Oxidative stress impedes recovery of canola (Brassica napus) plants from waterlogging by inhibiting aquaporin-mediated root water transport

Abstract

We exposed hydroponically grown canola plants for three days to root hypoxia (waterlogging) followed by re-aeration. Hypoxia decreased root hydraulic conductivity ( L pr ) and the apoplastic contribution to water transport, which impacted gas exchange and plant water relations. However, the most severe reduction of L pr was one day following re-aeration and it was accompanied by an increase in the contribution of apoplast to water flow. After one day of re-aeration, a sharp increase in ROS in roots was measured together with a decrease in transcript abundance of most BnPIP2 aquaporins in roots and leaves. A water permeability assay of these BnPIP2 s heterologously expressed in yeast confirmed that they are fast water transporters. All yeast strains displayed decreased water permeability with increased concentrations of applied H 2 O 2 and exogenous application of H 2 O 2 to plant roots resulted in a decrease of L pr . The yeast H 2 O 2 survival assay demonstrated that BnPIP1;2 and BnPIP1;3 facilitate H 2 O 2 transport and, therefore, the increase in gene expression of these aquaporins during re-aeration likely contributed to plant waterlogging recovery. A gradual recovery of L pr following re-aeration was accompanied by up-regulation of BnPIP s in roots and leaves and the activation of antioxidant enzymes in roots. Net photosynthesis, transpiration rates, and shoot water contents remained depressed one day after re-aeration but recovered over time. Collectively, the results demonstrate that oxidative burst had a decisive impact on modulating the hydraulic recovery of plants upon re-aeration. Since plant injury from root hypoxia involved both the hypoxic event and the ROS burst that occurred soon after root aeration, the ability of plants to recover from waterlogging was partly determined by their ability to handle oxidative stress. • Both root hypoxia and oxidative burst during re-aeration of canola plants had a severe impact on root hydraulic properties and gas exchange. • Increases in gene expression of BnPIPs in hypoxic and reaerated roots likely helped facilitate oxygen and hydrogen peroxide transport. • Sincehypoxia injury involves the hypoxic event and oxidative burst following aeration, waterlogging recovery requires resistance to both stresses.