采前套袋对黄肉桃货架期果皮超微结构的影响

Effect of preharvest bagging on ultrastructural changes of yellow-peach pericarp during shelf-life

【目的】探讨黄肉桃采后果皮衰老期间细胞器的变化规律和细胞水平的衰老特征及其与果实耐贮性的相关性,为鲜食黄桃品种的改良和贮运技术的研究提供一定的科学依据和实践指导。【方法】以耐贮性较强的‘沪454’和耐贮性略差‘锦绣’黄桃为试材,利用透射电镜观察货架期间2个黄桃品种果皮细胞壁、有色体、嗜饿颗粒和线粒体的超微结构及其变化规律。【结果】随着贮藏时间的延长和果实的衰老,黄桃果实果皮细胞壁变形,部分降解,结构松散,细胞间隙增大;果皮有色体中嗜饿颗粒数目增多,后期嗜饿颗粒数目减少但体积增大,有色体中片层类囊体膜结构瓦解、变形;嗜饿颗粒数目的增多和个体的增大与果实的耐贮性有密切相关;果皮线粒体结构变得模糊,线粒体变形、拉长,内基数目减少,结构解体出现空洞;果皮中线粒体的衰老进程迟于有色体;‘沪454’黄桃果皮有色体和线粒体较‘锦绣’黄桃稳定。【结论】2个品种黄桃果皮中细胞超微结构及其稳定性与果实耐贮性密切相关。果皮组织细胞的超微结构变化可导致组织细胞功能衰弱和丧失,加速果实的衰老。

