Morphophysiological responses of sweet basil (Ocimum basilicum L.) to the nickel stress and inoculation with Pseudomonas strains

Nickel is a heavy metal that has adverse effects on plants. The present study aimed to evaluate the morpho-physiological responses of sweet basil (Ocimum basilicum L.) to Pseudomonas strains (Pseudomonas fluorescens strain 150 and 159, and Pseudomonas putida strain 10) inoculation under Ni-contaminated soil (0, 75, 100, 150 mg Ni per kg of soil). Growth parameters as well as photosynthetic pigments were reduced during nickel exposure, whereas Pseudomonas treatment increased them. Additionally, the highest proline content was associated with the inoculation of P. fluorescens 159 and P. putida 10 under 100 and 150 mg.kg(-1) Ni, respectively (0.86 and 0.96 mol g(-1) FW). Also, screening of the Ni contents of shoots and roots showed that all strains of Pseudomonas reduced the accumulation of Ni. However, both strains of P. fluorescens (150 and 159) increased the Ni contents in the root compared to the non-inoculated plants. P. putida 10 (P1) was the only Pseudomonas species which was able to reduce the nickel concentration in both root and shoot compared to P0. P. fluorescens 159 (P2) was recorded as the most effective treatment to reduce nickel accumulation in the shoot. Additionally, Pseudomonas inoculation became more effective than Ni stress at improving antioxidant enzyme activity (CAT and POD) in sweet basil plants. Finally, the current study suggests that the Pseudomonas inoculation can reduce the negative impact of nickel stress for sweet basil plants.