Plants in nature show species-specific nitrogen dioxide (NO 2 ) uptake and a wide variation in NO 2 assimilation. This specific NO 2 uptake or assimilation is affected not only by the structural, physiological and genetic make up of leaves, but also by various environmental factors. This review focuses on the processes of leaf NO 2 uptake. We describe the influence of stomatal traits on foliar NO 2 uptake, discuss the interactions between NO 2 uptake and apoplastic antioxidant (ascorbate and glutathione), and present the roles of cuticles in NO 2 deposition and emission. Further progress is proposed to gain a better understanding of the dynamic uptake of NO 2 and NO 3 -transporters in leaves.

Nitrogen dioxide (NO2) is produced in certain industrial processes. Point exposure to high concentration of NO2 (>100 ppm), such as in silo filler's disease and during chemical warfare, produces acute lung injury, and death in the worst cases. Acute exposure to lower concentration of NO2 (0.5-15 ppm) may increase airway responsiveness, especially in patients with obstructive airway diseases. The effects of chronic exposure to ambient NO2 (<0.5 ppm) are much harder to quantify, in part due to the low concentration and the existence of other co-pollutants. Because NO2 is a reactive gas, it remains possible that exposure to ambient concentration of NO2 for a prolonged period of time may result in cellular and biochemical changes that ultimately cause pulmonary dysfunction.