PsbI Affects the Stability, Function, and Phosphorylation Patterns of Photosystem II Assemblies in Tobacco

Photosystem II (PSII) core complexes consist of CP47, CP43, D1, D2 proteins and of several low molecular weight integral membrane polypeptides, such as the chloroplast-encoded PsbE, PsbF, and PsbI proteins. To elucidate the function of PsbI in the photosynthetic process as well as in the biogenesis of PSII in higher plants, we generated homoplastomic knock-out plants by replacing most of the tobacco psbI gene with a spectinomycin resistance cartridge. Mutant plants are photoautotrophically viable under green house conditions but sensitive to high light irradiation. Antenna proteins of PSII accumulate to normal amounts, but levels of the PSII core complex are reduced by 50%. Bioenergetic and fluorescence studies uncovered that PsbI is required for the stability but not for the assembly of dimeric PSII and supercomplexes consisting of PSII and the outer antenna (PSII-LHCII). Thermoluminescence emission bands indicate that the presence of PsbI is required for assembly of a fully functional QA binding site. We show that phosphorylation of the reaction center proteins D1 and D2 is light and redox-regulated in the wild type, but phosphorylation is abolished in the mutant, presumably due to structural alterations of PSII when PsbI is deficient. Unlike wild type, phosphorylation of LHCII is strongly increased in the dark due to accumulation of reduced plastoquinone, whereas even upon state II light phosphorylation is decreased in ΔpsbI. These data attest that phosphorylation of D1/D2, CP43, and LHCII is regulated differently. Photosystem II (PSII) core complexes consist of CP47, CP43, D1, D2 proteins and of several low molecular weight integral membrane polypeptides, such as the chloroplast-encoded PsbE, PsbF, and PsbI proteins. To elucidate the function of PsbI in the photosynthetic process as well as in the biogenesis of PSII in higher plants, we generated homoplastomic knock-out plants by replacing most of the tobacco psbI gene with a spectinomycin resistance cartridge. Mutant plants are photoautotrophically viable under green house conditions but sensitive to high light irradiation. Antenna proteins of PSII accumulate to normal amounts, but levels of the PSII core complex are reduced by 50%. Bioenergetic and fluorescence studies uncovered that PsbI is required for the stability but not for the assembly of dimeric PSII and supercomplexes consisting of PSII and the outer antenna (PSII-LHCII). Thermoluminescence emission bands indicate that the presence of PsbI is required for assembly of a fully functional QA binding site. We show that phosphorylation of the reaction center proteins D1 and D2 is light and redox-regulated in the wild type, but phosphorylation is abolished in the mutant, presumably due to structural alterations of PSII when PsbI is deficient. Unlike wild type, phosphorylation of LHCII is strongly increased in the dark due to accumulation of reduced plastoquinone, whereas even upon state II light phosphorylation is decreased in ΔpsbI. These data attest that phosphorylation of D1/D2, CP43, and LHCII is regulated differently. Analyses of the polypeptide composition of the oxygenevolving PSII, 4The abbreviations used are: PS, photosystem; BN, blue native; DCMU, 3-[3′, 4′-dichlorphenyl]-1,1-dimethylurea; LHCII, light-harvesting protein complex (outer antenna of photosystem II); LMW, low molecular weight; RC, reaction center; TL, thermoluminescence; WT, wild type. 4The abbreviations used are: