Study Of Different Light Quality On Physiological And Biochemical Effects Of Senescence In Flue-cured Tobacco Leaves

In order to investigate the mechanism involved in the different responses of flue-cured tobacco leaf senescence to light qualities,the interaction effects of different lights on endogenous hormones,membrane lipid peroxidation and quality indexes in the maturation of flue-cured tobacco leaves were investigated on field conditions by covering white?W?,yellow?Y?,red?R?,purple?P?and blue?B?polyethylene films above tobacco plants Yunyan 87?Nitcotiana tobacum L.?to obtain different quality lights as experimental material.The experiment which carried in the field.In order to provide support for improving the quality of tobacco leaf.In this paper,the main physiological changes in the process of tobacco leaf senescence,active oxygen metabolism,antioxidant metabolism and endogenous hormone changes were explored.The main results were as follows.1.After topping the plastid pigment in tobacco were entering degradation and transformation stage and decreased flatly in the early stage and fast latter.Compared with control,the content of chlorophyll a,chlorophyll b,total chlorophyll and carotenoid content of red light higher than that of under the white,and purple light and blue light treatment's total chlorophyll,chlorophyll a,chlorophyll band carotenoid content in tobacco leaves is lower than that of under the white.During the maturation and senescence proceccing of tobacco leaves,the red light inhibited the degradation of plastid pigment,purple and blue promotes degradation of plastid pigment in tobacco,pigment degradation rate during the whole degradation process in different light quality processing from big to small is as follows: the purple > blue >yellow >red >control.2.The red light treatment decreased the content of protein,in the contrast,purple light and blue light increased the content of protein.Light quality also have obvious influence on photosynthesis in tobacco leaves.The net photosynthetic rate?Pn?,intercellular CO₂ concentration?Ci?,the transpiration rate?Tr?and stomatal conductance?Gs?of tobacco leaves under red light and white light exhibit obvious double peak curve with midday depression.The diurnal variation of photosynthesis of yellow light,blue light and purple light appeared as single peak cuerve without midday depression.The transpiration rate and stomatal conductance presented a trendof synchronous change,first increased and then decreased.Intercellular CO₂ concentration showed high in the morning and evening,noon low trend.the overall photosynthetic performance of tobacco leaves under the different light quality condition was: red > white >yellow >blue >purple.3.Content of superoxide radical?O₂^-?? hygrogen peroxide?H₂O₂?and malondiadehyde?MDA?and relative conductivity increased gradually in tobacco leaves of all treatments during senescence process.Compared with control,the red light treatment reduced content of O₂-,H₂O₂ and MDA,and reduced the relative conductivity during the leaf senescence process,the content of O₂-,H₂O₂,MDA and relative conductivity were significantly higher under blue light and purple light than those under the control and other treatments.4.Compared with white light,red light increased the activities of superoxide dismutase?SOD?,catalase?CAT?in flue-cured tobacco leaves,and reduced the content of active oxygen in tobacco leaves during aging,and made the content of MDA at a relatively low level,thus delaying plant senescence.Blue light and purple light decreased the activity of SOD,POD and CAT in tobacco leaves,the content of MDA andreactive oxygen species was significantly higher than that of under the control and other treatments,accelerating the senescence of flue-cured tobacco leaves.5.Compared with control,red light could significantly increase the contents of cytokinin?CTK?and gibberellin?GA?,in contrast,abscisic acid?ABA?was reduced significantly.Blue light and purple lights had no impact on raising the content of CTK,but they inceared the content of ABA in tobacco leaves.The decline of auxin?IAA?content under blue light and purple light was earlier than that under red and yellow.The results revealed that the IAA,CTK,GA protein levels of tobacco leaves were increased,whereas the contents of H₂O₂,MDA and ABA were reduced under red light treatment,that could delay aging of flue-cured tobacco leaves and improve the quality of tobacco leaves.