| Hydroponic culture with orthogonal design method was conducted to investigate the effects of Mn and Zn on the growth, metal accumulation and nitrogen metabolism in hyperaccumulating plants Polygonum pubescens Blume. 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 pralines. The results showed that under single treatment of Zn, the plant height, dry weight, root length and chlorophyll content decreased as Zn concentrations increased. At 100 mg·L-1 Zn treatment, the plant height, dry weight were 78% and 56% of those under control, respectively. The growth of P. pubescens were not affected significantly when treated by Mn alone; Under combined pollution of Mn and Zn, the plant height, dry weight, root length and chlorophyll content decreased as Zn concentrations increased. Both single Zn and Mn treatment have varied impact on the contents of nitrate nitrogen, ammonium nitrogen, free prolines and soluble protein as well as enzymatic activities of GOGAT, GS, NR and GDH. Overall, Mn, and Zn com bined treatment lowered the contents of nitrate nitrogen in roots（2.60%~70.13%） and leaves（12.67%~64.79%）. But increased the contents of ammonium nitrogen, free proline and soluble protein. For the same Zn level, increased Mn addition raised the contents of free proline, and soluble protein, as well as GOGAT, GS, NR, and GDH enzymatic activities in varying degrees, indicating that Mn may effectively relieve Zn stress. |
