Evidence for an association of the early light-inducible protein (ELIP) of pea with photosystem II

The precursor to the nuclear-coded 17 kDa early light-inducible protein (ELIP) of pea has been transported into isolated intact chloroplasts. The location of the mature protein in the thylakoid membranes was investigated after using cleavable crosslinkers such as DSP and SAND in conjunction with immuno-fractionation methods and by application of mild detergent fractionation. We show that ELIP is integrated into the membranes via the unstacked stroma thylakoids. After isolation of protein complexes by solubilization of membranes with Triton X-100 and sucrose density-gradient centrifugation the crosslinked ELIP comigrates with the PS II core complex. Using SAND we identified ELIP as a 41–51 kDa crosslinked product while with DSP four products of 80 kDa, 70 kDa, 50–42 kDa and 23–21 kDa were found. The immunoprecipitation data suggested that the D₁-protein of the PS II complex is one of the ELIP partners in crosslinked products.Abbreviations chl chlorophyll - D₁ herbicide-binding protein - DSP dithiobis-(succinimidylpropionate) - ELIP early light-inducible protein - LHC I and LHC II light-harvesting chlorophyll a/b complex associated with photosystem I or II - PAGE polyacrylamide gel electrophoresis - poly(A)-rich RNA polyadenyd mRNA - PS I and PS II photosystems I and II - SAND sulfosuccinimidyl 2-(m-azido-o-nitro-benzamido)-ethyl-1,3-dithiopropionate - Triton X-100 octylphenoxypolyethoxyethanol     

Isolation of pigment-binding early light-inducible proteins from pea.

The early light-inducible proteins (ELIPs) in chloroplasts possess a high sequence homology with the chlorophyll a/b-binding proteins but differ from those proteins by their substoichiometric and transient appearance. In the present study ELIPs of pea were isolated by a two-step purification strategy: perfusion chromatography in combination with preparative isoelectric focussing. Two heterogeneous populations of ELIPs were obtained after chromatographic separation of solubilized thylakoid membranes using a weak anion exchange column. One of these populations contained ELIPs in a free form providing the first isolation of these proteins. To prove whether the isolated and pure forms of ELIP bind pigments, spectroscopic and chromatographic analysis were performed. Absorption spectra and TLC revealed the presence of chlorophyll a and lutein. Measurements of steady-state fluorescence emission spectra at 77 K exhibited a major peak at 674 nm typical for chlorophyll a bound to the protein matrix. The action spectrum of the fluorescence emission measured at 674 nm showed several peaks originating mainly from chlorophyll a. It is proposed that ELIPs are transient chlorophyll-binding proteins not involved in light-harvesting but functioning as scavengers for chlorophyll molecules during turnover of pigment-binding proteins.     

Light-induced fluorescence quenching in the light-harvesting chlorophyll a/b protein complex

Summary Irradiation of the principal photosystem II light-harvesting chlorophyll-protein antenna complex, LHC II, with high light intensities brings about a pronounced quenching of the chlorophyll fluorescence. Illumination of isolated thylakoids with high light intensities generates the formation of quenching centres within LHC II in vivo, as demonstrated by fluorescence excitation spectroscopy. In the isolated complex it is demonstrated that the light-induced fluorescence quenching: a) shows a partial, biphasic reversibility in the dark; b) is approximately proportional to the light intensity; c) is almost independent of temperature in the range 0–30°C; d) is substantially insensitive to protein modifying reagents and treatments; e) occurs in the absence of oxygen. A possible physiological importance of the phenomenon is discussed in terms of a mechanism capable of dissipating excess excitation energy within the photosystem II antenna.Abbreviations chla chlorophyll a - chlb chlorophyll b - F₀ fluorescence yield with reaction centers open - F_m fluorescence yield with reaction centres closed - F_i fluorescence at the plateau level of the fast induction phase - LHC II light-harvesting chlorophyll a/b protein complex II - PS II photosystem II - PSI photosystem I - Tricine N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine     

Chlorophyll a/b-binding proteins, pigment conversions, and early light-induced proteins in a chlorophyll b-less barley mutant.

