The effect of temperature on the metabolic response of lamb’s lettuce (Valerianella locusta, (L), Laterr.) cells to sugar starvation

• Sugar starvation can occur in leafy vegetables, causing economic losses.
• Effect of sugar starvation on leafy vegetables is affected by temperature.
• Combining metabolomics and 13C fluxomics to study metabolome and fluxome of isolated cells.
• Sugar starvation alters metabolism.
• Switch of alternative sources of substrate upon sugar starvation.

Fresh leafy vegetables are highly perishable and may suffer from sugar starvation during postharvest storage. To fully understand their metabolic response to sugar starvation, isolated lamb’s lettuce (Valerianella locusta, (L) Laterr.) cells were used as a model system to study biochemical and metabolic stress response to sugar starvation at 1 °C, 18 °C and 25 °C. The effect of sugar starvation was minimal at 1 °C. While the higher temperature showed clear impact of sugar starvation on the overall metabolic profile no significant differences were observed between the starvation at either 18 °C or 25 °C for the main sugars (glucose, glucose-6-phosphate, fructose, fructose-6-phosphate and sucrose). Biochemical and metabolic changes of the isolated cells upon sugar starvation involved a decrease in the levels of sugars, except for trehalose and ribose, as well as an increase in the levels of sugar alcohols. Sugar starvation altered the central metabolism by decreasing the levels of the intermediates of the glycolytic pathway, except for 3-phosphoglycerate and pyruvate. Increased levels of the intermediates of the tricarboxylic acid cycle were also observed. 13C labelling data showed a decreased label accumulation in almost all metabolites, except for mannitol, myo-inositol, and trehalose. The increase in the levels of free soluble amino and fatty acids with a corresponding decrease in their 13C label suggested a breakdown of protein and triacylglycerides.