Fig. 1.

The SNP, NONOate and cPTIO-dose responses of nitrate reductase activity in roots of tomato. The seedlings were fed in 0·5 mm (A, C, E) and 5 mm nitrate (B, D, F) for 2 weeks and were then transferred to the nutrient solution containing different concentrations of nitric oxide donor SNP (A, B) or DEA/NONOate (C, D) or cPTIO (E, F). Nitrate reductase activity was measured 3 h after treatment. Error bars show s.d. (n = 5), asterisks denote a significant difference from the control at P < 0·05.