NO处理延缓采后枇杷果实木质化劣变及其与能量代谢的关系

Study of Lignification's Delaying and Its Relationship with Energy Metabolism in Loquat Fruits after Nitric Oxide Fumigation

【目的】枇杷果实采后生命活动旺盛,衰老速度快,常温下极易变质腐烂。低温贮藏虽然可以有效延长贮藏期,减少腐烂,但会出现果皮难以剥离、果肉木质化并褐变、质地糙硬少汁等品质劣变现象,这是造成冷藏枇杷商品性丧失和损失的主要原因,已成为其市场拓展的限制因素,是当前枇杷果实在冷链集散和流通中急需解决的关键问题。探讨外源NO处理对冷藏枇杷果肉木质化劣变进程的作用机制,并分析木质化劣变与能量代谢的关系,以期为进一步研究采后枇杷果实低温品质劣变进程调控的分子生物学机理和贮运保鲜技术奠定基础。【方法】将‘解放钟’枇杷(Eriobotrya japonica Lindl.)果实在密闭容器中用0(对照组)、15和25μL·L-1 NO熏蒸2 h后,取出通风20 min,然后将各处理果实置于5℃、相对湿度85%条件下贮藏,测定冷藏期间各处理组果实细胞膜透性、硬度、出汁率、木质素含量、ATP含量、ADP含量、AMP含量、能荷值及琥珀酸脱氢酶(SDH)、细胞色素氧化酶(CCO)、H+-ATPase和Ca2+-ATPase活性的变化,并分析NO处理后木质素含量与能荷值间的相关性。【结果】随着贮藏时间的延长,枇杷果实细胞膜透性和硬度逐渐上升,出汁率逐渐下降,贮藏10 d后木质素含量迅速上升,果实冷害症状明显。与对照组相比,NO处理能延缓细胞膜透性和硬度的上升及出汁率的降低,显著抑制木质素的合成,较好地保持细胞膜的完整性,从而减轻果实冷害的发生。冷藏期间,枇杷果实ATP含量逐渐下降,贮藏前10 d ADP含量迅速下降并最终维持在较低水平,贮藏中后期(15—30 d)SDH、CCO、H+-ATPase和Ca2+-ATPase活性急剧下降,表明线粒体功能受损导致枇杷果实能荷水平迅速下降。与对照组相比,NO处理可以延缓ATP、ADP含量的下降,且显著抑制贮藏中后期SDH、CCO、H+-ATPase和Ca2+-ATPase活性的降低,保持枇杷果实较好的线粒体功能;贮藏30 d后,15和25μL·L-1 NO处理的枇杷果实能荷值分别比对照组高11.8%和12.9%。相关性分析表明,15和25μL·L-1 NO处理的枇杷果实能荷值和木质素含量呈极显著负相关,相关系数(r)分别为-0.715**、-0.598**。【结论】低温条件下,能量代谢失调与枇杷果实木质化劣变密切相关,NO处理可以通过调节SDH、CCO、H+-ATPase、Ca2+-ATPase线粒体代谢相关酶活性,维持较高的能量水平,从而有效地提高冷藏枇杷果实抗低温的能力,进而延缓果实木质化进程,其中以25μL·L-1 NO处理效果较好。

【Objective】Loquat（Eriobotrya japonica Lindl.） fruit is a famous southern fruit in China with its special texture and high metabolism. High metabolism rates reflect fast consumption of energy and rapid depletion of reserves such as carbohydrates and organic acids, so that its senescence is quick after harvest, and they are very liable to spoilage under improper storage conditions（such as room temperature）. The cold storage can effectively prolong the shelf life and reduce the decay of loquat fruits, but the phenomenon of the peeling difficulty, flesh lignification, browning and hardening will occur in cold-stored loquat fruits. The quality deterioration of cold-stored loquat fruit is a main reason causing postharvest losses, and has become a limiting factor in market distribution of loquat fruits. The objectives of present study were to investigate the effect of nitric oxide（NO） treatment on the flesh lignification of loquat fruits and the relationship between flesh lignification and energy metabolism, to provide a better foundation for further researches on molecular biological mechanism of regulation on quality deterioration in cold-stored loquat fruits and storage technology of postharvest loquat fruits.【Method】Loquat fruits（E. japonica Lindl.cv. Jiefangzhong）were fumigated with 0（control group）, 15 and 25 μL·L-1 NO gas for 2 h in a sealed container and then ventilated for 20 min. The fruits were stored at 5℃ and 85% RH. The changes of membrane permeability, firmness, juice percentage, lignin content, adenosine triphosphate（ATP） content, adenosine diphosphate（ADP） content, adenosine monophosphate（AMP） content, energy charge and the activities of succinate dehydrogenase（SDH）, cytochrome oxidase（CCO）, H＋-ATPase and Ca2＋-ATPase were determined during cold storage, and the correlation between lignin content and energy charge was analyzed after NO treatments. 【Result】 Membrane permeability and firmness of loquat fruits increased gradually and the juice percentage decreased during the storage. Lignin content increased rapidly 10 days later and the chilling injury symptoms of loquat fruits were obvious. As compared with the control group, NO treatments delayed the increase of membrane permeability and fruit firmness, postponed the decrease of juice percentage, and significantly inhibited the formation of lignin content, kept the integrity of the cell membrane, thereby reducing the chilling injury of loquat fruits. ATP content decreased during cold storage. ADP content dropped rapidly in the first 10 days and stayed lower level eventually. The activities of SDH, CCO, H＋-ATPase, and Ca2＋-ATPase dropped sharply at the middle and later storage（15-30 d）. These results showed that mitochondrial function was impaired which lead to energy charge level of loquat fruits drop rapidly. As compared with the control group, NO treatments delayed the decline of ATP and ADP content, inhibited the decrease of the activities of SDH, CCO, H＋-ATPase, and Ca2＋-ATPase significantly at the middle and later storage, which maintained better mitochondrial function. After 30 days of storage later, energy charge of loquat fruits by 15 and 25 μL·L-1 NO treatments were 11.8% and 12.9%, respectively, higher than control group. Correlation analysis showed that energy charge was very significantly negatively related with lignin content of loquat fruits and the correlation indexes were-0.715＊＊ and-0.598＊＊, respectively, in 15 and 25 μL·L-1 NO treatments.【Conclusion】Energy deficit had a closely relationship with lignification of loquat fruits during cold storage. All the results indicated that NO treatments maintained high energy level by regulating the activities of SDH, CCO, H＋-ATPase, and Ca2＋-ATPase of mitochondria metabolism-related enzymes, thereby enhanced the chilling tolerance and delayed the development of loquat fruits＇ lignification, the treatment with 25 μL·L-1 NO was better.