Chlorophyll b is involved in long-wavelength spectral properties of light-harvesting complexes LHC I and LHC II.

Chlorophyll (Chl) molecules attached to plant light-harvesting complexes (LHC) differ in their spectral behavior. While most Chl a and Chl b molecules give rise to absorption bands between 645 nm and 670 nm, some special Chls absorb at wavelengths longer than 700 nm. Among the Chl a/b-antennae of higher plants these are found exclusively in LHC I. In order to assign this special spectral property to one chlorophyll species we reconstituted LHC of both photosystem I (Lhca4) and photosystem II (Lhcb1) with carotenoids and only Chl a or Chl b and analyzed the effect on pigment binding, absorption and fluorescence properties. In both LHCs the Chl-binding sites of the omitted Chl species were occupied by the other species resulting in a constant total number of Chls in these complexes. 77-K spectroscopic measurements demonstrated that omission of Chl b in refolded Lhca4 resulted in a loss of long-wavelength absorption and 730-nm fluorescence emission. In Lhcb1 with only Chl b long-wavelength emission was preserved. These results clearly demonstrate the involvement of Chl b in establishing long-wavelength properties.     

Absence of the Lhcb1 and Lhcb2 proteins of the light-harvesting complex of photosystem II - effects on photosynthesis,grana stacking and fitness

We have constructed Arabidopsis thaliana plants that are virtually devoid of the major light-harvesting complex, LHC II. This was accomplished by introducing the Lhcb2.1 coding region in the antisense orientation into the genome by Agrobacterium-mediated transformation. Lhcb1 and Lhcb2 were absent, while Lhcb3, a protein present in LHC II associated with photosystem (PS) II, was retained. Plants had a pale green appearance and showed reduced chlorophyll content and an elevated chlorophyll a/b ratio. The content of PS II reaction centres was unchanged on a leaf area basis, but there was evidence for increases in the relative levels of other light harvesting proteins, notably CP26, associated with PS II, and Lhca4, associated with PS I. Electron microscopy showed the presence of grana. Photosynthetic rates at saturating irradiance were the same in wild-type and antisense plants, but there was a 10-15% reduction in quantum yield that reflected the decrease in light absorption by the leaf. The antisense plants were not able to perform state transitions, and their capacity for non-photochemical quenching was reduced. There was no difference in growth between wild-type and antisense plants under controlled climate conditions, but the antisense plants performed worse compared to the wild type in the field, with decreases in seed production of up to 70%.     

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.     

Protein domains required for formation of stable monomeric Lhca1- and Lhca4-complexes

The peripheral light-harvesting complex of Photosystem I consists of two subpopulations, LHC I-680 and LHC I-730. The latter is composed of the two apoproteins Lhca1 and Lhca4. Recently, reconstitution of monomeric LHC I using bacterially overexpressed Lhca1 or Lhca4 was achieved. In order to obtain insight into the structure requirements for formation of monomeric light-harvesting complexes, we produced a series of N- and C-terminal deletion mutants and used the overexpressed proteins for reconstitution experiments. We found the entire extrinsic N-terminal region dispensable for monomer formation in Lhca1 and Lhca4. Also at the C-terminus, both subunits revealed similarity since all amino acids up to the end of the fourth helix could be removed without abolishing monomer formation. In connection with former corresponding results for Lhcb1, the dispensability of these regions appears to be a general feature in LHC-formation. In LHC I, however, a stabilising effect can be ascribed to these regions since the yield of complexes was decreased. In the majority of the mutant LHC I versions no effect on pigment binding was detected. However, in the LHC with the most extensively N-terminally truncated mutant of Lhca4 a dramatic shift in the 77 K fluorescence emission to shorter wavelengths was observed. This suggests that chlorophylls involved in long wavelength fluorescence emission are located in the chlorophyll array located towards the stromal face of the thylakoid membrane assuming a pigment arrangement corresponding to that in LHC II and CP29. This revised version was published online in June 2006 with corrections to the Cover Date.     