[Objective] This study was designed to research ultrastructural changes such as the cell walls, mitochondrion, osmiophilic globules and chromoplast of yellow-peach pericarp which were stored at room-temperature, and to explore the aging characteristics of the cellular level and the relationship with the storage characteristics of yellow-peach pericarp after postharvest. All of the above was performed in order to research the effects of preharvest bagging on ultrastructural changes of yellow-peach and to pro- vide a certain scientific basis and practical guidance for fresh peach variety improvement and technology research. With the progress of transmission electron microscopy （SEM） technology and the study of cell ul- trastructure in-depth, electron microscopy （SEM） technology has been widely applied in fruit trees. The cell walls, mitochondrion, osmiophilic globules and chromoplast of two varieties of yellow-peach pericarp were observed by transmission electron microscopy in this study. [Methods] The pericarp of the ＇Hu454＇ and ＇ Jinxiu＇ yellow-peach was selected as material for this study. A total of 600 ＇ I-Iu454＇ and ＇ Jinxiu＇ yellow peaches were harvested respectively from the experimental orchard of the Shanghai Academy of Ag- ricultural Sciences in Shanghai. The fruit was immediately moved to the analysis lab within 30 rain and placed at 20 ℃ for 2 h. Maturity was assessed on a sample of the fruit that were similar in size, skin color and absence of mechanical damage, and then randomly divided into four groups, and then packed with bubble nets into plastic crates, and stored at （25＋2） ℃ and 75%-80% humidity. The yellow-peach peri- carp was taken at intervals of 2, 4, 6 and 8 d and stored at room-temperature. The ultrastructural changes were determined by JEM21200EX SEM, Six fruits were randomly taken from each group, then peeled from the cross area of the equator and ordinate with a surgical blade, the thickness of each peel was 0.1 cm, and the area was 0.05 cruX0.05 cm. There were 3 fruit peel from every fruit, the total number of fruit peels was 72. Materials were put in 2.5% glutaraldehyde （pH=7.2） for 4 h at 4 ℃. They were then cleaned 3 times in a concentration of 0.1 phosphate buffer, then fixed with 1% osmic acid for 2h, dehydrated with different concentrations of ethanol dehydration, and then the materials were transferred to a different con- centration of acetone, and then the materials were imbedded with epoxy resin and vibrated for 24 h. Mate- rials were sliced at a 70 nm thickness using a LEICA-UC6 ultra microtome, double stained with uranyl acetate and citrate, and then photos were taken and observed using a 120 kV Biology Transmission Electron Microscope, the model was a Tecnai G2 spirit Biotwin. [ Results ] As the extension of st^rage time and ag- ing increased, there were plasmolysis phenomenon in the cell wall of the yellow-peach periearp noted for different degrees, which were different significantly between the two varieties. Eight days after posthar- vest, the mesoglea of the cell wall in the ‘Hu 454＇ yellow-peach pericarp was still legible, the structure of the cell wall was white speckled with grey, and was bent, damaged, and exhibited a slightly loose struc- ture. The cell wall in the ‘Jinxiu＇ yellow-peach periearp was collapsed, the structure of the cell wall was seriously loose, and there were no obvious cell line, the micro filaments forming the three-dimensional cellulose was degraded and diffused, and the plasmolysis also occurred. It showed that the structure and the shape of the cell wall in the ‘Hu 454＇, whose storability was stronger, was more stable than in the ＇ Jinx- iu＇ yellow-peach, whose storability was worse. As the extension of storage time and the aging increased, the number of osmiophilic globules in the chromoptast of the yellow-peach pericarp increased in the early stage, then the number decreased and the volume increased in the late stage. The structure of the thyla- koid membrane in the chromoplast also collapsed and deformed. Six days after postharvest, there were visi- ble and complete envelopes and a few lamellar structures of thylakoid membrane in the ‘Hu 454＇ yellow- peach. Compared to the harvest, the number of osmiophilic globules increased. The envelope of the thyla- koid membrane in the ‘Jinxiu＇ yellow-peach was blurred and indistinct, the lamellar structure was col- lapsed and deformed, and it was full of osmiophilic globules in the ehromoplast. Eight days after posthar- vest, the lamellar structure and thylakoid membrane in the chromoplast of the ‘Hu 454＇ yellow- peach pericarp gradually disintegrated. The chromoplast of the ‘Jinxiu＇ yellow-peach was severely deformed, the thylakoid membrane was collapsed, the volume of osmiophilic globules became bigger and mutual dis- solution was noted with each other. The Stroma lamella and grana lamella of the chromoplast was disinte- grated most of all. It showed that the disintegration and deformation of the chromoplast, and the increase of the number and volume were directly related with the storability of the yellow-peach. The structure and the shape of the chromoplast of the ‘Hu 454＇ whose storability was stronger, was more stable than the ＇ Jinxiu＇ whose storability was bad. As the extension of storage time and the aging increased, the structure of the mitochondria became blurred, deformed and disintegrated, and the number of the Golgi apparatus decreased. From 6 d to 8 d after postharvest, the structure of the mitochondria in the ‘Jinxiu＇ yellow- peach periearp was blurred, deformed and disintegrated, and the number of Golgi apparatus decreased. There was also a double membrane structure in the mitochondria of the ‘Hu 454＇ yellow-peach pericarp, the structure was tight, and lightly collapsed. It also showed that the structure of the mitochondria was more stable than the chromoplast, and the time of disintegration was also later than the chromoplast. The structure and the shape of the mitochondria in the ‘Hu 454＇, whose storability was stronger, was more sta- ble than the ‘Jinxiu＇ whose storability was bad. [ Conclusion] With the extension of storage time and the aging of the yellow-peach, the cell wall of the yellow-peach periearp deformed and showed partial degra- dation, the structure was loose, and the intercellular space was increased. The number of osmiophilie glob- ules increased, and the number of osmiophilie globules decreased and the volumeincreased. The mitoehon- dria structure became blurred, the mitoehondria deformed, stretched, and the number of the Gorgias re- duced and the structure collapsed. The aging process of the mitoehondria was later than the ehromoplast. The mitoehondria and chromoplast of the ‘Hu 454＇ yellow-peach periearp were more stable than the ＇ Jinxiu＇ yellow-peach. The ultrastrueture and its stability for the two varieties of peach periearp is close- ly related to fruit storage resistance characteristics. The ultrastruetural changes of the peach periearp could be due to its debilitation and loss, which accelerated the aging and decay of the fruit.