PS, photosystem; BN, blue native; DCMU, 3-[3′, 4′-dichlorphenyl]-1,1-dimethylurea; LHCII, light-harvesting protein complex (outer antenna of photosystem II); LMW, low molecular weight; RC, reaction center; TL, thermoluminescence; WT, wild type. the most complex assembly of the thylakoid system, have uncovered the presence of the intriguing number of 16 low molecular weight proteins (LMWs) that are generally conserved from cyanobacteria to higher plants (for review, see Refs. 1Minagawa J. Takahashi Y. Photosynth. Res. 2004; 82: 241-263Crossref PubMed Google Scholar, 2Shi L.-X. Schröder W.P. Biochim. Biophys. Acta. 2004; 1608: 75-96Crossref PubMed Scopus (129) Google Scholar, 3Dekker J.P. Boekema E.J. Biochim. Biophys. Acta. 2005; 1706: 12-39Crossref PubMed Scopus (660) Google Scholar). In photosynthetic eukaryotes, the majority, namely PsbE, F, H, I, J, K, L, M, N, Tc, and Z, are plastome-encoded; the remaining five, PsbR, Tn, W, X, and Y1/Y2, are encoded by nuclear genes (4Thornton L.E. Roose J.L. Pakrasi H. Wydrzynski T. Satoh K. Photosystem II: the Water/Plastoquinone Oxido-reductase in Photosynthesis. Kluwer Academic Publishers, Dordrecht, The Netherlands2005: 121-138Google Scholar). The high homology between the plastome-encoded and cyanobacterial LMWs suggests conserved roles, as has been proposed for PsbE and PsbF, the α and β subunits of the two-chain cytochrome b559. Cytochrome b559 is a mandatory constituent of PSII that plays a major role in PSII function and biogenesis (5Pakrasi H.B. Williams J.G. Arntzen C.J. EMBO J. 1988; 2: 325-332Crossref Scopus (122) Google Scholar, 6Morais F. Kuhn K. Stewart D.H. Barber J. Brudvig G.W. Nixon P.J. J. Biol. Chem. 2001; 276: 31986-31993Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar, 7Swiatek M. Regel R.E. Meurer J. Wanner G. Pakarasi H.B. Ohad I. Herrmann R.G. Mol. Genet. Genomics. 2003; 268: 699-710Crossref PubMed Scopus (58) Google Scholar). The LMW components of PSII are generally bitopic, i.e. harbor a single transmembrane helix, and in all members, except for PsbK and PsbTc, the N-terminal domain has been suggested to be exposed to the stromal face of the membrane complex (PsbE, PsbF, PsbH, PsbI, PsbJ, PsbL, and PsbM) (for review, see Ref. 2Shi L.-X. Schröder W.P. Biochim. Biophys. Acta. 2004; 1608: 75-96Crossref PubMed Scopus (129) Google Scholar). PsbH is the only known LMW component, which is phosphorylated in the chloroplast, but its phosphorylation is missing in cyanobacteria (8Bennett J. Nature. 1977; 269: 344-346Crossref Scopus (287) Google Scholar). Apart from PsbH, the other major thylakoid phosphoproteins are those of the light-harvesting protein complex (LHCII) and of the PSII core (CP43 and the reaction center proteins D1 and D2) (9Bellafiore S. Barneche F. Peltier G. Rochaix J.D. Nature. 2005; 433: 892-895Crossref PubMed Scopus (534) Google Scholar, 10Bonardi V. Pesaresi P. Becker T. Schleiff E. Wagner R. Pfannschmidt T. Jahns P. Leister D. Nature. 2005; 437: 1179-1182Crossref PubMed Scopus (346) Google Scholar, 11Vainonen J.P. Hansson M. Vener A.V. J. Biol. Chem. 2005; 280: 33679-33686Abstract Full Text Full Text PDF PubMed Scopus (161) Google Scholar). Biochemical approaches and x-ray crystallography have been instrumental in determining the localization of the LMW proteins within the PSII assembly. For the thermophile cyanobacterial PSII core complex, the location of these proteins has been specified with increasing precision (12Vasil'ev S. Orth P. Zouni A. Owens T.G. Bruce D. