which was higher than 80.99% for 0.3% tetramycin AS 5000-time dilution liquid and significantly (p < 0.01) higher than 40.66% for chitosan 100-time dilution liquid. Chitosan could significantly (p < 0.05) improve the promoting effects of tetramycin on total phenolics, total flavonoids, SOD activity of kiwifruit compared to tetramycin during storage for 0-28 days and enhance the disease resistance of kiwifruit. Moreover, the co-application of chitosan and tetramycin was more effective than tetramycin or chitosan alone in enhancing fruit growth, improving fruit quality and increasing fruit aroma. This study highlights that chitosan can be used as an adjuvant to enhance tetramycin against soft rot of kiwifruit and promote tetramycin's improvement for the single fruit volume and weight, vitamin C, soluble sugar, soluble solid, dry matter, soluble protein, titratable acidity and aroma of kiwifruit.

Fermentative production of enantiopure (S)-linalool using a metabolically engineered Pantoea ananatis.

BACKGROUND: Linalool, an acyclic monoterpene alcohol, is extensively used in the flavor and fragrance industries and exists as two enantiomers, (S)- and (R)-linalool, which have different odors and biological properties. Linalool extraction from natural plant tissues suffers from low product yield. Although linalool can also be chemically synthesized, its enantioselective production is difficult. Microbial production of terpenes has recently emerged as a novel, environmental-friendly alternative. Stereoselective production can also be achieved using this approach via enzymatic reactions. We previously succeeded in producing enantiopure (S)-linalool using a metabolically engineered Pantoea ananatis, a member of the Enterobacteriaceae family of bacteria, via the heterologous mevalonate pathway with the highest linalool titer ever reported from engineered microbes. RESULTS: Here, we genetically modified a previously developed P. ananatis strain expressing the (S)-linalool synthase (AaLINS) from Actinidia arguta to further improve (S)-linalool production. AaLINS was mostly expressed as an insoluble form in P. ananatis; its soluble expression level was increased by N-terminal fusion of a halophilic ß-lactamase from Chromohalobacter sp. 560 with hexahistidine. Furthermore, in combination with elevation of the precursor supply via the mevalonate pathway, the (S)-linalool titer was increased approximately 1.4-fold (4.7 ± 0.3 g/L) in comparison with the original strain (3.4 ± 0.2 g/L) in test-tube cultivation with an aqueous-organic biphasic fermentation system using isopropyl myristate as the organic solvent for in situ extraction of cytotoxic and semi-volatile (S)-linalool. The most productive strain, IP04S/pBLAAaLINS-ispA*, produced 10.9 g/L of (S)-linalool in "dual-phase" fed-batch fermentation, which was divided into a growth-phase and a subsequent production-phase. Thus far, this is the highest reported titer in the production of not only linalool but also all monoterpenes using microbes. CONCLUSIONS: This study demonstrates the potential of our metabolically engineered P. ananatis strain as a platform for economically feasible (S)-linalool production and provides insights into the stereoselective production of terpenes with high efficiency. This system is an environmentally friendly and economically valuable (S)-linalool production alternative. Mass production of enantiopure (S)-linalool can also lead to accurate assessment of its biological properties by providing an enantiopure substrate for study.

Proteomics and Metabolomics Reveal the Regulatory Pathways of Ripening and Quality in Post-Harvest Kiwifruits.

Understanding the metabolic modulation of major quality traits during ripening is critical for fruit quality improvement in kiwifruits. Here, integrated proteomic and metabolomic profiling was undertaken to comprehensively examine the dynamics of kiwifruit ripening. This data set presents a global view of the critical pathways involved in fruit ripening, and the contributions of key events to the regulation of kiwifruit ripening and softening, amino acid metabolism, balance in sugar accumulation and organic acid metabolism, glycolysis, and tricarboxylic acid (TCA) pathways were discussed. We suggested key enzymes for starch synthesis and degradation, including AGPase, SS, and SBE, especially for BMY, which was considered a key enzyme for starch degradation. In addition, our analysis implicated the key enzymes ACO4 and ACS9 in ethylene synthesis and the aspartate aminotransferase ASP3 in the conversion of amino acids. These results provide new insights into the modulation of fruit ripening, metabolism, and quality in post-harvest kiwifruits.

The kiwifruit enzyme actinidin enhances the hydrolysis of gluten proteins during simulated gastrointestinal digestion.

