Figure 1.

NO production in S. nigrum roots exposed to Zn²⁺ or to Zn²⁺ and Fe²⁺. Two-week-old S. nigrum seedlings grown in Hoagland solution were treated with 200 or 400 μm ZnCl₂ in the presence or absence of 200 μm Fe-EDTA. NO content was determined by the methemoglobin method as described in “Materials and Methods.” Symbols are as follows: black diamonds, control; purple squares, 200 μm ZnCl₂; red triangles, 400 μm ZnCl₂; green squares, 400 μm ZnCl₂ plus 200 μm Fe-EDTA. Asterisks indicate values significantly different from those of the roots treated with 400 μm ZnCl₂ alone: * Student’s t test with P < 0.05. FW, Fresh weight.