Nitrate assimilation and partitioning in detached culms of wheat

Abstract

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), K 15NO 3 (15 mM), or glutamine (7.5 mM) plus K 15NO 3 (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.