This study investigated the effect of actinidin, a cysteine protease in kiwifruit, on the hydrolysis of gluten proteins and digestion-resistant gluten peptides (synthetic 33-mer peptide and pentapeptide epitopes) under static simulated gastrointestinal conditions. Actinidin efficacy in hydrolysing gliadin was compared with that of other gluten-degrading enzymes. Actinidin hydrolysed usually resistant peptide bonds adjacent to proline residues in the 33-mer peptide. The gastric degree of hydrolysis of gluten proteins was influenced by an interaction between pH and actinidin concentration (P < 0.05), whereas the pentapeptide epitopes hydrolysis was influenced only by the actinidin concentration (P < 0.05). The rate of gastric degree of hydrolysis of gliadin was greater (P < 0.05) by actinidin (0.8%/min) when compared to papain, bromelain, and one commercial enzyme (on average 0.4%/min), while all exogenous enzymes were able to hydrolyse the pentapeptide epitopes effectively. Actinidin is able to hydrolyse gluten proteins under simulated gastric conditions.

De novo biosynthesis of linalool from glucose in engineered Escherichia coli.

Linalool is an important terpenoids of floral scents and has wide applications. In the past, several groups reported on a strategy to establish biosynthesis of linalool in yeast based on co-expression of Saccharomyces cerevisiae farnesyl diphosphate synthase ERG20 and Actinidia arguta linalool synthase LIS. However, ERG20 has both geranyl diphosphate synthase and farnesyl diphosphate synthase activities, which can lead to metabolic flow to farnesyl diphosphate. In this study, a heterologous linalool biosynthesis pathway was constructed in Escherichia coli and showed that using Abies grandis geranyl diphosphate synthase GPPS2 instead of ERG20 can effectively improve linalool biosynthesis. Subsequently, we further improved the biosynthesis of linalool by overexpression of isopentenyl diphosphate isomerase Idi.

Effect of heat shock and potassium sorbate treatments on gray mold and postharvest quality of 'XuXiang' kiwifruit.

We determined whether heat and chemical treatments could reduce the decay of kiwifruit caused by Botrytis cinerea during postharvest storage. Kiwifruits were treated with 5 g/L (w/v) potassium sorbate (PS), with a 48 °C hot water treatment (HT), and with a combined treatment (HT + PS). Mycelial growth of B. cinerea and the postharvest quality of 'XuXiang' kiwifruits were evaluated. HT + PS significantly inhibited mycelial growth, germ tube growth, and spore germination of B. cinerea. This treatment also reduced the incidence of gray mold in kiwifruit postharvest, and enhanced activities of defense-related enzymes in kiwifruit tissues. Compared with the control, all treatments resulted in lower malondialdehyde (MDA) contents and higher total phenolic contents in kiwifruits. HT + PS also increased the activities of chitinase and ß-1,3-glucanase and the transcript levels of their encoding genes. HT + PS can improve kiwifruit quality and reduce decay during postharvest storage.

Methyl Jasmonate Enhances Ethylene Synthesis in Kiwifruit by Inducing NAC Genes That Activate ACS1.

Cross-talk between various hormones is important in regulating many aspects of plant growth, development, and senescence, including fruit ripening. Here, exogenous ethylene (ETH, 100 µL/L, 12 h) rapidly accelerated 'Hayward' kiwifruit (Actinidia deliciosa) softening and ethylene production and was enhanced by supplementing with continuous treatment with methyl jasmonate (MeJA, 100 µM/L, 12 h) (ETH+MeJA). ETH+MeJA enhanced ACC synthase (ACS) activities and 1-aminocyclopropane-1-carboxylic acid (ACC) accumulation but not ACC oxidase (ACO) activity. Increased transcripts of ACS genes AdACS1 and AdACS2, ACS activity, and ethylene production were positively correlated. The abundance of AdACS1 was about 6-fold higher than AdACS2. RNA-seq identified 6 transcription factors among the 87 differentially expressed unigenes induced by ETH+MeJA. Dual-luciferase and electrophoretic mobility shift assays (EMSA) indicated that AdNAC2/3 physically interacted with and trans-activated the AdACS1 promoter 2.2- and 3.5-fold, respectively. Collectively, our results indicate that MeJA accelerates ethylene production in kiwifruit induced by exogenous ethylene, via a preferential activation of AdACS1 and AdACS2.

ABF2 and MYB transcription factors regulate feruloyl transferase FHT involved in ABA-mediated wound suberization of kiwifruit.

