Cadmium Stress Stimulates Nitric Oxide Production by Wheat Roots

Study was conducted to elucidate the nitrite-dependent nitric oxide (NO) production by wheat roots grown in hydroponics under cadmium (Cd) stress. In a long-term Cd exposure experiment, plants were grown for 4 weeks under 1 μM Cd. The root Cd concentration in the Cd-stressed plants was 2.5 mM compared to 0.1 mM in the untreated plants. Most of the Cd taken up by plants was restricted to roots where its concentration was 9 times higher than that in shoots. Despite the high Cd concentration in roots and shoots, the plant growth was not affected. However, Cd stress caused a 1.7-fold decrease in the root respiration, whereas it produced a 2.4-fold increase in NO emission (detected by gas phase chemiluminescence). In a short-term Cd exposure experiment, freshly harvested Cd-free roots were exposed to 10 μM Cd for 3 h. Here also, the root respiration decreased by 42% and NO production increased by 73%, thus confirming the stimulatory effect of Cd stress on NO production by wheat roots.