Nitrate assimilation and partitioning in detached culms of wheat

Detached wheat culms (Triticum aestivum L. cv. Doublecrop) collected from field-grown plants 16 days after anthesis were cultured for 5 days with nutrient solution containing glutamine (7.5 mM), K¹⁵NO₃ (15 mM), or glutamine (7.5 mM) plus K¹⁵NO₃ (15 mM). Kernel growth rate of cultured culms equaled or exceeded that of intact field-grown plants (1.46 mg kernel^-1 day^-1). Net mobilization of reduced N from the peduncle occured, but this accounted for less than 23% of the net increase in grain N after 5th day of culture, regardless of N source. Glutamine had no effect on the assimilation of [¹⁵N]nitrate or the partitioning of reduced [¹⁵N]-labelled products. Peduncles contained less than 4-8% of total reduced[¹⁵N] excess recovered in all plant parts. Grain accumulation of reduced [¹⁵N] was linear,as was solution depletion, and accounted for an increasing proportion of the total reduced[¹⁵N] excess in all culm parts. These results provide direct evidence for nitrate assimilation by spike components.