Plant sink-source relationships and carbon isotopic labeling techniques . Taher Barzegar* and Fatemhe Nekounam

The concept of source and sink strength is presently well-recognized and accepted by the scientific community as a pertinent approach describing the mechanisms of carbohydrate partitioning into the different and competing organs at a whole plant or canopy scales. Sink–source relationships have a clear role in the size of sink organs. Besides the effect on organ size, sink/source ratio might also affect photosynthesis. Crop biomass productivity is closely related to source and sink capacities and the balance between them. Determination of the carbon balance of a whole plant and relation between source and sink were studied by carbon isotopic labeling techniques. Techniques using 14C or 13C have been used for many years to study the allocation of carbohydrates produced by photosynthesis between different parts of the plant. This method also allows calculation of the proportion of the total carbon accumulated in each sink that was supplied by all source leaves, as well as the growth contribution from each source leaf to the main plant sinks. These data are vital to determine the productivity of each source leaf.