Kinetic modelling of the metabolic response of isolated lamb’s lettuce (Valerianella locusta L.) cells to sugar starvation
Leafy vegetables are highly perishable, as they are exposed to carbohydrate starvation during their postharvest storage life, leading to premature quality loss. An in-depth knowledge of the fundamental metabolic regulation and control mechanisms of these leafy vegetables to sugar starvation is beneficial in understanding how they modify their metabolism to survive in the absence of sugar. To this end, isolated lamb's lettuce cells were incubated in the dark to trigger sugar starvation at different temperatures (25, 18 and 1°C) to monitor the dynamic changes in the metabolome over time. To understand which pathways were up- or downregulated, the isolated cells were preloaded with uniformly labelled 13C-glucose and the distribution of the 13C label throughout the different metabolic pathways was monitored. The metabolite and the corresponding 13C label data were used to construct an integrated compartmentalised central metabolic model, containing both first-order and Michaelis-Menten kinetics, to quantify the effect of sugar starvation on the kinetic parameters and, thus, to calculate fluxes of the respiratory metabolism and to analyse the metabolic control mechanisms that plants have to adopt upon sugar starvation as a function of storage temperature. From this study, a decrease in flux was observed in the respiratory metabolism of cells when they were incubated at 1°C compared with 25 and 18°C. When sugar starvation was induced at 18 and 25°C, a decrease in the fluxes was observed in the glycolytic pathway metabolites as compared with that of the tricarboxylic acid cycle metabolites, which increased during sugar starvation. Moreover, an increased flux coming from protein and phospholipid breakdown was observed, resulting in increased concentrations of free amino and fatty acids, suggesting proteolytic and β-oxidation reactions.
Baiye Mfortaw Mbong, V., Hertog, M.L.A.T.M., Geeraerd, A.H. and Nicolai, B.M. (2017). Kinetic modelling of the metabolic response of isolated lamb’s lettuce (Valerianella locusta L.) cells to sugar starvation. Acta Hortic. 1154, 91-98
lamb’s lettuce cells, sugar starvation, temperature, kinetic modelling