Impact of 1-methylcyclopropene and controlled atmosphere storage on polyamine and 4-aminobutyrate levels in "Empire" apple fruit.

Kristen L Deyman,Carolyne J Brikis,Gale G Bozzo,Barry J Shelp

doi:10.3389/fpls.2014.00144

Abstract

1-Methylcyclopropene (1-MCP) delays ethylene-meditated ripening of apple (Malus domestica Borkh.) fruit during controlled atmosphere (CA) storage. Here, we tested the hypothesis that 1-MCP and CA storage enhances the levels of polyamines (PAs) and 4-aminobutyrate (GABA) in apple fruit. A 46-week experiment was conducted with “Empire” apple using a split-plot design with four treatment replicates and 3°C, 2.5 kPa O2, and 0.03 or 2.5 kPa CO2 with or without 1 μL L-1 1-MCP. Total PA levels were not elevated by the 1-MCP treatment. Examination of the individual PAs revealed that: (i) total putrescine levels tended to be lower with 1-MCP regardless of the CO2 level, and while this was mostly at the expense of free putrescine, large transient increases in soluble conjugated putrescine were also evident; (ii) total spermidine levels tended to be lower with 1-MCP, particularly at 2.5 kPa CO2, and this was mostly at the expense of soluble conjugated spermidine; (iii) total spermine levels at 2.5 kPa CO2 tended to be lower with 1-MCP, and this was mostly at the expense of both soluble and insoluble conjugated spermine; and (iv) total spermidine and spermine levels at 0.03 kPa were relatively unaffected, compared to 2.5 kPa CO2, but transient increases in free spermidine and spermine were evident. These findings might be due to changes in the conversion of putrescine into higher PAs and the interconversion of free and conjugated forms in apple fruit, rather than altered S-adenosylmethionine availability. Regardless of 1-MCP and CO2 treatments, the availability of glutamate showed a transient peak initially, probably due to protein degradation, and this was followed by a steady decline over the remainder of the storage period which coincided with linear accumulation of GABA. This pattern has been attributed to the stimulation of glutamate decarboxylase activity and inhibition of GABA catabolism, rather than a contribution of PAs to GABA production.

Highlights

Introduction1-methylcyclopropene (1-MCP) has been adopted by the apple industry as a means of delaying ethylenemediated fruit ripening and senescence, especially in combination with storage under controlled atmosphere (CA) conditions (i.e., 0–3◦C, 2–2.5 kPa O2, 2–4 kPa CO2; DeEll et al, 2008; Fawbush et al, 2008; Watkins, 2008). 1-MCP inhibits ethylene binding and production in apple fruit held at ambient or chilling temperature, and reduces the expression of genes responsible for ethylene biosynthesis (Dal Cin et al, 2006; Pang et al, 2006; Vilaplana et al, 2007; Figure 1)
The ratios between free and conjugated PAs vary among plant species (Bagni and Tassoni, 2001), and some evidence exists for interconversion between free and conjugated PAs (Bassard et al, 2010), which could influence our interpretation of the impact of 1-MCP and controlled atmosphere (CA) on PAs and possibly GABA in apple fruit (Figure 1)
It is well known that 1-MCP treatment should inhibit the autocatalytic production of ethylene in apple fruit (Pang et al, 2006; DeEll et al, 2008; Fawbush et al, 2008; Jung and Watkins, 2011), reduce the expression of genes involved in ethylene biosynthesis (Dal Cin et al, 2006; Pang et al, 2006; Vilaplana et al, 2007), and decrease the level of ACC (Bulens et al, 2012)

Summary

Introduction

1-methylcyclopropene (1-MCP) has been adopted by the apple industry as a means of delaying ethylenemediated fruit ripening and senescence, especially in combination with storage under controlled atmosphere (CA) conditions (i.e., 0–3◦C, 2–2.5 kPa O2, 2–4 kPa CO2; DeEll et al, 2008; Fawbush et al, 2008; Watkins, 2008). 1-MCP inhibits ethylene binding and production in apple fruit held at ambient or chilling temperature, and reduces the expression of genes responsible for ethylene biosynthesis (Dal Cin et al, 2006; Pang et al, 2006; Vilaplana et al, 2007; Figure 1). 1-MCP inhibits ethylene binding and production in apple fruit held at ambient or chilling temperature, and reduces the expression of genes responsible for ethylene biosynthesis (Dal Cin et al, 2006; Pang et al, 2006; Vilaplana et al, 2007; Figure 1). During the ripening of a bulky fruit such as tomato, there is an inverse relationship between the production of higher PAs and ethylene (Lasanajak et al, 2014), 1-MCP treatment inhibits autocatalytic ethylene production without affecting SAM levels (Van de Poel et al, 2013), and decreased levels of ethylene in RNAi-1-aminocyclpropane-1-carboxylate synthase fruits enhance PA levels and upregulate PA biosynthesis genes (Gupta et al, 2013). There is a transient increase in the level of Put only, and no changes in the level of Spd, Spm, or total PAs in apple fruit stored at 24◦C, even though the expression of only one of two SAM decarboxylases (SAMDCs) is repressed (Pang et al, 2006)

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