Effects Of Low Temperature On The Differentiation And Growth Of Tobacco Bud In Seeding Stage

Flower bud differentiation is correlated with initiation of leaves, flower bud differentiate early could transfer from vegetative to reproductive development, resulted in a few leaves, which is called early flowering. Tobacco is an important economic crop aiming to harvest leaves. Tobacco planted on mountain region usually influenced by low temperature and sunshine, resulted in tobacco with early flowering, low and poor leaves. In order to know the mechanism of low temperature affecting plant development and flower bud differentiation in tobacco, Yunyan 97, Yunyan 85 and Xingyan 1 were treated with low temperature (12 ℃) for 10 days at seedling stage, treating at normal temperature (28℃) were used as control. Yunyan 97 was derived from the cross between Yunyan 85 with CV87, Xingyan 1 with many leaves was selected from the offspring of Yunyan 85 via self-pollination. Yunyan 85 and Yunyan 97 had 18-22 leaves when harvest, while Xingyan 1 had more than 25, which was significantly more than Yunyan 85 and Yunyan 97.In the present study, in order to know the process of flower bud differentiation, the time of bud formation, flowering time, agronomic traits and chemical components in the leaves was detected by successively sampling of these three varieties. Genes expression correlated with flower bud differentiation was identified by RT-PCR. The results were as follows:(1) Low temperature caused the flower bud initiate early, comparing with the ones in the normal temperature via observing the stem meristem under stereomicrosco-pe. The time of flower bud initiation, bud formation and flowering in Yunyan 97 and Yunyan 85 was 5 days earlier than control, while Xingyan 1 was only 3 days earlier. The sensitivity of low temperature effects on flower bud differentiation was Yunyan 85 > Yunysn97> Xingyan 1.(2) Comparison agronomic traits and leaves biomass of the varieties treated at low temperature with ones at room temperature, the plant height, the length of the longest leaf, the width of the widest leaf and the number of effective leaves of Xingyan 1 decreased 5%,5.4%,9.1% and 6.3%, respectively. They decreased 7.5%,7.2%,1.2% and 9.4% in Yunyan 97, respectively. While these traits of Yunyan 85 decreased 10%, 10.7%,15.1% and 11.7%, respectively. It indicated that the low temperature caused Yunyan 85 with the most decrease in the agronomic traits, Xingyan 1 with lowest decrease, and Yunyan 97 with less decrease.(3) In the present study, nicotine, potassium, chlorine, reducing sugars, total nitrogen of the leaves at the middle and top position of plant were detected, and they were used to measure coordination chemistry scores. It showed that decrease of number of leaves was caused by low temperature, it resulted in the chlorine, nicotine and total nitrogen increase, potassium and reducing sugars decrease, which made the ratio of potassium/chlorine and coordination chemistry scores decrease. It indicated that the chemical components in Yunyan 85 were more sensitive than Yunyan 97 and Xingyan 1.(4)Specific primers were designed to detect the gene expression of flower bud differentiation via real-time PCR. Low temperature inhibited the expression of stem apex of NtFLC and promoted the expression of NtSOC1 and NtFT gene, while NtFLC gene inhibited the expression of NtSOC1 and NtFT. The expression of NtFLC was inhibited after low temperature treatment. After transplanting 14 days, the expression of NtFLC gene significantly up-regulated in the control tobacco stem tip of all varieties, the difference among treatments increased gradually and reached the maximum on 21 days after transplanting, then gradually disappeared at 35 days after transplanting. After low temperature treatment, the expression of NtSOC1 and NtFT gene increased gradually. At the same time, the difference among treatments increased gradually and reached the maximum after transplanting 21 days, then the difference in expression of NtSOCl gene among treatments decreased to balance after transplanting 35 days, while the difference in the expression of NtFT gene among treatments decreased to balance after transplanting 28 days. The variance of NtLFY gene expression in low temperature was lower than that of NtSOCl and NtFT gene.In all,1) low temperature of seeding stage could induce the tobacco plant flower early, influence the plant development; 2) low temperature of seeding stage could depress the plant growth, decrease leaves number, leaf area, and plant height, cause the chemical components become poor, with low coordination chemistry scores; 3) low temperature of seeding stage regulated flowering genes expression. For example, it depressed NtFLC gene expression, but overexpress NtSOC1 and NtFT gene expression, inducing tobacco flower early. However, NtLFY was not regulated by low temperature. The sensitivity of varieties by low temperature was:Yunyan 85 > Yunyan97 > Xingyan 1. In Xingyan 1, its leaves number was correlated with the less effect by low temperature.