Suberin is a cell-wall biopolymer with aliphatic and aromatic domains that is synthesized in the wound tissues of plants in order to restrict water loss and pathogen infection. ω-hydroxyacid/fatty alcohol hydroxycinnamoyl transferase (FHT) is required for cross-linking of the aliphatic and aromatic domains. ABA is known to play a positive role in suberin biosynthesis but it is not known how it interacts with FHT. In this study, the kiwifruit (Actinidia chinensis) AchnFHT gene was isolated and was found to be localized in the cytosol. Transient overexpression of AchnFHT in leaves of Nicotiana benthamiana induced massive production of ferulate, ω-hydroxyacids, and primary alcohols, consistent with the in vitro ability of AchnFHT to catalyse acyl-transfer from feruloyl-CoA to ω-hydroxypalmitic acid and 1-tetradecanol. A regulatory function of four TFs (AchnABF2, AchnMYB4, AchnMYB41, and AchnMYB107) on AchnFHT was identified. These TFs localized in the nucleus and directly interacted with the AchnFHT promoter in yeast one-hybrid assays. Dual-luciferase analysis indicated that AchnABF2, AchnMYB41, and AchnMYB107 activated the AchnFHT promoter while AchnMYB4 repressed it. These findings were supported by the results of transient overexpression in N. benthamiana, in which AchnABF2, AchnMYB41, and AchnMYB107 induced expression of suberin biosynthesis genes (including FHT) and accumulation of suberin monomers, whilst AchnMYB4 had the opposite effect. Exogenous ABA induced the expression of AchnABF2, AchnMYB41, AchnMYB107, and AchnFHT and induced suberin monomer formation, but it inhibited AchnMYB4 expression. In addition, fluridone (an inhibitor of ABA biosynthesis) was found to counter the inductive effects of ABA. Activation of suberin monomer biosynthesis by AchnFHT was therefore controlled in a coordinated way by both repression of AchnMYB4 and promotion of AchnABF2, AchnMYB41, and AchnMYB107.

Molecular cloning and functional characterization of AcGST1, an anthocyanin-related glutathione S-transferase gene in kiwifruit (Actinidia chinensis).

KEY MESSAGE: AcGST1, an anthocyanin-related GST, may functions as a carrier to transport anthocyanins from ER to tonoplast in kiwifruit. It was positively regulated by AcMYBF110 through directly binding to its promoter. Anthocyanins are synthesized in the cytoplasmic surface of the endoplasmic reticulum but accumulate predominantly in the vacuole. Previous studies in model and ornamental plants have suggested that a member of the glutathione S-transferase (GST) gene family is involved in sequestration of anthocyanins into the vacuole. However, little is known about anthocyanin-related GST protein in kiwifruit. Here, four putative AcGSTs were identified from the genome of the red-fleshed Actinidia chinensis cv 'Hongyang'. Expression analyses reveal only the expression of AcGST1 was highly consistent with anthocyanin accumulation. Molecular complementation of Arabidopsis tt19 demonstrates AcGST1 can complement the anthocyanin-less phenotype of tt19. Transient expression in Actinidia arguta fruits further confirms that AcGST1 is functional in anthocyanin accumulation in kiwifruit. In vitro assays show the recombinant AcGST1 increases the water solubility of cyanidin-3-O-galactoside (C3Gal) and cyanidin-3-O-xylo-galactoside (C3XG). We further show that AcGST1 protein is localized not only in the ER but also on the tonoplast, indicating AcGST1 (like AtTT19) may functions as a carrier protein to transport anthocyanins to the tonoplast in kiwifruit. Moreover, the promoter of AcGST1 can be activated by AcMYBF110, based on results from transient dual-luciferase assays and yeast one-hybrid assays. EMSAs show that AcMYBF110 binds directly to CAGTTG and CCGTTG motifs in the AcGST1 promoter. These results indicate that AcMYBF110 plays an important role in transcriptional regulation of AcGST1 and, therefore, in controlling accumulation of anthocyanins in kiwifruit.

Phenolic Profiles, Antioxidant Capacities, and Inhibitory Effects on Digestive Enzymes of Different Kiwifruits.

