The potential of Actinoplanes spp. for alleviating the oxidative stress induced by thallium toxicity in wheat plants.

ABSTRACT

To reduce heavy metal toxicity, like that induced by thallium (TI) in plants, growth-promoting bacteria (GPB) are a widely used to enhance plant tolerance to heavy metals toxicity. In our study, we characterized seven GPB and identified Actinoplanes spp., as the most active strain. This bioactive strain was then applied to alleviate TI phytotoxicity. TI contamination (20 mg/kg soil) induced TI bioaccumulation, reducing wheat growth (biomass accumulation) and photosynthesis rate, by about 55% and 90%, respectively. TI stress also induced oxidative damages as indicated by increased oxidative markers (H2O2 and lipid peroxidation (MDA)). Interestingly, Actinoplanes spp. significantly reduced growth inhibition and oxidative stress by 20% and 70%, respectively. As a defense mechanism to mitigate the TI toxicity, wheat plants showed improved antioxidant and detoxification defense including increased phenolic and tocopherols levels as well as peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), and glutathione reductase (GR) enzymes activities. These defense mechanisms were further induced by Actinoplanes spp. Additionally, Actinoplanes spp. increased the production of heavy metal-binding ligands such as metallothionein, phytochelatins, total glutathione, and glutathione S-transferase activity by 100%, 90%, 120%, and 100%, respectively. This study, therefore, elucidated the physiological and biochemical bases underlying TI-stress mitigation impact of Actinoplanes spp. Overall, Actinoplanes spp. holds promise as a valuable approach for ameliorating TI toxicity in plants. KEYBOARD Actinobacteria, Bioaccumulation, Detoxification, Membrane damage, Redox regulation.