Signal transducer of IAA related gene expression induces transporters of hyperaccumulator <i>Arabis alpina</i> for Pb accumulation

Lead (Pb) pollution in soil affects growth of plants. Plants' endogenous hormones play an important role in resistance to Pb of plant. In order to explore the hormone-based mechanisms of Pb accumulationin in hyperaccumulator <i>Arabis alpina</i>, a pot experiment was conducted to analyze the contents of endogenous hormones (auxin, gibberellin, abscisic acid, and cytokinin) and related genes expressions, and Pb contents of <i>A. alpina</i>, as well as the transporter (cation exchangers (CAX), heavy metal ATPases (HMA), and ATP-binding cassette (ABC)) concentrations under foliar spraying of indoleacetic acid (IAA). The results showed that the soluble components (vacuoles) Pb contents under 300 mg kg^-1 Pb²⁺ treatment in shoots and roots increased by 238.8% and 896.3%, respectively, compared to 100 mg kg^-1 Pb²⁺ treatment. The content of endogenous hormones in leaves and roots increased under increasing Pb-treatment concentrations. Compared with the control (0 mg kg^-1 Pb²⁺ treatment), the content of auxin in roots and leaves under the 100 mg kg^-1 Pb treatment increased by 176.2% and 585.3%, respectively. The auxin content in xylem saps under the 100 and 300 mg kg^-1 Pb treatments increased by 283.1% and 100.3%, respectively. The gene expression related to auxin transport was up-regulated. The expression of three genes related to the auxin-repressed 12.5 kDa protein and the auxin-responsive GH3 (Gretchen Hagen 3) family were down-regulated. Under foliar spraying of IAA, the Pb content in leaves increased by 29.81%, and the Pb content in the symplast sap was higher than that without IAA spraying treatment. The concentrations of CAX and HMA in the roots of <i>A. alpina</i> increased by 9.6% and 8.8%, respectively, with foliar spraying treatment with IAA, while the ABC concentration decreased by 21.9%. In general, the transport and accumulation of Pb is related to the IAA content and the gene expression of <i>AaGDCST</i>, a signal transducer for inducing increased concentrations of the transporter CAX and HMA in the roots of <i>A. alpina</i>. Pb transport <i>via</i> the symplast pathway under IAA application. Regarding the Pb hyperaccumulation of <i>A. alpina</i>, gene <i>AaGDCST</i> has the potential to be utilized as a candidate gene.