Effects Of Dark Treatment And UV-B Radiation On The Energy Transfer Process Of Chloroplast

Under different light condition,photosynthetic energy transfer process of plant performed differently according to the changes.Most plants turned etiolated and present some abnormal characteristics with dark treatment,photosynthesis of plant can't work normally at this condition.Moreover,enhanced UV-B radiation destroyed the photosynthesis apparatus of organism,restrain the electron transfer of photosynthesis,and prohibit photosynthesis.This study focus on that under the two light adversities:enhanced UV-B radiation and dark condition,study the photosynthetic energy transfer and utilization process of plant,and analysis the physiological and biochemical characteristics of etiolated seedlings.In order to investigate the effect of different light environments on plants and the adaptation mechanism of plants to different light environments.Using steady-state fluorescence spectrum to detect the thylakoid membrane of etiolated maize seedling and photosystemⅡ(PSⅡ) of spinach under enhanced UV-B radiation,discuss the energy transfer process between pigment-protein complexes which absorb light energy.And analyse the physiological and biochemical index such as photosynthetic pigments,MDA content,soluble protein content and antioxidant enzymes activity of etiolated maize seedlings, investigate physiological and biochemical characteristics of maize seedlings under dark condition.The following are the result from this experiment:Excitation spectra showed that light captured by chlorophyll of etiolated maize seedlings which grew in the dark can not be effectively excited and transferred to the reaction center of PSⅡ.Emission spectroscopy revealed that the efficiency of light-harvesting chlorophyll in PSⅡantenna system of thylakoid membrane of etiolated seedlings was declined,light can not be effectively transfer to PSⅡreaction center,so the fluorescence emission intensity of reaction center is relatively lower.Deconvolution analysis was employed to investigate the fluorescence emission spectra of T which under dark condition and CK which excited by 436nm,473nm and 507nm.Results showed that energy transfer pathways in thylakoid membranes of etiolated corn seedlings were altered,the energy assignment between PSⅡand PSⅠwas changed,and intensity of fluorescence was also decreased.Analyse the steady-state fluorescence spectrum of PSⅡof spinach under UV-B radiation,it was found that even very low radiation dose(15μw.cm^-2) and shorter irradiance time(30min) of direct UV-B irradiation could lead to clearly fluorescence quenching of PSⅡ,and simultaneously,energy transfer pathways in antenna system was also altered by direct UV-B irradiation.However,if plants were irradiated under UV-B for 7 days,no fluorescence quenching of PSⅡwhich separated from leaves of irradiated plants was detected.Short-term direct radiation changed the pathway which initially excited by Chlαmolecules,but these changes did not happen in the pathway carried by Car obviously.In addition,both long-term indirect and short-term direct UV-B radiation could change the energy assignment between PSⅡand photosystemⅠ(PSⅠ).Study on the etiolated maize seedlings under dark condition by determining physiological and biochemical characteristics.Results showed that compared with the maize seedlings grew in filed condition,the content of chlorophyll a,chlorophyll b,and carotenoid in the etiolated seedling decreased,especially the content of chlorophyll a decreased sharply,and the MDA content enhanced.Meanwhile,the etiolated seedling enhanced the antioxidant enzymatic activities(SOD,POD and CAT) and increased the soluble protein contents.The results indicated that synthesize of chlorophyll a was affected and cell lipid membrane turned peroxidation,so etiolated maize seedlings improved the capability of eliminating active oxygen species and alleviated the damage to photosynthetic organization.To sum up,the energy can not effectively transfer to the reaction center under dark condition, meanwhile different wavelengths of lights changed their energy transfer channels under UV-B radiation,especially the path of energy transfer changed in the antenna system,and the energy distribution among PSⅠand PSⅡchanged under dark condition and UV-B radiation.The results of this study will improve the understanding and awareness of the energy process in photosystem of plants under different light conditions.