Abstract:

Arsenic, a high toxic heavy metal, is one of the most serious contaminants in soil and a potential threat to crop growth and human health. Nitrogen metabolism plays an important role in growth and development as well as in yield and quality of flue-cured tobacco. It is necessary to study arsenic toxicity to nitrogen metabolism of flue-cured tobacco. Therefore, a systematic experiment was conducted on the farm of Henan Agricultural University, Zhengzhou, China. using Yunyan 85 (Nicotiana tabacum L.) planted in 400 mm×340 mm plastic pots, with the treatments of five arsenic levels of 0(CK), 5, 20, 40, and 60 mg·kg^-1 [added to sodium arsenate (Na₃AsO₄·12H₂O)] to determine the effects of arsenic toxicity on metabolism of nitrogen. The results showed that arsenic toxicity significantly affected nitrogen metabolism in flue-cured tobacco. On one hand, activity of nitrate-reductase (NR) during the growing period was reduced, and on the other hand, glutamine synthetase activity (GS) during the growing period was increased. These indicated that assimilation of NO₃^--N was inhibited and assimilation of NH₄⁺-N was enhanced by arsenic toxicity. The activities of both glutamate-pyruvate transaminase (GPT) and asparaginase (ASG) during the growing period, and content of the free amino acids after budding stage were increased, indicating that arsenic toxicity enhanced nitrogen transformation metabolism in flue-cured tobacco. In the mean time, compared with those in CK, protein content during the early growing stage and nicotine content during the whole growing period were decreased. However, protein content was increased during the middle and late growing stages.

Key words: Arsenic, Flue-cured tobacco, Nitrogen metabolism, Assimilation, Transformation, Accumulation