To investigate the effect of plant growth-promoting bacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) on phytoremediation in saline-alkali soil contaminated by petroleum, saline-alkali soil samples were artificially mixed with different amount of oil, 5 and 10 g/kg, respectively. Pot experiments with oat plants (Avena sativa) were conducted under greenhouse condition for 60 days. Plant biomass, physiological parameters in leaves, soil enzymes, and degradation rate of total petroleum hydrocarbon were measured. The result demonstrated that petroleum inhibited the growth of the plant; however, inoculation with PGPR in combination with AMF resulted in an increase in dry weight and stem height compared with noninoculated controls. Petroleum stress increased the accumulation of malondialdehyde (MDA) and free proline and the activities of the antioxidant enzyme such as superoxide dismutase, catalase, and peroxidase. Application of PGPR and AMF augmented the activities of three enzymes compared to their respective uninoculated controls, but decreased the MDA and free proline contents, indicating that PGPR and AMF could make the plants more tolerant to harmful hydrocarbon contaminants. It also improved the soil quality by increasing the activities of soil enzyme such as urease, sucrase, and dehydrogenase. In addition, the degradation rate of total petroleum hydrocarbon during treatment with PGPR and AMF in moderately contaminated soil reached a maximum of 49.73%. Therefore, we concluded the plants treated with a combination of PGPR and AMF had a high potential to contribute to remediation of saline-alkali soil contaminated with petroleum.
Petroleum is potentially toxic to living organisms, and there are worldwide efforts to develop methods for bioremediation of petroleum-contaminated soils. Phytoremediation is an effective method to reduce the concentration of petroleum in soils, and plant growthpromoting rhizobacteria (PGPR) play an important role in the phytoremediation. Two PGPR, Pseudomonas aeruginosa SLC-2 and Serratia marcescens BC-3, were isolated from the rhizophere of Echinochloa grown in petroleumcontaminated soil. These isolates showed capacities for 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, indole acetic acid production, siderophore synthesis, and the degradation of petroleum. The ACC deaminase activity of SLC-2 and BC-3 was 2.52 ± 0.03 lmol a-KA (mg PrÁh) -1 and 38.52 ± 0.37 lmol a-KA (mg PrÁh) -1 , respectively. On the other hand, when the concentration of L-Trp increased, the IAA synthesis of BC-3 also increased, while the synthesis of SLC-2 did not change significantly. The ability of synthesized siderophore of SLC-2 was much higher than that of BC-3. The petroleum degradations of SLC-2 and BC-3 increased 4.78 and 7.36 %, respectively. The pot experiment of oat was performed to evaluate the plant growth-promoting abilities of SLC-2 and BC-3. Compared with non-inoculated controls, the height and fresh weight of stems increased (23.64 and 42.57) % and (16.98 and 28.3) %, respectively, whereas the length and fresh weight of roots also increased (10.34 and 20.84) and (24.13 and 43.11) %, respectively, when inoculated with SLC-2 and BC-3. The results indicated that P. aeruginosa SLC-2 and S. marcescens BC-3 can serve as promising microbes for increasing plant growth in petroleum-contaminated soil to improve the phytoremediation efficiency.
Nitrobenzene is an important organic intermediate widely used in industry that can be hazardous to the environment. In our previous study, nitrobenzene showed genotoxic effect on soybean and tobacco plants at concentrations in the culture medium higher than 10 mg/L. The genotoxicity of nitrobenzene has been hypothesized to be multifactorial and reflective of the generation of free radicals; however, the mechanism has not been fully elucidated. The aim of this study was to investigate the relationship between the induction of genotoxicity and the production of free radicals in young seedlings of V. faba exposed to nitrobenzene, nitrobenzene + Vitamin C, and the controls (distilled water or Vitamin C). Micronucleus and chromosome aberration assays performed on root and leaf tissue of V. faba seedlings exposed to nitrobenzene (25 mg/L) demonstrated genotoxic effects which were partly reduced by Vitamin C at 25 mg/L. Increases in lipid peroxidase, O2•-, H2O2, superoxide dismutase and catalase activities were also observed in these tissues along with an attenuation of their induction by Vitamin C. Concomitant occurrence of genotoxicity and the generation of free radicals that are attenuated in the presence of Vitamin C, a scavenger of cellular free radicals, indicate that reactive oxygen species may contributes to genotoxicity of nitrobenzene in V. faba. These results are valuable for further understanding the genotoxicity mechanism of nitrobenzene.
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