The Effect of Vehicle Exhaust Pollution on Some Morphological and Physiological Characteristics of Lettuce and Spinach

Abstract

Air pollution caused by vehicles, are responsible for 75 percent of the pollution in the urban environment. Agricultural fields and the plants which are in the vicinity of urban polluted areas and around the highways, are increasingly exposed to these pollutants. According to the considerable amount of cultivated lettuce and spinach, especially in Iran, are in outdoors and on the side of the roads or contaminated urban areas, therefore, the effects of the vehicle exhaust pollutants on both physiological and morphological characteristics of lettuce and spinach were investigated. The experiment was conducted in factorial test based on a completely randomized design with three replications in greenhouse of Isfahan University of Technology. Lettuce and spinach seedlings were exposed seprately to the exhaust emissions in three different exposure times.(10, 20 and 30 days) and after the exposure time, their morphological and physiological traits were measured and compared with  morphological and physiological traits of control plants. Results obtained in lettuce, showed significant increases in traits including catalase, ascorbate peroxidase, guaiacol peroxidase, proline, electrolyte leakage, relative water content and number of stomata and significant decreases in chlorophyll a, chlorophyll b, total chlorophyll, photosynthesis rate, stomotal conductance, intercellular carbon dioxide, chlorophyll fluorescence, leaf area, height, aerial fresh weight, aerial  dry weight and length of stomata in lettuce plants which were exposed to exhaust emissions for 30 days, compared to controls. Also significant increases in antioxidant enzymes, proline, electrolyte leakage, and the number of stomata per unit and significant reduction of chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, photosynthesis rate, stomotal conductance, chlorophyll fluorescence, relative water content, height, fresh weight, dry weight and length of stomata were observed in spinach plants were exposed to exhaust emissions for 30 days, compared to controls. increase in photosynthetic pigments, the rate of photosynthesis and stomotal conductance, leaf area, height and fresh and dry weight of lettuce and spinach seedlings were exposed to exhaust emissions for 10 days, most likely, indicate the nutritional role of output gases from generator in the short period time of exposure (10 days). After coloring and cutting out the samples and observation of microscope slides, it was observed that the anatomical features of contaminated samples have been changed by pollution.