Modulation of growth, antioxidant system in seedling of mustard under different levels of Nickel in adaptive response to metal resistant bacteria

Abstract

Plant growth is hindered by high concentration of metals in soil by disturbing various physiological processes. However, some bacteria with plant growth promoting features have been recognized to alleviate stress in plants even under elevated levels of metal concentration. The two bacterium NWM 71 and NWM 103, identified as Pseudomonas sp. and Bacillus sp. respectively were found to be resistant to the toxic effects of nickel (Ni2+) and were identified with plant growth promoting features. Both the strains showed the production of indole acetic acid (IAA) and solubilisation of phosphate. Brassica juncea (mustard) was used as a test plant to identify the plant growth promoting activity of the selected strains of bacteria. The growth was positively influenced by the inoculation of both the strains. The tests for the measurement of chlorophyll contents and antioxidative activity were carried out to determine the level of stress in plants. High levels of Ni decreased the growth and chlorophyll content, however, significant increase in the antioxidant activity was recorded along the treatment. Inoculation of both the selected strains of bacteria increased the shoot and root biomass of mustard grown in both unspiked and spiked soil. This positive influence on growth can be attributed to the solubilisation of phosphate and production of IAA. Furthermore the observed high levels of antioxidant enzymes led to decrease in the toxic effects of Ni. This led to enhanced growth and chlorophyll content which in turn might have enhanced the photosynthetic capacity of the plants.