The localisation of acids, sugars, potassium and calcium in developing grape berries

Abstract

Grape berries (Vitis vinifera cv. Chardonnay) were divided into four concentric zones in order to follow the developmental changes in the concentrations of malate, tartrate, glucose, fructose, potassium and calcium within the skin and the fruit flesh. Green berries showed a definite malate gradient, increasing in concentration from the skin towards the seeds; tartaric acid, on the other hand, was highest in concentration at the periphery and lowest in the berry center. With progressing maturity, the ratio between the tartrate concentration in the skin and the corresponding values in the berry core decreased, whereas the reverse was true for malate. In the ripe berry an acid gradient could also be found in the axial direction, decreasing from the pedicel towards the stylar scar. Before the onset of ripening, the highest glucose and fructose concentrations were observed in the skin and the berry center. The accumulation of these sugars in the pulp began without any apparent lag phase at a rate of about 2 mg/ berry · d. After veraison, the highest concentrations were found in the fruit core and the tissue below the peripheral vascular bundles. Both potassium and calcium were mainly localized near the peripheral and central vascular bundles. The potassium content increased during the entire period of berry development at a constant rate of 0.04 mg/berry · d, whereas calcium accumulation stopped about 30 d after anthesis. At this time, the calcium content was approximately 0.1 mg/berry.