Nitric oxide (NO) emission by higher plants

In experiments conducted on trace gas emission from plants in a continuously stirred tank reactor we found that several nitrate nourished plant species (sunflower, soybean, corn, spinach, tobacco, sugar cane) emitted NO during the photoperiod of up to 1.1 10-14 mol cm-2 s−1 (one sided leaf area). Emission rates were independent of nitrate concentrations between 0.07–3.5 mM nitrate in the nutrient solution but decreased when plants were transfered to N-free or ammonium nutrient solution. NO emission was dependent on light flux, increasing with higher light intensities. During the photoperiod similar ratios for the rate of NO emission and the CO2 uptake were obtained for all plants studied. During darkness all plant species studied except sugar cane evolved small to negligible amounts of NO. Sugar cane evolved NO in high quantities every night. NO emission during darkness could be induced in all plants by adding nitrate to the nutrient solution. In the dark period following application emission rates of up to 3.9 10-13 mol cm-2 s−1 were measured. Our results imply that NO emission is a physiological characteristic common to all plants and that plants may contribute significantly to the NO-budget of the continental background atmosphere.