Ornamental cabbage (Brassica oleracea L.) belongs to the family Brassicaceae. Heavy metals, including lead (Pb), are considered among the most important soil pollutants due to their non-degradable nature and long half-life. In this context, bacteria, particularly plant growth–promoting bacteria (PGPB), represent an important strategy for alleviating such stresses. Therefore, the present study investigated the effects of the plant growth promoting bacteria Bacillus subtilis and Pseudomonas putida on mitigating lead stress and improving morphophysiological traits in ornamental cabbage cultivar ‘Kamum’. The experiment was conducted as a factorial arrangement in a completely randomized design (CRD). The first factor consisted of lead stress at three levels: 0 (control), 25, and 50 ppm. The second factor included three inoculation treatments: non-inoculated control, inoculation with Bacillus subtilis, and inoculation with Pseudomonas putida, applied at a concentration of 10⁸ CFU mL⁻¹. The experiment was carried out with four replications under greenhouse conditions at the Faculty of Agriculture, University of Zanjan. Morphophysiological traits including: leaf number, leaf surface, root length, fresh and dry root weight, chlorophyll a and b, carotenoid, ion leakage, malondialdehyde, total phenol and leaf lead were measured. The results indicated that lead stress and effectiveness of bacteria on all traits was significant. The effect of interaction between bacteria against lead stress was also significant positively in some features such as amount of phenol, number of leaves and their area, fresh and dry weight and length of roots. The lead treatment decreased root fresh and dry weight, root length, carotenoid and chlorophyll content and increased phenol. The application of P. putida in the absence of lead led to the improvement of growth indicators including the number and area of leaves, fresh and dry weight and length of root. P. putida increased chlorophyll, carotenoid and phosphorus and decreased ion leakage, malondialdehyde and lead under stress conditions compared to the control. Given that heavy metal stress causes significant disturbances in plants, it is essential to identify the characteristics affected by such stresses and the strategies to mitigate them. The research findings indicate that lead stress and bacteria have a significant impact on all examined traits. The interaction effect of bacteria against lead stress also influenced certain traits, such as phenol content, leaf number and area, fresh and dry root weight, and root length. Furthermore, the application of Pseudomonas bacteria under lead stress conditions resulted in increased chlorophyll, carotenoids, and phosphorus levels, while decreasing ion leakage, malondialdehyde, and lead concentrations compared to the control group. Overall, the results of this study highlight the importance of using beneficial bacteria like Pseudomonas to enhance plant growth under lead stress conditions. This approach can serve as an effective strategy in sustainable agriculture and phytoremediation processes. |
