Abstract: 【Objective】Jujube (Ziziphus jujuba Mill.) is native to China, is China's endemic fruit tree, with saline, drought, adaptability and other advantages, jujube fruit is rich in nutrients, both edible and medicinal.There are nearly 20 million farmers for whom jujube is the main source of income, and the income from the jujube industry in key jujube-producing counties accounts for 40 per cent of the income of jujube farmers, and in some cases as much as 80 per cent.The cell wall materials,cell wall degrading enzymes,and peel structure are closely related to the occurrence of fruit crack-ing.The purpose of this experiment is to explore the changes in fruit water-immersion cracking rate, cell wall substances and cell wall degrading enzymes in different period of time of different cracking date varieties, so as to provide scientific basis for the prevention and control of cracking of jujube fruits. 【Methods】The test materials were fruits of the extremely easy-to-split jujube variety ‘Fucuimi’ and the anti-split variety ‘Dalizhizao’, which were taken from the jujube germplasm resource nursery of the Horticultural Experiment Station of Tarim University.Single-plant plots with three replications, 80 fruits were sampled in four periods of pre-white ripening, white ripening, half-red stage and full-red stage, and kept in an ice box to bring back to the laboratory for separation of pulp and pericarp, and then treated with liquid nitrogen and put into -80 ℃ ultra-low-temperature refrigerator for storage.Observations were made to analyse the rate of fruit splitting by immersion, pericarp cell wall composition (cellulose, hemicellulose, water-soluble pectin, ion-bound pectin and covalently bound pectin) and the activities of related degrading enzymes (polygalacturonase, cellulase, catalase, superoxide dismutase). 【Results】Pericarp strength, which can be used to measure the ease with which fruit cracking occurs, was positively correlated with the content of cell wall components and negatively correlated with fruit cracking rate. Cellulose, hemicellulose and pectin are components of the cell wall, and the content of cell wall material decreases in the middle and late stages of fruit growth and development.Near fruit maturity, water-soluble pectin, covalently bound pectin, and ion-bound pectin content decreased in the pericarp of crack-resistant and crack-prone varieties, ion-bound pectin, covalently bound pectin content, and cellulose content decreased in the pulp of crack-resistant varieties, and ion-bound pectin and covalently bound pectin content increased in the pulp of crack-prone varieties.Near fruit maturity, crack-resistant and crack-prone varieties showed an increase in hemicellulose content in the pericarp and pulp, an increase in soluble pectin content in the pulp, and a decrease in cellulose content in the pulp of jujube fruit.Covalently bound pectin and hemicellulose were higher in the pericarp of crack-resistant varieties than in crack-prone varieties.Water-soluble pectin, ion-bound pectin, covalently bound pectin, and cellulose content in the pericarp were not correlated with the rate of fruit splitting, while water-soluble pectin content and the rate of fruit splitting in the pulp showed a highly significant positive correlation, and cellulose content showed a highly significant negative correlation with the rate of fruit splitting.The pericarp of easy-to-fracture varieties contains less water-soluble pectin, hemicellulose, and more ion-bound pectin and covalently bound pectin.Pectinase and cellulase activities in the pericarp affect the occurrence of cracking, and at the semi-red fruit stage, the pericarp polygalacturonase(PG) and cellulase activities of crack-resistant varieties were higher than those of crack-prone varieties.Polyphenol oxidase(PPO) activity in the pericarp of crack-resistant varieties was significantly greater than that of crack-prone varieties, and there was a highly significant positive correlation between PPO activity in the pulp and the rate of fruit cracking.The activities of Superoxide dismutase(SOD), Catalase(CAT), PPO,Cellulase(CE) and PG in the pericarp were not correlated with the rate of fruit cracking. The pericarp CAT activity of the crack-resistant varieties at the semi-red stage of fruiting was highly significant greater than that of the crack-resistant varieties, the activity of SOD was highly significant less than that of the crack-resistant varieties, and the decrease in the pericarp PG activity of the crack-resistant varieties was greater than that of the crack-resistant varieties. The decrease of PG activity in the pericarp of crack-resistant varieties was greater than that of crack-resistant varieties.PG activity and CAT activity in the pulp of crack-resistant varieties were significantly or highly significantly higher than those of crack-prone varieties, and cellulase activity was higher than those of crack-prone varieties; PPO activity was highly significantly lower than those of crack-prone varieties, and SOD activity was lower than those of crack-prone varieties. 【Conclusion】Fruits at the brittle ripening stage are sensitive to water, and the earlier the appearance of cracked fruits under water-soaked conditions, the higher the rate of late cracking of varieties.During the sensitive period of fruit splitting (semi-red stage), ‘Dalizhizao’ showed high content of covalently bound pectin and hemicellulose in the pericarp, and high content of ion-bound pectin, covalently bound pectin and cellulose in the pulp.Varieties with high PG, cellulase and CAT activities in the pericarp and pulp were more resistant to cracking, and the lower the PG and cellulase activities in the pericarp and the higher the PPO and CAT activities, the greater the resistance to cracking.
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