Effects of manganese on the growth and nitrogen metabolism in hyper-accumulators Polygonum pubescens blume and Polygonum hydropiper L.
Mn对超富集植物短毛蓼和水蓼生长、Mn吸收及氮素代谢的影响

Hydroponic culture was conducted to investigate the effects of Mn on the growth, metal accumulation and nitrogen metabolism in hyper-accumulating plants Polygonum pubescens Blume and Polygonum hydropiper L..The enzymatic activities of nitrogen metabolism were determined including nitrate reducatse (NR), glutamine synthelase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH) as well as the nitrate nitrogen, ammonium nitrogen, and free and soluble prolines.The results indicated that the Mn contents rose significantly (p<0.05) in the tissues of both plants with the increased concentrations of Mn treatment.However, Mn levels in P.pubescens were always higher than those in the same tissue in P.hydropiper L. under the same Mn treatment.The plant height and dry weight of P.pubescens were not affected significantly when exposed to Mn concentrations lower than 1 mmol · L-1, but significant changes were found for P.hydropiper, indicating that P.pubescens is more Mn-tolerant. Compare to the control, the contents of nitrate nitrogen in P.pubescens decreased significantly (p<0.05), while the contents of soluble protein increased.The contents of nitrate nitrogen and ammonium nitrogen as well as soluble protein in P.hydropiper L. increased significantly in the treatment of 8 mmol · L-1 Mn.The contents of free proline in both plants increased compared with those of the control, indicating that free proline played an important role in detoxifying Mn.Both activities of NR in P.hydropiper and GS in P.pubescens declined significantly (p<0.05) due to the Mn treatment.The activity of NR reached maximum in P.hydropiper at 1 mmol · L-1 Mn treatment.The activities of GOGAT in both plant tissues decreased significantly (p<0.05) with the Mn concentrations from 2 to 8 mmol · L-1.At 8 mmol · L-1 treatment, the GDH activities in both plant leaves (p<0.05) were 16.29 and 1.29 times of those under control, respectively.