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Ahmad Sattar Khan and Zora Singh

, and celluloses undergo depolymerization and structural modifications during fruit softening ( Chin et al., 1999 ). Enzymes that are associated with fruit softening include polygalacturonase (PG), pectin esterase (PE), cellulase, and β

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Hong-Wei Zhou, Lilian Sonego, Andrai Khalchitski, Ruth Ben-Arie, Amnon Lers, and Susan Lurie

Most `Flavortop' nectarines [Prunus persica (L.) Batsch (Nectarine Group)] that were placed directly into 0 °C storage developed chilling injury after removal, while preconditioning fruit for 2 days at 20 °C (delayed storage) reduced chilling injury substantially. Chilling injury was expressed as the development of a dry, woolly flesh texture during ripening. Delayed-storage fruit were as firm as control fruit when placed in storage, but softened more during storage. Analysis of cell wall components showed that in woolly fruit a higher percentage of pectin was retained in the sodium carbonate fraction, although during ripening polymers in this fraction decreased in molecular mass (Mr). In the guanidine thiocyanate hemicellulose fraction of woolly fruit, the associated pectin and hemicellulose remained as large polymers, while in delayed-storage fruit they decreased in Mr during ripening. Endo-polygalacturonase (PG), pectin esterase (PE), and endo-glucanase (EGase) activities of delayed-storage fruit were the same as control fruit at the beginning of storage, although exo-PG was higher. However, differences were observed at the end of storage. Endo-PG activity was lower in control than delayed-storage fruit at the end of storage while PE activity was higher, and exo-PG and EGase activities were similar. These differences in activity were not reflected in the mRNA abundance of the respective enzymes. Endo-PG and PE message was similar in all fruit at the end of storage and increased during ripening, while EGase message was low at all times except in control fruit after storage and development of woolliness. Prevention of chilling injury by delayed storage appears to be due to the ability of the fruit to continue a progressive, slow cell wall degradation in storage which allows normal ripening to proceed when the fruit are rewarmed. Regulation of the softening process did not appear to be by enzyme synthesis, since mRNA levels of the enzymes did not correspond with enzyme activity.

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Shaolan Yang, Changjie Xu, Bo Zhang, Xian Li, and Kunsong Chen

wall disassembly and the disruption of adhesion between cells. Various enzymes, such as polygalacturonase ( Bonghi et al., 1996 ), pectin esterase ( Redgwell and Harker, 1995 ), cellulase ( Gallego and Zarra, 1997 ), xyloglucan endotransglycosylase

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Liping Kou, Yaguang Luo, Wu Ding, Xinghua Liu, and William Conway

.D. Hanzon, J. Irwin, P.L. Ben-Shalom, N. Lurie, S. 1995 Pectin esterase activity and pectin methyl esterification in heated Golden Delicious apples Phytochem. 39 491 494 Kou, L. Liu, X

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Marisa M. Wall, Kate A. Nishijima, Lisa M. Keith, and Mike A. Nagao

in CL or MP having softer arils due to their longer time in storage. Aril breakdown is associated with pectin esterase, polygalacturonase, and cellulase activities in early stages and with β-galactosidase activity during late phase breakdown ( Lin et

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Karthik-Joseph John-Karuppiah and Jacqueline K. Burns

development and abscission J. Expt. Bot. 53 2333 2339 Ratner, A. Goren, R. Monselise, S.P. 1969 Activity of pectin esterase and cellulase in the abscission zone of citrus leaf explants Plant Physiol. 44