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8602-8607Crossref PubMed Scopus (112) Google Scholar, 13Zouni A. Witt H.T. Kern J. Fromme P. Krauss N. Saenger W. Orth P. Nature. 2001; 409: 739-743Crossref PubMed Scopus (1747) Google Scholar, 14Kamiya N. Shen J.R. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 98-103Crossref PubMed Scopus (986) Google Scholar, 15Kashino Y. Lauber W.M. Carroll J.A. Wang Q. Whitmarsh J. Satoh K. Pakarasi H.B. Biochemistry. 2002; 41: 8004-8012Crossref PubMed Scopus (277) Google Scholar, 16Biesiadka J. Loll B. Kern J. Irrgang K.-D. Zouni A. Phys. Chem. Chem. Phys. 2004; 6: 4733-4736Crossref Scopus (261) Google Scholar, 17Ferreira K.N. Iverson T.M. Maghlaoui K. Barber J. Iwata S. Science. 2004; 303: 1831-1838Crossref PubMed Scopus (2796) Google Scholar, 18Loll B. Kern J. Saenger W. Zouni A. Biesiadka J. Nature. 2005; 15: 1040-1044Crossref Scopus (1583) Google Scholar). These components are either located at the periphery of the PSII core monomers or centrally, at the interface of the two PSII monomers forming a dimer (17Ferreira K.N. Iverson T.M. Maghlaoui K. Barber J. Iwata S. Science. 2004; 303: 1831-1838Crossref PubMed Scopus (2796) Google Scholar). However, besides the psbEFLJ operon products (19Regel R.E. Ivleva N.B. Zer H. Meurer J. Shestakov S.V. Herrmann R.G. Pakarasi H.B. Ohad I. J. Biol. Chem. 2001; 276: 41473-41478Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar, 7Swiatek M. Regel R.E. Meurer J. Wanner G. Pakarasi H.B. Ohad I. Herrmann R.G. Mol. Genet. Genomics. 2003; 268: 699-710Crossref PubMed Scopus (58) Google Scholar), relatively little is known about the function of the other LMWs, their interactions with PSII core components, or their relevance for lipid-protein interactions for the assembly and the energy transfer processes. The majority of LMWs of PSII in cyanobacteria define the boundary between the dimeric complex and the surrounding lipids of the thylakoid membrane, whereas in the chloroplast many of these proteins form the border between the core complex and the minor light-harvesting antenna system, CP29, CP26, and CP24, and presumably also the trimeric LHCII, constituting the mobile antenna of the complex (3Dekker J.P. Boekema E.J. Biochim. Biophys. Acta. 2005; 1706: 12-39Crossref PubMed Scopus (660) Google Scholar). Consequently, the LMWs in the chloroplast may be involved in processes different from those of their cyanobacterial counterparts and, for instance, affect regulation of state transition or antenna-related processes like light-trapping or non-photochemical quenching (20Bassi R. Sandona D. Croce R. Physiol. Plant. 1997; 100: 769-779Crossref Google Scholar, 21Niyogi K.K. Annu. Rev. Plant Physiol. Plant Mol. Biol. 1999; 50: 333-359Crossref PubMed Scopus (1586) Google Scholar). Because of an evolutionary functional divergence, inactivation of homologous LMWs in cyanobacteria and green algae/higher plants can lead to quite different phenotypes, as has recently been shown for PsbJ and PsbL (22Ohad I. Dal Bosco C. Herrmann R.G. Meurer J. Biochemistry. 2004; 43: 2297-2308Crossref PubMed Scopus (44) Google Scholar). Although the loss of these proteins has only a minor effect in Synechocystis sp. PCC6803, relatively dramatic changes of PSII function and stability have been noted in the corresponding tobacco mutants. Inactivation of PsbJ and PsbL in plants affects the QA re-oxidation kinetics and the back-electron flow from plastoquinol to QA, respectively (19Regel R.E. Ivleva N.B. Zer H. Meurer J. Shestakov S.V. Herrmann R.G. Pakarasi H.B. Ohad I. J. Biol. Chem. 2001; 276: 41473-41478Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar, 22Ohad I. Dal Bosco C. Herrmann R.G. Meurer J. Biochemistry. 