In order to obtain high-quality kiwifruits with health-promoting characteristics, physicochemical properties, phenolic profiles, antioxidant capacities, and inhibitory effects on digestive enzymes (pancreatic lipase and α-glucosidase), of fourteen different types of kiwifruit obtained from China were systematically investigated and compared. Noticeable variations in the fruits' physicochemical properties and phenolic profiles were observed among them. The total phenolic content of Actinidia chinensis cv. Hongshi, A. chinensis cv. Jinshi, and A. chinensis cv. Jinlong were 16.52 ± 0.26 mg GAE/g DW (dry weight), 13.38 ± 0.20 mg GAE/g DW, and 11.02 ± 0.05 mg GAE/g DW, respectively, which were much higher than those of the other tested kiwifruits. According to high performance liquid chromatography (HPLC) analysis, phenolic compounds, including procyanidin B1, procyanidin B2, (-)-epicatechin, chlorogenic acid, gallic acid, and quercetin-3-rhamnoside, were found to be the major compounds in kiwifruits, while procyanidin B1, procyanidin B2, and chlorogenic acid were the most abundant phenolic compounds. Furthermore, all the tested kiwifruits exerted remarkable antioxidant capacities and inhibitory effects on pancreatic lipase and α-glucosidase. Indeed, A. chinensis cv. Hongshi, Actinidia chinensis cv. Jinshi, and Actinidia chinensis cv. Jinlong exhibited much better antioxidant capacities and inhibitory effects on digestive enzymes than those of the other tested kiwifruits. Particularly, A. polygama showed the highest inhibitory activity on α-glucosidase. Therefore, Actinidia chinensis cv. Hongshi, Actinidia chinensis cv. Jinshi, and Actinidia chinensis cv. Jinlong, as well as A. polygama could be important dietary sources of natural antioxidants and natural inhibitors against pancreatic lipase and α-glucosidase, which is helpful for meeting the growing demand for high-quality kiwifruits with health-promoting characteristics in China.

Enzymatic hydrolysis-induced degradation of a lactose-coupled supramolecular hydrogel.

Amphiphilic urea 1 with a hydrophilic lactose group was prepared as a low-molecular-weight hydrogelator, which formed a transparent supramolecular hydrogel. Enzymatic hydrolysis of the lactose moiety using ß-galactosidase allowed a gel-to-sol phase transition of the supramolecular hydrogel. A ß-galactosidase inhibitor enables us to control the time course of this phase transition.

Melatonin Improves Heat Tolerance in Kiwifruit Seedlings through Promoting Antioxidant Enzymatic Activity and Glutathione S-Transferase Transcription.

Evidence exists to suggest that melatonin (MT) is important to abiotic stress tolerance in plants. Here, we investigated whether exogenous MT reduces heat damage on biological parameters and gene expression in kiwifruit (Actinidia deliciosa) seedlings. Pretreatment with MT alleviates heat-induced oxidative harm through reducing H2O2 content and increasing proline content. Moreover, MT application raised ascorbic acid (AsA) levels and the activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). We also observed elevation in the activity of enzymes related to the AsA-GSH cycle, such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, MT application increased the expression of 28/31 glutathione S-transferase (GST) genes, reducing oxidative stress. These results clearly indicate that in kiwifruit, MT exerts a protective effect against heat-related damage through regulating antioxidant pathways.

High oxygen facilitates wound induction of suberin polyphenolics in kiwifruit.

BACKGROUND: Rapid wound healing would be critical for successful long-term storage of fruits and vegetables. However, there was no direct evidence for the requirement and efficiency of oxygen in the fruit wound-healing process. This study was conducted to investigate the role of oxygen in wound-induced suberization by analyzing melanin, suberin polyphenolics (SPPs) and related enzymes in half-cut kiwifruits exposed to 100%, 50%, 21% and 0% oxygen. RESULTS: By 3 days after wounding, the wound surface of kiwifruit in high (50 and 100%) oxygen appeared as a continuous layer of melanin and SPPs underneath, which effectively prevent excessive water vapor loss from the fruit halves. In contrast, melanin and SPPs deposition in the wound surface in 0% oxygen was significantly reduced, with high water vapor loss. Rapid decrease of soluble phenolic acids (caffeic, p-coumaric, ferulic acids) was coupled with the increase of bound ferulic acid (coniferyl diacetate) especially in high oxygen by 9 days after wounding. Meanwhile, high oxygen enhanced peroxidase, catalase, phenylalanine ammonia-lyase, and polyphenol oxidase activities. CONCLUSION: Oxygen is required for wound-induced melanin and SPPs formation, and high oxygen is effective in promoting wound suberization in postharvest kiwifruit. © 2017 Society of Chemical Industry.

