Influences Of Pre-spraying3Different Chemical Solutions On Ecophysiology Of Nicotiana Tabacum L. Seedling Under Chilling Stress

Tobacco（Nicotiana tabacum L.） is thermophilic crop which originates in subtropical. It will delay and decrease germination of tobacco seeds and cause slow growth of seedling or flowering earlier if the temperature is below12℃. Lower temperature at early spring affect growth and development of Flue-cured tobacco seedling and yield and quality of Flue-cured tobacco leaves finally in southern tobacco cultivated area. Previous researches found that spraying with exogenous chemical substances can improve the cold resistance of plants. Hence, it is very important to select suitable exogenous chemicals increasing flue-cured tobacco seedling cold resistance, which help to reduce production problems caused by low temperature stress.In this study, Msk326and Yunyan85, which were planted widely in southwest tobacco region, were used as experimental materials to study ecophysiology of tobacco seedling under chilling stress after pre-spraying different chemical solutions （CaCl2, DMSO, SA）. the experiment was conducted with low temperature8℃for72h. There are two controls without praying exogenous chemicals solutions, one is low temperature with8℃, and the other is normal temperature with25℃for72h. Some physiology parameter, such as photosynthetic index, contents of MDA and so on, were measured. The result is followed as below:1. For low temperature controls （CK2） of Msk326and Yunyan87, net photosynthetic rate（Pn）, intercellular CO2concentration （Ci）, transpiration rate （Tr）, stomatal conductance （Gs） and chlorophyll relative content were significantly lower than those in normal controls （CK1） of Msk326and Yunyan87; Activities of catalase （CAT） and peroxidase （POD） of low temperature control （CK2） were significantly decreased as well as contents of soluble sugar decreased, however, contents of malondialdehyde （MDA） and free proline increased for Msk326and Yunyan87.2. Pre-spraying0.5%-2.0%CaCl2solutions enhanced net photosynthetic rate（.Pn）, intercellular CO2concentration （Ci）, transpiration rate （Tr）, stomatal conductance （Gs）, chlorophyll relative content, and activities of catalase （CAT） and peroxidase （POD） for Yunyan87and Msk326under low temperature stress. There were better result when concentrations of CaC1₂solution were1.0%-1.5%, in which1%CaC1₂solution could significantly improve the photosynthesis, raised activities of catalase（CAT） and peroxidase（POD） and contents of soluble sugar and proline of Flue-cured Tobacco Seedlings under low temperature stress, meanwhile, decreased contents of malondialdehyde （MDA） of Yunyan87and Msk326.3. After Pre-spraying0.05%-0.35%dimethyl sulfoxide （DMSO） solutions, photosynthetic indexes, activities of catalase （CAT） and peroxidase（POD）, contents of malondialdehyde （MDA）, soluble sugar and proline reached significant difference than those of low temperature control （CK2） except stomatal conductance （Gs）.0.25%-0.35%dimethyl sulfoxide （DMSO） solution could effectively improve the activities of CAT and POD, the contents of chlorophyll, soluble sugar and free proline, and reduce contents of MDA for Yunyan87and Msk326under low temperature stress. However, photosynthesis parameters of flue-cured tobacco seedlings were still significantly lower than normal control （CK1）. Pre-spraying0.25%DMSO solutions could alleviate effectively chilling damage of flue-cured tobacco seedlings with the best result.4. After pre-spraying0.5-2.0mmol/L salicylic acid （SA） solution, activities of catalase （CAT） and peroxidase （POD）, contents of soluble sugar and proline under low temperature stress increased while malondialdehyde （MDA） content decreased for Msk326,Yunyan87. There were better result when concentrations salicylic acid （SA） solution were1.0mmol/L-1.5mmol/L, especially, l.Ommol/L salicylic acid （SA） solution could significantly improve cold-resistance of flue-cured tobacco seedlings under low temperature stress, and lessened damage of chilling stress forYunyan87and Msk326.5. It is important to select suitable concentration range if improving cold resistance of tobacco seedling through pre-spraying three exogenous chemical substances. Functions of cold resistance under suitable concentration for three exogenous chemical substances are in turn:CaCl₂> DMSO> SA. In addition, Msk326is more sensitive to the low temperature than Yunyan87.