Translocation of C-13-assimilates in the spring following fall assimilation of (CO2)-C-13 by 'Nijisseiki' pear (Pyrus pyrifolia Nakai)

Three-year- old 'Nijisseiki' pear (Pyrus pyrtfolia Nakai) trees were treate d twice with (CO2)-C-13 in October (fall). The distribution of labeled C-13 within the tree during dormancy and remobilization in the following season were determined. After leaf-fall, about 63% of the total C-13 recovered fr om the tree was distributed in the roots. At anthesis the (13) C content fr om the previous season's organs showed a significant decrease: the aerial o rgans decreased by about 53% and the roots by nearly 60%. About 35% of the total C-13 recovered from the trees after leaf-fall was consumed by respira tion until anthesis. New shoot, flower, and root growth accounted for 8.5%, 9.9%, and 3.9% of the total (13) C recovered from the tree after leaf-fall , respectively. One month after anthesis, the C-13 remaining in the previou s season's organs, had further decreased, having been exported to the new l eaves and current shoots. The C-13 remaining in the fruitlets dramatically decreased because of the abscission of sepals, petals, stamens, and partial pistils (style and stigma). New roots had the highest concentration of C-1 3 among all new organs. These data suggest that root systems play a special role in the storage of carbohydrates in young pear trees. All organs depen d on carbohydrate reserves for spring growth, especially new roots which se em to depend on reserves for a longer time.