Individual and Combinatorial Applications of Arbuscular Mycorrhizal Fungi and Plant Growth-Promoting Rhizobacteria Increase Morpho-Physio-Biochemical Responses in Rice (Oryza sativa L.) under Cadmium Stress

In the current industrial scenario, cadmium (Cd) as a metal is of great importance but poses a major threat to the ecosystem because of its toxicity, but fewer studies have been conducted on its effects and alleviation strategies by using arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR). Taking into consideration the positive effects of Rhizophagus irregularis as an AMF and Azospirillum brasilense as a PGPR in reducing Cd toxicity in plants, the present study was conducted. A pot experiment was conducted to determine the effects of single and/or combined application of different levels [10 and 20 ppm] of R. irregularis and A. brasilense (10 and 20 ppm) on Cd accumulation, morpho-physio-biochemical attributes of rice (Oryza sativa L.) exposed to severe Cd stress [0 (without Cd stress), and 100 mu M)]. The research outcomes indicated that elevated levels of Cd stress in the soil significantly (p <= 0.05) decreased plant growth and biomass, photosynthetic pigments, and gas exchange attributes. However, Cd stress also induced oxidative stress in the plants by increasing malondialdehyde (MDA) and hydrogen peroxide (H2O2), which also induced increased compounds of various enzymatic and non-enzymatic antioxidants and also the gene expression and sugar content. Furthermore, a significant (p <= 0.05) increase in proline metabolism, the ascorbate-glutathione (AsA-GSH) cycle were observed. Although, the application of R. irregularis and A. brasilense showed a significant (p <= 0.05) increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds, and their gene expression and also decreased oxidative stress. In addition, the application of R. irregularis and A. brasilense enhanced cellular fractionation and decreased the proline metabolism and AsA-GSH cycle in O. sativa plants. Research findings, therefore, suggest that the application of R. irregularis and A. brasilense can ameliorate Cd toxicity in O. sativa, resulting in improved plant growth and composition under metal stress, as depicted by balanced antioxidant defense mechanism.