EFFECTS OF ARSENIC TOXICITY ON CARBON AND NITROGEN METABOLISM AND THE YIELD AND QUALITY OF FLUE-CURED TOBACCO

Abstract

Background and Aims Arsenic (As) exists ubiquitously in our environment and in various forms that can be harmful to human beings as well as agricultural crops. In order to study mechanisms of carbon and nitrogen metabolism in flue-cured tobacco, Nicotiana tabacum, contaminated by arsenic, a systematic experiment was conducted on the farm of Henan Agricultural University, Zhengzhou, China. Methods Five arsenic treatment levels (0, 5, 20, 40, 60 mg·kg -1 (added as sodium arsenate Na3AsO4·12H2O)) were used to determine the effects of arsenic toxicity on carbon and nitrogen metabolism and on the yield and quality of potted (400 mm×340 mm) flue-cured tobacco plants (Nicotiana tabacum L. cv. ‘Yunyan 85’). Key Results The results showed that arsenic toxicity inhibited assimilation and transformation of carbon, decreased chlorophyll content and photosynthetic rates, and caused the accumulation of soluble sugar content during the whole growth period, and the decrease of starch content during the last part of the growing period. Arsenic toxicity also altered nitrogen metabolism and resulted in a decrease in nitrogen assimilation capacity during the early growing stage. Nitrate-reductase (NR) activity, and protein and total nitrogen content were decreased compared with the control. Nitrogen transformations resulted in an increase in the content of the free amino acids and activity of glutamate-pyruvate transaminase (GPT), an accumulation of protein and total nitrogen during the middle and late growth stages, but a decrease in nicotine content during the whole growing period. The results also showed that arsenic toxicity lowered tobacco yields and their economic value, Although the sugar-nitrogen ratio and the increase of the total content of soluble sugars related to carbon-nitrogen metabolism was beneficial, the decrease of nicotine content and the increase of the content of protein and total nitrogen, as well as high sugar-nicotine and nitrogen-nicotine ratios were not favorable for the formation of leaves with high chemical quality. Conclusions Arsenic toxicity had significant effects on carbon and nitrogen metabolism during the whole growing period, and lowered yield and economic value of flue-cured tobacco. Besides, it was unfavorable for the formation of leaves with high chemical quality, and led to an accumulation of arsenic in the leaves. Therefore, it was suggested that flue-cured tobacco not be planted in arsenic contamination regions.