Enhancing rice (Oryza sativa L.) resilience to cadmium stress through nanoparticle and rhizobacterial strategies: A sustainable approach to heavy metal remediation

Abstract

Soil contamination with toxic heavy metals such as cadmium (Cd) is becoming a serious global problem due to rapid industrial and agriculture expansion. Although nanoparticles (NPs) and plant growth-promoting rhizo-bacteria (PGPR) are the major protectants to alleviate metal toxicity. A pot experiment was conducted under controlled conditions by using sand, mixed with different levels of Cd i.e., 0, 50, and 100 mg kg⁻¹ together with the application of FeO–NPs (50 and 100 mg L⁻¹) and B. megaterium (5 and 10 ppm) levels to monitor different growth, gaseous exchange, oxidative stress, antioxidative responses, minerals accumulation, organic acid exudation patterns of O. sativa seedlings. Our results depicted that Cd exposure significantly reduced plant biomass, photosynthetic efficiency, and mineral uptake, while increasing malondialdehyde (MDA), H₂O₂, and electrolyte leakage, indicating oxidative stress. Antioxidant enzymes (SOD, POD, CAT, and APX) were enhanced at 50 mg kg⁻¹ Cd but declined at 100 mg kg⁻¹. Cd stress also suppressed anthocyanins and soluble proteins while increasing Cd accumulation in roots and shoots. Application of FeO–NPs and B. megaterium mitigated these adverse effects by improving growth, photosynthesis, antioxidant defenses, mineral uptake, and reducing oxidative damage and organic acid exudation. These treatments also lowered Cd retention in plant tissues. Research findings, therefore, suggested that application of FeO–NPs and B. megaterium can ameliorate Cd toxicity in O. sativa seedlings and resulted in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.