Some Responses of Inoculated Persian Clover with Rhizobium to SO 2 Pollution

Abstract

Sulfur dioxide (SO 2 ) is one of the most common and harmful air polluta nts. High concentrations of SO 2 can cause stress and limit growth in plants. Some of the plants can resist stress by bacterial symbiosis such as Rhizobium symbiosis. Rhizobium is a beneficial bacterium that enhances plant growth and yield. To study the effects of SO 2 pollution on growth indexes, protein, proline and sulfur content s, 31 days old plants of Trifolium resupinatum (Persian clover), inoculated with native and standa rd Rhizobium were exposed to the different concentrations of SO 2 (0 as control, 0.5, 1, 1.5 and 2 ppm) for 5 consecutive days. Results showed that inoculation i ncreased leaf area, leaf number, shoot height, root length, shoot fresh and dry weight and protein content of Persian clover but didn’t show any significant effect on proline and s ulfur contents. Different concentrations of SO 2 had a significant effect on leaf number, shoot hei ght, root length, shoot fresh and dry weight, protein, proline and sulfur contents bu t didn’t have effects on leaf area. 0.5 ppm concentration of SO 2 increased growth indexes and protein content. Prol ine and sulfur contents didn’t change in 0.5 ppm. Increasin g SO 2 decreased growth indexes and protein, and increased proline and sulfur contents. Interaction between Rhizobium inoculation and SO 2 treatment improved the stress effects of high conc entrations of SO 2 on growth indexes, protein, proline and sulfur cont ents. It was therefore concluded that Rhizobium can increase tolerance and resistance of this plan t to the abiotic stresses such as SO 2 pollution . Keywords : Air pollution, Persian clover, Protein, Rhizobium , Sulfur