Energy transfer for low temperature fluorescence in PS II mutant thylakoids

The Chl-protein complexes of three maize (Zea mays L.) mutants and one barley (Hordeum vulgare L.) mutant were analyzed using low temperature Chl fluorescence emissions spectroscopy and LDS-polyacrylamide gel electrophoresis. The maize mutants hcf-3, hcf-19, and hcf-114 all exhibited a high Chl fluorescence (hcf) phenotype indicating a disruption of the energy transfer within the photosynthetic apparatus. The mutations in each of these maize mutants affects Photosystem II. The barley mutant analyzed was the well characterized Chl b-less mutant chlorina-f2, which did not exhibit the hcf phenotype. Chlorina-f2 was used because no complete Chl b-less mutant of maize is available. Analysis of hcf-3, hcf-19, and hcf-114 revealed that in the absence of CP43, LHC II can still transfer excitation energy to CP47. These results suggest that in mutant membranes LHC II can interact with CP47 as well as CP43. This functional interaction of LHC II with CP47 may only occur in the absence of CP43, however, it is possible that LHC II is positioned in the thylakoid membranes in a manner which allows association with both CP43 and CP47.Abbreviations hcf high chlorophyll fluorescence - LDS lithium dodecyl sulfate - LHC II light-harvesting complex of Photosystem II - LHC I light-harvesting complex of Photosystem I - CPIa chlorophyll-protein complex consisting of LHC I and the PS I core complex - CPI chlorophyll-protein complex consisting of the PS I core complex - CP47 47 kDa chlorophyll-protein of the Photosystem II core - CP43 43 kDa chlorophyll-protein of the Photosystem II core - CP29 29 kDa chlorophyll-protein of Photosystem II - CP26 26 kDa chlorophyll-protein of Photosystem II - CP24 24 kDa chlorophyll-protein of Photosystem II - fp free pigments     

Identification of Lhcb gene family encoding the light-harvesting chlorophyll-a/b proteins of photosystem II in Chlamydomonas reinhardtii

The Lhcb gene family in green plants encodes several light-harvesting Chl a/b-binding (LHC) proteins that collect and transfer light energy to the reaction centers of PSII. We comprehensively characterized the Lhcb gene family in the unicellular green alga, Chlamydomonas reinhardtii, using the expressed sequence tag (EST) databases. A total of 699 among over 15,000 ESTs related to the Lhcb genes were assigned to eight, including four new, genes that we isolated and sequenced here. A sequence comparison revealed that six of the Lhcb genes from C. reinhardtii correspond to the major LHC (LHCII) proteins from higher plants, and that the other two genes (Lhcb4 and Lhcb5) correspond to the minor LHC proteins (CP29 and CP26). No ESTs corresponding to another minor LHC protein (CP24) were found. The six LHCII proteins in C. reinhardtii cannot be assigned to any of the three types proposed for higher plants (Lhcb1-Lhcb3), but were classified as follows: Type I is encoded by LhcII-1.1, LhcII-1.2 and LhcII-1.3, and Types II, III and IV are encoded by LhcII-2, LhcII-3 and LhcII-4, respectively. These findings suggest that the ancestral LHC protein diverged into LHCII, CP29 and CP26 before, and that LHCII diverged into multiple types after the phylogenetic separation of green algae and higher plants.     

Excitation energy transfer in Photosystem I from oxygenic organisms

This Review discusses energy transfer pathways in Photosystem I (PS I) from oxygenic organisms. In the trimeric PS I core from cyanobacteria, the efficiency of solar energy conversion is largely determined by ultrafast excitation transfer processes in the core chlorophyll a (Chl a) antenna network and efficient photochemical trapping in the reaction center (RC). The role of clusters of Chl a in energy equilibration and photochemical trapping in the PS I core is discussed. Dimers of the longest-wavelength absorbing (red) pigments with strongest excitonic interactions localize the excitation in the PS I core antenna. Those dimers that are located closer to the RC participate in a fast energy equilibration with coupled pigments of the RC. This suggests that the function of the red pigments is to concentrate the excitation near the RC. In the PS I holocomplex from algae and higher plants, in addition to the red pigments of the core antenna, spectrally distinct red pigments are bound to the peripheral Chl a/b-binding light-harvesting antenna (LHC I), specifically to the Lhca4 subunit of the LHC I-730 complex. Intramonomeric energy equilibration between pools of Chl b and Chl a in Lhca1 and Lhca4 monomers of the LHC I-730 heterodimer are as fast as the energy equilibration processes within the PS I core. In contrast to the structural stability of the PS I core, the flexible subunit structure of the LHC I would probably determine the observed slow excitation energy equilibration processes in the range of tens of picoseconds. The red pigments in the LHC I are suggested to function largely as photoprotective excitation sinks in the peripheral antenna of PS I. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pigment binding of photosystem I light-harvesting proteins

