Effect of microorganisms on reducing cadmium uptake and toxicity in rice (Oryza sativa L.)

Abstract

This study analyzed the application of three microorganism inoculums, including Bacillus subtilis, Bacillus cereus, and commercial effective microorganism (EM) solution in order to determine cadmium (Cd) reduction in rice (Oryza sativa L.) and rice growth promotion. Rice was grown in Cd-contaminated soil (120 mg/kg) and selected microorganisms were inoculated. Cd concentration and rice weight were measured at 45 and 120 days of the experiment. The result showed that B. subtilis inoculation into rice can highly reduce Cd accumulation in every part of rice roots and shoots (45 days), and grains (120 days). This species can effectively absorb Cd compared to other inoculums, which might be the main mechanism to reduce Cd transportation in rice plants. Interestingly, plants that were inoculated with bacterial species individually harbored higher calcium (Ca) and magnesium (Mg) accumulation; B. subtilis-inoculated plants had the highest levels of Ca and Mg compared to other inoculated ones. Moreover, inoculating rice plants with these microorganisms could increase the dry weight of the plant and protect them from Cd stress because all the inoculums presented the ability to solubilize phosphate, produce indole-3-acetic acid (IAA), and control ethylene levels by 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. After 120 days, quantification of each inoculum by quantitative polymerase chain reaction (qPCR) confirmed the root colonization of bacterial species, with B. subtilis showing higher 16S rRNA gene copy numbers than the other species. B. subtilis was classified as a non-human pathogenic strain, reassuring the safe application of this plant growth-promoting bacterium as a crop inoculum.

Metal resistant PGPR lowered Cd uptake and expression of metal transporter genes with improved growth and photosynthetic pigments in Lycopersicon esculentum under metal toxicity

“…cereus when inoculated to Cd exposed O . sativa plants resulted in the higher root and shoot biomass 48 . This is possibly due to plant growth hormone production (IAA) by assisted microbes that regulate the hormones within plant tissues and make them acclimatize towards stress conditions 48 .…”

Rhizosphere microorganisms can influence the timing of plant flowering

“…Several auxins have decisive functions in the establishment of plant developmental and reproductive programs [13, 14]. Auxins can be synthesized by rhizosphere microorganisms [15, 16], raising the intriguing possibility that root microbiota may regulate plant growth and development through phytohormone production.…”

Differential effects of plant growth promoting rhizobacteria on chilli (Capsicum annuum L.) seedling under cadmium and lead stress

“…PGPRs are useful for plant growth enhancement via two mechanisms first is the direct mechanisms such as nitrogen fixation, phosphate solubilization, growth-regulating agents production, increasing availability of nutrients to the plant, production of plant hormones and vitamins such as gibberellin, cytokinin and auxin, and the second is the indirect mechanisms includes antibiotics synthesis, make iron available, competing with root-inhabiting species (13, 14) causing systemic resistance in the plant, production of HCN, and promoting plant resistance in stress conditions caused by non-living factors (13,14). Cd and Pb tolerant bacteria develop few survival strategies such as intracellular bioaccumulation and biosorption (15,16) that play important roles in the mobilization or immobilization of different heavy metals into plant body (15,(17)(18)(19)(20). Plants and PGPRs in association can improve biomass production and tolerance of the plants to heavy metals (18,20,21).…”