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Superficial scald is a significant physiological disorder causing economic loss to the apple and pear fruit industry. Despite treatments to prevent the scald, fundamental biochemical knowledge about the injury is not completely known. To investigate the protein changes in association with scald development during storage and in response to treatments of diphenylamine and 1-MCP, two quantitative proteomic experiments employing stable isotope labeling by peptide dimethylation were conducted on two scald susceptible cultivars ‘Cortland’ and ‘Red Delicious’. Apples were untreated or treated with 2 g L −1 DPA or with/without 1 μL L −1 1-MCP, then stored at CA (3.0 kPa O 2 + 1.0 kPa CO 2 ) at 0–1 °C for up to 7 months. Among the quantified proteins, 428 proteins were common to both cultivars and 110 increased in abundance and 48 decreased during the onset of scald development. Fifty seven and 67 proteins changed significantly in abundance in response to DPA and 1-MCP treatments after 4 and 7 months storage, respectively. When combining the results from both cultivars, 14 proteins increased in abundances and 4 proteins decreased in abundance with scald development but inhibited and enhanced by both DPA and 1-MCP treatments, respectively, which were proposed to be in association with scald development of apples. Our results reveal and confirm that antioxidant and redox system, phenylpropanoid metabolism, ethylene biosynthesis, allergens, sulfur amino acids containing proteins and program cell death have direct link to the scald development. [ABSTRACT FROM AUTHOR]

Abstract: Ethylene plays an important role in regulating fruit ripening and senescence and directly influences the development of the eating quality of fresh apples, including appearance, color, texture, and flavor. Apple fruit (Malus domestica Borkh.) is a well-known climacteric fruit and a good model system to study fruit ripening and senescence. To better understand fruit ripening and the role of ethylene perception and signal transduction, apples harvested at a pre-climacteric stage were allowed to naturally ripen, or ripening was either stimulated by treatment with 36μLL−1 ethylene for 24h or inhibited by 1-MCP treatment (1.0μLL−1 for 24h), respectively. Postharvest physiological indices including respiration and ethylene production were monitored for 22d for ethylene treatment and 47d for 1-MCP treatment. Based on an efficiency test, 20 genes in relation to ethylene biosynthesis and perception were investigated using real-time qPCR during the post-treatment period. The ETR2, ETR5, ERSs, EIL4, ERFs genes together with ACS1 and ACO1 genes were significantly up-regulated in fruit during ripening. Ethylene treatment further enhanced the expression of ACO2, ETR1, CTR1s and EIN2A genes, while the ACS3 and ACO3, and EIN2B genes were only slightly affected. 1-MCP treatment significantly inhibited expression of ACS1, ACO1 and ACO2 ethylene biosynthesis genes, which coincided with ethylene production. 1-MCP treatment also reduced expression of ETR1, ETR2, ETR5, ERSs, CTR1, EIN2A, EIL4 and ERFs genes, while having a limited effect on ACS3, ACO3, and EIN2B. This study demonstrated the complexity and dynamic changes of transcriptional profiles of ethylene perception and biosynthesis in response to fruit ripening, ethylene, and 1-MCP treatment. Understanding of the significant changes of these genes and their function may help to explore the mechanisms controlling apple fruit ripening and its response to exogenous ethylene stimuli and action inhibition at the receptor level during ripening and senescence. [Copyright &y& Elsevier]

Abstract: Certain proteins or families of proteins present in plants and in many fruits can act as allergens that may cause an overreaction of the human immune system. Recent findings showed that apple consumption can cause allergic reactions in some consumers, especially among northern and central European populations, due to the presence of allergenic proteins. Investigations of apple fruit allergens have indicated that production of allergens is influenced by many biotic and abiotic factors. To better understand the regulation of allergen production during fruit ripening, and to examine the influence of ethylene on expression of genes encoding allergens in fruit, apples harvested at the pre-climacteric stage were allowed to ripen naturally, or ripening was either stimulated by treatment with 36μLL−1 ethylene for 24h or inhibited with 1-MCP treatment (1μLL−1 for 24h). As an indicator of physiological status, ethylene production, was monitored up to 21d after ethylene treatment or up to 47d after 1-MCP treatment. Real-time qPCR was used to identify allergen genes that were differentially expressed in ethylene- and 1-MCP-treated fruit. Sixteen allergen genes representing four gene families were investigated. Transcript abundance of several genes was found to change significantly during ripening. Genes encoding Mal d1.01, Mal d1b, Mal d1d, Mal d1e, Mal d1-associated protein (MdAP), and Mal d4.01 were significantly up-regulated in fruit during ripening, and further enhanced after ethylene treatment. By contrast, expression of Mal d1.04, Mal d2.01, Mal d2.02, Mal d2.03, Mal d3.01, and Mal d4.03 genes decreased. Declining expression of Mal d3.01, Mal d4.02, and Mal d4.03 during fruit ripening was also found. Treatment with 1-MCP and ethylene generally produced opposite effects, which provides additional evidence that regulation of these genes is ethylene dependent. Overall, changes in the transcriptional profiles of genes encoding apple fruit allergens during ripening and senescence, and in response to ethylene, were complex and dynamic. Characterization of changes in these allergens during storage will potentially aid in the control of quality and safety of apple fruit. [Copyright &y& Elsevier]

