Translocation and partitioning of C-13-photosynthates in the shoot with emphasis on berry coloration in 'Pione' grapes

Scions from two mature 'Pione' vines, which bore well-colored berries (vine s A and B, superior berry color, SEC) and two with poorly colored ones (vin es C and D, inferior berry color, IBC) annually, were grafted on Teleki 5BB rootstocks. The vines of the two strains were then planted in the same vin eyard. Shoot growth and berry development on each vine were recorded throug hout the growing season. The partitioning of C-13-photosynthates from leave s into the various parts of the shoot of the two strains, which were expose d to (CO2)-C-13 at two weeks after veraison, was investigated. No significa nt differences in shoot elongation, increment of leaf area per shoot, and c hanges in chlorophyll content of leaves between the two strains were observ ed. No notable difference in berry enlargement between the two strains was observed, although the berries at harvest from vines B and D were significa ntly heavier than those from vines A and C. The total soluble solids conten ts of the juice and anthocyanin levels of the skins were higher in berries from SEC vines than in those from IBC vines throughout the ripening stage; they increased significantly in the SEC vines two to three weeks after vera ison. At harvest, anthocyanin content in the berry skins from vines of SEC was two to three times higher than in those from vines of IBC. At the end o f (CO2)-C-13 feeding, the leaves on the main shoot of the SEC vines contain ed significantly more C-13 label than those of the IBC vines. 13C concentra tion in leaves on both main and lateral shoots on all vines decreased rapid ly for 24 hr after feeding followed by a gradual decrease, whereas it incre ased in berries with time. At 72 hr and 120 hr after feeding, C-13-photosyn thates were translocated into berries larger in SEC vines than those in IBC vines. At 120 hr after feeding, the distribution ratio of C-13-photosyntha tes in the berries was higher in SEC vines than in IBC vines, while it was the reverse in the leaves on the main shoot. The relationship between trans location and partitioning of photosynthates and the accumulation of sugar a nd anthocyanin in berries, which differed between vines of the two strains, is discussed.