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

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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