Cultivar-dependent grape berry dehydration in later ripening phases may be associated with energy regulation and ionic homeostasis

Abstract

Climate warming and drought may alter the progression of sugar accumulation by the grape berry, and contribute to pre-harvest berry shrivel and cell vitality loss which were hypothesised to be associated with solute accumulation cessation and energy status in the berries. To explore the relationship between energy and cultivar-dependent berry cell death, we characterised the variations of pericarp constituents and energy status across five time points, five ripening phases, and three cultivars with various levels of berry shrivel and cell death. Grape berries of Shiraz, Chardonnay and Flame Seedless at the Eichorn-Lorenz stages 33 to 39 were sampled at 5:00, 9:00, 13:00, 17:00 and 21:00 on each sampling day, which were used in the analysis of water percentage, adenosine triphosphate (ATP), ethanol, sugar, L-malic acid, as well as elements with vascular mobility, including potassium (K) and sodium (Na). Shiraz and Chardonnay ceased accumulating sugar and phloem mobile elements during the later ripening phase, while Flame Seedless did not undergo water loss or cease to accumulate solutes in pericarps. Shiraz berry ripening was distinguished by greater pericarp water loss, ATP reduction, increased ion disorder susceptibility as indicated by a lower K/Na ratio, and higher ethanol concentration in the later ripening phase. The Chardonnay pericarp contained the highest ATP concentration and K/Na ratio among the three cultivars. The Flame Seedless pericarp maintained a low but stable K/Na ratio throughout berry ripening. Berry ripening phase impacted the diurnal variations of pericarp water percentage and ATP concentration. The results indicated that energy regulation and ionic homeostasis may be associated with cultivar-dependent grape pericarp hydration, solute accumulation and cell vitality during berry ripening.