Evidence of iron cyanides as supplementary nitrogen source to rice seedlings.

The effect of iron cyanides on activities of nitrate reductase (NR) and glutamine synthetase (GS) of plants was investigated. Young rice seedlings (Oryza sativa L. cv. XZX 45) were grown in the nutrient solutions containing KNO(3) or NH(4)Cl and treated with ferro-cyanide [K(4)Fe(CN)(6)] or ferri-cyanide [K(3)Fe(CN)(6)]. Total cyanide and free cyanide in solutions and in plant materials were analyzed. Activities of NR and GS in different parts of plants were assayed in vivo. Results indicated that all rice seedlings exposed to either ferro- or ferri-cyanide showed positive growth. The phyto-assimilation rates of both iron cyanide species by rice seedlings were positively correlated to the doses supplied. Seedlings grown on NO(3)(-) showed significantly higher assimilatory potential for both ferro- and ferri-cyanide than those on NH(4)(+). Rice seedlings grown on NH(4)(+)-containing nutrient solution accumulated more cyanide in plant materials, majority being in roots rather than shoots, than these grown on NO(3)(-)-containing nutrient solution, suggesting that the presence of ammonium (NH(4)(+)) in the nutrient solution caused a negative impact on botanical assimilation of both iron cyanides. Sensitivity of NR and GS in rice seedlings exposed to ferro- and ferri-cyanide was identical, where conspicuous effects were only observed at the highest concentration supplied. The evidence offered here suggests that both iron cyanides can be a supplementary source of nitrogen to plant nutrition.