Study On Exogenous Calcium Regulation Of Fruit Cracking And Its Mechanism In Junzao Jujube

Junzao is one of the main economic pillar industries in South Xinjiang.The quality of Junzao decreases because of the serious cracking of Junzao fruit during the period of crisp ripening,which restricts the development of Junzao industry chain.In this paper,Junzao was used as experimental material,and CaCl₂ was sprayed on Junzao at different developmental stages to investigate the cracking rate of Junzao at different developmental stages,and observe the microstructure of Junzao at different developmental stages,the contents of cell wall substance,activities of cell wall related metabolic enzymes,contents of total calcium,different forms of calcium,Ca M and activities of Ca²⁺-ATPase,NADK,etc.,the dynamic changes of calcium transport and components of calcium messenger system during fruit development of junzao jujube were further clarified,and the accumulation of calcium in jujube fruit was revealed,to provide theoretical basis for improving calcium nutrition and reducing fruit cracking of jujube.The main findings are as follows:1.The natural fruit cracking rate of Junzao was as high as 22.67%during the brittle-ripening period,and CaCl₂ treatment could significantly reduce the fruit cracking rate.2.CaCl₂ treatment can increase the thickness of cuticle,cuticle and subcuticle of pericarp cells,reduce the occurrence of chap and cell cavity,and maintain the integrity of pericarp,it can also make the fruit keep high hardness,elasticity and stickiness.3.The contents of cell wall cellulose,hemicellulose,protopectin,covalent-bound pectin and ion-bound pectin in Ziziphus jujuba cv.Junzao were significantly increased by spraying CaCl₂,the content of water-soluble pectin in pericarp and the activities of pectinase,cellulase and cellulase in cell wall were decreased.4.The content of calcium components in the fruit of Junzao at 4 different developmental stages was water-soluble calcium content>pectin calcium content>calcium phosphate content>calcium oxalate content.During the fruit development of Junzao jujube,the content of total calcium increased first and then decreased,and reached the maximum at the color-changing stage,the contents of calcium phosphate and calcium oxalate increased linearly with fruit development.The contents of total calcium,water soluble calcium and pectin calcium increased significantly,while the contents of calcium phosphate and calcium oxalate decreased significantly.5.CAM content and NAD kinase activity of Junzao were different in 4 developmental stages,but the trend of change was basically the same.The activity of Ca²⁺-atpase increased at first and then decreased.The activity of Ca²⁺-atpase decreased sharply and the ability of C^a2+-ATPase to regulate both intracellular and extracellular Ca²⁺decreased during fruit ripening.Spraying CaCl₂ could significantly increase the content of CAM,the activity of Ca²⁺-ATPase and the activity of NAD kinase in fruits.