Metabolic profiling reveals a coordinated response of isolated lamb's (Valerianella locusta, L.) lettuce cells to sugar starvation and low oxygen stress

Sugar starvation is a common phenomenon occurring in most leafy vegetables after harvest and storage. Additionally, leafy vegetables are subjected to low O-2 stress when stored in modified atmosphere conditions. In this study, the metabolism of isolated lamb's lettuce cells was studied upon sugar starvation under O-2 stress conditions, using C-13 labelled glucose. Fast depletions of the soluble sugars were observed, being more pronounced under aerobic conditions than under low O-2 stress conditions. Sugar starvation under aerobic conditions resulted in increased levels and decreased C-13 label incorporation of TCA cycle intermediates and amino and fatty acids originating from glycolytic and TCA cycle pathways, compared to starving cells incubated under low O-2 stress. On incubation under low O-2 stress a switch in metabolism from aerobic to fermentation metabolism was observed. Under low O-2 stress conditions, increased levels and C-13 label incorporated in hexose phosphates, pyruvate, lactate, GABA, alanine, together with increased levels of acetaldehyde, ethanol and ethyl acetate was observed indicating fermentative metabolism was triggered. (C) 2016 Elsevier B.V. All rights reserved.