15n Moved to the Grain of Winter Wheat When Applied as Nitrate to Senescing Flag Leaves.

Abstract

Flag leaves of wheat in the field took up a solution containing 30 mM K15NO3 through their cut tips. Treatment was applied 37 days after anthesis and uptake was allowed to continue for intervals up to 76 h by which time about 0.6 mg of 15N nitrate nitrogen was taken up. At the time of treatment, the flag leaves from plants grown under two levels of nitrogen nutrition had lost half of their nitrogen content and were exporting it at about 0.2 mg per day. Despite this state of senescence the flag leaves were able to reduce the nitrate and 30-40% of that taken up was translocated to the grain within 3 days. No nitrate accumulated in the leaves or grain. Emission spectrometry was sufficiently sensitive to detect 15N which increased from 0.02 to 1.18% of grain nitrogen during the 76 h of accumulation.