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

Abstract

Understanding the patterns of source–sink relationships in wheat under field conditions is crucial to determine the physiological factors limiting grain filling. The aim of this investigation was to assess the time-course of source–sink interactions in wheat after anthesis under Cuban field conditions. For this purpose, plants of wheat, cultivar Cuba C-204, were sown in the field at six dates with contrasting temperature conditions. The duration of grain filling, patterns of partitioning of 14C-photoassimilates between organs and incorporation of the label into starch in the kernels 24 h after feeding the flag leaf blade with 14CO 2, were investigated to evaluate source–sink balance. The proportion of 14C converted into starch in the kernels increased during the first 10 days of grain filling. Throughout the grain filling phase the proportion of total 14C fixed partitioned to the grains increased, whereas that allocated to the internodes decreased. At the beginning of grain filling, the patterns of 14C-photoassimilate partitioning differed among sowing dates. Additionally, the proportion of 14C incorporated into starch in the kernels correlated positively with the proportion of the label partitioned to the grains, but negatively with 14C accumulation in the internodes. This supports that the accumulation of 14C 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 change from sink-limited to source-limited situation early after anthesis. In conclusion, the supply of photoassimilates under field conditions in Cuba limits grain filling, except the first days after anthesis, when it was sink-limited.