| Aluminum (Al) toxicity and Manganese (Mn) toxicity are two major constraints of crop productivity on acid soils. In the present study, hydroponics experiments were performed to determine the interaction between Al and Mn at low pH in soybean, and we collect 4 soybean cultivars pre-screened in our laboratory, and after a systematic screening, Jiyu41 was selected as the Al-tolerant cultivars, and Jilin62 was the Al-sensitive cultivars, respectively. Subsequently Jilin62 was selected for further studies on the interaction and physiological mechanisms between Al and Mn at low pH. Results were as follows: (1) accumulation of Mn in roots, stems, and leaves of soybean decreased significantly with increasing Al supply, the toxicity symptoms of shoot under excess Mn was alleviated with Al supply; Excess Mn supply decreased accumulation of Al in roots, aggravated the toxicity degree of roots; Subcellular distribution showed that High level of Al supply mainly deduced accumulation of Mn both in cell walls and organelles, and excess Mn supply significantly increased accumulation of Al in the cell wall. (2) Excess Al or Mn increased O2?—product rate, the content of H2O2 and MDA, and also increased the activity of SOD, APX, GPX in soybean leaves, high level of Al supply decreased the increasing of the O2?—product rate, the content of H2O2 and MDA, the activity of SOD, APX, GPX; the changes of antioxidants enzymes only were the stress reaction under high level of Al and Mn coexistence, but not the cause of Al relieved Mn toxicity of soybean leaves. (3) Mn toxicity can not be ameliorated by citric acid which secreted under Al stress; we can not affirm the possible role of pH on Mn uptake and transport, proved that Al affect Mn uptake and transport possible by competing the negatively charged site in the cell wall of root. Excess Mn supply increased pectin contents under Al stress, which could explain how excess Mn supply increased accumulation of Al in roots.
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