Responses of Nitrogen Metabolism to Lead Stress in Jatropha curcas Cotyledon

In vitro embryo germination and culture experiments were performed to investigate the responses of nitrogen metabolism to lead stress in J. curcas cotyledons at the three developmental stages. Lead (Pb2+) concentrations of 100 and 200 mu M in Murashige and Skoog (MS) medium were used. The fresh weights of cotyledons were not affected by Pb treatments; however, the dry weights decreased significantly, while the relative water contents increased as compared to the control. The nitrate, nitrite and ammonium levels also decreased significantly at three developmental stages compared to the control. Nitrate- and nitrite- reductase activities in the treated plants showed significant decline at days 2,4 and 6. The Pb treatment led to a marked increase in glutamine synthetase activity except during the exposure to 200 mu M Pb2+ at day 2. Glutamate synthase activity was also considerably enhanced by Pb application. The NADH-GDH and NAD-GDH activities were raised at the three developmental stages after 100 and 200 mu M Pb treatments. The alanine- and aspartate- aminotransferase activities were increased after the 100 and 200 mu M Pb treatments. The results showed that Pb stress may cause the changes in nitrogen metabolism and relative enzymes during the developmental stages of, J curcas cotyledons. (C) 2013 Friends Science Publishers