Interaction of cyanide uptake by sorghum and wheat with nitrogen supply

Cyanide occurs naturally in soils, arising from biological cyanogenesis and also in some cases from anthropogenic contamination. Plant utilization of cyanide at non-toxic concentrations as a supplemental source of nitrogen has been a topic of recent scientific interest and it was investigated here using sorghum (Sorghum bicolor L.) and wheat (Triticum aestivum L.). The accumulation of cyanogenic nitrogen in plant tissues was assessed under nitrogen regimes with specific combinations of cyanide, ammonium, and nitrate or each nitrogen source alone. Cyanogenic nitrogen accumulated in plant tissues when in combination with nitrate and accumulation of cyanogenic nitrogen decreased when ammonium was present. A greater increase of nitrogen in tissue from cyanide was observed in both species when cyanide was substituted for ammonium, but accumulation of cyanogenic nitrogen decreased when ammonium was present. A reciprocal nitrogen labeling experiment showed that nitrogen from nitrate and ammonium was accumulated preferentially over cyanogenic nitrogen. Differences in biomass and relative growth rate were observed in response to the treatments where plants were grown with nitrate, ammonium, or cyanide as the sole nitrogen source, but not when cyanide was present along with ammonium and nitrate. Physiological nitrogen use efficiency did not differ significantly within a species for any treatment imposed. The results suggest that cyanide as a nitrogen source can potentially support plant growth and development for up to eight weeks, but more effectively in combination with ammonium and nitrate.