Nitrogen supply and cyanide concentration influence the enrichment of nitrogen from cyanide in wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L.)

Abstract

Cyanide assimilation by the β-cyanoalanine pathway produces asparagine, aspartate and ammonium, allowing cyanide to serve as alternate or supplemental source of nitrogen. Experiments with wheat and sorghum examined the enrichment of 15N from cyanide as a function of external cyanide concentration in the presence or absence of nitrate and/or ammonium. Cyanogenic nitrogen became enriched in plant tissues following exposure to 15N-cyanide concentrations from 5 to 200 μ m, but when exposure occurred in the absence of nitrate and ammonium, 15N enrichment increased significantly in sorghum shoots at solution cyanide concentrations of ≥50 μ m and in wheat roots at 200 μ m cyanide. In an experiment with sorghum using 13C15N, there was also a significant difference in the tissue 13C:15N ratio, suggestive of differential metabolism and transport of carbon and nitrogen under nitrogen-free conditions. A reciprocal 15N labelling study using KC15N and 15NH4+ and wheat demonstrated an interaction between cyanide and ammonium in roots in which increasing solution ammonium concentrations decreased the enrichment from 100 μ m cyanide. In contrast, with increasing solution cyanide concentrations there was an increase in the enrichment from ammonium. The results suggest increased transport and assimilation of cyanide in response to decreased nitrogen supply and perhaps to ammonium supply. © 2010 Blackwell Publishing Ltd.