Monospecific polyclonal antibodies have been raised against synthetic peptides derived from the primary sequences from different plant light-harvesting Chl a/b-binding (LHC) proteins. Together with other monospecific antibodies, these were used to quantify the levels of the 10 different LHC proteins in wild-type and chlorina f2 barley (Hordeum vulgare L.), grown under normal and intermittent light (ImL). Chlorina f2, grown under normal light, lacked Lhcb1 (type I LHC II) and Lhcb6 (CP24) and had reduced amounts of Lhcb2, Lhcb3 (types II and III LHC II), and Lhcb4 (CP 29). Chlorina f2 grown under ImL lacked all LHC proteins, whereas wild-type ImL plants contained Lhcb5 (CP 26) and a small amount of Lhcb2. The chlorina f2 ImL thylakoids were organized in large parallel arrays, but wild-type ImL thylakoids had appressed regions, indicating a possible role for Lhcb5 in grana stacking. Chlorina f2 grown under ImL contained considerable amounts of violaxanthin (2-3/reaction center), representing a pool of phototransformable xanthophyll cycle pigments not associated with LHC proteins. Chlorina f2 and the plants grown under ImL also contained early light-induced proteins (ELIPs) as monitored by western blotting. The levels of both ELIPs and xanthophyll cycle pigments increased during a 1 h of high light treatment, without accumulation of LHC proteins. These data are consistent with the hypothesis that ELIPs are pigment-binding proteins, and we suggest that ELIPs bind photoconvertible xanthophylls and replace "normal" LHC proteins under conditions of light stress.     

Suppression of both ELIP1 and ELIP2 in Arabidopsis does not affect tolerance to photoinhibition and photooxidative stress

ELIPs (early light-induced proteins) are thylakoid proteins transiently induced during greening of etiolated seedlings and during exposure to high light stress conditions. This expression pattern suggests that these proteins may be involved in the protection of the photosynthetic apparatus against photooxidative damage. To test this hypothesis, we have generated Arabidopsis (Arabidopsis thaliana) mutant plants null for both elip genes (Elip1 and Elip2) and have analyzed their sensitivity to light during greening of seedlings and to high light and cold in mature plants. In particular, we have evaluated the extent of damage to photosystem II, the level of lipid peroxidation, the presence of uncoupled chlorophyll molecules, and the nonphotochemical quenching of excitation energy. The absence of ELIPs during greening at moderate light intensities slightly reduced the rate of chlorophyll accumulation but did not modify the extent of photoinhibition. In mature plants, the absence of ELIP1 and ELIP2 did not modify the sensitivity to photoinhibition and photooxidation or the ability to recover from light stress. This raises questions about the photoprotective function of these proteins. Moreover, no compensatory accumulation of other ELIP-like proteins (SEPs, OHPs) was found in the elip1/elip2 double mutant during high light stress. elip1/elip2 mutant plants show only a slight reduction in the chlorophyll content in mature leaves and greening seedlings and a lower zeaxanthin accumulation in high light conditions, suggesting that ELIPs could somehow affect the stability or synthesis of these pigments. On the basis of these results, we make a number of suggestions concerning the biological function of ELIPs.     

Pigment and protein composition of reconstituted light-harvesting complexes and effects of some protein modifications

