| Tobacco(Nicotiana tobacum L.) is an important cash crop in yunnan province ang China, temperature is an important environment factor, plays an important role on the growth and development of tobacco plants, leaf quality and secondary metabolites. Therefore, comprehensive and in-depth studying on effects of temperature on tobacco quality mechanism has important significance. This paper, taking the tobacco plants(Yunyan 87) as materals, studied the effects of different growth temperature on growth, photosynthetic characteristics, plastid pigment and nicotine metabolism in tobacco plants with different developmental stages, to investigate the machanisms of temperature effects on the growth and development, plastid pigment and nicotine metabolism of tobacco plants, and to provide theoretical support for tobacco leaf production. 1. Effects of different growth temperature on alkaloids content and nicotine metabolism based on the de novo transcriptome and RNA-seq analysis in tobacco plantsUsing tobacco plants growing in artificial climate chamber simulating different environment temperature as materials, studied the effect of different growth temperature(mean temperature of 30.5, 23.5, and 16.5 ℃) on tobacco growth alkaloid content and nicotine metabolism. The results showed that, different temperature influenced tobacco growth, higher temperature(30.5 ℃) and lower temperature(16.5 ℃) treatment inhibited the growth tobacco plants. Alkaloid content and nicotine metabolism-related gene expression changed under different growth temperatures in tobacco plants. The higher temperature treatment lowered nicotine, anatabine, anabasine and nornicotine content in roots, stems and leaves; on the other hand, lower temperature treatment raised the alkaloid content in root and stem of tobacco plants, and medium temperature treatment made leaves maintain the highest alkaloid content.A de novo assembly of whole transcriptome(including root and leaf) was performed to act as a reference, which yielded a total 178704 contigs, and 83061 unigenes, and the average length of contigs was 627 bp, the average G+C content was 43.25 %. Functional annotation and classification of unigene revealed that 83,061 unigenes anotated to the COG of 25 possible functional family. The main functions involved in five categories, including: general function, transcription, replication, recombination and repair, signal transduction mechanisms and posttranslation modification, protein turnover, chaperones. RNA-seq and qPCR results have good linear correlation.Nicotine metabolism-related gene clustering analysis showed that the higher temperature lowered the 7 nicotine metabolism-related gene expression, medium and lower temperature incresed the gene expression. Higher temperature could quickly stimulate the synthesis of nicotine and nicotine translocation to the leaves; medium temperature was beneficial to the long lasting accumulation of nicotine, the accumulated amount is higher than the higher and lower temperatures; lower temperature inhibited the nicotine translocation. 2. Effects of different growth temperature on alkaloids content and nicotine metabolism of tobacco plant at different growth stagesTo investigate the effects of different growth temperature on alkaloid content and nicotine metabolism in tobacco leaves at different growth stages, the tobacco cultivar‘Yunyan 87’was used as experimental material, and different growth temperature was simulated in artificial climate chambers similar to the temperatures in Jiangchuan Yunnan, Zunyi Guizhou, and Xiangxian Henan during the transplanting to resettling stage, resettling to squaring stage and mature stage of ‘Yunyan 87’ plants. The results indicated that the growth temperature treatments simulated to the above-mentioned three regions tobacco nicotine content had increased, compared with the blade, the higher nicotine content pre-roots content, then content is more stable, anatabine and anabasine and nornicotine content and nicotine content is consistent with trends with prolonged tobacco growth and development stages.In general, different growth temperature all could influence nicotine content and gene expression to some extent in tobacco plant at different growth stages. Compare to other growth stages, the temperature at mature stage demonstrated the most significant effects on nicotine content. Xiangxian, which had higher growth temperature than the other two regions, was more suitable for nicotine content in tobacco plant. These results explain why tobacco leaves from these three regions have great difference in tobacco flavor style based on nicotine content to some extent. 3. Effects of different growth temperature on photosynthesis and plastid pigment catabolism of tobacco leaves at different growth stagesTo investigate the effects of different growth temperature on photosynthesis, content of plastid pigments, enzyme activities and gene expression of plastid pigment catabolism in tobacco leaves at different growth stages, the tobacco cultivar ‘Yunyan 87’ was used as experimental material, and different growth temperature was simulated in artificial climate chambers similar to the temperatures in Jiangchuan Yunnan, Zunyi Guizhou, and Xiangxian Henan during the transplanting to resettling stage, resettling to squaring stage and mature stage of ‘Yunyan 87’ plants. The results indicated that the growth temperature treatments simulated to the above-mentioned three regions had similar effects on photosynthetic rate, content of chlorophyll and carotenoid, and activities of metabolism related enzymes with prolonged tobacco growth and development stages, which firstly showed an lower level at early growth stage, then rise at middle growth stage, and gradually decline at mature stage, like a parabolic type. In general, different growth temperature all could influence photosynthetic rate, content of plastid pigments, activities of metabolism related enzymes and gene expression to some extent in tobacco leaves at different growth stages. Compare to other growth stages, the temperature at mature stage demonstrated the most significant effects on photosynthetic rate and content of plastid pigments. Xiangxian, which had higher growth temperature than the other two regions, was more suitable for photosynthesis and accumulation of plastid pigments in tobacco leaves. In addition, the temperature simulated to Zunyi was also suitable for carotenoid accumulation. These results explain why tobacco leaves from these three regions have great difference in tobacco flavor style based on photosynthesis and plastid pigment catabolism to some extent. |
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