Arbuscular mycorrhizal fungi induce flavonoid synthesis for mitigating oxidative damage of trifoliate orange under water stress

Abstract

Arbuscular mycorrhizal (AM) fungi can increase the tolerance of host plants to drought, whereas the intrinsic mechanisms are not still fully elucidated. Flavonoids are a kind of antioxidants to scavenge reactive oxygen species (ROS), whereas whether and how flavonoids are involved in increased drought tolerance of host plants by AM fungi is not known. Here, Funneliformis mosseae , was inoculated into potted trifoliate orange seedlings, which were subjected to adequate water and water stress conditions. The AM effect on plant growth, concentrations of flavonoid substances and total flavonoids, and activities and expression levels of enzymes related to flavonoids synthesis (clnnamate 4-dydroxylate (C4H), phenylalanine ammonialyase (PAL), chalcone isomerase (CHI), and 4-coumaroyl-CoA ligase (4CL)) in roots was analyzed, along with changes in scavenging activity of ROS by root flavonoid extracts. Compared with non-AM control, F . mosseae inoculation distinctly improved plant growth performance and increased phenylalanine, glycitin, luteolin-7- O -glucoside, and total flavonoid concentrations, coupled with the decrease in p -coumaric acid, regardless of soil water regimes. Activities of C4H, CHI, 4CL, and PAL and expression levels of PtPAL1 and Pt4CL were induced by F . mosseae inoculation under water stress. AM plants exhibited higher scavenging activity of hydroxyl radical and superoxide (O 2 •− ) by root flavonoid extracts under water stress, along with lower levels of O 2 •− and hydrogen peroxide and the degree of membrance lipid peroxidation, compared with non-AM plants. It is concluded that AM fungi accelerated flavonoids synthesis of trifoliate orange for mitigating oxidative damage under water stress. • AMF increased phenylalanine, glycitin, luteolin-7- O -glucoside, and total flavonoid concentrations, regardless of soil moisture regimes. • C4H, CHI, 4CL, and PAL activities and PtPAL1 and Pt4CL expressions were induced by AMF under water stress. • AMF plants exhibited higher scavenging activity of ROS by root flavonoid extracts under water stress. • AM fungi accelerated flavonoids synthesis for mitigating oxidative damage under water stress.