Exogenous calcium deflects grape berry metabolism towards the production of more stilbenoids and less anthocyanins.

Calcium supplements have increasingly been used at pre- and post-harvest stages for improving fruit firmness, but elevated calcium levels in grape cells were shown to reduce total anthocyanin content. In this study, we hypothesized that exogenous calcium influences specific polyphenolic compounds, and performed targeted UPLC-MS analysis in fruits collected from vines cv. "Vinhão" sprayed with 2% (w/v) CaCl2 throughout the fruiting season, in two consecutive vintages, and in grape cell cultures elicited with calcium. Results showed that anthocyanin content is reduced upon calcium treatment, while stilbenoid synthesis is generally stimulated, in line with UFGT and STS expression patterns. The main metabolites involved in this response were malvidin-3-O-glucoside, E-piceid, E-ε-viniferin and E-resveratrol. The accumulation of phenolic acids, catechin and some quercetin derivatives was also favored by calcium, while other flavonols and flavan-3-ols were affected according to the vintage and berry developmental stage. In cell cultures, the entire flavonoid pathway was repressed.