Heavy metal pollution of soil is a significant environmental problem and has a negative impact on human health and agriculture. Phytoremediation can be an alternative environmental treatment technology, using the natural ability of plants to take up and accumulate pollutants or transform them. Proper development of plants in contaminated areas (e.g. heavy metals) requires them to generate the appropriate protective mechanisms against the toxic effects of these pollutants. This paper presents an overview of the physiological mechanisms of stress avoidance and tolerance by plants used in phytoremediation of heavy metals.
Biological control of plant diseases is strongly emerging as an effective alternative to the use of chemical pesticides and fungicides. Stress tolerance is an important attribute in the selection of bacteria for the development of microbial inoculants. Fourteen salt-tolerant bacteria showing different morphological features isolated from the rhizosphere of maize were evaluated for different plant growth-promoting activities. All isolates showed auxin production ranging from 5 to 24 μg ⋅ ml–1 after 48 h incubation in tryptophan supplemented media. Phosphate solubilization ranged from 15 to 419 μg ⋅ ml–1. 1-aminocycloproprane- 1-carboxylate (ACC) deaminase activity was shown by 6 isolates, ammonia production by 9 isolates, siderophore production by 8 isolates while HCN production by 4 isolates. Four bacterial isolates with all plant growth-promoting properties also showed strong antagonistic activities against Fusarium oxysporum, F. verticillioides, Curvularia lunata and Alternaria alternata and abiotic stress tolerance against salinity, temperature, pH and calcium salts. Two selected bacterial isolates significantly enhanced the growth of pea and maize test plants under greenhouse conditions. The bacterial isolate M1B2, which showed the highest growth promotion of test plants, was identified as Bacillus sp. based on phenotypic and 16S rDNA gene sequencing. The results indicated that Bacillus sp. M1B2 is a potential candidate for the development of microbial inoculants in stressful environments.