The structure and heterogeneity of LHC II were studied by in vitro reconstitution of apoproteins with pigments (Plumley and Schmidt 1987, Proc Natl Acad Sci 84: 146–150). Reconstituted CP 2 complexes purified by LDS-PAGE were subsequently characterized and shown to have spectroscopic properties and pigment-protein compositions and stoichiometries similar to those of authentic complexes. Heterologous reconstitutions utilizing pigments and light-harvesting proteins from spinach, pea and Chlamydomonas reinhardtii reveal no evidence of specialized binding sites for the unique C. reinhardtii xanthophyll loroxanthin: lutein and loroxanthin are interchangeable for in vitro reconstitution. Proteins modified by the presence of a transit peptide, phosphorylation, or proteolytic removal of the NH₂-terminus could be reconstituted. Evidence suggests that post-translational modification are not responsible for the presence of six electrophoretic variants of C. reinhardtii CP 2. Reconstitution is blocked by iodoacetamide pre-treatment of the apoproteins suggesting a role for cysteine in pigment ligation and/or proper folding of the pigment-protein complex. Finally, no effect of divalent cations on pigment reassembly could be detected.Abbreviations cab chlorophyll a/b-binding protein genes - Chl chlorophyll - CP2 light-harvesting chlorophyll A+b-protein complex fractionated by mildly denaturing LDS-PAGE from Photosystem II in thylakoids - CP 43 and CP 47 chlorophyll a-antenna complexes fractionated from Photosystem II in thylakoids by mildly denaturing LDS-PAGE at 4°C - IgG gamma immunoglobulin - LDS lithium dodecyl sulfate - LDS-PAGE lithium dodecyl sulfate polyacrylamide gel electrophoresis at 4°C - LHC I and LHC II thylakoid light-harvesting chlorophyll a+b-protein holocomplexes associated with Photosystems I and II, respectively - PS II Photosystem II - TX100 Triton X-100 - TX100-derived LHC light-harvesting complexes enriched in LHC II following fractionation of thylakoids by TX100     

Changes in lipid composition of Photosystem 1 particles from thylakoids phosphorylated under reductive or anaerobic conditions

Changes in lipid composition of Photosystem 1 (PS 1) particles isolated from thylakoids phosphorylated under reductive or anaerobic conditions have been studied. Under reductive conditions, there was an increase in monogalactosyldiacylglycerol containing highly saturated fatty acids and phosphatidylglycerol containing transhexadecenoic fatty acid. Under anaerobic conditions, the amount of all lipid classes was increased. As we have shown earlier (S. V. Manuilskaya, O. I. Volovik, A. I. Mikhno, A. I. Polischuk and S. M. Kochubey (1990) Photosynthetica 24: 419–423) these changes were due to a co-migration of some lipid species and light-harvesting chlorophyll a/b complex LHC II from PS 2 to PS 1. These data allow us to conclude that LHC II consists of the lipoproteins containing specific lipids. Different composition of lipids co-migrating with LHC II under various conditions of phosphorylation might be caused by the variety of LHC II subpopulations transferred under each reductive condition.Abbreviations PS 1 Photosystem 1 - PS 2 Photosystem 2 - LHC II light-harvesting chlorophyll a/b protein complex II - Chl chlorophyll - MGDG monogalactosyldiacylglycerol - DGDG digalactosyldiacylglycerol - PG phosphatidylglycerol - SQDG sulfoquinovosyldiacylglycerol     

Formation of early-light-inducible-protein complexes and status of xanthophyll levels under high light and cold stress in barley (Hordeum vulgare L.)

In our previous work we found considerable accumulation of early light-inducible proteins (ELIPs) in barley during adaptation to combined high light and cold stress, an accumulation which occurred preferentially in the apical part of the leaves (M.-H. Montané et al., 1997, Planta 202: 293–302). Here we studied, under the same conditions, the effect of adaptation on the composition of thylakoid membrane proteins and pigments, particularly xanthophylls and chlorophyll, and their distribution within the barley leaf. It was observed that high light fluxes appeared to favour the trimerization of the light-harvesting complex of photosystem II (LHC II) whereas cold appeared to favour the monomers of LHC II. High light, cold or the combination of both factors had only a small effect on the protein composition of the thylakoid membranes except for the proteins of LHC II which were found to decrease under high light to a greater extent at 25 °C than at 5 °C. The total xanthophyll-cycle carotenoid content increased linearly with cellular development, the highest amount being observed in the apical part of the leaf. Cold and high light acted synergistically to induce less than a doubling in the amount of total xanthophylls, while chlorophylls a and b remained nearly constant. The fraction consisting of antheraxanthin plus zeaxanthin was up to 4- to 5-fold higher at 5 °C than at 25 °C. As determined previously (Montané et al. 1997), the same conditions caused a 15-fold increase in the accumulation of ELIPs. Consequently, neither the distribution of total xanthophylls nor that of antheraxanthin plus zeaxanthin along the leaf followed the same pattern as ELIP. Thus, the accumulation of xanthophylls cannot be stoichiometrically correlated with that of ELIPs. Using electrophoresis in the presence of decylmaltoside, we could demonstrate for the first time that ELIPs of 13.5 kDa are contained in high-molecular-mass complexes of >100 kDa, which are located in the unstacked stroma lamellar region of the thylakoid membranes. Received: 6 April 1998 / Accepted: 26 January 1999     

