采后柑橘果实磷脂酶D对橘油的响应及油胞病的调控机制

Oleocellosis of citrus fruit is a kind of physiological diseases, which has been widespread in citrus-growing region. Oleocellosis is related to citrus oil released by oil gland on citrus peel，which is caused by environmental stresses. Citrus oil could make significant changes in ultrastructure of citrus peel organization and do harm to cell membrane. Phospholipase D plays an important role in lipid catabolism pathways, which has a close relationship with the external stresses, such as low temperature, drought, osmotic stress, mechanical damage, pathogen, exogenous hormones stimulation, thermal damage and so on. However, the way citrus oil does harm to cell membrane and the response mechanism of phospholipase D to citrus oil have not been reported yet. In this work, the hydrolysis and signal transduction mechanisms of phospholipase D in response to exogenous citrus oil will be studied through the use of citrus oil to induce oleocellosis. Besides, the mechanism of the effects of phospholipase D activator and inhibitor on oleocellosis will be discussed in order to further illuminate the response mechanism to citrus oil and regulatory mechanism to oleocellosis of phospholipase D. We can provide a theoretical and technical support for more reasonable and effective measures to control postharvest citrus fruit oleocellosis in the future, which is of great importance in both theory and practice.

柑橘果实油胞病目前已经成为我国柑橘产区普遍发生的一种生理性病害。油胞病的发生与环境胁迫引起的果皮油胞中橘油的释放有关，橘油导致果皮组织内部超微结构发生显著变化、细胞膜受损。磷脂酶D在细胞膜膜脂分解代谢途径中起重要的调控作用，与低温、干旱、渗透胁迫、机械损伤、病原菌刺激、外源激素刺激、热损伤等外界胁迫具有密切的关系，但橘油是如何导致柑橘果实细胞膜损伤及磷脂酶D对于橘油的响应机制未见相关报道。本项目拟通过橘油诱导油胞病，探讨柑橘果实在油胞病发病过程中磷脂酶D响应橘油诱导的水解机制，进一步研究磷脂酶D响应橘油诱导的信号转导机制，并通过研究磷脂酶D激活剂和抑制剂处理对柑橘果实油胞病发生机制的影响，进一步解释磷脂酶D对橘油的响应机制和对油胞病的调控机制。本项目研究成果可为将来采取更加合理、有效的技术以控制油胞病的发生提供理论依据和技术支撑，具有十分重要的理论和实践意义。

油胞病是一种主要的柑橘生理性病害，在果实生长发育和采后贮藏过程中均有发生；油胞病对果实食用品质影响不大，但大大降低了果实的外观品质和商品价值，病变部位也易受病原菌侵染而引起果实腐烂，严重制约柑橘产业的可持续发展。目前研究认为油胞病发病与橘油泄露有关。本项目采用橘油处理，通过果皮塌陷指数和变色指数评价，构建了两种成熟度柑橘果实的油胞病发病模式，明确了柑橘果实磷脂酶D（PLD）对橘油响应的水解特性；通过考察果实不同油胞病发病时期PLD相关基因表达、磷脂酸（PA）下游膜脂过氧化相关信号分子的变化规律和细胞膜结构及物质变化，从而明确PLD对橘油响应的信号转导特性；通过不同浓度CaCl2处理对采后柑橘果实油胞病发病情况的影响以及不同油胞病发病时期PLD水解底物变化研究，揭示PLD激活剂（Ca2+）对柑橘果实油胞病的调控机制。研究结果表明，橘油处理可诱导两种成熟度的柑橘果实发生油胞病，其中起主要作用的是橘油中的挥发性成分，一方面通过PLD活性增强以及磷脂酰胆碱（PC）、磷脂酰肌醇（PI）含量下降和PA含量上升而使得细胞膜水解进程加快；一方面促使机体的抗氧化能力受到限制，活性氧不能得到及时清除，细胞膜结构和功能受损使得果皮油胞病加剧。而PLD激活剂（CaCl2）处理果实能通过稳定细胞膜、延缓细胞膜降解的作用以及降低活性氧的产生从而有效控制油胞病。这些研究将为进一步明确柑橘果实油胞病的发生机理，并在此基础上寻找控制油胞病的措施提供新的、更加可行的思路和方法。