Fig. 2.

(A) Effect of external nitrate supply on H₂O₂ in maize seedlings, and (B) responses of root elongation of maize seedlings incubated in 0·01 mm and 10 mm nitrate solutions to exposure to exogenous H₂O₂ for 48 h. In (A), seedlings were cultivated for 7 d in nutrient solutions varying in nitrate concentration as indicated, and the H₂O₂ content in the root apices is expressed as relative to that observed in the 0·01 mm nitrate treatment. Data are means ± s.e. of three independent measurements. In (B), relative root elongation was determined in the presence of varying concentrations of H₂O₂ for seedlings grown in 0·01 or 10 mm nitrate solution, and the data are normalized to the value at 0·01 mm nitrate solution without H₂O₂. Data are mean ± s.e. of at least eight roots for each treatment. Different letters indicate significantly different values (P = 0·05).