2004; 43: 2297-2308Crossref PubMed Scopus (44) Google Scholar). Similarly, inactivation of PsbH, PsbI, and PsbK in cyanobacteria and chloroplasts of algae resulted in quite diverse phenotypes (for details and review, see Refs.1Minagawa J. Takahashi Y. Photosynth. Res. 2004; 82: 241-263Crossref PubMed Google Scholar and 2Shi L.-X. Schröder W.P. Biochim. Biophys. Acta. 2004; 1608: 75-96Crossref PubMed Scopus (129) Google Scholar). It is, therefore, conceivable to conduct comparative studies on different evolutionary lineages in a phylogenetic context. Moreover, the biogenesis of PSII components differs in cyanobacteria and higher plants. Because of the dual genetic origin of the thylakoid system in higher plants, the biogenesis depends largely on factors encoded by the nuclear genome. For instance, HCF136, one of these factors, is essential for the biogenesis of the PSII core complex in higher plants, but its homologous protein appears to be largely dispensable in cyanobacteria (23Meurer J. Plücken H. Kowallik K.V. Westhoff P. EMBO J. 1998; 17: 5286-5297Crossref PubMed Scopus (172) Google Scholar, 24Shen G. Zhao J. Reimer S.K. Antonkine M.L. Cai Q. Weiland S.M. Golbeck J.H. Bryant D.A. J. Biol. Chem. 2002; 277: 20343-20354Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). The assignment of several LMW subunits including PsbI (4.8 kDa) to the x-ray structure of PSII still remains to be settled (25Kern J. Loll B. Zouni A. Saenger W. Irrgang K.D. Biesiadka J. Photosynth. Res. 2005; 84: 153-159Crossref PubMed Scopus (48) Google Scholar, 26Zheleva D. Sharma J. Panico M. Morris H.R. Barber J. J. Biol. Chem. 1998; 273: 16122-16127Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar). Earlier studies of the cyanobacterial PSII x-ray structure placed the transmembrane helix of PsbI opposite to the dimerization axis and close to Chlz D2 (13Zouni A. Witt H.T. Kern J. Fromme P. Krauss N. Saenger W. Orth P. Nature. 2001; 409: 739-743Crossref PubMed Scopus (1747) Google Scholar), whereas the crystallographic studies located the PsbI protein at the periphery of PSII core, in close proximity to Chlz D1, the helices A and B of the D1 protein, and the helix VI of CP43 (17Ferreira K.N. Iverson T.M. Maghlaoui K. Barber J. Iwata S. Science. 2004; 303: 1831-1838Crossref PubMed Scopus (2796) Google Scholar, 18Loll B. Kern J. Saenger W. Zouni A. Biesiadka J. Nature. 2005; 15: 1040-1044Crossref Scopus (1583) Google Scholar). PsbI was present in PSII reaction center (RC) preparations of both spinach and cyanobacteria (27Ikeuchi M. Koike H. Inoue Y. FEBS Lett. 1989; 251: 155-160Crossref Scopus (25) Google Scholar). No knock-out strains for psbI are currently available from higher plants. Mutants lacking PsbI have been generated from Chlamydomonas reinhardtii (28Künstner P. Guardiola A. Takahashi Y. Rochaix J.D. J. Biol. Chem. 1995; 270: 9651-9654Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar) and Synechocystis (29Ikeuchi M. Shukla V.K. Pakarasi H.B. Inoue Y. Mol. Gen. Genet. 1995; 249: 622-628Crossref PubMed Scopus (36) Google Scholar). Inactivation of psbI in Synechocystis and Thermosynechococcus elongatus strain BP-1 caused some reduction of PSII activity, resulting in decreased oxygen evolution to 70-80% of WT levels, but the mutants grew photoautotrophically. The Synechocystis ΔpsbI mutant was found to be slightly more sensitive to light than the corresponding WT (29Ikeuchi M. Shukla V.K. Pakarasi H.B. Inoue Y. Mol. Gen. Genet. 