Partitioning and conversion of C-14-photoassimilates in developing grains of wheat plants grown under field conditions in Cuba

Understanding the patterns of source-sink relationships in wheat under fiel d conditions is crucial to determine the physiological factors limiting gra in filling. The aim of this investigation was to assess the time-course of source-sink interactions in wheat after anthesis under Cuban field conditio ns. For this purpose, plants of wheat, cultivar Cuba C-204, were sown in th e field at six dates with contrasting temperature conditions. The duration of grain filling, patterns of partitioning of C-14-photoassimilates between organs and incorporation of the label into starch in the kernels 24 h afte r feeding the flag leaf blade with (CO2)-C-14, were investigated to evaluat e source-sink balance. The proportion of C-14 converted into starch in the kernels increased during the first 10 days of grain filling. Throughout the grain filling phase the proportion of total C-14 fixed partitioned to the grains increased, whereas that allocated to the internodes decreased. At th e beginning of grain filling, the patterns of C-14-photoassimilate partitio ning differed among sowing dates. Additionally, the proportion of C-14 inco rporated into starch in the kernels correlated positively with the proporti on of the label partitioned to the grains, but negatively with C-14 accumul ation in the internodes. This supports that the accumulation of C-14 in the stem was closely related to the uptake capacity of the grains. The lack of such a relationship at later stages in grain development indicates a chang e from sink-limited to source-limited situation early after anthesis. In co nclusion, the supply of photoassimilates under field conditions in Cuba lim its grain filling, except the first days after anthesis, when it was sink-l imited. (C) 2001 Elsevier Science B.V. All rights reserved.