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Location of Photosystem I and Photosystem II Reaction Centers in Different Thylakoid Regions of Stacked Chloroplasts

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Location of Photosystem I and Photosystem II Reaction Centers in Different Thylakoid Regions of Stacked Chloroplasts Volume 146, number 1 FEBS LETTERS September 1982 Location of photosystem I and photosystem II reaction centers in different thylakoid regions of stacked chloroplasts Bertil Andersson and Wolfgang Haehnel* Dept. of Biochemistry, University of Lund, PO Box 740, S-220 07 Lund, Sweden and * Lehrstuhl far Biochemie der Pflanzen, Abt. Biologie, Ruhr-Universitgit Bochum, ND-3, Postfach 10 21 48, D-4630 Bochum 1, FRG Received 7 July 1982 Photosynthesis Thylakoid organization Thylakoid subfractionation Membrane lateral heterogeneity Photosystem reaction centre Electron transport 1. INTRODUCTION rectly determined by measuring the light-induced absorbance changes of P700 and Q, respectively. Stacked chloroplast thylakoids are structurally The results present experimental evidence for the differentiated into the appressed regions of the suggested, extreme lateral heterogeneity in the lo- grana (partitions), and the non-appressed regions cation of the two photosystems, particularly by de- of grana end membranes, margins and stroma monstrating virtually no P700 in the appressed lamellae. This structural differentiation is also ac- grana partitions. companied by differences in function (cf. [1-3]). In early fractionation studies small stroma 2. MATERIALS AND METHODS lamellae vesicles highly enriched in photosystem (PS)I were separated from rapidly sedimenting Spinach leaves obtained either from a growth grana containing both PSI and PS2 [4]. This sug- chamber or from the local market were used to gested that the grana were the site for linear elec- prepare stacked chloroplast thylakoids as in [8]. tron transport by PS 1 and PS2 in close physical as- The thylakoids, suspended in 150 mM NaCI - sociation while stroma lamellae was mainly 50 mM sodium phosphate buffer (pH 7.4), were involved in PSI-mediated cyclic electron flow. fragmented by 2 passages through a Yeda press This view of thylakoid organization has been chal- [5,8] and centrifuged at 40 000 x g for 30 min. The lenged by the availability of a fraction enriched in supernatant material was spun down at 100 000 x inside-out vesicles shown to originate from the ap- g for 60 min yielding the Y-100 fraction. The pellet pressed grana partitions [5-8]. Analyses of this (Y-40) was suspended in 100mM sucrose - fraction with respect to photochemical activities [8] 10 mM sodium phosphate buffer (pH 7.4) - 5 mM and content of chlorophyll(Chl)-proteins [9] re- NaCI and passed twice through the press. These vealed a pronounced PSI depletion. Based upon membrane fragments were fractionated by aque- this, it was postulated that PS 1 is mainly excluded ous polymer 2-phase partition as in [5], yielding from the appressed grana regions into the non-ap- the T2- and B3-fractions. pressed regions thereby separated from most of For measurements, the vesicles were suspended PS2 which is concentrated in the appressed regions in 50mM Tricine-NaOH buffer (pH7.5) - [2,9,10]. This model implies linear electron trans- 10 mM KC1 - 5 mM MgCI2. Absorbance changes port between spatially separated photosystems in- of Q induced by Xe-flashes (t10-90 = 6 ~s) of sat- volving lateral shuttling of electron carriers be- urating intensity were monitored at 335 nm (band- tween the different thylakoid regions. width 4 nm FWHM) with a photomultiplier (Type Here the amount of PSI and PS2 reactions cen- 9818 QB), digitalized in a transient recorder (Bio- tres in the various thylakoid subfractions were di- mation) and averaged in a signal processor Published by Elsevier Biomedical Press 00145793/82/0000-0000/$2.75 © 1982 Federation of European Biochemical Societies 13 Volume 146, number 1 FEBS LETTERS September 1982 (Tracor). The wavelength of 335 nm was chosen rather than that at the maximum for Q'- (320 nm) to minimize superimposed plastoquinone absor- bance changes [11]. The differential flattening fac- % YPH tor at 335 nm determined as in [12] ranged be- tween 1.07-1.16 for the various particle prepara- E ..... : .... tions• The molar ratio of Chl/Q was estimated by i- using an extinction coefficient of 10.7mM -l • cm -1 for Q'-/Q at 335 nm [13]. Absorbance changes of P700 were measured as in [14]. An ex- tinction coefficient of 64 mM -1 , cm -1 was used z for P700 at 703 nm. Plastocyanin from spinach had , &A= 10-t, a ratio ofA278/A597 = 1.1. All measurements were .i"! carried out in a 1 × 1 cm cuvette at room tempera- I ture. \-~. B3 3. RESULTS z < • _ _ _ _ ~ .. ~,~,,~?.~.. :,~.