Environmental biology

Effects of lanthanum(III) on nitrogen metabolism of soybean seedlingsunder elevated UV-B radiation


CAO Rui , HUANG Xiao-hua , ZHOU Qing , CHENG Xiao-ying

DOI:

Received February 01, 2007,Revised May 09, 2007, Accepted , Available online

Volume 19,2007,Pages 1361-1366

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The hydroponic culture experiments of soybean bean seedlings were conducted to investigate the e ect of lanthanum (La) on nitrogen metabolism under two di erent levels of elevated UV-B radiation (UV-B, 280–320 nm). The whole process of nitrogen metabolism involves uptake and transport of nitrate, nitrate assimilation, ammonium assimilation, amino acid biosynthesis, and protein synthesis. Compared with the control, UV-B radiation with the intensity of low level 0.15 W/m2 and high level 0.45 W/m2 significantly a ected the whole nitrogen metabolism in soybean seedlings (p < 0.05). It restricted uptake and transport of NO3-??, inhibited activity of some key nitrogen-metabolism-related enzymes, such as: nitrate reductase (NR) to the nitrate reduction, glutamine systhetase (GS) and glutamine synthase (GOGAT) to the ammonia assimilation, while it increased the content of free amino acids and decreased that of soluble protein as well. The damage effect of high level of UV-B radiation on nitrogen metabolism was greater than that of low level. And UV-B radiation promoted the activity of the anti-adversity enzyme glutamate dehydrogenase (GDH), which reduced the toxicity of excess ammonia in plant. After pretreatment with the optimum concentration of La (20 mg/L), La could increase the activity of NR, GS, GOGAT, and GDH, and ammonia assimilation, but decrease nitrate and ammonia accumulation. In conclusion, La could relieve the damage e ect of UV-B radiation on plant by regulating nitrogen metabolism process, and its alleviating e ect under low level was better than that under the high one.

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