Abstract
Leaves represent the largest pool of nitrogen in vegetative grasses. As leaves expand, large quantities of nitrogen flux into them; with more than 60% of this deriving from internal remobilization. As leaves age, influx decreases and efflux becomes the major factor determining leaf N content. N flux within the plant should therefore be non-uniform through time. Leaves connect together at a small organ through which all leaf N must pass, known as the tiller axis. To test our hypothesis of non-uniform N concentrations in the tiller axis, we measured the N concentration in ryegrass, barley and wheat, finding strong evidence of a steady oscillation, which correlates with leaf growth and developmental patterns, and is hypothesized to be a potential control mechanism. This oscillation appears to be genotype specific, predominantly driven by protein turnover, and sensitive to environmental conditions, such as exogenous N supply and temperature.
