Impact of 1-MCP and controlled atmosphere on physiological disorders in stored apples: GABA and polyamine metabolism

目前，加拿大生产的新鲜市场苹果中约有30-40%（农场价值1.64亿美元）使用1-甲基环丙烯（1-MCP）处理，这有助于保持水果质量并延长保质期，从而增加营销机会。唯一的负面反应是某些苹果品种在控气贮藏期间对低温和二氧化碳相关疾病的敏感性增加。CA条件可导致细胞水平氧化和还原过程之间的不平衡，以及称为γ -氨基丁酸（GABA）的代谢物的积累。众所周知，GABA积累是光合组织对所有胁迫的反应，但其在非光合组织中的作用及其积累机制在很大程度上尚未被探索。在这项提案中，我们打算研究GABA和γ -羟基丁酸（GHB）（一种密切相关的代谢物，其积累受氧化还原状态调节）及其潜在的前体（多胺与谷氨酸）是否与两种受欢迎的加拿大品种（“Empire”和“McIntosh”）苹果的外部损伤和果肉褐变有关。苹果将在不同温度和二氧化碳的CA条件下储存，有或没有1-MCP处理，代谢物谱和果实质量将使用反相高效液相色谱和质谱测定作为储存时间的函数。此外，我们打算利用生化（酶活性、示踪剂）和分子（基因表达）分析相结合的方法来研究苹果果实中多胺和谷氨酸来源的GABA产生的相对重要性。这个项目应该会有所改进

Currently, about 30-40% of the fresh market apples produced in Canada (farm gate value of $164M) is treated with 1-methylcyclopropene (1-MCP), which helps to maintain fruit quality and extend shelf life, thereby increasing marketing opportunities. The only negative response has been increased susceptibility to low temperature- and CO2-related disorders in certain apple cultivars during controlled atmosphere (CA) storage. CA conditions can result in an imbalance between oxidative and reductive processes at the cellular level and in the accumulation of a metabolite called gamma-aminobutyrate (GABA). While GABA accumulation is a well known response to all stresses in photosynthetic tissues, its role and the mechanisms associated with its accumulation in non-photosynthetic tissues are largely unexplored. In this proposal, we intend to investigate whether GABA and gamma-hydroxybutyrate (GHB), a closely related metabolite whose accumulation is regulated by redox status, and their potential precursors (polyamines versus glutamate), are associated with external injury and flesh browning in apples from two popular Canadian cultivars ('Empire' and McIntosh'). The apples will be stored under various CA conditions of temperature and CO2 with or without 1-MCP treatment and metabolite profiles, as well as fruit quality, will be determined as a function of storage time using reverse-phase HPLC and mass spectrometry. Also, we intend to investigate the relative importance of polyamine- and glutamate-derived GABA production in apple fruit using a combination of biochemical (enzyme activities, tracer) and molecular (gene expression) analyses. This project should lead to improved