Physiological responses of wine grape berries to postharvest ethylene treatments

The application of ethylene to harvested grapes affects wine composition mainly in terms of phenol concentration and aroma compound profiling. Microarray analysis performed on skins of wine grapes (Vitis vinifera, ‘Sangiovese’) treated, after harvest, with 1,000 ppm of ethylene for 36 h revealed no difference between control and treated samples in terms of flavonoid-related genes, thus supporting the hypothesis of an effect of exogenous ethylene on extractability during vinification rather than on increasing flavonoid biosynthesis. Changes in specific lipophilic compound concentration have been observed with antheraxanthin and violaxanthin accumulating in ethylene-treated berries and neoxanthin (and, at lesser extent, β-carotene) more abundant in control samples. A correlation network analysis based on transcript-metabolite data integration showed that antheraxanthin was strongly correlated (|ρ|>0.90) with SAMDC gene expression (direct) and β-carotene (inverse). Taking into account the relationships existing between carotenoids and abscisic acid (ABA) and considering that, in other plant species, SAMDC expression is induced by exogenous ABA, these results suggest that responses to exogenous ethylene in harvested grape berries are mediated by ABA. This hypothesis is also strengthened by the HORMONEMETER analysis performed on microarray data, pointing out a general correlation with ABA, indicating a positive action of the ethylene treatment upstream abscisic acid biosynthesis/metabolism possibly resulting in ABA concentration increase. Our data further confirm that the interplay between ABA and ethylene may represent a key physiological aspect impacting the final stages of grape berry development.