Impact of 1-MCP and Controlled Atmosphere on Physiological Disorders in Stored Pome Fruit: Biochemical Signatures of Oxidative Stress Metabolism

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In controlled atmosphere (CA) storage, the metabolic activity of pome fruit is decreased by controlling the oxygen and carbon dioxide partial pressures, as a supplement to a reduction in temperature. The optimal conditions are a compromise among: (i) maintaining firmness/quality; (ii) promoting uniform ripeness during re-warming; and, (iii) minimizing the incidence of physiological storage disorders such as scald and internal browning which can cause economic loss. CA conditions can result in an imbalance between oxidative and reductive (redox) processes at the cellular level and in the loss of endogenous antioxidants (e.g. ascorbate, NADPH) and accumulation of oxidative stress metabolites, like gamma-aminobutyrate (GABA) and gamma-hydroxybutyrate (GHB). In this proposal, we intend to investigate whether the shifts in redox and GABA metabolism are temporally associated with external injury and flesh browning in pears and apples stored under controlled atmosphere conditions. In addition, treatment of pome fruit with pre-storage chemicals, such as 1-methylcyclopropene or 1-MCP, aimed at preserving fruit quality via inhibition of ethylene mediated ripening may influence oxidative stress metabolism. The redox pairs and stress metabolites will be determined as a function of storage time and 1-MCP treatment via reverse-phase HPLC, GC-mass spectrometry, and with UV/Vis spectrophotometry. Also, we intend to investigate the relative importance of GHB production as a precursor to physiological disorders in apple fruit using a rapid-flowering line transformed with RNAi constructs of the GHB-forming enzyme, glyxoylate/succinic semialdehyde reductase. This project should lead to improved understanding of the mechanisms responsible for physiological disorders in stored apples and pears, and could contribute to improved storage protocols for maintaining quality of product, and the development of diagnostics/technologies for assessing injury potential and genetic engineering strategies for ameliorating physiological disorders during storage.