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Biosynthesis of P700-Chlorophyll a Protein Complex, Plastocyanin, And

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Biosynthesis of P700-Chlorophyll a Protein Complex, Plastocyanin, And Plant Physiol. (1986) 81, 60-66 0032-0889/86/81 /0060/07/$0 1.00/0 Biosynthesis of P700-Chlorophyll a Protein Complex, Plastocyanin, and Cytochrome b6/fComplex' Received for publication September 12, 1985 and in revised form December 18, 1985 TERUHIRO TAKABE*, TETSUKO TAKABE, AND TAKASHI AKAZAWA Department ofChemistry, Faculty ofScience and Technology, Meijo University, Tenpaku, Nagoya 468, Japan (Teruhiro Takabe); and Research Institutefor Biochemical Regulation, School ofAgriculture, Nagoya University, Chikusa, Nagoya 464, Japan (Tetsuko Takabe, T.A.) ABSTRACT ofseveral subunit components (4, 16, 17, 23). The subunit I (60- 65 kD) is comprised of reaction center Chl (P700) and directly Changes in the amount of P700-chlorophyll a protein complex, plas- involved in the photochemical reaction (23). Although the func- tocyanin, and cytochrome b6/f complex during greening of pea (Pisum tion ofthe small subunits is largely obscure, it has been postulated sativum L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare that they have a role as electron acceptors of P700 and/or L.) leaves were analyzed by an immunochemical quantification method. structural components of the protein complex (4, 12). Recently, Neither subunit I nor II of P700-chlorophyll a protein complex could be Nechushtai and Nelson (18) have reported that a significant detected in the etiolated seedlings ofall three plants and the accumulation amount of subunit I is present in the etiolated seedlings of oat, of these subunits was shown to be light dependent. On the other hand, a bean, and spinach and its amount does not significantly change small amount of plastocyanin was present in the etiolated seedlings of all during greening, whereas the small subunits of P700-Chl a pro- three plants and its level increased about 30-fold during the subsequent tein complex accumulate only after those plants are illuminated. 72-hour greening period. Furthermore, cytochromef, cytochrome b6, and On the contrary, the absence ofsubunit I in the etiolated seedlings Rieske Fe-S center protein in cytochrome b6/fcomplex were also present of barley has been reported by Viering and Alberte (27). The in the etiolated seedings of all three plants. The level of each subunit effects of light on the biosynthesis of subunit I reported by these component increased differently during greening and their induction two groups are clearly different. Moreover, relatively few workers pattern differed from species to species. The accumulation of cytochrome have studied the synthesis of the small subunits of P700-Chl a bd/fcomplex was most profoundly affected by light in pea leaves, and the protein complex. We have studied the biosynthesis of large and levels of cytochrome Jf cytochrome b6, and Rieske Fe-S center protein small subunits of P700-Chl a protein complex during greening increased during greening about 10-, 20-, and more than 30-fold, respec- using other plant species. tively. In comparison to the case of pea seedlings, in wheat and barley Most biochemical studies on the accumulation of plastocy- leaves the level ofeach subunit component increased much less markedly. anin, Cytfl and Cyt b6 during greening have been performed by The results suggest that light regulates the accumulation of not only the spectroscopic methods (3, 7, 8, 10, 19). Previous results have chlorophyll protein complex but also the components of the electron shown that in the dark-grown bean leaves, only a very small transport systems. amount of Cyt fand b6 is present and a marked accumulation starts upon illumination (7). In contrast, dark-grown barley leaves contain a large amount of Cytfand b6 and there is little increase upon illumination (3, 8, 10, 19). In addition to Cyt f and b6, it is known that Cyt b6/fcomplex contains a Rieske Fe- S center protein and a 17 kD protein ofunknown function (13). Dark-grown higher plants are incapable of photosynthesis, The biosynthesis of Rieske Fe-S center protein and 17 kD primarily because they lack Chl and some polypeptides essential polypeptide during greening has not been studied. We have for the photosynthetic reactions (6). Upon illumination ofdark- measured the levels of above described proteins during chloro- grown plants, the synthesis of Chl and previously missing poly- plast development in pea, wheat, and barley by using an immu- peptides occurs together with the induction of photosynthetic nochemical quantification method (25). For this study, specific activities. antibodies raised against subunits I and II ofP700-Chl a protein The expression of both nuclear and chloroplastic genomes is complex, plastocyanin, Cyt f Cyt b6, and Rieske Fe-S center required to achieve light-regulated chloroplast development. The protein were used throughout. biosynthesis of light-harvesting Chl a/b protein associated