枣果实裂果的组织结构及水势变化的原因

【目的】阐明壶瓶枣发育过程中果皮组织结构和水势变化，完善枣裂果机理研究。【方法】以易裂品种——壶瓶枣（Ziziphus jujube Mill. cv. Huping）为试材，跟踪果实发育进程，分别采用石蜡切片、TUNEL细胞凋亡检测及常规生理生化技术，探讨果皮中细胞壁组成成分和解剖结构变化及细胞凋亡与裂果的关系。【结果】壶瓶枣裂果主要发生在半红期至全红期，而幼果期和膨大期不发生裂果。果实发育过程中，果皮中原果胶、纤维素含量降低，水溶性果胶含量增加；SOD、POD、CAT活性逐渐下降，细胞质膜相对透性增大。石蜡切片结果表明，果皮解剖结构随果实发育而发生明显的变化，半红期表皮和皮下层细胞明显皱缩。TUNEL检测表明，半红期和全红期果皮细胞存在细胞凋亡现象。壶瓶枣果肉吸水能力明显强于果皮，且在不同部位果肉之间存在水势梯度，形成了“外界—果皮—果肉”水分渗透系统。【结论】半红期壶瓶枣果皮细胞发生凋亡甚至死亡，细胞质膜相对透性增大；果皮外部自由水分在水势梯度的驱动下，大量进入果肉中，引起果肉细胞膨胀而导致裂果。

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.