Effects Of Light-induced D1 Dephosphorylation And Disaggregation Of D1 Adducts On D1 Protein Degradation In Photoinhibited Spinach Leaves

Visible light is essential for photosynthesis as source at energy. Howerer, excessive exposure of plants to light causes significant damage to photosynthesis machinery. When the light energy absorbed by chlorophyll is beyond to what photosynthesis could utilize, the light-induced inactivation of photosynthesis, called photoinhibition occurred. The major target of photoinhibition is photosystem II (PSII) on which photoinhibition make photosynthetic efficiency decreased, electronic transportation blocked and reaction center protein Dl photodamaged. Recovery of this photoinhibition is a complicate but orderly course, including degradation of photodamaged D1, synthesis and assembly of new one, etc.Using lincomycin to block the replacement of new synthetic Dl protein into photodamaged one, the spinach leaves was exposed to highlight, giving rise to photoinhibition before the thylakiod membranes were isolated. Urea-SDS-PAGE electrophoresis was introduced to separated different subunit proteins on membranes. Westen immunoblotting with Dl antibody and an approach detecting thylakiod phosphorylated proteins were used to check Dl proteins of different forms, Quantitive scranner to count abundances of proteins and fluorometry to detect the maxmin fluorescence (Fm) of chlorophylls and influorescence of proteins. The results show that: photoinhibition treatment on leaves (1) give rise to decrease of quantity of chlorophylls' Fm but (2) little change of influorescence of proteins on thylakiod membrance. (3) photoinhibition induced Dl to be phosphorylated and aggregated respectively with CP43 and D2, forming the aggregators of 7o kD and 65 kD. (4) phosphatase treatment on thylakiod membrance decrease the abundance of Dl aggregators. From above, we indicate that: photoinhibition cause chlorophyll an"bleak" while influorecsence of proteins on thylakiod membrances has no prominent response to it. What's more, photoinhibiton induce D1 protein phosphorylated and aggregated, forming the aggregators with phosphorylated D1.On study of the lowlight-dependent recovery of photoinhibited leaves, our figure also showed that: (1) the abundances of phosphorylated Dl (P-Dl),P-Dl's aggregators and total Dl proteins have little response to dark treatment of photoinhibited leaves whereas they show great decrease in exposing the leaves on lowlight.(2) Although both the amounts of P-D1 and its aggregators reduced by lowlight treatment, their irradance-dependent kinetics seem to be different to each other from which we predict decrease of Dl aggregators was privious to that of P-D1 while the decrease of dephosphorylated Dl followed that of P-D1. (3) treatment of NaF,a common inhibitor of phosphatasescarried out while light-induced recovery can not prevent Dl aggregators from being deaggregated but inhibit P-D1 dephosphorylated and dephosphorylated Dl degradated. From above, we can indicate: in lowlight-induced recovery, aggregators of P-D1 at first be deggregated and then P-D1 dephosphorylated which degradation of dephosphorylated D1 followed.In addition, changed on maximin fluorescence (Fm) in chlorophyll and emissive influorescence (Fem) on thylakiod membrance proteins were examined in lowlight-dependent recovery with or without NaF treatment. Our figures manifest that: (1) the quantity of the chlorophyll's Fm has a transcient reduce and subsuquent increase behavor in the recovry while that of Fem of membrance proteins excited at 278nm and 295nm show an direct increase in this process. (2) compared with control sample, NaF treatment can reduce the quantity of both chlorophyll's Fm and membrance proteins' Fem ecited at 278nm and 295nm. We confer NaF treatment may inhibit the recovery of chlorophyll's capacity of electronic transportation and effect the change of the influorescence of membrance proteins under the lowlight.