Abstract
Burley tobacco is a genotype of chloroplast-deficient mutant with accumulates high levels of tobacco-specific nitrosamines (TSNAs) which would induce malignant tumors in animals. Nitrate is a principle precursor of tobacco-specific nitrosamines. Nitrate content in burley tobacco was significantly higher than that in flue-cured tobacco. The present study investigated differences between the two tobacco types to explore the mechanisms of nitrate accumulation in burley tobacco. transcripts (3079) related to the nitrogen and carbon metabolism were observed. Expression of genes involved in carbon fixation, glucose and starch biosynthesis, nitrate translocation and assimilation were significantly low in burley tobacco than flue-cured tobacco. Being relative to flue-cured tobacco, burley tobacco was significantly lower at total nitrogen and carbohydrate content, nitrate reductase and glutamine synthetase activities, chlorophyll content and photosynthetic rate (Pn), but higher nitrate content. Burley tobacco required six-fold more nitrogen fertilizers than flue-cured tobacco, but both tobaccos had a similar leaf biomass. Reduced chlorophyll content and photosynthetic rate (Pn) might result in low carbohydrate formation, and low capacity of nitrogen assimilation and translocation might lead to nitrate accumulation in burley tobacco.
Highlights
Burley, known as yellow green leaf color tobacco, is a chloroplast-deficient mutant tobacco type with reduced pigment content [1]
The results showed that leaf biomass between the two tobacco types was equal at 24 mmol/L nitrogen level for burley tobacco and 4 mmol/L nitrogen level for flue-cured tobacco during seedling stage (Figure 1a)
Eighteen cDNA libraries (2 varieties * 3 treatments * 3 biological replicates) were prepared to analyze the differences in nitrogen and carbon metabolism between burley tobacco and flue-cured tobacco seedlings
Summary
Known as yellow green leaf color tobacco, is a chloroplast-deficient mutant tobacco type with reduced pigment content [1]. Little has been reported on the effect of chloroplast-deficient mutant in burley tobacco. The amount of nitrogen fertilizers used on burley tobacco was almost 3–5 times more than that on flue-cured tobacco, but the yield between them was not significantly different [3], indicating a much lower nitrogen utilization efficiency by burley tobacco. The nitrate content in air-cured burley tobacco was at least 50 times greater than that in flue-cured tobacco [4] and was regarded as an important cause of high tobacco-specific nitrosamines (TSNAs) formation in burley tobacco than that in flue-cured tobacco. It is well known that burley tobacco has high levels of nitrate, little is known about the mechanism of high level accumulation of nitrate in cultivation
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