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2017 ASHS Annual Conference

The Involvement of Laccase in Development of Superficial Scald in Apple Fruit

Wednesday, September 20, 2017: 8:15 AM
King's 2 (Hilton Waikoloa Village)
YiHui Gong, College of Horticulture, South China Agriculture University, Guangzhou, China
Lina Du, College of Horticulture, South China Agriculture University, GuangZhou, China
Jun Song, Agriculture and Agri-Food Canada, Kentville, NS, Canada
Melinda Vinqvist, Agriculture and Agri-Food Canada., Kentville, NS, Canada
Leslie Campbell Palmer, Agriculture and Agri-Food Canada, Kentville, NS, Canada
Sherry A.E. Fillmore, Agriculture and Agri-Food Canada, Kentville, NS, Canada
Xuequn Pang, South China Agricultural University, Guangzhou, China
ZhaoQi Zhang, College of Horticulture, South China Agriculture University, GuangZhou, China
Superficial scald is a physiological disorder causing significant economic loss for the apple and pear fruit industry worldwide. Despite commercial treatments using diphenylamine or ethoxyquin (6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline) to prevent this disorder, the fundamental mechanism leading to browning color in fruit pericarp tissue is not completely understood. In our study, the full-length complementary DNAs encoding laccase gene, an anthocyanin degradation enzyme, were obtained from different tissues including flowers, calyx, leaves and fruit peel of ‘Cortland’ and ‘Red delicious’ apple cultivars. The similarity of apple laccases was showed at 56-75 % compared to Arabidopsis and litchi. The biological roles of laccase in association with scald development during storage and in response to treatments of diphenylamine and 1-MCP were investigated on two scald susceptible cultivars ‘Cortland’ and ‘Red delicious’. Apples were treated with/without 2 g L-1 DPA or with/ without 1 µL L-1 1-MCP, then stored at CA (3.0 kPa O2+1.0 kPa CO2) at 0-1°C for up to 7 months. The transcript abundance of seven LACs (2, 7, 9, 12, 14, 15 and 16) in fruit peel tissues was measured employing the RT-PCR. Five of them were significantly increased in scald tissues and significantly reduced by both DPA and 1-MCP treatments after 4- and 7- month storage. Purified laccase protein in apple peels was also obtained. The enzyme activity of laccase was found to be significantly reduced by DPA and 1-MCP treatments as compared with control. Quantitative changes in phenolic compounds in apple peel tissues were analyzed using HPLC. The phenolic compounds decreased during storage and showed no significant effect resulting from DPA and 1-MCP treatments except for an increase of chlorogenic acid. In contrast, an increase of phlorizin, rutin equivalents and cyanidin-3-glucoside equivalents was induced by DPA and 1-MCP treatments following 4 month storage. Overall, this study indicates that laccase plays important roles in apple superficial scald development. Based on these results, the potential strategy to prevent scald is also discussed.

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