Absorption of atmospheric NO2by plants and soils

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Abstract
NO. uptake by leaves and reduction systems of nitrite produced were investigated using 3-week-old kidney bean, sunflower, and com plants, which were grown in vermiculite beds supplied with tap water. The plants were fumigated with 4 ppm NO2 for 6 hr in an artificially-lit chamber (30 klux), and the following things were observed. Fumigation in the light at daytime caused severe injury (wilting) in kidney bean leaves, and slight injury in sunflower leaves, but com leaves were tolerant to this treatment. A high concentration of nitrite rapidly accumulated in the kidney bean leaves, but the nitrite reductase activity was only increased to a small extent. In sunflower leaves a high concentration of nitrite was accumulated, and the nitrite reductase activity also increased rapidly. Fumigation in the dark at nighttime caused low concentration of nitrite to accumulate in kidney bean and sunflower leaves, and it was leveled down at the later fumigation time. The nitrite reductase activity of the two plants was increased with a slow rate continuously during the NO2 fumigation period. On the other hand, in the com leaves, nitrite was not detected in the daytime, but only a low concentration of nitrite was detected in the nighttime. A high activity of nitrite reductase was detected compared with the other two plants. Application of nitrate through the culture solution reduced nitrite accumulation in the light but not in the dark. These results indicate that acute NO. injury is mainly related to nitrite accumulation. Therefore, low NO2 absorption and high nitrite reductase activity (including its rapid induction) may reduce injury in leaves. When kidney bean and sunftower plants were fumigated with 4 ppm NO2 at different times of the day, a high concentration of nitrite accumulated only in the daytime, and not in the nighttime even if they were fumigated in the light. Absorption of 15NO3 at night by sunflower leaves was around 14% that at daytime. These indicate that a diurnal change of NO2 uptake is operating.