Alleviation of Mercury Toxicity in Wheat by the Interaction of Mercury-Tolerant Plant Growth-Promoting Rhizobacteria

Abstract

Heavy metal contamination of agricultural soils has increased along with industrialization. Mercury is a toxic heavy metal and a widespread pollutant in the ecosystem. Mercury-tolerant and plant growth-promoting rhizobacteria (PGPR) HG 1, HG 2, and HG 3 were isolated from the rhizosphere of plants growing in a mercury-contaminated site. These isolates were able to grow in the presence of mercury ranging from 10 to 200 lM in minimal medium and 25 to 500 lM in LB medium. The strains were characterized by morphological, biochemical, and plant growth-promoting traits. In the present study, these PGPR strains were analyzed for their involvement in metal stress tolerance in Triticum aestivum (wheat). Two bacterial strains, namely, Enterobacter ludwigii (HG 2) and Klebsiella pneumoniae (HG 3), showed better growth promotion of T. aestivum seedlings under metal stress. Different growth parameters like, water content and biochemical properties were analyzed in the PGPR-inoculated wheat plants under 75 lM HgCl 2 . Shoot length, root length, shoot dry weight, root dry weight and relative water content (RWC) were significantly higher in inoculated plants compared to uninoculated plants under stress condition. Proline content, electrolyte leakage, and malondialdehyde content (shoots and roots) were significantly lower in inoculated plants with respect to uninoculated plants under mercury stress. Therefore, it could be assumed that all these parameters collectively improve plant growth under mercury stress conditions in the presence of PGPR. Hence, these PGPRs can serve as promising candidates for increasing plant growth and also have immense potential for bioremediation of mercury-contaminated soils.

Plant Growth Enhancement using Rhizospheric Halotolerant Phosphate Solubilizing Bacterium Bacillus licheniformis QA1 and Enterobacter asburiae QF11 Isolated from Chenopodium quinoa Willd

“…However, QA1 showed a higher performance in producing siderophores compared to QF11 ( Figure 3 ). Siderophores are known to enhance P availability [ 9 ], as they solubilize minerals and chelate heavy metals, which in turn increases nutrient uptake and plant growth [ 66 ]. Whipps in 2001 reported that the low iron availability in soil would suppress plant pathogenic fungi [ 67 ].…”

“…Comparatively, our results support the role of IAA in inducing morphological changes, increased length of the root as well as number of root hairs/laterals, which are crucial for nutrient uptake [ 88 ]. In addition, Bacillus , Pseudomonas and Enterobacter applied as bioinoculants promote plant growth and biomass through production of phytohormones (e.g., auxins and cytokinins) [ 66 , 89 ]. In this aspect, growth and grain yield improvement of wheat plants were associated with PSB inoculation and phytohormone-producing strains such as Azospirillum , Bacillus and Enterobacter [ 90 ].…”

Exogenous cysteine alleviates mercury stress by promoting antioxidant defence in maize (Zea mays L.) seedlings

“…Mercury is one of the most dangerous heavy metals for plants with phytotoxic properties that cause redox imbalance, change in photosynthetic activity, impair growth rate, and a decrease in production (Cui et al, 2015;Gontia-Mishra et al, 2016;Zhang et al, 2017). The high amount of mercury accumulation in plants leads to the death of cells and tissues (Sahu et al, 2012).…”

Endophytic fungal communities of Polygonum acuminatum and Aeschynomene fluminensis are influenced by soil mercury contamination

“…In plants, mercury ions can replace the magnesium of photosynthetic pigments and interfere with electron transport in chloroplasts, affecting photosynthesis and oxidative metabolism [ 117 , 118 ], which may explain reduction of the growth of A . fluminensis under the effect of mercury, especially in the reduction of the chlorophyll (approximately 70%) in non-inoculated plants.…”