| The quality of tobacco leaves, which is largely constrained by eco-environment, is the main issue that researchers concern. Among all environmental factors, light is the most important player that affects plant growth and metabolism by regulating photosynthesis, morphogenesis, root development, metabolism, and gene expression.To better understand the effect of light on the quality of tobacco leaves and on tobacco seedling growth and development, latitudinal and vertical changes of solar spectral radiance in different tobacco planting region was analyzed, the change pattern of solar spectral radiance over tobacco development and its correlation with flavor component in tobacco leaves was studied. We also clarified the effect of monochromic light on tobacco leaves metabolism with varies LED, investigated how red and blue light developmentally and physiologically regulate tobacco seedling with hydroponics, and further studies the mechanism of how red and blue light regulate tobacco seedling lateral root development. Taken together, this study showed that:(1). Based on the measurements of solar spectrum radiation in 15 places including Tianzhu(Guizhou), Zunyi(Guizhou), Qianxi(Guizhou), Guiding(Guizhou), Kaiyang(Guizhou), Yuqing(Guizhou), Panxian(Guizhou), Weining(Guizhou), Daozhen(Guizhou), Linqu(Shangdong), Wulong(Chongqing), Wushan(Chongqing), Zhucheng(Shandong), Sangzhi(Hunan), Xunyang(Shanxi), the Characteristics of the solar spectrum were analyzed. The results showed that ultraviolet radiation accounts for 2.9%~10% of total solar radiation. The proportion of visible radiation and infrared radiation is 44.3%~48.9%, 44.7%~51.2% respectively. The proportion of ultraviolet radiation is the most instable one while the visible radiation proportion is the stablest. Ultraviolet radiation proportion is positively related to latitude and negatively related to altitude. On the contrary, blue light radiation is negatively and positively related to latitude and altitude respectively. There were no significant correlation between the stability of solar spectral radiation proportion and latitude, altitude. There wre no significant effect of latitude and altitude on total solar radiation. There was a significantly positive correlation between infrared radiation and total solar radiation while visible radiation was negatively related to it. There was a significantly negative correlation between ultraviolet radiation proportion and total solar radiation in most of the places.(2). To study the effect of the solar spectrum on aroma substances in flue-cured tobacco, we measured the radiation of solar spectrum after tobacco plants were transplanted into field in 19 tobacco planting regions. We also measured the aroma substance concentration in tobacco leaves of the corresponding place mentioned above and analyzed the canonical correlation between the solar spectrum radiation and aroma substance concentration. The results showed that: total solar radiation and spectroradio of the whole growth period in different observation sites are significantly different; the distributions of total solar radiation and spectroradio in different growth stages among the 19 observation sites were significantly different; the proportions of spectroradio in total solar radiation were different among these observation sites; there were significantly canonical correlations between all the solar spectrum radiation and aroma substance concentration except green ligh radiationt; strong correlationships were found between chemical concentrations and spectroradio in late mature period but none in the prematuration period; we also found significantly canonical correlation between chemical concentrations and the radiation of UV, red light in root-extended period and blue, red, infrared light in vigorous growth period.(3). Metabolite profiling of tobacco leaves(Nicotianatabacum L.) was performed to investigate the short-term responses to different light-emitting diode(LED) lights, UV-A(ultraviolet A), blue, green, yellow, red, white, by using non-targeted method based GC/MS and targeted method based on GC/FID and UPLC. Results showed that: 1) 68 GC/MS-stable metabolites were detected by non-targeted method and analyzed with multivariate analysis. In the PLS-DA score plot, tobacco leaf samples showed clear grouping in each light cultivating condition. 61 metabolites were identified in mass spectra library. Besides, 45 metabolites, mainly including organic acids, carbohydrates, TCA cycle intermediate metabolites and amino acids, showed significant differences among six treatments. HCA(Hierarchical Cluster Analysis) and heat map showed that differential metabolites can be divided into five groups, and there were significant differences among six treatments, especially for red and blue light. Except for the metabolites of group B, almost all other metabolites contents in tobacco leaves treated with red light were higher than that of blue. 2) Contents of solanesol, 3 alkaloids and 5 polyphenols were measured with targeted method. 4 alkaloids, including nicotine detected by non-targeted method, showed similar variation trend among all treatments, of which red and yellow light increased alkaloid accumulation significantly; kaempferol-3-O-rutinoside and rutin showed similar variation trend among 6 treatments, with lowest content under blue light and highest content under yellow light, nevertheless, 3 other polyphenols were differently affected by light qualities; aolanesol accumulation was significantly repressed by yellow light, but show highest content under blue light.(4). To provide the basis for the light condition optimization in tobacco seedling culture greenhouse, the effects of red and blue monochromatic light on tobacco seedling growth and development were studied with white light treatment as control. The results showed that red light increased the leaf area, fresh biomass, 1°and 2° lateral root numbers and root system superficial area significantly; stalk length of tobacco seedlings was in?uenced by light quality, i.e. promoted by blue light and suppressed by the red light while stalk thick was unaffected; white light increased content of chlorophyll and carotenoid, Pn and Gs. Blue light inhibited the photosynthesis probably by decreasing Gs, but red light inhibited photosynthesis by limitation of nonstomatal factors.(5). Light is an important environmental regulator of diverse growth and developmental processes in plants. However, the mechanisms by which light quality regulates root growth are poorly understood. We analyzed lateral root(LR) growth of tobacco seedlings in response to three kinds of light qualities(red, white and blue). Primary(1°) LR number and secondary(2°) LR density were elevated under red light(on days 9 and 12 of treatment) in comparison with white and blue light. Higher IAA concentrations measured in roots and lower in leaves of plants treated with red light suggest that red light accelerated auxin transport from the leaves to roots(in comparison with other light qualities). Corroborative evidence for this suggestion was provided by elevated DR5::GUS expression levels at the shoot/root junction and in the 2° LR region. Applications of N-1-naphthylphthalamic acid(NPA) to red-light-treated seedlings reduced both 1° LR number and 2° LR density to levels similar to those measured under white light; DR5::GUS expression levels were also similar between these light qualities after NPA application. Results were similar following exogenous auxin(NAA) application to blue-light-treated seedlings. Direct [3H]IAA transport measurement indicated that the polar auxin transport from shoot to root was increased by red light. Red light promoted PIN3 expression levels and blue light reduced PIN1, 3-4 expression levels in the shoot/root junction and in the root, indicating that these genes play key roles in auxin transport regulation by red and blue light. Overall, our findings suggest that three kinds of light qualities regulate LR formation in tobacco seedlings through modification of auxin polar transport. |
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