with PSII and ribulose 1,5-bisphosphate carboxylase has been exten- MATERIALS AND sively studied (2, 5, 20, 26). The increased formation of these METHODS proteins occurring upon illumination of dark-grown plants is Plant Materials. The pea (Pisum sativum L.), wheat (Triticum partly due to the increase in levels ofthe corresponding mRNAs aestivum L.), and barley (Hordeum vulgare L.) seeds were soaked (2, 5, 20, 26). In contrast, there is a paucity of information in tap water overnight and planted in vermiculite. Pea seedlings concerning the biosynthesis of P700-Chl a2 protein complex, were grown in darkness at 20°C, and both wheat and barley plastocyanin, and Cyt b6/fcomplex. seedlings were grown at 28°C. The period of etiolation was 12 d The P700-Chl a protein complex in higher plants is composed for pea, 10 d for wheat, and 8 d for barley. At the end of these periods, the plants were illuminated with tungsten lamps provid- ' Supported in part by a Grant-in-Aid for Scientific Research from the ing 10 W/m2. After exposure to light for various times, apical Ministry of Education, Science and Culture ofJapan. buds approximately 2 cm long of pea and the upper 4 to 5 cm 2 Abbreviation: P700, reaction center chlorophyll of photosystem I. of primary leaves of wheat and barley were harvested and used 60 BIOSYNTHESIS OF CHLOROPLAST PROTEINS 61 for protein extraction. Electron paramagnetic resonance spectra were made using a Protein Extraction. Seedlings (2 g) were frozen in liquid N2, JEOR JES-FE 1 XG X band spectrometer with an Oxford Instru- powdered by means of pestle and mortar, and further homoge- ment liquid helium cryostat and variable temperature system. nized using 2 ml of 50 mM Tris-HCl (pH 8.0) buffer containing Microwave power and temperature for electron paramagnetic 0.2 M sucrose, 10 mM NaCl, 0.1% (w/v) NaN3, and 1 mM resonance spectra were 5 mW and 13 K, respectively. Spectro- phenylmethylsulfonyl fluoride. The homogenate was filtered scopic method to estimate the contents of Cyt f and b6 in the through two layers of Miracloth (Calbiochem) and used as the membranes was carried out using a Hitachi 557 double beam total protein fraction of leaves. The membrane and soluble spectrophotometer according to the procedure ofLeto and Miles protein fractions of leaves were prepared by centrifugation ofthe (15). total fraction for 5 min at 15,800g. Each fraction was frozen and Electrophoresis was carried out usually on 13% (w/v) acryl- stored at -80°C until analyzed. amide-SDS gels according to Laemmli (14). Proteins and hemes Protein Purification and Antibody Preparation. The P700-Chl were stained with Coomassie brilliant blue R-250 and 3,3',5,5'- a protein complex from spinach chloroplasts was purified as tetramethylbenzidine/hydrogen peroxidase (24), respectively. previously described (23). The photochemically active reaction Protein was determined according to the method of Lowry and center protein containing only subunit I was prepared from the Chl was determined according to Arnon as previously described. purified P700-Chl a protein complex as previously described (23). The polypeptides of subunits I and II of P700-Chl a protein RESULTS complex were prepared by electroelution from polyacrylamide gels after SDS-electrophoresis of the purified reaction center Protein Isolation and Antibody Preparation. Polypeptides of protein and P700-Chl a protein complex, respectively. Cyt b6 and Rieske Fe-S center protein were isolated from the preparation of native Cyt b6/fcomplex as described under "Ma- Cyt b6/fprotein complex from spinach was purified according terials and Methods." The absorption spectrum of the Cyt b6/f to the method of Hurt and Hauska (13) after a minor modifica- complex preparation was essentially the same as that reported by tion. After fractionation by (NH4)2SO4, Cyt b6/f complex was Hurt and Hauska (13) (data not shown). The specific activity of applied to a Sephacryl S-300 column (90 cm x 3 cm2) equili- plastoquinol-plastocyanin oxidoreductase was high (about 10 brated with 10 mm Tris-HCl (pH 8.0) and 0.05% (v/v) Triton .umol-nmol-'.h'). The electron paramagnetic resonance spec- X-100. Fractions rich in Cyt b6/fcomplex were concentrated by trum of the purified Cyt b6/fcomplex showed the characteristic ultrafiltration (Millipore Immersible CX-10) and applied to the of Rieske center same column once again. Cyt b6 and Rieske Fe-S center proteins signal (g= 1.89) Fe-S protein (data not shown). were prepared by the electroelution of a polyacrylamide gel after The polypeptide composition of the purified Cyt b6/f complex tested by SDS-PAGE is presented in Figure 1 track 1. The four SDS-electrophoresis of the purified Cyt b6/fcomplex. Cyt fand main bands of 33, 23, 20, and 17 kD can be seen by Coomassie plastocyanin were purified from Brassica komatsuna and spin- blue staining. Two heme-associated bands of 33 and 23 kD were ach, respectively, as previously described (21, 22). identified as Cyt fand b6, respectively (Fig. 1, track 2).
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