逐步降温对‘鸭梨’果心褐变及其相关基因表达的影响

Effect of gradient cooling on the core browning and its related gene expression in ‘Yali’ pear fruit

‘鸭梨’贮藏期果心褐变是困扰当前梨产业发展的主要问题之一,因此,解析其发生机制对于将来开发保鲜新技术具有重要的理论指导意义。本研究以‘鸭梨’为材料,探究了直接冷藏(直冷)和逐步降温(逐降) 2种方式对贮藏期果实品质和果心褐变相关基因表达模式的影响。结果表明:与直冷相比,逐降处理促使‘鸭梨’果实贮藏期间呼吸高峰提前,提高了乙烯生成速率;逐降处理‘鸭梨’果心在贮藏第60天时发生褐变,而直冷处理则在贮藏第85天时果心褐变。逐降处理‘鸭梨’果心褐变初期,总酚含量显著低于直冷处理,而PPO活性则相反。贮藏第60天时,逐降处理‘鸭梨’果心中Pb PAL1和Pb PAL2表达量显著高于直冷处理‘鸭梨’果心,并且它们的表达模式与果心褐变指数密切相关;与PbPALs相似,逐降处理‘鸭梨’果心PbPPO1、PbPPO4、PbPPO5和PbPPO6表达量在褐变初期均显著高于直冷处理,但只有PbPPO1和PbPPO5表达模式与果心褐变指数和PPO活性显著正相关,表明PbPPO1和PbPPO5是参与‘鸭梨’贮藏期果心褐变的关键基因。综上,逐降处理通过提高PbPAL1、PbPAL2、PbPPO1和PbPPO5等基因表达,促使PPO和酚类物质主导的酶促褐变反应发生,进而加剧果心衰老性褐变。因此,建议生产中在采用逐步降温贮藏‘鸭梨’时,应充分考虑采收期和果实采收品质。

The core browning of ‘Yali’ pear during storage is one of the main problems that perplex the development of industry at present.Therefore,studying the mechanism of core browning in ‘Yali’ pear is an important theoretical guiding for developing new preservation technologies in the future.In this work,‘Yali’ pear was explored to evaluate the effects of direct cold storage and gradient cooling treatments on the fruit quality and the expression pattern of browning-related genes in core of the fruit during storage.Compared with direct cooling treatment,gradient cooling treatment promoted the peak appearance of respiration earlier,and increased the ethylene production rate.The gradient cooling-treated ‘Yali’ pear fruit appeared core browning on the 60th day of storage,while the direct cooling-treated fruit appeared core browning on the 85th day of storage.At the early stage of core browning,the total phenol content in the core of gradient cooling-treated ‘Yali’ pear fruit was significantly lower than that of direct cooling-treated fruit,but the PPO activity was opposite.On the 60th day of storage,the expression levels of Pb PAL1 and Pb PAL2 in the core of gradient cooling-treated ‘Yali’ pear fruit were markedly higher than those of direct cooling-treated fruit,and moreover,their expression patterns were closely related to the core browning index.Similar to Pb PALs,the expression levels of Pb PPO1,Pb PPO4,Pb PPO5 and Pb PPO6 in the core of gradient cooling-treated ‘Yali’ pear fruit were also obviously higher than those of direct cooling-treated fruit at the early stage of core browning,but only the expression patterns of Pb PPO1and Pb PPO5 were significantly positively correlated with the core browning index and PPO activity,indicating that Pb PPO1 and Pb PPO5 were the key genes involved in the core browning of ‘Yali’ pear during storage.In conclusion,gradient cooling treatment promoted enzymatic browning reaction dominated by PPO and phenols through increasing the expression levels of Pb PAL1,Pb PAL2,Pb PPO1 and Pb PPO5,and then aggravated the aging browning of core in ‘Yali’ pear fruit.Therefore,it is suggested that the harvest time and fruit quality should be fully considered when the technology of gradient cooling is used to store ‘Yali’ pear fruit.