Regulatory Role Of Endogenous Salicylic Acid In Arabidopsis Thaliana Response To Nitrogen Dioxide Stress

With the rapid development in industry, and increasing consumption of natural resources,environmental pollution is becoming more serious. Air pollution is not only harmful to human health, but causes damage to plants. Nitrogen oxides is one of the main air pollutants, wherein nitrogen dioxide is the strongest toxicity.Salicylic acid(SA) as an important endogenous signal molecule, not only regulates plant normal physiological processes, but involves in biotic and abiotic stress responses, such as activation of plants against pathogens of hypersensitive response and systemic acquired resistance, induced pathogenesis related protein expression and promote the synthesis of resistance related enzymes, and improve plant resistance to plant stress.In order to study nitrogen dioxide damage to Arabidopsis plants and the role of endogenous salicylic acid in this process, we used 5 kinds of Arabidopsis genotypes related to SA levels or signaling transduction: wild type(Columbia), and its mutant snc1(containing high level of endogenous salicylic acid), Nah G(transgenic plants with a deficience of endogenous salicylic acid), sid2(with a deficience in endogenous salicylic acid synthesis), and npr1-1(with a SA signaling blockage). Firstly, we selected appropriate tested NO2 concentration by fumigating six-week-old wild type Arabidopsis plants using a nitrogen dioxide concentration gradient of 0, 3, 6, 9, 18, and 36 ppm, and found that the dose of 6 ppm was a moderate concentration which had induced a slight seen damage to plants. Five kinds of tested Arabidopsis genotype plants were placed in self-made fumigation chamber, and 6 ppm NO2 was pumped. Plants were fumigated 3 hours per day for 7 days, then samples were collected and used to analyse physiological and chemical indices, the main results and conclusions are as follows:1. Nitrogen dioxide of 6 ppm had caused physiological damage. And the increasing of endogenous salicylic acid eased the NO2-induced damage to plants, such as a less decrease in the contents of chlorophyll a and chlorophyll b, the contents of soluble sugar, and a less increase in malondialdehyde production, ion permeability, and a more increase in the contents of soluble protein. Endogenous Salicylic acid deficiency and signal transduction blocked, the plant photosynthetic systems and membrane systems and osmotic balance and other physiological damage are more serious.2. Nitrogen dioxide stress caused changes in antioxidant capacity, such as increases in antioxidative enzyme activities including superoxide dismutase(SOD) and peroxidase(POD),and antioxidant contents including glutathione and ascorbic acid. The increasing of endogenous salicylic acid further increased the antioxidative capacity.Endogenous Salicylic acid deficiency and its signal transduction blocked will make plant antioxidant capacity weakened.3. Nitrogen stress made plants absorb a large number of nitrate and the induction of NR synthesis, improve the metabolism of nitrate nitrogen, thus reducing the harm caused by nitrogen dioxide stress. And the role of Endogenous Salicylic acid can better maintain cell homeostasis and to maintain redox homeostasis, such as MDA growth is slow, the decline in photosynthetic pigments is smaller, and enhance the activity of NR, increase the rate of nitrate assimilation, thereby more effectively resist threats of nitrogen dioxide injury forced.