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Growth of rhizobial strains and their plant growth promoting activity under heavy metal stress
Pešić, Mila
Delić, Dušica
Stajković-Srbinović, Olivera
Abstract: Heavy metals increase in the soils has become a worldwide issue. The growth and nutrient balance of different legumes including alfalfa could be disrupted in soils with increased nickel concentrations. Inoculation of legumes with rhizobia, nitrogen-fixing bacteria, can decrease concentrations of heavy metals in plants and could be used for phytostabilization of heavy-metal contaminated soils. The mechanisms of rhizobia for plant growth promotion partly overlap with protection mechanisms used by metal-tolerant rhizobacteria. Besides nitrogen fixation, some of them are the producers of plant hormones, which promote plant growth; such is indole-3 acetic acid. Therefore, the purpose of this study was to select nickel tolerant rhizobial strains and evaluate their indole-3 acetic acid production under nickel stress. Screening alfalfa rhizobial strains for nickel tolerance showed that all of the tested strains could grow well in the medium supplemented with 0.1 mM Ni, and some of the tested strains could tolerate up to 1.1 mM Ni, that is the highest Ni concentration tested in this study. Generally, the addition of Ni in the range from 0.05 to 0.4 mM affected the production of IAA in the medium supplemented with tryptophan, as a precursor for IAA, but the IAA levels still remained very high. The IAA was not detected at 0.7 mM Ni. The alfalfa rhizobial isolates are overall relatively sensitive to Ni concentrations. Some strains with high nitrogen fixation capacity and IAA production were sensitive to Ni, indicating the importance of metal tolerance evaluation. The selected IAA producing Ni tolerant rhizobial strains are potential candidates for further investigation in nickel biosorption assays and heavy metal stress alleviation in plants.
engleski
2024
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alfalfa rhizobia; heavy metals; plant growth promotion