Arbuscular Mycorrhizal Fungus Alleviates Chilling Stress by Boosting Redox Poise and Antioxidant Potential of Tomato Seedlings

The universal symbiotic associations between arbuscular mycorrhizal fungi (AMF) and plant roots remarkably stimulate plant growth, nutrient uptake, and stress responses. The present study investigated the stress ameliorative potential of the AM fungus Funneliformis mosseae against chilling in tomato seedlings. AMF-inoculated tomato seedlings exhibited significantly higher fresh weight and dry weight than non-AMF control plants under both control (25/15 °C) and low temperature (8 °C/4 °C) treatments. Under chilling stress, AMF inoculation significantly reduced the level of MDA, H2O2, and O 2 ·− along with increased calcium precipitates in the apoplast and vacuole of root cells compared with the non-AMF control. Furthermore, AMF inoculation induced activities of antioxidant enzymes and transcripts of related genes under chilling stress. Notably, AMF inoculation resulted in reduced redox state in root cells as evident by significantly increased content of reduced ascorbate, reduced glutathione, redox ratio, and the activity of l-galactono-1,4-lactone dehydrogenase in the tomato roots both under control and low temperature. Taken together, these results indicate that AMF could play an important role in optimizing chilling resistance by maintaining redox poise and calcium balance in tomato seedlings.