A Process-Based Model of TCA Cycle Functioning to Analyze Citrate Accumulation in Pre- and Post-Harvest Fruits

Abstract

Citrate is one of the most important organic acids in many fruits and its concentration plays a critical role in organoleptic properties. The regulation of citrate accumulation throughout fruit development, and the origins of the phenotypic variability of the citrate concentration within fruit species remain to be clarified. In the present study, we developed a process-based model of citrate accumulation based on a simplified representation of the TCA cycle to predict citrate concentration in fruit pulp during the pre- and post-harvest stages. Banana fruit was taken as a reference because it has the particularity of having post-harvest ripening, during which citrate concentration undergoes substantial changes. The model was calibrated and validated on the two stages, using data sets from three contrasting cultivars in terms of citrate accumulation, and incorporated different fruit load, potassium supply, and harvest dates. The model predicted the pre and post-harvest dynamics of citrate concentration with fairly good accuracy for the three cultivars. The model suggested major differences in TCA cycle functioning among cultivars during post-harvest ripening of banana, and pointed to a potential role for NAD-malic enzyme and mitochondrial malate carriers in the genotypic variability of citrate concentration. The sensitivity of citrate accumulation to growth parameters and temperature differed among cultivars during post-harvest ripening. Finally, the model can be used as a conceptual basis to study citrate accumulation in fleshy fruits and may be a powerful tool to improve our understanding of fruit acidity.

Putting primary metabolism into perspective to obtain better fruits

“…Note that parameters that are very difficult or impossible to measure can be fitted (model calibration). Weighing scale Calculation of relative growth rate and fresh to dry weight ratio (Gary et al, 1998) Initial fruit hydrostatic pressure (turgor) P Whole fruit or specific tissue of fresh fruit Pressure probe or calculated from fruit water potential and osmotic pressure Model initialization (Lechaudel et al, 2007) Fruit water potential P Chilled mirror hygrometer Calculation of hydrostatic pressure (turgor) in fruit initialization (Lechaudel et al, 2007) Fruit surface conductance to water P Whole fruit Mass loss registered using weighing scales Calculation of fruit transpiration (Gibert et al, 2005) Fruit hydrostatic pressure (turgor) P Pressure probe or calculated from water potential and osmotic pressure Estimation of cell wall extensibility/elasticity and yield threshold (Lechaudel et al, 2007) Fruit osmotic pressure P Fruit juice Freezing point (osmometer) Calculation of hydrostatic pressure (turgor) in fruit (Galindo et al, 2016) Fruit pH P, K pH meter Parameterization of vacuolar H+-coupled transport (Beauvoit et al, 2014;Etienne et al, 2015) Fruit growth respiration P Whole fruit or specific tissue of fruit Estimated from carbon and nitrogen content of fruit ashes Calculation of growth respiration coefficient (Gary et al, 1998) Stem phloem sugar concentration P Stem apex, cut stem or petioles Aphid stylectomy or phloem exudation Analysis of phloem metabolic composition Calculation of sugar mass flow from phloem into fruit and active uptake of sugars (Grossman and DeJong, 1994;Palmer et al, 2013) Osmotic pressure of other solutes in stem phloem P Fruit mineral concentrations P…”

“…Fruit turgor pressure depends on carbon partitioning between soluble and insoluble solids. While soluble solids such as sugars and organic acids have rarely been the subject of modelling work, a sugar accumulation model (Génard and Souty, 1996) and two models for the accumulation of citrate (Lobit et al, 2003;Etienne et al, 2015) and malate (Lobit et al, 2006;Etienne et al, 2014) have been developed. The sugar accumulation model represents the transformation of phloemic sugars into different sugars accumulating in the fruit pulp (mainly sucrose, glucose and fructose), a part of which is used for synthesizing compounds other than sugars and for respiration.…”

Genome-Wide Identification, Phylogeny, and Expression Analyses of the 14-3-3 Family Reveal Their Involvement in the Development, Ripening, and Abiotic Stress Response in Banana

“…Overall, these results suggested the key roles of 14-3-3 genes in regulating early fruit development. During the postharvest ripening processes, numerous physiological, biochemical, and molecular changes occur (Roy Choudhury et al, 2009 ; Shiga et al, 2011 ; Moser et al, 2012 ; Etienne et al, 2015 ) which influence the quality of banana fruit. Thus, postharvest ripening is critical to improving fruit quality and extending fruit shelf life in banana.…”

3‐D microstructural changes in relation to the evolution of quality during ripening of mango (Mangifera indica L. cv. Carabao)

“…Biochemical studies relate the decrease in citrate concentration during ripening to the decrease in mitochondrial malate transport, which could be altered by the changes in membrane integrity. 54 Electrolyte leakage related to microstructural changes The increase in electrolyte leakage in the peel during ripening (Fig. 6) can be attributed to cell-membrane modifications.…”