Study On Characteristics And Activation Of Photosystem Ⅱ Particles In Plants

Photosystemâ…¡(PSâ…¡) was compounds of chromoprotein in the thylakoid membrane.PSâ…¡absorbed light, catalysed photoinduction and water splitting. The basal units of PSâ…¡were PSâ…¡-LHCâ…¡supramolecular compounds which were made up of outer antenna proteins(LHCâ…¡) and PSâ…¡core complex. This kind of structure ensured the fast and effective transferof the energy which was absorbed by the LHCâ…¡, which was source of oxygen evolving inphotosynthesis as well as beginning of electron transport chain. Therefore, it has greatsignificance to study on PSâ…¡. In this paper, Spinacia oleracea L., Betula platyphlla, Morusalba, et al. were chosen as materials, the characteristics and activation of photosystemâ…¡particles in higher plants were investigated by SDS-PAGE and chlorophyll fluorescenceanalysis technique. On the other hand, using Betula platyphlla as experimental material treatedwith drought, high temperature and high light stress respectively, the different characteristics ofphotosystemâ…¡particles in higher plants under stress were investigated and analyzed toelucidate photosynthetic mechanism.from PSâ…¡. The results are as follows:(1) The quantity of thylakoid membrane and PSâ…¡particles that could be prepareddecreased significantly with the time of high temperature, drought or high light stress. Afterexposure sudden to high temperature stress for 36 hours, the quantity of thylakoid membraneand PSâ…¡particles were reduced by 65% and 71% respectively. At the same time, thepreparation of thylakoid membrane and PSâ…¡particles were less affected by high temperatureand high light stress. It suggested that this result was possibly caused by nonsensitivity of outerantenna proteins (LHCâ…¡) and PSâ…¡core complex in leaves of Betula platyphlla to the lightstress. If duration of stress time was lengthened, the quantity of prepared thylakoid membraneand PSâ…¡particles will decrease, which is proved in the future.(2) The polypeptide compositions of PSâ…¡core complex were degraded to different extentunder drought, high temperature, or high light stress. The contents of D₁, D₂, 29 kD, CP43,CP47 decreased significantly. Therefore, contents of LHCâ…¡and inner antenna chromoproteincomplex in the chloroplast capturing and absorbing light in the plants under stress coulddecreased, and some proteins of absorbing and transferring light happened to degrade. Themore duration of stress time lengthened, the more these components degraded so as to destroyprotein composions drastically. The decrease of LHCâ…¡will influence adjustment ability ofexcited energy distribution between two photosystems. The balance distribution was necessaryinner microenvironment for plants to maintain high photosynthesis efficiency. So thephotoinhibition happened to a certainty under the stress.(3) The Fv/Fm, Fv, qP,ΦPSâ…¡in leaves of plants were reduced by 6.8%, 41.7%, 66.5% and 71%, respectively under 13 d drought stress. The capacity of the PSâ…¡plastoquinone pooldiminished under drought stress, so PSâ…¡potential activity was restrained. Drought directlyinfluenced the electron transport and CO₂ assimilation progress. Drought interdicted theelectron transport from plastoquinone to P700, so the activation of the whole electron transferfelled, qP reduced by 50.8% after being treated by high temperature an high light stress. Thefast reduction of qP showed the inhibition of electron current to the PSâ…¡reaction center. Thehigh temperature reduced the quotient of light absorbed by the antenna pigment to processphotochemistry electron transfer.(4) The Pinus Koreaiensis could prepare much more PSâ…¡particles than Morus alba andSpinacia oleracea L. or Betula platyphlla. The PSâ…¡particles of Pinus koreaiensis werecomposed of proteins 15 kD,17 kD, 24 kD, D₁, D₂, CP43, CP47, 98 kD; The PSâ…¡particles ofMorus alba composed of proteins 15 kD, 17 kD, 19 kD, 24 kD, 26 kD, 29 kD, D₁, D₂, CP43,CP47 and 67kD. With a evolvement angle of view, the higher evolutionary status means, themore complicated oxygen evolution mechanism and less high molecular polypeptides. At thesame time, during the preparation of PSâ…¡particles, the different pants needs the differentquantity of Triton X-100. It showed that PSâ…¡complex with the different evolution status hadthe dissimilar combination with thylakoid membrane and polarization extent.