Assimilation of exogenous cyanide cross talk in Oryza sativa L. to the key nodes in nitrogen metabolism.

Exogenous cyanide (CN-) effects on nitrogen (N) uptake, transport, and assimilation in rice seedlings were investigated at the biochemical and molecular levels. Seedlings were treated with either a 2-d or 4-d supply of potassium cyanide (KCN) in the nutrient solution containing nitrate (NO3-) or ammonium (NH4+). Although a KCN-induced increase was recorded in the activity of β-cyanoalanine synthase (β-CAS) in rice tissues of both NH4+-fed and NO3--fed seedlings, the former showed a significantly greater assimilation rate for CN- than the latter. The addition of KCN decreased NO3- uptake and assimilation, whereas a negligible impact was observed in NH4+ treatments. Enzymatic assays showed a marked activities enhancement of glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) in NH4+-fed seedlings after KCN exposure. Similarly, the rises occurring in nitrate reductase (NR) and GDH activity in NO3--fed seedlings were also detected after 2-d exposure to KCN, whereas a significant reduction of GS and GOGAT activities was determined. The results suggest that although exogenous KCN at moderate or high concentrations caused repressively effects on biomass growth of both NH4+-fed and NO3--fed rice seedlings, the nontoxic concentration of KCN supplied can serve as a supplemental N source in plant nutrition and N metabolism.