Changes of Histological Structure and Water Potential of Huping Jujube Fruit Cracking

【Objective】 The changes of histological structure and water potential during Huping jujube fruit development were studied in order to provide a reliable evidence for better understanding of the mechanism of fruit cracking. 【Method】 The changes in composition of cell wall and the histological structure, as well as the pericarp cell apoptosis were studied during the fruit development by paraffin slice, TUNEL detection and regular physiological and biochemical technology.【Result】The fruit cracking of Huping jujube occurred mainly at the part-red stage to the full-red stage, and no obvious cracking was observed at the young fruit and swelling stages. During the fruit development, the content of protopectin and cellulose in pericarp decreased gradually, while the water soluble pectin increased. Furthermore, the activity of SOD, POD, and CAT decreased, and the cell membrane relative permeability increased. The results of paraffin slice indicated that there was a significant change in the histological structure during fruit development, and the obviously shrinking was found in the epidermal and hypodermic layer cells at part-red stage. The TUNEL analysis showed that there was obvious cell apoptosis in the pericarp cells at the part-red and full-red stages. The water absorbing ability of pulp was significantly higher than the pericarp, and a water potential gradient was founded between different parts of pulp,which caused the formation of water permeation system between outside, pericarp, and pulp.【Conclusion】All the results suggested that the apoptosis or death of pericarp cells at part-red stage resulted in the increasing of cell membrane relative permeability, and the free water adhered on the fruit surface driven by the water potential gradient through the ‘outside-pericarp-pulp' system, was absorbed largely by pulp, which resulted in the fruit cracking, finally.