Fig. 2.

Time course of the effect of SNP and cPTIO on nitrate reductase activity in roots of tomato. The seedlings were fed with 0·5 mm (A, C) and 5 mm nitrate (B, D) for 2 weeks, and were then transferred to the nutrient solution without or with 5 µM SNP or 10 µM cPTIO under continuous light conditions. Nitrate reductase activity was measured at 0, 3, 6, 12 and 24 h. Error bars show the s.d. (n = 5), asterisks denote a significant difference from the control at P < 0·05.