Salix Matsudana Tolerance To Lead Enhanced By Spermidine And The Related Mechanism

Salix is rich in China and might be suitable candidates for phytoremediation species because of their high genetic variability, biomass production, metal tolerance and high accumulation ability to cadmium and zinc. Polyamines have been deemed as antioxidant and play a vital role in plant growth and metabolism. Salix matsudana was chose in this experiment to study the toxic mechanism of lead to plant and the alleviation effect of exogenous spermidine (Spd). The object of this paper is to further understand the toxic mechanism of heavy metals to plants and the regulation function of polyamines. This research also offers a theoretical basis for the application of exogenous Spd.The regulation function of exogenous Spd on plant growth and metabolism was investigated by a hydroponic experiment in S. matsudana. The direct effect of Pb on plant growth is decreasing root and leave weights, while the application of Spd elevated the growth parameters and tolerance indexes. The regulation mechanism of exogenous Spd on Salix growth and metabolism mainly included the following aspects:1) regulating the endogenous polyamines level;2) elevating soluble proteins;3) regulating the micronutrient contents;4) inhibiting the accumulation of reactive oxygen species and malondialdehyde;5) regulating the function of antioxidant system;6) influencing the absorption and translocation of Pb. Results showed that Pb stress significantly increased putresine (Put) content but decreased Spd content. Exogenous Spd application elevated Spd content and decreased Put, thus maintenance the balance of polyamine metabolism. Spd elevated the soluble protein contents which were significantly decreased by Pb stress, thus increased the tolerance to Pb. Pb stress influenced the absorption and translocation of micronutrients and Spd regulated the levels of micronutrients also there were no statistical differences. More importantly, exogenous Spd could regulate the function of antioxidant system under Pb stress in S. matsudana. Pb stress increased the accumulation of superoxide anion (O2·-), hydrogen peroxide (H2O2), and malondialdehyde (MDA), while exogenous Spd declined all these three parameters to a different level. Correlation analysis showed that Spd played a vital role in the inhibition of free radical production and lipid peroxidation. In addition, Pb stress declined the activity of superoxide dismutase (SOD), peroxidase (POD), glutathione reductase (GR) and the content of reduced ascorbate (ASA), reductive glutathione (GSH), and nitric oxide (NO). Pb stress increased the activity of catalase (CAT) and ascorbate peroxidase (APX). The application of Spd restored the level of SOD, POD, GR, ASA, GSH, and NO, while did not reverse the activity of CAT and APX in leaves of S. Matsudana. All these antioxidative paramaters except for CAT and APX were close to control value with Spd application compared to the only Pb-treated group. Exogenous Spd regulated the absorption, translacation, and accumulation of Pb. Exogenous Spd increased the accumulation of Pb in root, inhibited the translocation of Pb from root to the above-ground organs, decreased the accumulation of Pb in leaves and twigs, and alleviated the damage of Pb to S. matsudana. In all, the application of Spd could elevate the level of endogenous Spd, regulate the function of antioxidant system, increase the tolerance to Pb, and promote the accumulation of Pb in root.