Abstract: Hydrogen peroxide (H2O2) is one of the important by-products produced by plant and fruit tissues during normal metabolism as well as under stress conditions. Evidence suggests that it is actively involved in many physiological activities in plants, including ripening, senescence and the development of disorders. Quantitative measurement of H2O2 in fruit has been a challenge due to variations in methodologies, and their sensitivities and interferences present in plant samples. Among the currently used methodologies, chemiluminescence (CL) is one of the most promising, due to its high specificity and sensitivity. However, direct application of CL methods developed for leaf analysis is not suitable for fruit, especially fruit peel tissues, possibly due to interfering compounds in fruit tissues. In this study, evaluation of the efficiency of removal of interfering compounds by PVP, PVPP and activated charcoal revealed that the PVPP is the most effective compound to remove the interference. This modified protocol can measure H2O2 content in apple peel and flesh tissues. ‘Red Delicious’ apple peel and flesh tissues were measured with amount of 1.48 and 1.03μmol/g FW, respectively. The established protocol can also be used for a wide variety of tissues in addition to apple fruit, including strawberry tissues (fruit, calyx and leaves) and spinach leaves. This protocol was applied to determine the H2O2 concentration in 1-MCP and DPA treated apples after 5 months of storage, but no significant difference in H2O2 in those samples was found. Direct comparison of CL with a commercial hydrogen peroxide measurement OXIS kit was also made. The challenges to accurately assay H2O2 in fruit/plant tissue were discussed. [Copyright &y& Elsevier]

‘Ambrosia’ apple is one of the emerging apple cultivars that have been gaining popularity in North America due to its superior eating quality. An effective postharvest storage regime has been established for optimal storage and quality maintenance. Unfortunately, a postharvest physiological disorder has often been reported, which shows symptoms similar to low temperature induced soft scald in ‘Honeycrisp’. Therefore, a delayed cooling strategy prior to storage has been developed and implemented as a successful and economical method to prevent this disorder. In order to reveal the molecular mechanism of soft scald development and delayed cooling in combating this low temperature induced disorder, a quantitative proteomic investigation employing stable isotope dimethylation labeling by peptides was conducted on ‘Ambrosia’ apples from three commercial orchards in BC, Canada. Quantitative changes in protein abundance in association with disorder development and in response to delayed cooling treatment after one and three month storage were found. Among the quantified proteins, 495 and 575 proteins were commonly presented in three biological replicates after one and three month storage; respectively. Among them, the abundance of 78 and 88 proteins were found to be significantly changed in response to delayed cooling as compared with normal cold storage for one and three months, respectively. These identified proteins were functionally annotated using MAPMAN software, which identified glycolysis, lipid metabolism, amino acids (including GABA shunt), hormone response, stress and signaling, redox and glutathione metabolism as the major pathways influenced by the delayed cooling treatment. A principal component analysis (PCA) revealed groups of proteins that play a major role in response to disorder development and a negative response to delayed cooling. In addition, an ABC transporter protein F family is correlated to the delayed cooling treatment. This study demonstrates the potential mechanism of the biological effect of delayed cooling on apple fruit at the proteomic level. It also provides in-depth insight on molecular mechanisms of the delayed cooling treatment in apples. [ABSTRACT FROM AUTHOR]

The effects of ethylene and 1-methylcyclopropene (1-MCP) on apple fruit volatile biosynthesis and gene expression were investigated. Statistical analysis identified 17 genes that changed significantly in response to ethylene and 1-MCP treatments. Genes encoding branched-chain amino acid aminotransferase ( BCAT ), aromatic amino acid aminotransferase (ArAT) and amino acid decarboxylases ( AADC ) were up-regulated during ripening and further enhanced by ethylene treatment. Genes related to fatty acid synthesis and metabolism, including acyl-carrier-proteins ( ACPs ), malonyl-CoA:ACP transacylase ( MCAT ), acyl-ACP-desaturase ( ACPD ), lipoxygenase ( LOX ), hydroperoxide lyase ( HPL ), alcohol dehydrogenase (ADH), pyruvate decarboxylase (PDC2), β-oxidation, acyl-CoA synthetase (ACS), enoyl-CoA hydratase (ECHD), acyl-CoA dehydrogenase (ACAD), and alcohol acyltransferases (AATs) also increased during ripening and in response to ethylene treatment. Allene oxide synthase (AOS), alcohol dehydrogenase 1 (ADH1), 3-ketoacyl-CoA thiolase and branched-chain amino acid aminotransferase 2 (BCAT2) decreased in ethylene-treated fruit. Treatment with 1-MCP and ethylene generally produced opposite effects on related genes, which provides evidence that regulation of these genes is ethylene dependent. [ABSTRACT FROM AUTHOR]