Coactive Application of Bacillus Mycoides PM35 and Calcium Oxide Nanoparticles Stimulate Gene Expression Responses in Maize (Zea Mays L.) under Chromium Stress

Plant growth-promoting rhizobacteria (PGPR) play a crucial role in ameliorating abiotic stress in plants. Abiotic stress refers to non-living environmental factors that negatively impact plant growth and development, such as drought, salinity, extreme temperatures, heavy metals, and nutrient deficiencies. On the other hand, calcium oxide (CaO) nanoparticles (NPs) have significant antimicrobial properties and unique structural and optical properties; environmentally, they are considered safe for all living organisms. Keeping in view the stress mitigation potential of CaO⎯NPS and Bacillus mycoides PM35, the existing research work was premeditated to inspect the beneficial role of seed priming with using different levels of CaO⎯NPs i.e., 0, 25 and 50 mg L^⎯1 and soil incubation with B. mycoides PM35 i.e., 0, 10 and 20 µL on biochemical, morphological and physiological characteristics of maize (Zea mays) plants under different levels of Cr in the soil i.e., 0, 50 and 100 mg kg^− 1. Results from the present study showed that the increasing levels of Cr in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants and altered the response of various antioxidants compounds such as superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) and the specific gene expression. In contrast, increasing levels of Cr in the soil significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage and also increased organic acid exudation patter in the roots of Z. mays. The negative impact of Cr toxicity can overcome the application of B. mycoides PM35 and CaO⎯NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in Z. mays by decreasing the Cr contents in the roots and shoots of the plants. Research findings, therefore, suggest that the individual application of B. mycoides PM35 and CaO⎯NPs can ameliorate Cr toxicity in Z. mays, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.