title: Magnesium Alleviates Adverse Effects of Lead on Growth, Photosynthesis, and Ultrastructural Alterations ofTorreya grandisSeedlings.
abstract: Magnesium (Mg2+) has been shown to reduce the physiological and biochemical stress in plants caused by heavy metals. To date our understanding of how Mg2+ameliorates the adverse effects of heavy metals in plants is scarce. The potential effect of Mg2+on lead (Pb2+) toxicity in plants has not yet been studied. This study was designed to clarify the mechanism of Mg2+-induced alleviation of lead (Pb2+) toxicity.Torreya grandis(T. grandis) seedlings were grown in substrate contaminated with 0, 700 and 1400 mg Pb2+per kg-1and with or without the addition of 1040 mg kg-1Mg2+. Growth parameters, concentrations of Pb2+and Mg2+in the plants' shoots and roots, photosynthetic pigment, gas exchange parameters, the maximum quantum efficiency (Fv/Fm), root oxidative activity, ultrastructure of chloroplasts and root growth were determined to analyze the effect of different Pb2+concentrations on the seedlings as well as the potential ameliorating effect of Mg2+on the Pb2+induced toxicity. All measurements were tested by a one-way ANOVA for the effects of treatments. The growth ofT. grandisseedlings cultivated in soils treated with 1400 mg kg-1Pb2+was significantly reduced compared with that of plants cultivated in soils treated with 0 or 700 mg kg-1Pb2+. The addition of 1040 mg kg-1Mg2+improved the growth of the Pb2+-stressed seedlings, which was accompanied by increased chlorophyll content, the net photosynthetic rate and Fv/Fm, and enhanced chloroplasts development. In addition, the application of Mg2+induced plants to accumulate five times higher concentrations of Pb2+in the roots and to absorb and translocate four times higher concentrations of Mg2+to the shoots than those without Mg2+application. Furthermore, Mg2+addition increased root growth and oxidative activity, and protected the root ultrastructure. To the best of our knowledge, our study is the first report on the mechanism of Mg2+-induced alleviation of Pb2+toxicity. The generated results may have important implications for understanding the physiological interactions between heavy metals and plants, and for successful management ofT. grandisplantations grown on soils contaminated with Pb2+.
authors.affiliation: The Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University Zhejiang, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Shen
authors.affiliation: The Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University Zhejiang, China.
authors.forename: Lili
authors.initials: L
authors.lastname: Song
authors.affiliation: New Zealand Institute for Plant and Food Research Limited, Ruakura Research Centre Hamilton, New Zealand.
authors.forename: Karin
authors.initials: K
authors.lastname: Müller
authors.affiliation: The Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University Zhejiang, China.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Hu
authors.affiliation: The Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University Zhejiang, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Song
authors.affiliation: The Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University Zhejiang, China.
authors.forename: Weiwu
authors.initials: W
authors.lastname: Yu
authors.affiliation: Key Laboratory of Soil Contamination Bioremediation of Zhejiang Province, Zhejiang A & F University Zhejiang, China.
authors.forename: Hailong
authors.initials: H
authors.lastname: Wang
authors.affiliation: The Nurturing Station for the State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University Zhejiang, China.
authors.forename: Jiasheng
authors.initials: J
authors.lastname: Wu
keywords: Torreya grandis; heavy metal phytotoxicity; lead toxicity; magnesium; phytoremediation