甜菜碱对果实采后冷害调控及其机制研究

Chilling injury (CI) is a major problem, which limits the application of cold storage in cold-sensitive fruits. Glycine betaine (GB) play an important role in enhancing cold tolerance of postharvest fruits, however, its mechanism is not clear. This study focused on the scientific issue of CI of postharvest fruits, and commenced from metabolism of GB and its physiological and biological function. The effect of exogenous GB treatment on CI, quality parameters, active oxygen radical metabolism, endogenous GB metabolism, activity and expression of betaine aldehyde dehydrogenase, cell membrane structure and lipid content, and programmed cell death (PCD) were investigated in cold-sensitive fruits including peaches and loquats. In addition, heat treatment and low temperature conditioning were applied on peaches and loquats, and the metabolism of endogenous GB was also evaluated. Thus, this study is supposed to illuminate the regulation and mechanism of GB improving membrane integrated and inhibiting PCD, and explain the mechanism of GB alleviating CI in cold-sensitive fruits. Moreover, the results of this study can enrich the theory of CI regulation in postharvest biology, provide theoretical principle in controlling CI and deterioration in cold-sensitive fruits during cold storage, and enhance competitive strength of China's fruit industry in the global market.

冷害是限制冷敏性果实低温贮藏的主要问题，甜菜碱具有提高果实抗冷性的作用，但其作用机制尚不明确。本项目以冷敏性果实桃、枇杷为试材，围绕果实采后冷害调控这一科学问题，从甜菜碱合成代谢及其生物学功能入手，研究外源甜菜碱处理对果实冷害、品质指标、活性氧代谢、内源甜菜碱含量、甜菜碱醛脱氢酶活性与表达、细胞膜结构、脂肪酸组分和细胞程序性死亡的影响。此外，研究热处理和低温预贮对冷敏性果实桃、枇杷内源甜菜碱代谢的影响。通过这些研究明确甜菜碱对果实细胞膜稳定性和细胞程序性死亡的调控机制，以揭示甜菜碱对果实采后冷害调控的机理。本项目的研究成果可丰富果实采后冷害调控的生物学理论，为控制我国冷敏性果实冷藏期间冷害劣变提供理论依据，对降低我国果品采后损失、增强我国果品在国际市场上的竞争力，都具有重要的现实意义。

桃和枇杷属于冷敏性果实，在冷藏期间易发生冷害，主要表现为果肉褐变、粉质化或木质化，果汁和香气减少等。冷害的发生不仅降低了桃和枇杷的食用品质和商品价值，还严重限制了果实的冷藏期和货架寿命。因此，研究调控果实冷害发生的技术及其机理具有重要的理论和实际意义。本研究以桃和枇杷果实为试验材料，研究了外源甜菜碱、低温预贮和热激处理对果实冷害、品质、活性氧代谢、内源甜菜碱和脯氨酸代谢、细胞膜透性、细胞膜脂肪酸组分、细胞程序性死亡的影响。研究结果表明，外源甜菜碱处理可维持桃和枇杷果实活性氧代谢平衡，提高果实内源甜菜碱、脯氨酸、总酚和蔗糖含量，诱导提高甜菜碱醛脱氢酶活性及其表达，从而提高果实抗冷性。此外，还发现外源甜菜碱处理可显著抑制桃和枇杷果实DNA的梯度降解，减轻细胞膜脂氧化损伤，维持细胞膜较好的功能，从而抑制果实细胞程序性死亡。低温预贮和热激处理，也可提高桃和枇杷果实内源甜菜碱含量，通过调控果实内源甜菜碱代谢，维持细胞结构与功能，抑制果实冷害发生。蛋白组分析结果表明，甜菜碱处理可提高桃和枇杷果实逆境胁迫蛋白的表达，维持蛋白的空间结构，减轻蛋白质的损伤。同时还通过增强氨基酸和糖代谢为细胞提供能量来源，减轻细胞的程序性死亡。这些研究结果阐明了外源甜菜碱通过调控桃和枇杷果实的不同代谢途径，提高果实抗冷性从而减轻冷害发生的主要机理。明确了外源甜菜碱通过抑制果实细胞程序性死亡，减轻细胞膜氧化损伤，从而抑制冷害的主要机制。本研究丰富了果实采后冷害调控的生物学理论，为控制果实冷害劣变提供理论依据。