Effects of different strains of bacterium Pseudomonas fluorescens on morphological and biochemical factors and antioxidant enzymes activities of Dill (Anethum graveolens L.) under Pb stress

Recently, various methods have been used to alleviate the detrimental effects of pollutants. The application of biofertilizers with respect to their positive impacts on soil characteristics and environment can be served as a suitable alternative to many of these methods. In order to investigate the two-way effect of bacterium Pseudomonas fluorescens on plant growth, physiological and biochemical characteristics of dill (Anethum graveolens L.) under Pb stress conditions, a factorial experiment based on a completely randomized design with three replications was conducted at Mohaghegh Ardabili University. Experimental treatments included Pb stress at two levels (0 and 600 ppm) and bacterial inoculation at three levels (inoculation with Pseudomonas fluorescens strains150 and 159 separately and without inoculation (control)). The results of this study showed that the growth characteristics such as leaf number, plant height, and shoot fresh and dry weight were significantly affected by Pb contamination and shoot fresh and dry weight, leaf number and plant height decreased by 22, 31, 19 and 9%, respectively. The content of proline and carbohydrates in dill showed a significant increase under the influence of lead. Bacterial inoculation also increased the content of proline and plant carbohydrates, which was more pronounced in inoculation with strain150. The activity of antioxidant enzymes was significantly influenced by Pb contamination and bacterial inoculation. Pb increased peroxidase but decreased catalase activity, but inoculation with Pseudomonas bacteria, especially strain 150, significantly increased the activity of both enzymes. In addition, the bacteria were able to reduce the amount of Pb in dill. In general, the results of this experiment indicated that Pseudomonas bacterial inoculation was effective in alleviating the effects of Pb stress on dill via growth promotion and improving enzymatic activity.