Abstract: Effects of different bagging treatments on the soluble sugar contents and sucrose metabolism of ‘Chili’（Pyrus bretschneideri Rehd.）fruit during growth and development were studied. The results showed that the contents of fructose，glucose，sucrose and total soluble sugar in the fruits increased with the fruit growth and development. Bagging，especially with yellow waxed paper bags，reduced the soluble sugar increases. Invertase（Ivr）activity decreased with fruit development，and bagging affected the acid invertase（AI）activity. AI activities in fruits of bagging treatments were lower than that in control in 75，90 and 150 d after flowering. The neutral invertase（NI）activity showed no significant difference between bagging treatments and control. Sucrose phosphate synthase（SPS）activity increased with the fruit development and affected markedly by bagging. Among 4 tested bags，the yellow waxed paper bags affected SPS activity of fruits more than the white waxed paper and non-woven fabric bags did，and there were not significant different between fruits in plastic film bags and non-bagging control in most of the tested points. Sucrose synthase（SUS）in synthesis activity（SSs）of fruits increased gradually and sucrose synthase in cleavage activity（SSc）decreased as fruit growth. Bagging did not showed significant effect on the SSs activity in most tested points，but depressed the SSc activity in fruit development late stage. Real-time fluorescent quantitative PCR analysis of sucrose metabolism related enzyme genes AIV1，AIV2，SPS1 and SUS1 expression showed that bagging reduced the relative expression of AIV2，and non-woven bags had more effects than plastic film bags. Bagging delayed the maximum accumulation time of SPS1，and the SPS1 relative expression were significantly lower in fruits with plastic film bags than in non-bagging control in the fruit growth early stage. Bagging altered the time course of SUS1 expression，the relative expression amount of SUS1 in fruits with plastic film bags did not reveal obvious peak，and in fruit with yellow waxed paper bags appeared a maximum accumulation 15 d earlier than control and became lower after.

Key words: pear, bagging, sugar, metabolism, enzyme activity, relative gene expression, real-time fluorescent quantitative PCR analysis