The light stress-induced protein ELIP2 is a regulator of chlorophyll synthesis in Arabidopsis thaliana

The early light-induced proteins (ELIPs) belong to the multigenic family of pigment-binding light-harvesting complexes. ELIPs accumulate transiently and are believed to play a protective role in plants exposed to high levels of light. Constitutive expression of the ELIP2 gene in Arabidopsis resulted in a marked reduction of the pigment content of the chloroplasts, both in mature leaves and during greening of etiolated seedlings. The chlorophyll loss was associated with a decrease in the number of photosystems in the thylakoid membranes, but the photosystems present were fully assembled and functional. A detailed analysis of the chlorophyll-synthesizing pathway indicated that ELIP2 accumulation downregulated the level and activity of two important regulatory steps: 5-aminolevulinate synthesis and Mg-protoporphyrin IX (Mg-Proto IX) chelatase activity. The contents of glutamyl tRNA reductase and Mg chelatase subunits CHLH and CHLI were lowered in response to ELIP2 accumulation. In contrast, ferrochelatase activity was not affected and the inhibition of Heme synthesis was null or very moderate. As a result of reduced metabolic flow from 5-aminolevulinic acid, the steady state levels of various chlorophyll precursors (from protoporphyrin IX to protochlorophyllide) were strongly reduced in the ELIP2 overexpressors. Taken together, our results indicate that the physiological function of ELIPs could be related to the regulation of chlorophyll concentration in thylakoids. This seems to occur through an inhibition of the entire chlorophyll biosynthesis pathway from the initial precursor of tetrapyrroles, 5-aminolevulinic acid. We suggest that ELIPs work as chlorophyll sensors that modulate chlorophyll synthesis to prevent accumulation of free chlorophyll, and hence prevent photooxidative stress.     

Sequence conservation of light-harvesting and stress-response proteins in relation to the three-dimensional molecular structure of LHCII

The structure of pea light-harvesting complex LHCII determined to 3.4 Å resolution by electron crystallography (Kühlbrandt, Wang and Fujiyoshi (1994) Nature 367: 614–621) was examined to determine the relationship between structural elements and sequence motifs conserved in the extended family of light-harvesting antennas (Chl a/b, fucoxanthin Chl a/c proteins) and membrane-intrinsic stress-induced proteins (ELIPs) to which LHCII belongs. It is predicted that the eukaryotic ELIPs can bind at least four molecules of Chl. The one-helix prokaryotic ELIP of Synechococcus was modelled as a homodimer based on the high degree of conservation of residues involved in the interactions of the first (B) and third (A) helices of LHCII.Abbreviations CAB Chl a/b-binding - ELIP early light-inducible protein - FCP fucoxanthin-Chl a/c protein - Lut1, Lut2 lutein molecules 1 and 2     

LHC II protein phosphorylation in leaves of Arabidopsis thaliana mutants deficient in non-photochemical quenching

