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

Abstract:【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 atroom-temperature, and to explore the aging characteristics of the cellular level and the relationship withthe storage characteristics of yellow-peach pericarp after postharvest. All of the above was performed inorder 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 technologyresearch. 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. Thecell walls, mitochondrion, osmiophilic globules and chromoplast of two varieties of yellow-peach pericarpwere 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‘Hu454'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 min andplaced at 20 ℃ for 2 h. Maturity was assessed on a sample of the fruit that were similar in size, skin colorand absence of mechanical damage, and then randomly divided into four groups, and then packed withbubble 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 changeswere determined by JEM21200 EX SEM. Six fruits were randomly taken from each group, then peeledfrom the cross area of the equator and ordinate with a surgical blade, the thickness of each peel was 0.1cm, and the area was 0.05 cm×0.05 cm. There were 3 fruit peel from every fruit, the total number of fruitpeels was 72. Materials were put in 2.5% glutaraldehyde(p H=7.2) for 4 h at 4 ℃. They were then cleaned3 times in a concentration of 0.1 phosphate buffer, then fixed with 1% osmic acid for 2h, dehydrated withdifferent 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 ac-etate and citrate, and then photos were taken and observed using a 120 k V Biology Transmission ElectronMicroscope, the model was a Tecnai G2 spirit Biotwin.【Results】As the extension of storage time and ag-ing increased, there were plasmolysis phenomenon in the cell wall of the yellow-peach pericarp noted fordifferent 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 structureof 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 pericarp was collapsed, the structure of the cell wall wasseriously loose, and there were no obvious cell line, the micro filaments forming the three-dimensional cel-lulose was degraded and diffused, and the plasmolysis also occurred. It showed that the structure and theshape 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 chromoplast of the yellow-peach pericarp increased in the earlystage, 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 chromoplast. Eight days after posthar-vest, the lamellar structure and thylakoid membrane in the chromoplast of the‘Hu 454'yellow-peachpericarp 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 increaseof the number and volume were directly related with the storability of the yellow-peach. The structure andthe 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 structureof the mitochondria became blurred, deformed and disintegrated, and the number of the Golgi apparatusdecreased. From 6 d to 8 d after postharvest, the structure of the mitochondria in the‘Jinxiu'yellow-peach pericarp 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 wasmore stable than the chromoplast, and the time of disintegration was also later than the chromoplast. Thestructure 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 theaging of the yellow-peach, the cell wall of the yellow-peach pericarp deformed and showed partial degra-dation, the structure was loose, and the intercellular space was increased. The number of osmiophilic glob-ules increased, and the number of osmiophilic globules decreased and the volumeincreased. The mitochon-dria structure became blurred, the mitochondria deformed, stretched, and the number of the Gorgias re-duced and the structure collapsed. The aging process of the mitochondria was later than the chromoplast.The mitochondria and chromoplast of the‘Hu 454'yellow-peach pericarp were more stable than the‘Jinxiu'yellow-peach. The ultrastructure and its stability for the two varieties of peach pericarp is close-ly related to fruit storage resistance characteristics. The ultrastructural changes of the peach pericarpcould be due to its debilitation and loss, which accelerated the aging and decay of the fruit.