Assessment of ammonium fertilization as a stimulus for proline accumulation in Oryza sativa L. during cyanide assimilation

The interactions between ammonium fertilization, cyanide (KCN) assimilation and proline accumulation in rice seedlings (Oryza sativa L. cv. XZX 45) were investigated during the current investigation. Results indicated that rice seedlings possess effective assimilation potential for exogenous CN− after 2-d exposure, where increases in the assimilation rates of CN− were negatively correlated with ammonium fertilization. During ammonium starvation, negligible change in proline content was detected in both rice tissue samples subjected to CN− exposure, suggesting that the degradation products of CN− by rice seedlings might not serve as nitrogen donors for proline synthesis. In the absence of exogenous CN−, proline accumulation in shoots was evident with enhancing ammonium fertilization, whereas marginal changes of proline content were observed in roots. Results also indicated that the addition of exogenous CN− significantly decreased proline content in shoots of rice seedlings fed with ammonium at the concentrations of 19.75–59.25 mg N/L. In conclusion, both the supplied ammonium and CN− were quickly assimilated into other nitrogen-containing compounds in rice seedlings through a nitrogen nutrient pathway; the contribution of nitrogen from ammonium assimilation into proline synthesis was evident in shoots after 2-d exposure, but it was repressed by exogenous CN−.