Root-associated symbiotic fungi enhance waterlogging tolerance of peach seedlings by increasing flavonoids and activities and gene expression of antioxidant enzymes

Root-associated symbiotic fungi can enhance the host plant's ability to tolerate adverse environmental conditions, but it's unclear whether and how they enhance waterlogged peach plants. This study aimed to investigate the effects of Funneliformis mosseae (Fm), an arbuscular mycorrhizal fungus, and Serendipita indica (Si), an endophytic fungus, on plant growth, root development, reactive oxygen species (ROS) levels, total flavonoids, ROS scavenging activity of flavonoids, and activities and gene expression of antioxidant enzymes in roots of waterlogged peach seedlings. Although waterlogging treatment had little effect on root development, Fm and Si, particularly Fm, improved root development variables to varying degrees. Waterlogging significantly promoted superoxide anion radicals (O2 center dot-) and hydrogen peroxide (H2O2) levels, whereas Fm and Si distinctly reduced O2 center dot- and H2O2 levels under waterlogging. Waterlogging triggered an increase in total flavonoids in fungi-inoculated seedlings, and the two fungi also significantly increased total flavonoid concentrations and the scavenging activity of total flavonoids to hydroxyl radical, O2 center dot-, and 2,2-diphenyl-1-picrylhydrazyl radical. In addition, root fungal colonization rate was negatively and significantly correlated with O2 center dot- and H2O2, but positively with total flavonoids. Under waterlogging conditions, Fm significantly raised root superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities, and Si likewise elevated root SOD, CAT, GPX, and peroxidase (POD) activities, compared with uninoculated treatment. Although the expression of various antioxidant enzyme genes in roots remained mostly unchanged or were inhibited by the waterlogging, Fm up-regulated the expression of PpSOD3 and PpSOD7, whereas Si up-regulated the expression of PpSOD3, PpCAT1, PpGPX6, PpGPX8, and PpPOD1. In conclusion, low oxidative bursts in Fm- and Si-inoculated peach plants exposed to waterlogging were associated with an increase in total flavonoids as well as activities and gene expression of antioxidant enzymes.