Heavy Metal and Drought Stress in Plants: The Role of Microbes—A Review

Abstract

Plants are composed of complex organisms that include morphological, physiological and biochemical segments. A number of environmental factors such as, heavy metals, drought, salinity, heat, and cold cause stress towards plants and impact on their growth and yield values. Heavy metal contamination and drought are considered to be two significant environmental (abiotic) factors that are receiving increased attention due their effects on plants. Many plant species from previously non-drought prone areas now face drought as a new stress factor and must develop their avoidance mechanisms. Comparing drought-related tolerance strategies, plants have developed a number of strategies to fight against heavy metal pollution due to its wide coverage. These heavy metal tolerance strategies include detoxification, compartmentalization, and storage in cell vacuoles in plants. Few similarities have been found in the mechanisms of both drought and heavy metal strategies. The use of beneficial microbes is considered as one of the most promising methods to improve stress tolerance because plant-associated microbes decrease metal accumulation while enhancing nutrient supply and water under such stress. In this review, we summarize how drought and heavy metals contamination effect on plant growth, with particular focus on stress avoidance and tolerance mechanisms, as well as, the role of microbes to enhance stress tolerance. Recommendations including irrigation, fertilization and molecular techniques to increase the plant’s tolerance mechanisms against heavy metal and drought conditions are also discussed.

Amaranthus Biochar-Based Microbial Cell Composites for Alleviation of Drought and Cadmium Stress: A Novel Bioremediation Approach

“…Cadmium is a highly mobile toxic heavy metal that causes harmful effects in humans and detrimental effects in plants. Being a naturally occurring element, it is released into the environment through human activities such as mining, industrial processes and the use of fertilizers and pesticides [ 1 , 2 , 3 ]. The problem of cadmium contamination in agricultural soil is particularly acute in areas where farming is intensive and there is a high demand for food production.…”

“…When both factors are prominent, they adversely affect plant physiological and biochemical processes which could lead to growth, biomass, and yield loss [ 4 , 5 ]. Many drought-prone regions such as different parts of China, Africa, Europe, and the Mediterranean shrubland, reported dynamic changes in the metal concentration in soil and its subsequent transfer in plants due to drought stress [ 2 , 6 , 7 , 8 ]. They severely affect seed germination, leaf water content, photosynthetic activity, chlorophyll content, and organelle structure and accelerates senescence [ 9 ].…”

“…Thus, they play a vital role in plant tolerance by inducing systematic resistance against biotic (pathogenic bacterial and fungal attack) and abiotic stress (drought, salinity, heavy metals). Apart from PGP characteristics, these rhizobacteria are well-identified for plenty of potential for bioremediation of metals from soil (through biosorption of metal ions by their functional anionic groups) and defense responses to drought [ 2 , 17 , 18 ].…”

Diet choices determine mercury exposure risks for people living in gold mining regions of Peru

“…In contrast to fruit, rice contained high MeHg proportions. The tendency of plants to accumulate metals will depend on bioavailability, which is impacted by soil pH, organic matter, cation exchange capacity, moisture, clay content, and redox potential [58]. When rice is grown under flooded, anoxic conditions that promote microbial methylation, most total Hg is present as MeHg [59,60].…”

Genome-wide survey of HMA gene family and its characterization in wheat (Triticum aestivum)

“…However, data regarding this gene family in hexaploid wheat is scanty. Limited similarities have been found in the mechanisms of both drought and heavy metal tolerance strategies in plants ( Islam & Sandhi, 2022 ). Signaling pathways activate proteins that make transporters, proteases, ROS detoxifying enzymes (alternative oxidase, glutathione peroxidase, glutathione reductase, copper-zinc superoxide dismutase, glutathione S transferase and chaperones ( Zhang & Sonnewald, 2017 )), which help plants to ameliorate stress.…”