Phosphorylation of the light-harvesting chlorophyll a/b complex II (LHC II) proteins is induced in light via activation of the LHC II kinase by reduction of cytochrome b₆f complex in thylakoid membranes. We have recently shown that, besides this activation, the LHC II kinase can be regulated in vitro by a thioredoxin-like component, and H₂O₂ that inserts an inhibitory loop in the regulation of LHC II protein phosphorylation in the chloroplast. In order to disclose the complex network for LHC II protein phosphorylation in vivo, we studied phosphorylation of LHC II proteins in the leaves of npq1-2 and npq4-1 mutants of Arabidopis thaliana. In comparison to wild-type, these mutants showed reduced non-photochemical quenching and increased excitation pressure of Photosystem II (PS II) under physiological light intensities. Peculiar regulation of LHC II protein phosphorylation was observed in mutant leaves under illumination. The npq4-1 mutant was able to maintain a high amount of phosphorylated LHC II proteins in thylakoid membranes at light intensities that induced inhibition of phosphorylation in wild-type leaves. Light intensity-dependent changes in the level of LHC II protein phosphorylation were smaller in the npq1-2 mutant compared to the wild-type. No significant differences in leaf thickness, dry weight, chlorophyll content, or the amount of LHC II proteins were observed between the two mutant and wild-type lines. We propose that the reduced capacity of the mutant lines to dissipate excess excitation energy induces changes in the production of reactive oxygen species in chloroplasts, which consequently affects the regulation of LHC II protein phosphorylation.     

Phosphatase activities in spinach thylakoid membranes-effectors, regulation and location

The dephosphorylation of seven phosphoproteins associated with Photosystem II or its chlorophyll a/b antenna in spinach thylakoids, was characterised. The rates were found to fall into two distinct groups. One, rapidly dephosphorylated, consisted of the two subunits (25 and 27 kD) of the major light harvesting complex of Photosystem II (LHC II) and a 12 kD polypeptide of unknown identity. A marked correlation between the dephosphorylation of these three phosphoproteins, strongly suggested that they were all dephosphorylated by the same enzyme. Within this group, the 25 kD subunit was consistently dephosphorylated most rapidly, probably reflecting its exclusive location in the peripheral pool of LHC II. The other group, only slowly dephosphorylated, included several PS II proteins such as the D1 and D2 reaction centre proteins, the chlorophyll-a binding protein CP43 and the 9 kD PS II-H phosphoprotein. No dephosphorylation was observed in either of the two groups in the absence of Mg²⁺-ions. Dephosphorylation of the two LHC II subunits took place in both grana and stroma-exposed regions of the thylakoid membrane. However, deposphorylation in the latter region was significantly more rapid, indicating a preferential dephosphorylation of the peripheral (or mobile) LHC II. Dephosphorylation of LHC II was found to be markedly affected by the redox state of thiol-groups, which may suggest a possible regulation of LHC II dephosphorylation involving the ferredoxin-thioredoxin system.Abbreviations CP 43 43 kD chlorophyll a- binding protein - D1 and D2 reaction centre proteins of PS II - LHC II light-harvesting complex of PS II - LHC II-25 25 kD subunit of LHC II - LHC II-27 27 kD subunit of LHC II - NEM N-ethylmaleimide - PP2C protein phosphatase 2C - PS II-H psb H gene product     

Novel aspects of chlorophyll a/b-binding proteins

The light-harvesting proteins (LHC) constitute a multigene family including, in higher plants, at least 12 members whose location, within the photosynthetic membrane, relative abundance and putative function appear to be very different. The major light-harvesting complex of photosystem II (LHCII) is the most abundant membrane protein in the biosphere and fulfil a constitutive light-harvesting function for photosystem II while the early light-induced proteins (ELIPs) are expressed in low amounts under stress conditions. Primary sequence analysis suggests that all these proteins share a common structure which was resolved at 3.7 Å resolution by electron crystallography in the case of the major LHCII complex: Three transmembrane helices connected by hydrophilic loops coordinate seven chlorophyll a and five chlorophyll b molecules by histidine, glutamine, asparagine lateral chains as well as by charge compensated ionic pairs of glutamic acid and arginine residues; moreover, at least two xantophyll molecules are located at the centre of the structure in close contact with seven porphyrins, tentatively identified as chlorophyll a. The antenna system is also involved in the regulation of excitation energy transfer to reaction centre II. This function has been attributed to three members of the protein family, namely CP29, CP26 and CP24 (also called minor chlorophyll proteins) which have been recently characterised and shown to bind most of the xantophyll cycle carotenoids, thus suggesting that the non-photochemical quenching mechanism is acting in these proteins. Further support to this assignment comes from the recent identification of protonation sites in CP29 and CP26 by covalent dicyclohexhylcarbodiimide binding suggesting that these respond to low lumenal pH. In addition, CP29 is reversibly phosphorylated under light and cold stress conditions, undergoing conformational change, supporting the hypothesis that these subunits, present in low amounts in photosystem II, have a major regulatory role in the light-harvesting function and are thus important in environmental stress resistance.     