1995; 249: 622-628Crossref PubMed Scopus (36) Google Scholar). Deletion of psbI in C. reinhardtii caused a more severe effect compared with that in cyanobacteria (28Künstner P. Guardiola A. Takahashi Y. Rochaix J.D. J. Biol. Chem. 1995; 270: 9651-9654Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar). Although the C. reinhardtii ΔpsbI mutant grows photoautotrophically under low light, its growth rate was quite sensitive to high light. Both the amounts of PSII and the oxygen evolution activity in the mutant were found to be only 10-20% of WT levels. In an attempt to evaluate the roles as well as biogenetic and phylogenetic aspects of the enigmatic LMW PSII subunits, we have systematically inactivated individual genes using a transplastomic approach in tobacco. Here we demonstrate that PsbI exerts a crucial role in the stability of dimeric PSII and the intrinsic electron flow as well as in the phosphorylation of proteins of the core complex and the light-harvesting antenna of PSII in tobacco. Knock-out Construct Strategy for ΔpsbI—In the tobacco plastome the psbI gene is located downstream of psbK, which also encodes a LMW PSII polypeptide (30Webber A.N. Packman L. Chapman D.J. Barber J. Gray J.C. FEBS Lett. 1989; 242: 259-262Crossref Scopus (71) Google Scholar, 31Murata N. Miyao M. Hayashida N. Hidaka T. Sugiura M. FEBS Lett. 1988; 235: 283-288Crossref Scopus (56) Google Scholar, 32Ikeuchi M. Inoue Y. FEBS Lett. 1988; 241: 99-104Crossref PubMed Scopus (147) Google Scholar). In a transplastomic approach, the psbI gene of Nicotiana tabacum cv. Petit Havanna, 110 bp in length (nucleotide position 8398-8508 on the plastid chromosome; GenBank™/EBI accession number Z00044), was inactivated by replacing most of the gene with the terminator-less, chimeric amino glycoside 3′ adenyl transferase (aadA) cassette conferring resistance to spectinomycin in reading frame orientation (7Swiatek M. Regel R.E. Meurer J. Wanner G. Pakarasi H.B. Ohad I. Herrmann R.G. Mol. Genet. Genomics. 2003; 268: 699-710Crossref PubMed Scopus (58) Google Scholar). For this, two PCR reactions were performed with primers psbI-1 (5′-GGA TCC AAA ATG CAA TTA TCT CTC C-3′) and psbI-2 (5′-AAG CTT GCA GCT GAA TTC TAC ACA ATC TCC AAG ATG-3′) and with primers psbI-3 (5′-GAA TTC AGC TGC AAG CTT ATC CCG GAC GTA ATC CTG G-3′) and psbI-4 (5′-ATC TCG AGA TTA CAA CTA TAA CAG GC-3′). PsbI-2 and psbI-3 generated overlapping products and introduced a diagnostic EcoRI restriction site. The third reaction was performed with primers psbI-1 and psbI-4 using the first PCR product as a template. Primers psbI-1 and psbI-4 introduced two flanking restriction sites, BamHI and XhoI, used for cloning into the vector pBluescript II KS-(Stratagene Inc., La Jolla, CA). The presence of a unique restriction site, BtrI, within the disrupted psbI gene allowed the insertion of the aadA cassette between the EcoRI and BtrI restriction sites. The details of the map construction, location of restriction sites, and primer annealing positions are shown in Fig. 1 A and B. The resulting construct (carrying the aadA cassette in the same polarity as psbI) was sequenced to verify correct copying of the gene and used for plastid transformation employed in a biolistic approach (33Svab Z. Hajdukiewicz P. Maliga P. Proc. Natl. Acad. Sci. U. S. A. 1990; 87: 8526-8530Crossref PubMed Scopus (498) Google Scholar). Selection and culture conditions of the transformed material as well as the check for homoplastomy were carried out as described (7Swiatek M. Regel R.E. Meurer J. Wanner G. Pakarasi H.B. Ohad I. Herrmann R.G. Mol. Genet. Genomics. 