Differential expression of nitrate reductase in response to potassium and sodium nitrate: realtime PCR analysis

Cucurbita pepo L. plants were grown in plastic pots with 2 kg washed sand per pot at three levels of potassium and sodium nitrate supplies to investigate the effects of nitrate supply on nitrate reductase activity and nitrate reductase expression in the leaves of the plants. Results demonstrated that starvation leads to decrease nitrate reductase activity and nitrate reductase expression. Supplementation of sodium and potassium nitrate had stimulatory effects on nitrate reductase activity and nitrate reductase expression in a dose dependent manner. However, potassium nitrate supplementation increased nitrate reductase activity and nitrate reductase expression more than sodium nitrate supplementation. In conclusion, both sodium and potassium nitrate, as inducers, had significant effects on both nitrate reductase activity and nitrate reductase expression in low concentrations. At high nitrate supplies, nitrate reductase activity and nitrate reductase expressions were suppressed probably due to nitrogen metabolite feedback inhibition and toxicity.