BMC Plant Biol

The acid component of grape berries, originating in the metabolism of malate and tartrate, the latter being less well-known than the former, is a key factor at play in the microbiological stability of wines destined for distillation. Grape acidity is increasingly affected by climate changes. The ability to compare two vintages with contrasted climatic conditions may contribute to a global understanding of the regulation of acid metabolism and the future consequences for berry composition. The results of the analyses (molecular, protein, enzymatic) of tartrate biosynthesis pathways were compared with the developmental accumulation of tartrate in Ugni blanc grape berries, from floral bud to maturity. The existence of two distinct steps during this pathway was confirmed: one prior to ascorbate, with phases of VvGME, VvVTC2, VvVTC4, VvL-GalDH, VvGLDH gene expression and abundant protein, different for each vintage; the other downstream of ascorbate, leading to the synthesis of tartrate with maximum VvL-IdnDH genetic and protein expression towards the beginning of the growth process, and in correlation with enzyme activity regardless of the vintage. Overall results suggest that the two steps of this pathway do not appear to be regulated in the same way and could both be activated very early on during berry development