Nitrite decreases ethanol production by intact soybean roots submitted to oxygen deficiency: a role for mitochondrial nitric oxide synthesis?

Nitrate increases the tolerance of plants to hypoxia, although the mechanisms related to this beneficial effect are still unclear. Recently, we observed that cultivation of soybean plants with nitrate reduced hypoxic accumulation of fermentation end products by isolated root segments compared with the ammonium treatment. Interestingly, the same decrease in the intensity of fermentation was detected when ammonium-grown root segments were incubated with nitrite, suggesting the involvement of this anion in the nitrate-mediated modulation of fermentative metabolism. Here we extended these experiments to intact plants subjected to root hypoxia and observed similar effects of nitrate and nitrite in reducing root ethanol production, which indicates the physiological relevance of the in vitro results. In both experimental systems, nitrite stimulated nitric oxide emission by ammonium-grown roots to levels similar to that of nitrate-cultivated ones. The involvement of mitochondrial reduction of nitrite to nitric oxide in the root response to hypoxia is suggested.