2003; 268: 699-710Crossref PubMed Scopus (58) Google Scholar). Independent transformants were obtained displaying an identical phenotype (data not shown). The transformed material was first grown (12-h photoperiod at 25 °C, 10-20 μmol m-2 s-1 light intensity) for 4-5 weeks on Murashige and Skoog (34Murashige T. Skoog F. Physiol. Plant. 1962; 15: 493-497Crossref Scopus (52758) Google Scholar) medium supplemented with 3% sucrose, 0.8% agar, and 500 mg/liter spectinomycin. Before transferring the plants to the greenhouse, they were kept for 4-5 weeks on Murashige and Skoog medium without sucrose. If not otherwise indicated, all analyses were carried out with young leaves of ∼2-month-old plants grown in vitro and under greenhouse conditions (day 27 °C, night 20 °C), respectively. Tobacco lines carrying the aadA cassette in a neutral insertion site and referred to as RV plants were used as WT control plants (22Ohad I. Dal Bosco C. Herrmann R.G. Meurer J. Biochemistry. 2004; 43: 2297-2308Crossref PubMed Scopus (44) Google Scholar). SDS-PAGE and Immunoblot Analysis—Thylakoid membrane proteins of 3-4-week-old plants were isolated and solubilized for SDS-PAGE as described (7Swiatek M. Regel R.E. Meurer J. Wanner G. Pakarasi H.B. Ohad I. Herrmann R.G. Mol. Genet. Genomics. 2003; 268: 699-710Crossref PubMed Scopus (58) Google Scholar). Proteins separated by SDS-Tris-glycine-PAGE (15% acrylamide) (35Laemmli U.K. Nature. 1970; 227: 680-685Crossref PubMed Scopus (205531) Google Scholar) were electroblotted to polyvinylidene difluoride membranes (Amersham Biosciences), incubated with monospecific polyclonal antisera (7Swiatek M. Regel R.E. Meurer J. Wanner G. Pakarasi H.B. Ohad I. Herrmann R.G. Mol. Genet. Genomics. 2003; 268: 699-710Crossref PubMed Scopus (58) Google Scholar), and visualized by the enhanced chemiluminescence technique (Amersham Biosciences). Equal loading of proteins was always checked by zinc-imidazole staining of the gels before blotting. Separation of Thylakoid Membrane Complexes by Sucrose Density Gradient Centrifugation—Thylakoid membranes used for the separation of protein complexes by sucrose density gradient centrifugation were isolated as described earlier (7Swiatek M. Regel R.E. Meurer J. Wanner G. Pakarasi H.B. Ohad I. Herrmann R.G. Mol. Genet. Genomics. 2003; 268: 699-710Crossref PubMed Scopus (58) Google Scholar). Resolution of Isolated Thylakoid Membrane Complexes by Blue Native (BN)-PAGE and in Vivo Labeling—Labeling of thylakoid membrane proteins was performed by incubation of cotyledons with [35S]methionine for 40 min as described (36Amann K. Lezhneva L. Wanner G. Herrmann R.G. Meurer J. Plant Cell. 2004; 16: 3084-3097Crossref PubMed Scopus (63) Google Scholar). BN-PAGE analysis was performed as described earlier (37Ossenbühl F. Göhre V. Meurer J. Krieger-Liszkay A. Rochaix J.D. Eichacker L.A. Plant Cell. 2004; 16: 1790-1800Crossref PubMed Scopus (96) Google Scholar). All solutions were supplemented with 10 mm NaF. Thylakoid membranes equivalent to 30 μg of chlorophyll were solubilized with dodecyl-β-d-maltoside (1% final concentration) and separated on a 4-12% acrylamide gradient. After electrophoresis, lanes of the BN polyacrylamide gel were excised, denatured, and run in the second dimension in SDS-PAGE with 15% acrylamide and 4 m urea. Subsequently, the gels were silver-stained or used for immunoblotting. Individual spots were labeled according to their determination by mass spectrometry (38Granvogl B. V. Eichacker L.A. 6: PubMed Scopus Google Scholar). In of PSII LHCII phosphorylation of WT and mutant was carried out as described H. M. S. Herrmann R.G. B. Ohad I. Biochemistry. 