Alleviation of drought stress by mycorrhizas is related to increased root H2O2 efflux in trifoliate orange

The Non-invasive Micro-test Technique (NMT) is used to measure dynamic changes of specific ions/molecules non-invasively, but information about hydrogen peroxide (H₂O₂) fluxes in different classes of roots by mycorrhiza is scarce in terms of NMT. Effects of Funneliformis mosseae on plant growth, H₂O₂, superoxide radical (O₂·-), malondialdehyde (MDA) concentrations, and H₂O₂ fluxes in the taproot (TR) and lateral roots (LRs) of trifoliate orange seedlings under well-watered (WW) and drought stress (DS) conditions were studied. DS strongly inhibited mycorrhizal colonization in the TR and LRs, whereas mycorrhizal inoculation significantly promoted plant growth and biomass production. H₂O₂, O₂·-, and MDA concentrations in leaves and roots were dramatically lower in mycorrhizal seedlings than in non-mycorrhizal seedlings under DS. Compared with non-mycorrhizal seedlings, mycorrhizal seedlings had relatively higher net root H₂O₂ effluxes in the TR and LRs especially under WW, as well as significantly higher total root H₂O₂ effluxes in the TR and LRs under WW and DS. Total root H₂O₂ effluxes were significantly positively correlated with root colonization but negatively with root H₂O₂ and MDA concentrations. It suggested that mycorrhizas induces more H₂O₂ effluxes of the TR and LRs, thus, alleviating oxidative damage of DS in the host plant.