Spatial heterogeneity of flesh-cell osmotic potential in sweet cherry affects partitioning of absorbed water

Abstract

A fleshy fruit is commonly assumed to resemble a thin-walled pressure vessel containing a homogenous carbohydrate solution. Using sweet cherry (<i>Prunus avium</i> L.) as a model system, we investigate how local differences in cell water potential affect H₂O and D₂O (heavy water) partitioning. The partitioning of H₂O and D₂O was mapped non-destructively using magnetic resonance imaging (MRI). The change in size of mesocarp cells due to water movement was monitored by optical coherence tomography (OCT, non-destructive). Osmotic potential was mapped using micro-osmometry (destructive). Virtual sections through the fruit revealed that the H₂O distribution followed a net pattern in the outer mesocarp and a radial pattern in the inner mesocarp. These patterns align with the disposition of the vascular bundles. D₂O uptake through the skin paralleled the acropetal gradient in cell osmotic potential gradient (from less negative to more negative). Cells in the vicinity of a vascular bundle were of more negative osmotic potential than cells more distant from a vascular bundle. OCT revealed net H₂O uptake was the result of some cells loosing volume and other cells increasing volume. H₂O and D₂O partitioning following uptake is non-uniform and related to the spatial heterogeneity in the osmotic potential of mesocarp cells.