A Study On Differently Expressed Proteins Of Thylakoid Membrane In Plant Adaption To Environmental Stresses

The effects of natural drought and salinity as well as progressive drought stress on physiological characteristics and protein components of thylakoid memebrane were studied by using blue native PAGE and Western-blot. Four ecotypes of reed, referred to as swamp reed (SR), dune reed (DR); heavy salt meadow reed (HSMR) and light salt meadow reed (LSMR) growing in the desert region of north-western China and potted maize under progressive drought treatment were used as experimental materials. The aim of the present study was to find the differential protein expression profiles of thylakoid membrane isolated from different ecotypes of reed in adapting to arid and saline habitats, which showed a transition tendency of photosynthetic pathway from C3 to C4. Besides, the effect of progressive drought treatment on the thylakoid membrane of the maize (Zea mays L.), a typical C4 model plantcomparative experiment was also observed. It is hoped that these experimental results obtained from different ecotypes of the same species in adaptation to natural extreme habitats as well as maize in response to progressive water deficit might help to our better understanding of photosynthetic regulation in plant's adaptation to natural drought and salinity. The main results are as follows:1. Gradient centrifugation with 30% and 80% percoll were used to isolate intactchloroplasts. Then the thylakois membrane was obtained by osmotically breaking the chloroplasts and centrifugating, which laid foundation for further analysis of thyalkoid membrane proteins.2. Effects of two different lysis bufferes which contained different concentrations ofDM and TritonX-100 during the solubilization of membrane proteins were tested.. The result showed that lysis buffer containing 2% DM was suitable one to soluble membrane proteins of three ecotypes 5%DM was suitable to DR.3. Drought and salt stress had significant effects on plant thylakoid membrane components. Compared with the swamp ecotype, the contents of ATPase/Cytb6f, CP43-less PS II, and LHC II monomer and trimer in the thylakoid membrane of three terrestrial ecotypes decreased.The protein profiles of above complexes in second SDS-PAGE which compared with the results published by other literates showed that the contents of Lhcb(1～3), Lhca(1～4) and the proteins of the PS react center, such as D1, D2, CP43, CP47, PsaA, PsaB, PsaD, PsaE, PsaF decreased in dune reed, except Lhcb1, which showed a higher level content in light salt meadow reed in comparison with the swampecotype. As far as the two terrestrial ecotypes were concerned, the effect of drought on thylakoid membrane components showed a more serious effect than that resulting from the salinity.4. Western-blotting tests showed that the contents of main protein complexes of PSII, light harvest complex Lhca(1～4) and Lhcb(1～6) in dune reeds and the contents of Lhca 4 and Lhcb(2～5) in salt meadow reed were less than those of the swamp ecotype, while PsaC, the major protein of the PS I, showed a higher level protein content in comparison with the swamp reed. As far as the two terrestrial ecotypes were concerned, effect of the drought on the thylakoid membrane was more serious than that resulting from the salinity.5. Under the drought condition, leaf water contents were decreased along with the decline in soil water contents. Chlorophyll fluorescence parameters derived from analyzing modulated chlorophyll fluorescence, such as such as Fv/Fm, Yeild and qP, showed a strong progressive drop on the days 3, 5, and 7 after water defitics application, showed a significant decreases in mize leaves in response to progressive water deficit. However, .qN showed a reverse trend. This implied that the declines in components of thylakoid membrane caused by water deficits and salinity might contribute to protect the photo synthetic apparatus against damage of excessive energy.6. Comparesd with the CK, the contents of PS I + LHC I complex, PSI, ATPase/Cytb6f, CP43-less PS II, LHC II monomer and LHC II trimer from the thylakoid membrane in stressed maize leaves decreased in varying degrees at 3, 5. and 7 days after water deficits treatment. The contents of all these six protein complexes could improve after rewatering for 3 days.