Biochemical and functional characterization of AcUFGT3a, a galactosyltransferase involved in anthocyanin biosynthesis in the red-fleshed kiwifruit (Actinidia chinensis).

Much of the diversity of anthocyanin pigmentation in plant tissues is due to the action of glycosyltransferases, which attach sugar moieties to the anthocyanin aglycone. This step can increase both their solubility and stability. We investigated the pigmentation of the outer and inner pericarps of developing fruits of the red-fleshed kiwifruit Actinidia chinensis cv. 'Hongyang'. The results show that the red color of the inner pericarp is due to anthocyanin. Based on expression analyses of structural genes, AcUFGT was shown to be the key gene involved in the anthocyanin biosynthetic pathway. Expression of AcUFGT in developing fruit paralleled changes in anthocyanin concentration. Thirteen putative UFGT genes, including different transcripts, were identified in the genome of 'Hongyang'. Among these, only the expression of AcUFGT3a was found to be highly consistent with anthocyanin accumulation. Fruit infiltrated with virus-induced gene silencing showed delayed red colorations, lower anthocyanin contents and lower expressions of AcUFGT3a. At the same time, transient overexpression of AcUFGT3a in both Actinidia arguta and green apple fruit resulted in higher anthocyanin contents and deeper red coloration. In vitro biochemical assays revealed that recombinant AcUFGT3a recognized only anthocyanidins as substrate but not flavonols. Also, UDP-galactose was used preferentially as the sugar donor. These results indicate AcUFGT3a is the key enzyme regulating anthocyanin accumulation in red-fleshed kiwifruit.

Kiwifruit actinidin digests salivary amylase but not gastric lipase.

Kiwifruit contains the cysteine proteinase actinidin whose strong activity allows kiwifruit to be used as a meat tenderiser. This raises the possibility digestive enzymes, also proteins, are themselves susceptible to degradation by actinidin. Salivary amylase and gastric lipase are exposed to the highest concentrations of actinidin whereas duodenal enzymes are less likely to be inactivated by actinidin due to dilution and inactivation of actinidin by gastric juice. The saliva of six volunteers was exposed to Actinidia deliciosa homogenate and then examined for loss of the starch digesting enzyme, alpha-amylase. In agreement with the known distribution of salivary amylase concentration in saliva, the range of amylase activity within the group of volunteers varied by around 100 fold. Within 5 minutes of incubation of 3 parts saliva to one part green kiwifruit at 37 °C, approximately 85% of the amylase activity was lost. The use of E-64, a selective inhibitor of cysteine proteinases, confirmed that the loss of amylase function was due to actinidin. Amylase protein degradation was followed by SDS-PAGE and western blotting. Recombinant human gastric lipase resisted digestion with kiwifruit even after 30 minutes incubation and remained functionally active after this time period. However, both mountain papaya and pineapple extracts degraded gastric lipase fully during a 30 minutes digestion period. Under conditions where cooked starch is consumed along with kiwifruit it is possible that starch digestion may be retarded whereas lipid digestion in the stomach is unlikely to be affected by kiwifruit consumption.

Cell separation in kiwifruit without development of a specialised detachment zone.

BACKGROUND: Unlike in abscission or dehiscence, fruit of kiwifruit Actinidia eriantha develop the ability for peel detachment when they are ripe and soft in the absence of a morphologically identifiable abscission zone. Two closely-related genotypes with contrasting detachment behaviour have been identified. The 'good-peeling' genotype has detachment with clean debonding of cells, and a peel tissue that does not tear. The 'poor-peeling' genotype has poor detachability, with cells that rupture upon debonding, and peel tissue that fragments easily. RESULTS: Structural studies indicated that peel detachability in both genotypes occurred in the outer pericarp beneath the hypodermis. Immunolabelling showed differences in methylesterification of pectin, where the interface of labelling coincided with the location of detachment in the good-peeling genotype, whereas in the poor-peeling genotype, no such interface existed. This zone of difference in methylesterification was enhanced by differential cell wall changes between the peel and outer pericarp tissue. Although both genotypes expressed two polygalacturonase genes, no enzyme activity was detected in the good-peeling genotype, suggesting limited pectin breakdown, keeping cell walls strong without tearing or fragmentation of the peel and flesh upon detachment. Differences in location and amounts of wall-stiffening galactan in the peel of the good-peeling genotype possibly contributed to this phenotype. Hemicellulose-acting transglycosylases were more active in the good-peeling genotype, suggesting an influence on peel flexibility by remodelling their substrates during development of detachability. High xyloglucanase activity in the peel of the good-peeling genotype may contribute by having a strengthening effect on the cellulose-xyloglucan network. CONCLUSIONS: In fruit of A. eriantha, peel detachability is due to the establishment of a zone of discontinuity created by differential cell wall changes in peel and outer pericarp tissues that lead to changes in mechanical properties of the peel. During ripening, the peel becomes flexible and the cells continue to adhere strongly to each other, preventing breakage, whereas the underlying outer pericarp loses cell wall strength as softening proceeds. Together these results reveal a novel and interesting mechanism for enabling cell separation.

