Effects Of Short-day Treatment At Seedling Stage On Early Flowering And Related Gene Expression In Tobacco

Tobacco is an important economic crop. Main planting areas of tobacco is high altitude mountains at southwest China. Tobacco can be influenced by environmental factors and field management, which lead to tobacco early flowering. Early flowering can severely reduces the yield and quality of tobacco. In order to research the effects of short-day at seedling stage on flue-cured tobacco floral bud differentiation and development in Chongqing, this experiment selected widely cultivated varieties. Yunyan 85, Yunyan 97 and Xingyan 1 as materials. Yunyan 97, Yunyan 85 and Xingyan 1 were treated with short-day (8h/d) and normal illumination (12h/d) as control for 30 days at seeding stage. There are main research results:1. T-microscope was used to detect tobacco differentiation process. The results showed that bud and flowering were related to short-day at seeding stage. Short-day caused the flower bud initiate early, comparing with the control. Both in the short-day and in the normal sunlight, the time of flower bud initiation of Yunyan 85 was the earliest, Yunyan 97 was the next, and Xingyan 1 was the last. This was the same as the field investigation of the time of bud and flowering. The time of flower bud initiation, bud formation and flowering in Xingyan 1 was 4 days earlier than control, while Yunyan 85 was 3 days earlier. In summary, Xingyan 1 was the most sensitive one to short-day, The sensitivity of Yunyan 85 was between Xingyan 1 and Yunyan 97 to short-day on flower bud differentiation and growth period.2. Short-day treatment at seedling stage could reduce the main agronomic traits of three varieties. Comparison agronomic traits of the varieties treated at short-day with ones at the normal sunlight, the plant height, the length of the longest leaf, the width of the widest leaf, the stem girth and the number of effective leaves of Xingyan 1 decreased 8.1%, 6.3%, 11.1%, 6.5% and 13.9%, respectively. They decreased 6.5%, 5.4%, 6.6%, 5.2% and 10.2% in Yunyan 85, respectively. While these traits of Yunyan 97 decreased 5.7%, 3.8%, 4.2%, 4.2% and 9.2% respectively. It indicated that the short-day treatment at seeding stage caused Xingyan 1 with the most decrease in the agronomic traits, Yunyan 85 with less decrease, and Yunyan 97 with lowest decrease.3. The present study showed that short-day treatment at seeding stage could reduce the internal quality of tobacco leaves at the middle and top position of plant. The results showed that the chlorine, nicotine and total nitrogen increased, potassium and reducing sugars decreased, which made the ratio of potassium/chlorine and coordination chemistry scores decrease. The chemical components of Xingyan 1 were most obvious reduced among three varieties, coordination chemistry scores in middle leaves and upper leaves were reduced 10.51 and 7.58. Yunyan 85 was the second, coordination chemistry scores in middle leaves and upper leaves were reduced 5.5 and 11.34. Yunyan 97 was lowest decrease, coordination chemistry scores in middle leaves and upper leaves were reduced 4.11 and 4.03.4. Through extracting total RNA of different period tobacco stem tips and detecting the expression of NtCO, NtFT, NtSOCl and NtLFY, it showed that short-day treatment at seeding stage could promote expression of these four genes, and increase relative expression of NtCO, NtFT, NtSOCl. These four genes promoted tobacco early flowering togetherr. The expression of NtCO was increased at first among these four genes, which expressed a lot after transplanting 14 days and caused expression of NtFT. The increase of NtFT’s expression result in NtSOCI’s expression increase. The expression of each gene showed attenuation trend after transplanting 35 days. The difference of NtLFYs expression in three varieties was weak,and NtLFY was still maintain a high level after flower bud differentiation.