Abscisic acid enhances lead translocation from the roots to the leaves and alleviates its toxicity in Populus × canescens

Abstract To shed light on physiological mechanisms underlying abscisic-acid(ABA)-mediated lead (Pb) uptake, translocation and detoxification, we exposed Populus× canescenssaplings to either 0 or 3 mM Pb 2+ in combination with either 0 or 10 μM exogenous ABA. Pb was taken up by the roots and accumulated mainly in the cortex. A fraction of the Pb in the roots was translocated to the leaves, thereby resulting in decreased photosynthesis and biomass. Pb accumulation caused a burst of reactive oxygen species (ROS), with higher concentrations of total thiols, glutathione, and ascorbate in the roots and/or leaves. Exogenous ABA stimulated Pb uptake, decreased Pb deposition in the cortex, and enhanced Pb vascular loading in the roots. Exogenous ABA alleviated the Pb-induced reductions in photosynthesis and root biomass, and decreased Pb-triggered ROS overproduction in the roots and/or leaves. Correspondingly, exogenous ABA stimulated the mRNA levels of a few genes involved in Pb uptake, transport, and detoxification, including NRAMP1.4 , ABCG40 , FRD3.1 , PCS1.1 , and ABCC1.1 . These results suggest that exogenous ABA enhances Pb uptake and translocation, and alleviates Pb toxicity in poplars through the ABA-induced movement of Pb from the root cortex to the vascular stele, and transcriptionally regulated key genes involved in Pb tolerance.