Consequences of LHC II deficiency for photosynthetic regulation in chlorina mutants of barley

The light-harvesting chlorophyll a/b proteins associated with PS II (LHC II) are often considered to have a regulatory role in photosynthesis. The photosynthetic responses of four chlorina mutants of barley, which are deficient in LHC II to varying degrees, are examined to evaluate whether LHC II plays a regulatory role in photosynthesis. The efficiencies of light use for PS I and PS II photochemistry and for CO₂ assimilation in leaves of the mutants were monitored simultaneously over a wide range of photon flux densities of white light in the presence and absence of supplementary red light. It is demonstrated that the depletions of LHC II in these mutants results in a severe imbalance in the relative rates of excitation of PS I and PS II in favour of PS I, which cannot be alleviated by preferential excitation of PS II. Analyses of xanthophyll cycle pigments and fluorescence quenching in leaves of the mutants indicated that the major LHC II components are not required to facilitate the light-induced quenching associated with zeaxanthin formation. It is concluded that LHC II is important to balance the distribution of excitation energy between PS I and PS II populations over a wide range of photon flux densities. It appears that LHC II may also be important in determining the quantum efficiency of PS II photochemistry by reducing the rate of quenching of excitation energy in the PS II primary antennae.Abbreviations Fm, Fv maximal and variable fluorescence yields in a light adapted state - LHC II light harvesting chlorophyll a/b protein complex associated with PS II - q_p photochemical quenching - A₈₂₀ light-induced absorbance change at 820 nm - ø_PSI, ø_PSII relative quantum efficiencies of PS I and PS II photochemistry - øCO₂ quantum yield of CO₂ assimilation     

The expression of early light-inducible proteins (ELIPs) under high-light stress as defense marker in Northern- and Southern European cultivars of barley (Hordeum vulgare)

Clones coding for the two small early light-inducible proteins (ELIP)-gene families of 13.5 and 17 kDa have been used as markers to study the effect of high-light intensities on gene expression in cultivars of barley which were bred for growth in Southern and Northern Europe. The mRNA levels of the light-harvesting chlorophyll a / b protein (LHC-II) and the small subunit of ribulose-1,5-bisphosphate carboxylase (SSU) were determined in addition. These data were correlated to the decay of PSII activity during high-light stress and its recovery. In all cultivars, the induction of ELIP mRNAs by high light was accompanied by a correspondent reduction of the LHC-II mRNA level. Furthermore, the LHC-II mRNA levels observed under low-light conditions used for the growth of the plants, were in all cases found to be inversely related to the amount of the ELIP which could be induced by a high-light treatment. In contrast, the amount of the SSU mRNA was reduced only at the highest investigated light intensity of 2 000 μmol m⁻² s⁻¹. During recovery from light-stress, the activity of PSII was quickly restored in all European cultivars. Of these cultivars, however, the cv. Otis which expressed the highest ELIP levels recovered considerably faster than the cultivar p4266N which accumulated the lowest amounts of ELIP under high light. Thus, it appears likely that ELIPs contribute to the restoration of PSII activity during and after photoinhibition.     