Light-harvesting complexes (LHC) of higher plants are composed of at least 10 different proteins. Despite their pronounced amino acid sequence homology, the LHC of photosystem II show differences in pigment binding that are interpreted in terms of partly different functions. By contrast, there is only scarce knowledge about the pigment composition of LHC of photosystem I, and consequently no concept of potentially different functions of the various LHCI exists. For better insight into this issue, we isolated native LHCI-730 and LHCI-680. Pigment analyses revealed that LHCI-730 binds more chlorophyll and violaxanthin than LHCI-680. For the first time all LHCI complexes are now available in their recombinant form; their analysis allowed further dissection of pigment binding by individual LHCI proteins and analysis of pigment requirements for LHCI formation. By these different approaches a correlation between the requirement of a single chlorophyll species for LHC formation and the chlorophyll a/b ratio of LHCs could be detected, and indications regarding occupation of carotenoid-binding sites were obtained. Additionally the reconstitution approach allowed assignment of spectral features observed in native LHCI-680 to its components Lhca2 and Lhca3. It is suggested that excitation energy migrates from chlorophyll(s) fluorescing at 680 (Lhca3) via those fluorescing at 686/702 nm (Lhca2) or 720 nm (Lhca3) to the photosystem I core chlorophylls.     

A nomenclature for the genes encoding the chlorophylla/b-binding proteins of higher plants

We propose a nomenclature for the genes encoding the chlorophylla/b-binding proteins of the light-harvesting complexes of photosystem I and II. The genes encoding LHC I and LHC II polypeptides are namedLhca1 throughLhca4 andLhcb1 throughLhcb6, respectively. The proposal follows the general format recommended by the Commision on Plant Gene Nomenclature. We also present a table for the conversion of old gene names to the new nomenclature.     

Chlorophyll fluorescence changes at high temperatures induced by linear heating of greening barley leaves

A relative decrease of the high temperature part (above 60°C) of the chlorophyll fluorescence temperature curve during 3 h to 10 h greening period of barley (Hordeum vulgare L.) leaves was found to be concomitant to a decrease of Chl alb ratio and to a gradual increase of LHCP/core ratio found by electrophoresis and the ratio of granal to total length of thylakoid membranes. It is suggested that the high temperature part of the fluorescence temperature curve depends inversely on the relative amount of LHC II in thylakoid membranes.Abbreviations Chl a(b) chlorophyll a(b) - CPa chlorophyll a protein complex of PS II - CP1 P700 chlorophyll a protein complex of PS I - FP free pigments - FTC fluorescence temperature curve - F(T30) fluorescence intensity at 30°C - LHC II light harvesting complex II - LHCP light harvesting chlorophyll protein - LHCP3 (LHCPm) monomeric form of LHC II - LHCPo oligomeric form of LHC II complex - M1 first maximum of FTC - M2 second maximum (region) of FTC - PAA polyacrylamide - PAR photosynthetically active radiation - PS I(II) Photosystem I(II) - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis     

光系统II蛋白磷酸化及其生理意义

蛋白磷酸化修饰在几乎所有的生命活动中都起重要的调节作用.该文结合作者研究组的研究工作,概述了光系统II(PS II)蛋白磷酸化的调节及其生理功能.PS II复合体中的核心组分D1、D2、CP43和PsbH蛋白以及外周捕光天线(LHC II)蛋白都可以发生磷酸化.PS II蛋白磷酸化受质醌(PQ)的氧化还原状态、细胞色素b6f (Cyt b6f ) 和硫氧还蛋白以及光调节.PS II蛋白磷酸化可以调节激发能在两种光系统(PS I和PS II)之间的分配,减轻光胁迫对PS II的压力,保护核心蛋白免于光破坏,稳定PS II复合体的结构.     