2003; PubMed Scopus Google Scholar). of the protein in the dark was obtained by the of reduced J. P. Biochim. Biophys. Acta. Scopus Google Scholar). was by the of and the proteins were by The of phosphorylation was with Inc., a a fluorescence kinetics of tobacco WT and mutant leaves was using a (22Ohad I. Dal Bosco C. Herrmann R.G. Meurer J. Biochemistry. 2004; 43: 2297-2308Crossref PubMed Scopus (44) Google Scholar). were for min before the fluorescence The and fluorescence and the fluorescence as as well as the which the of the reaction of PSII E. Annu. Rev. Plant Physiol. Plant Mol. Biol. Scopus Google Scholar), were at and non-photochemical quenching and were as and respectively Photosynth. Res. 1990; PubMed Scopus Google Scholar). of activity was on leaves as changes at by light and in the or presence of light 20 and μmol of m-2 using the of C. U. Google Scholar). The of at the light was as the Thermoluminescence were performed using a (22Ohad I. Dal Bosco C. Herrmann R.G. Meurer J. Biochemistry. 2004; 43: 2297-2308Crossref PubMed Scopus (44) Google Scholar). Thylakoid were by leaves in a 20 mm mm and mm material was and used for μg were on the at 20 for min and to The were with by a at at light was upon the at a rate of The or were at of 10 and to the electron transfer from For the B the were and were between 1 and by to emission were performed with from young leaves of WT and ΔpsbI plants E. Photosynth. Res. 6: PubMed Scopus Google Scholar). Thylakoid membranes μg were into a for fluorescence and in was at and the emission was between and All were with a with a of 1 were the of PSII to leaves of WT and ΔpsbI plants grown under greenhouse conditions were exposed to 500 μmol of m-2 and the of PSII was as To the PSII process the to the high light were exposed to a light with a of for 30 min before the light For control were incubated in To the and the to from leaves were also exposed to μmol of m-2 s-1 a loss of activity was in both WT and ΔpsbI as and incubated at low light μmol m-2 for to the 1 of psbI in the tobacco plastid caused an increased light but young leaves normal green in with but different from (19Regel R.E. Ivleva N.B. Zer H. Meurer J. Shestakov S.V. Herrmann R.G. Pakarasi H.B. Ohad I. J. Biol. Chem. 2001; 276: 41473-41478Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar, 7Swiatek M. Regel R.E. Meurer J. Wanner G. Pakarasi H.B. Ohad I. Herrmann R.G. Mol. Genet. Genomics. 2003; 268: 699-710Crossref PubMed Scopus (58) Google Scholar), ΔpsbI was of photoautotrophically on under greenhouse fluorescence data of ΔpsbI suggested a in PSII ΔpsbI Mutants a Photosystem II of PSII of ΔpsbI plants grown an increased a reduced between and on the as compared with a of in the The was found in a loss of with of the The in young leaves from the of the plants was in the of a higher in at low light μmol of m-2 and a in when the light was to μmol of m-2 The quenching in ΔpsbI at both light in WT and in WT at 20 and μmol of m-2 and data of WT and ΔpsbI of of PSII reaction by of of PSII reaction by state of of fluorescence by and of of PSII reaction by of of PSII reaction by of fluorescence by and in a To the of the electron flow between PSII and with that between and its final electron in the of as was using changes at in the of different of light in the state and μmol of m-2 The higher levels of in the