Effects Of Enhanced UV-B On The Phosiology And Quality Of Flue-Cured Tobacco Leaves

Ultraviolet(UV), a major component of the sunlight reaching the Earth, has a significant effect on the Earth’s environment. In recent years, the use of chlorofluorocarbons(CFCs) by human beings has taken a heavy toll on the ozone layer, leading to a increase of UV-B radiation. This becomes one of the most serious environmental problems. Present studies about effects on plants by increased UV-B radiation intensity have focused on wheat, corn, rice, soybean, cassava and other crops. Results showed that, to some extent, increased UV-B influenced crops’ growth and development, morphology, physiology and biochemistry, and biomass. Tobacco, one of the important economic crops, ranks first by its annual output for the world. Leaves, as the major target of tobacco’s harvest, is a direct part receiving UV-B radiation. The pigment (chlorophyll, carotenoids) and their degradation products are the most important flavor matters in tobacco leaves, so the content of them directly determine the quality of flue-cured tobacco. As received UV-B radiation changes, the content of plastid pigment in leaves varies. This preliminary study through greenhouse and field experiment is to investigate the effects by different UV-B radiation intensity, not only on flue-cured tobacco’s growth and parts of physiological metabolism, but on the metabolism of plastid pigment in leaves and the activity of related enzymes during flue-cured tobacco’s growth and development. The results will provide important information about flue-cured tobacco production.1. Pot experiments were conducted to study the effects of different UV-B radiation(ordinary light,8.71±2.13μ·Wcm-2,24.00±4.06μW·cm-2) on growth, plastid pigment content, malondialdehyde (MDA) content, proline content, UV-absorbing compounds and flavonoid content in flue-cured tobacco(Nicotiana tabacum L. K326) seedling. The results showed that:enhanced UV-B radiation inhibited the growth of flue-cured tobacco seedlings, and also reduced the dry weight; chlorophyll a, chlorophyll b and total chlorophyll contents had the same trend as growth and weight. And the differences reached significant level. While, the carotenoid content decreased slightly by enhanced UV-B radiation. However, enhanced UV-B radiation had a positive effect on malondialdehyde, which is the decomposition product of polyunsaturated fatty acids (PUFA) of biomembranes; Proline and flavonoid as natural osmotic properties, the contents also has been increased in tobacco leaves. Therefore, we can draw conclusion that UV-B radiation inhabit the growth of tobacco seedlings.2. By investigating flue-cured tobacco (Nicotiana tabacum L. Yunyan 87) through field experiments, the UV-B radiation’s effects on chlorophyll, carotenoids, chlorophyllase activity and the lipoxygenase activity were studied during the growth and development period. Results showed that:with the treatment of increased UV-B radiation, contents of chlorophyll,β-carotene and lutein in tobacco leaves were higher than those of the control. Meanwhile, chlorophyll enzyme changed greatly with its activity lower than that of the control in early processing period and higher than that of the control at later time. The change of lipoxygenase enzyme activity in treated leaves was consistent with that of the control. And the lipoxygenase enzyme activity was higher in treated when measured at the 20th day and 70th day of treatment.Increased UV-B radiation had adverse effects on the yield, the product value, the ratio of the top class and the middle class of tobaccos and caused a great loss on the economy interest. Also, Increased UV-B radiation affected the contents of aroma in flue-cured tobacco leaves. Neophytadienewas not sensitive to UV-B radiation while the total content of volatile aroma component increased. The UV-B radiation had no effect on nonvolatile organic acids, however, the content of higher fatty acids decreased. The amount of arotenoid and degraded compounds of carotenoid、maillard reaction products and aromatic amino acids metabolism products in flue-cured tobacco leaves significantly increased after the treatment of the UV-B radiation.