The present study was aimed to investigate the physiological responses of the leaves of Ulmus minor to air pollutants such as ozone, carbon monoxide, and nitrogen dioxide in order to achieve a plant species that has the ability to resistant to air pollutants. The leaves of Ulmus minor Mill. were collected from one location in Mazandaran province (with lower air pollutions) and three locations in Tehran province (with higher air pollutions). The leaves were randomly collected from the middle part of the crowns in each sampling location with four replicates and the growth and physiological parameters were measured. The climate factors of the sampling locations were also evaluated. The results showed that the content of dry matter, protein, chlorophyll a, anthocyanin and activity of peroxidase enzyme in the leaves of plants grown in location 4 with higher amount of air pollutants was almost 35, 50, 30, 50, and 40 percent higher than those of the leaves of plants grown in sampling locations 1 with the lower amount of air pollutants, respectively. The number and intensity of peroxidase isoenzyme bands were significantly enhanced in the leaves of plants collected from the locations in Tehran province. However, the prominent role of rainfall on the physiological responses of Ulmus minor cannot be ignored. It seems that Ulmus minor is a resistant tree to air pollutants and as an application, it might be considered as a biological filter in removing gaseous pollutants in areas like Tehran city to improve air quality.
