The nitric oxide production and NADPH-diaphorase activity in root tips of Vicia faba L. under copper toxicity

Copper (Cu) toxicity on plants has become a major problem with increasing agricultural and environmental pollution. The effect of Cu on NADPH-diaphorase (NADPH-d) activity, commonly employed as a marker for nitric oxide synthase (NOS) activity and nitric oxide (NO) production, was investigated in root tips of Vicia faba L. We found that Cu stress stunted root growth and development of root hair. Cu treatment also caused an increase in NADPH-d activity and NO release in roots. Application of the NO donor sodium nitroprusside (SNP) efficiently alleviated the copper toxicity effects. The Cu-induced NO in vascular bundles was associated primarily with the presence of the induced NADPH-d activity. Our results suggested that NOS-like enzyme, but not the nitrate reductase, was the source of inducible NO generation in roots of V. faba under Cu stress. This is the first report on NADPH-d activity and its distribution in plants under Cu toxicity.