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

ZHOU Huijuan; YE Zhengwen; WANG Ge; SU Mingshen; DU Jihong; LI Xiongwei

doi:10.13925/j.cnki.gsxb.20160070

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 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 provide 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 ultrastructure 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 ‘Hu454' and ‘Jinxiu' yellow peaches were harvested respectively from the experimental orchard of the Shanghai Academy of Agricultural Sciences inShanghai.The fruit was immediately moved to the analysis lab within 30 min 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 pericarp was taken at intervals of 2,4,6 and 8 d and stored at room-temperature.The ultrastructural changes were determined by JEM2120OEX 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 cm×0.05 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 concentration of acetone,and then the materials were imbedded with epoxy resin and vibrated for 24 h.Materials 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 storage time and aging increased,there were plasmotysis phenomenon in the cell wall of the yellow-peach pericarp noted for different degrees,which were different significantly between the two varieties.Eight days after postharvest,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 structure.The cell wall in the ‘Jinxiu' yellow-peach pericarp 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 ‘Jinxiu' 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 early stage,then the number decreased and the volume increased in the late stage.The structure of the thylakoid membrane in the chromoplast also collapsed and deformed.Six days after postharvest,there were visible and complete envelopes and a few lamellar structures of thylakoid membrane in the ‘ Hu 454' yellowpeach.Compared to the harvest,the number of osmiophilic globules increased.The envelope of the thylakoid membrane in the ‘Jinxiu' yellow-peach was blurred and indistinct,the lamellar structure was collapsed and deformed,and it was full of osmiophilic globules in the chromoplast.Eight days after postharvest,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 dissolution was noted with each other.The Stroma lamella and grana lamella of the chromoplast was disintegrated 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' yellowpeach 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 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 stable 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 pericarp deformed and showed partial degradation,the structure was loose,and the intercellular space was increased.The number of osmiophilic globules increased,and the number of osmiophilic globules decreased and the volumeincreased.The mitochondria structure became blurred,the mitochondria deformed,stretched,and the number of the Gorgias reduced 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 closely related to fruit storage resistance characteristics.The ultrastructural changes of the peach pericarp could be due to its debilitation and loss,which accelerated the aging and decay of the fruit.