New insights into the effects of ethylene on ABA catabolism, sweetening and dormancy in stored potato tubers.

R Tosetti,L.A Terry,G.A Chope,M.C Alamar,S Mcwilliam,A.J Thompson,K Cools,A Waters

doi:10.1016/j.postharvbio.2020.111420

Abstract

Continuous ethylene supplementation suppresses postharvest sprouting, but it can increase reducing sugars, limiting its use as an alternative to chlorpropham for processing potatoes. To elucidate the mechanisms involved, tubers were treated after curing with or without the ethylene binding inhibitor 1-methylcyclopropene (1-MCP at 1 μL L-1 for 24 h), and then stored in air or air supplemented with continuous ethylene (10 μL L-1). Across three consecutive seasons, changes in tuber physiology were assessed alongside transcriptomic and metabolomic analysis. Exogenous ethylene alone consistently induced a respiratory rise and the accumulation of undesirable reducing sugars. The transient respiratory peak was preceded by the strong upregulation of two genes encoding 1-aminocyclopropane-1-carboxylate oxidase (ACO), typical of wound and stress induced ethylene production. Profiles of parenchymatic tissue highlighted that ethylene triggered abscisic acid (ABA) catabolism, evidenced by a steep fall in ABA levels and a transient rise in the catabolite phaseic acid, accompanied by upregulation of transcripts encoding an ABA 8'-hydroxylase. Moreover, analysis of non-structural carbohydrate-related genes revealed that ethylene strongly downregulated the expression of the Kunitz-type invertase inhibitor, already known to be involved in cold-induced sweetening. All these ethylene-induced effects were negated by 1-MCP with one notable exception: 1-MCP enhanced the sprout suppressing effect of ethylene whilst preventing ethylene-induced sweetening. This study supports the conclusions that: i) tubers adapt to ethylene by regulating conserved pathways (e.g. ABA catabolism); ii) ethylene-induced sweetening acts independently from sprout suppression, and is similar to cold-induced sugar accumulation.

Highlights

Maintaining dormancy and low reducing sugars content during storage are key priorities for the global potato processing industry
Respiration was monitored in situ throughout storage: within seventy-two hours from the start of continuous ethylene supplementa tion (10 μL L− 1), ethylene-treated tubers showed a transient increase in CO2 production, which peaked at five days before declining, whereas no increase was detected in the absence of ethylene (Fig. 3)
In years 2 and 3, to elucidate the additional effect of 1-MCP pre-storage treatment, the analysis focused on each in dividual treatment, but for cv

Summary

Introduction

Maintaining dormancy and low reducing sugars content during storage are key priorities for the global potato processing industry. Control of dormancy during commercial storage is overly reliant on a longstanding synthetic sprout suppressant, chlorpropham (CIPC), with 85 % of ware potatoes treated in the UK alone (Hinchcliffe et al, 2018). The inhibition of potato sprout growth by ethylene is well-known; and similar effects of using ethylene to extend ecodormancy have been described in other low-ethylene-producing storage organs, like onion bulbs (Cools et al, 2011; Ohanenye et al, 2019) and sweetpotato roots (Amoah et al, 2016). Continuous ethylene supplementation induced an accumulation of abscisic acid (ABA) in potato tubers (Fou karaki et al, 2016a), and has been associated with tuber dormancy (Alamar et al, 2017a; Sonnewald and Sonnewald, 2014)

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Conclusion