1-Methylcyclopropene (1-MCP) Effects on Ethylene Biosynthesis in Relation to Flesh Browning of ‘Empire' Apple Fruit

It has been hypothesized that inhibited ethylene production as a result of storage temperatures such as 0.5 ^oC, or by 1-methylcyclopropene (1-MCP) treatment at warmer temperatures such as 3-4 ^oC, is a causal factor in flesh browning of controlled atmosphere (CA) stored ‘Empire’ apples.  In this study we have investigated the effects of 1-MCP at storage temperatures of 0.5 and 3 ^oC on ethylene biosynthesis of CA stored fruit. Internal ethylene concentrations (IECs), 1-aminocyclopropane-1-carboxylate (ACC) and malonyl ACC (MACC) concentrations, and activities of ACC synthase (ACS) and ACC oxidase (ACO) in peel and flesh, and gene expression of ACS, ACO and ACC N-malonyl transferase (MT) peel, was assessed.  Flesh browning occurred in all treatments except for untreated fruit stored at 3 ^oC, and this was the only treatment where IECs increased during storage. The most distinct patterns of change were detected in peel tissues; ACS1 expression, ACS activity and ACC concentrations were highest in untreated fruit stored at 3 ^oC and were lowest in untreated and 1-MCP treated fruit stored at 0.5 ^oC. However, they increased in a similar fashion in 1-MCP treated fruit stored at 3 ^oC.  ACO1 and ACO2 expression remained low in 1-MCP treated fruit irrespective of storage temperature.  MT expression and MACC concentrations increased towards the end of storage.  The effects of treatment on ethylene in relation to flesh browning will be discussed.