Two Subclasses of Differentially Expressed TPS1 Genes and Biochemically Active TPS1 Proteins May Contribute to Sugar Signalling in Kiwifruit Actinidia chinensis.

Trehalose metabolism and its intermediate trehalose-6-phosphate (T6P) are implicated in sensing and signalling sucrose availability. Four class I TREHALOSE-6-PHOSPHATE SYNTHASE (TPS1) genes were identified in kiwifruit, three of which have both the TPS and trehalose-6-phosphate phosphatase (TPP) domain, while the fourth gene gives rise to a truncated transcript. The transcript with highest sequence homology to Arabidopsis TPS1, designated TPS1.1a was the most highly abundant TPS1 transcript in all examined kiwifruit tissues. An additional exon giving rise to a small N-terminal extension was found for two of the TPS1 transcripts, designated TPS1.2a and TPS1.2b. Homology in sequence and gene structure with TPS1 genes from Solanaceae suggests they belong to a separate, asterid-specific class I TPS subclade. Expression of full-length and potential splice variants of these two kiwifruit TPS1.2 transcripts was sufficient to substitute for the lack of functional TPS1 in the yeast tps1Δ tps2Δ mutant, but only weak complementation was detected in the yeast tps1Δ mutant, and no or very weak complementation was obtained with the TPS1.1a construct. Transgenic Arabidopsis lines expressing kiwifruit TPS1.2 under the control of 35S promoter exhibited growth and morphological defects. We investigated the responses of plants to elevated kiwifruit TPS1 activity at the transcriptional level, using transient expression of TPS1.2a in Nicotiana benthamiana leaves, followed by RNA-seq. Differentially expressed genes were identified as candidates for future functional analyses.

Effect of Putrescine Treatment on Chilling Injury, Fatty Acid Composition and Antioxidant System in Kiwifruit.

We investigated the effects of different concentrations (0, 1, 2 and 4 mM) of putrescine on chilling injury, fruit quality, ethylene production rate, fatty acid composition and the antioxidant system of cold-stored kiwifruit (Actinidia chinensis Planch. var. chinensis 'Hongyang'). We achieved a significant decrease in ethylene production, maintained fruit quality and alleviated chilling injury during storage via treatment with 2 mM putrescine. Furthermore, putrescine treatment inhibited increases in superoxide anion production rate and H2O2 concentration, while maintaining higher membrane lipid unsaturation as well as increased activities of superoxide dismutase and catalase. In addition, putrescine treatment enhanced the activities of antioxidant enzymes related to the ascorbate-glutathione cycle while causing higher levels of ascorbic acid and reduced glutathione. Our results suggest that induced tolerance against chilling injury via putrescine treatment in cold-stored kiwifruit may be due to enhanced antioxidant activity, increased unsaturation of membrane lipids, and inhibited ethylene production.

Comparative analysis on the distribution of protease activities among fruits and vegetable resources.

In this study, a comparative analysis on the distribution of protease activities among 90 plant resources, including fruits and vegetables, has been performed. Protease activities of plant extracts were assayed at different pH values (pH 3.0, pH 7.5 and pH 10.5) using casein as a substrate. Ten fruits and thirteen vegetables show protease activities above 10U/g. Pineapple, fig and papaya, which are used for commercial protease production, exhibited high protease activities. Additionally, high protease activities were detected in kiwifruit (28.8U/g), broccoli (16.9U/g), ginger (16.6U/g), leek (32.7U/g) and red pepper (15.8U/g) at different pH values. SDS-PAGE and zymograms confirmed that various types of proteases existed in the five plant extracts and might be explored. Furthermore, five plant extracts were treated by different protease inhibitors. These results show that there are still many plant resources unexplored, which may be promising candidates for plant-derived protease production.