Seed development in cereals is a highly controlled process and depends on nutrient supply from vegetative tissues. The development of barley glumes is tightly coordinated with the developmental status of the grain, and can be separated into three phases that characterise glumes´ transition from sink to source tissues. During the pre-storage phase, glumes act as temporary resource buffers that accumulate N compounds. When grain sink-strength increases due to storage product accumulation, remobilisation processes are triggered, and N compounds are relocated to the grains, before glumes undergo senescence. Efficient nutrient exchange depends on active transport processes, and expression patterns of N transporters allows identifying candidates with specific functions either in sink or source tissues. The increase of sink-strength in developing grains can positively influence yield and protein content in wheat, and thus represents a promising approach for further crop improvement.