Polyamines in the photosynthetic apparatus

The three main polyamines putrescine (Put), spermidine (Spd) and spermine (Spm) were characterized by HPLC in intact spinach leaf cells, intact chloroplasts, thylakoid membranes, Photosystem II membranes, the light-harvesting complex and the PS II complex. All contain the three polyamines in various ratios; the HPLC polyamine profiles of highly resolved PS II species (a Photosystem II core and the rection center) suggest an enrichment in the polyamine Spm.Abbreviations Chl chlorophyll - HPLC high performance liquid chromatography - LHC light-harvesting complex - PS II Photosystem II - PS II-RC Photosystem II reaction center - Put putrescine - Spd spermidine - Spm spermine - 10%S-core D₁-D₂-Cyt b559-47 kD-43 kD complex     

The 28 kDa apoprotein of CP 26 in PS II binds copper

Photosystem II (PS II) particles isolated from spinach in the presence of 10 M CuSO₄ contained 1.2 copper/300 Chl that was resistant to EDTA. When CuSO₄ was not added during the isolation, PS II particles contained variable amounts of copper resistant to EDTA (0.1–1.1 copper/300 Chl). No correlation was found between copper content and oxygen evolving capacity of the PS II particles. To identify the copper binding protein, we developed a fractionation procedure which included solubilisation of PS II particles followed by precipitation with polyethylene glycol. A 22-fold purification of copper with respect to protein was achieved for a 28 kDa protein. Partial amino acid sequence of a 13 kDa fragment, obtained after V8 (endo Glu-C) protease treatment, showed identity with CP 26 over a 14 amino acid stretch. EPR measurements on the purified protein suggest oxygen and/or nitrogen as ligands for copper but tend to exclude sulfur. We conclude that the 28 kDa apoprotein of CP 26 from spinach binds one copper per molecule of CP 26. A possible function for this copper protein in the xanthophyll cycle is discussed.Abbreviations CP 26 and CP 29 chlorophyll a/b protein complex 26 and 29 - LHC II light-harvesting chlorophyll a/b protein complex of Photosystem II - SB14 sulfobetaine 14 A preliminary report of these results was presented at the IX Int. Congress on Photosynthesis, Nagoya, Japan, 1992.     

Action spectra and functional antenna sizes of Photosystems I and II in relation to the thylakoid membrane organization and pigment composition

The functional organization of competent photosynthetic units in developing thylakoids from intermittent-light grown pea as well as in the unstacked, stacked and phosphorylated stacked thylakoids from its mature chloroplasts was characterized by polarographic measurements of action spectra, reaction centre contents and optical cross-sections for PS I-mediated O2 uptake and PS II-mediated O2 evolution. The minimum antenna sizes of 60 and 37 chlorophyll a molecules for PS I and PS II, respectively, were determined in developing thylakoids with a ratio of Chl a/Chl b>50. In mature chloroplasts, the embedded light-harvesting chlorophyll a/b-binding (LHC) protein complexes increased the PS I and PS II effective antenna sizes by 3–6 times depending on the thylakoid membrane organization. In unstacked thylakoids, a randomization of PS I, PS II and LHC II led to the most uniform spectral distribution of light harvesting between the two photosystems but caused the maximal difference of their antenna sizes to be 370 and 100 Chls for the competent PS I and PS II units, respectively. Following the Mg2+-induced stacking of thylakoids, opposite complementary changes of the action spectra, antenna sizes and Chl a/Chl b ratios indicated a redistribution of a LHC II pool of 100 Chl ( a + b) molecules from PS I to PS II. Unlike to the stroma-exposed PS II in unstacked thylakoids, the granal PS II units of 200 Chls demonstrated an additional 2-fold increase of the effective antenna size due to energy transfer within PS II dimers under strong background illumination, which closed >90% of reaction centres. Protein phosphorylation of the stacked thylakoids induced a significant inactivation of the O2-evolving PS II centres but did not cause complementary changes of the action spectra and antenna sizes of the competent PS I and PS II. In this case, light harvesting parameters of the O2-evolving PS II units were nearly unaffected, whereas the obvious relative increase of the PS I activity at 650 nm and its decrease at >700 nm both in the action spectrum and optical cross-section measurements might suggest a substitution of PS I units in the O2-reducing fraction by another distinct fraction of -type which in turn is not the same to PS I units in unstacked thylakoids.