~ The stoichiometry of the primary acceptor of u B PS2 (Q) and the PSI reaction centre chlorophyll (P700) was determined in 5 different thylakoid fractions. The starting Yeda press homogenate Y - I00 (YPH) was separated by centrifugation into a grana stack fraction (Y-40) and a stroma lamellae I I I I vesicle fraction (Y-100). The latter fraction con- 0 1 2 3 ms tained around 5-10% of the chlorophyll. After fur- TIME ther press treatment, the Y-40 fraction was sepa- rated by phase partition into two distinct Fig.l. Absorbance change of Q at 335 nm induced by a membrane populations, designated T2 and B3 short flash in different membrane fractions: (A) Yeda [5,8]. The latter was enriched in inside-out thy- press homogenate; (B) B3-fraction enriched in ap- lakoids shown to originate from the grana parti- pressed thylakoid regions; (C) Y-100 fraction from non- tions, and comprised around 20% of the Y-40 ma- appressed thylakoid regions. The standard reaction mix- ture contained 10.1 ~g Chl/ml and in addition 10 I~M terial while the remaining material (T2) consisted phenyl-p-benzoquinone. 200 signals were averaged at of right-sided thylakoids from both appressed and 5/~s/address with a repetition rate of 5 Hz. The dashed non-appressed regions [5-8]. line extrapolates the slow components of the absorbance change monitored for 50 ms (not shown). 3.1. Distribution of Q Fig.l shows absorbance changes at 335 nm of the Yeda press homogenate, Y-100 and B3 frac- nates from PS2 with impaired water splitting tions in presence of the lipophilic electron acceptor where Q is reoxidized via cyclic electron flow phenyl-p-benzoquinone. The amplitude of the B3- provided an electron acceptor is present [15,16]. material is much bigger compared to the starting For quantification the slow components are extra- material while the amplitude of Y-100 is close to polated to the beginning at the time of the flash the detection limit• In all fractions the absorbance (fig.l) to give the amplitude of the 2 fast compo- increase in the flash is followed by decay kinetics nents representing total Q in the thylakoid frac- with 2 fast components with respective half-times tion. The molar ratios of Chl/Q are given in table of - 100 and 600 ~s and considerably slower com- 1 after correcting the amplitudes for flattening ponents with 5 ms and longer halftimes. The effects [12]. The values of 380 and >8000 for the 600 ~ component represents Q reoxidation in in- B3- and Y-100 fraction, respectively, indicate an tact PS2 [11], while the 100/~s component origi- uneven distribution of PS2 reaction centers with an 14 Volume 146, number 1 FEBS LETTERS September 1982 Table 1 Distribution of Q and P700 in thylakoid fractions / derived from the different thylakoid regions / •.. / Fraction Chl/Q Chl/P700 Q/P700 Chl a/b E Yeda press 540 580 1.1 3.0 B " ...... B3*PC homogenate Y-40 510 665 1.3 2.9 W T2 570 515 0.9 3.2 < B3 380 1300 3.4 2.3 CD Y- 100 > 8000 240 < 0.03 6.2 0 m /~" Y - I00 The molar ratios of chlorophyll (Chl) to Q and Chl/ ,a 0 • / ? P700 were determined for all fractions from measure- / / ments as shown in fig.l and 2, respectively # <Z .1- u almost exclusive location of PS2 centers in ap- 10-3 pressed grana regions. 3.2. Distribution of P700 ON OFF Fig.2 shows the absorbance changes at 703 nm I 0 100 200 ms of the YPH, Y-100 and B3 material. During the TIME long flash P700 is fully oxidized. After the flash, reduced 2,6-dichlorophenolindophenol reduces total P700 + independently of the sidedness of the Fig.2. Absorbance change of P700 at 703 nm induced by membranes or the presence of plastocyanin [17,18]. a long flash in different membrane fractions: (A) Yeda Thus, the amplitudes can be used to calculate the press homogenate; (B) B3-fraction in the presence of Chl/P700 molar ratios of the various thylakoid plastocyanin (PC); (C) B3-fraction; (D) Y-100 fraction. fractions (table 1). The high P700 content in the Y- The standard reaction mixture with 9.9 ~tg Chl/ml con- tained in addition 20 ~M diuron (DCMU), 0.1 mM 2,6- 100 fraction is in agreement with previous mea- dichlorophenolindophenol (except for trace B), I mM surements [4,8] and in combination with the very sodium ascorbate and 50/~M methylviologen. In (B) 2,6- low content in the B3 fraction indicative of a pre- dichlorophenolindophenol was replaced by 2/~M plasto- dominant location of PSI to non-appressed re- cyanin. 5 signals were averaged with a repetition rate gions. of 0.2 Hz. The illumination period of 67 ms is marked A PSI enrichment is always accompanied by a by arrows. PS2 depletion and an increase in the Chl a/b ratio (table 1). The Q/P700 ratios of the subfractions (table 1) deviate significantly from the ratio of 1.1 content in the appressed regions or is due to con- in the starting material, a value normal for chlo- tamination by right-sided non-appressed material.
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