Assembly and composition of the chlorophyll a-b light-harvesting complex of barley (Hordeum vulgare L.): Immunochemical analysis of chlorophyll b-less and chlorophyll b-deficient mutants

The chlorina-f2 mutant of barley (Hordeum vulgare L.) contains no chlorophyll b in its light-harvesting antenna, whereas the chlorina-103 mutant contains approximately 10% of the chlorophyll b found in wild-type. The absolute chlorophyll antenna size for Photosystem-II in wild-type, chlorina-103 and chlorina-f2 mutant was 250, 58 and 50 chlorophyll molecules, respectively. The absolute chlorophyll antenna size for Photosystem-I in wild-type, chlorina-103 and chlorina-f2 mutant was 210, 137 and 150 chlorophyll molecules, respoectively. In spite of the smaller PS I antenna size in the chlorina mutants, immunochemical analysis showed the presence of polypeptide components of the LHC-I auxiliary antenna with molecular masses of 25, 19.5 and 19 kDa. The chlorophyll a-b-binding LHC-II auxiliary antenna of PS II contained five polypeptide subunits in wild-type barley, termed a, b, c, d and e, with molecular masses of 30, 28, 27, 24 and 21 kDa, respectively. The polypeptide composition of the LHC-II auxiliary antenna of PS II was found to be identical in the two mutants, with only the 24 kDa subunit d present at an equal copy number per PS II in each of the mutants and in the wild-type barley. This d subunit assembles stably in the thylakoid membrane even in the absence of chlorophyll b and exhibits flexibility in its complement of bound chlorophylls. We suggest that polypeptide subunit d binds most of the chlorophyll associated with the residual PS II antenna in the chlorina mutants and that is proximal to the PS II-core complex.Abbreviations CP chlorophyll-protein - LHC the chlorophyll a-b binding light-harvesting complex - LHC-II subunit a the Lhcb4/5 gene product - subunit b the Lhcb1 gene product - subunit c Lhcb2 the gene product - subunit d the Lhcb3 gene product - subunit e the Lhcb6 gene product - PMSF phenylmethane sulphonyl fluoride - RC reaction center - Q_A the primary quinone electron acceptor of Photosystem-II - P700 the reaction center of PS I     

Tracing the evolution of the light-harvesting antennae in chlorophyll a/b-containing organisms

The light-harvesting complexes (LHCs) of land plants and green algae have essential roles in light capture and photoprotection. Though the functional diversity of the individual LHC proteins are well described in many land plants, the extent of this family in the majority of green algal groups is unknown. To examine the evolution of the chlorophyll a/b antennae system and to infer its ancestral state, we initiated several expressed sequence tag projects from a taxonomically broad range of chlorophyll a/b-containing protists. This included representatives from the Ulvophyceae (Acetabularia acetabulum), the Mesostigmatophyceae (Mesostigma viride), and the Prasinophyceae (Micromonas sp.), as well as one representative from each of the Euglenozoa (Euglena gracilis) and Chlorarachniophyta (Bigelowiella natans), whose plastids evolved secondarily from a green alga. It is clear that the core antenna system was well developed prior to green algal diversification and likely consisted of the CP29 (Lhcb4) and CP26 (Lhcb5) proteins associated with photosystem II plus a photosystem I antenna composed of proteins encoded by at least Lhca3 and two green algal-specific proteins encoded by the Lhca2 and 9 genes. In organisms containing secondary plastids, we found no evidence for orthologs to the plant/algal antennae with the exception of CP29. We also identified PsbS homologs in the Ulvophyceae and the Prasinophyceae, indicating that this distinctive protein appeared prior to green algal diversification. This analysis provides a snapshot of the antenna systems in diverse green algae, and allows us to infer the changing complexity of the antenna system during green algal evolution.     

Rapid isolation of photosystem I chlorophyll-binding proteins by anion exchange perfusion chromatography

With the new method of anion exchange perfusion chromatography we have devised an extremely rapid technique to subfractionate spinach Photosystem I into its chlorophyll a containing core complex and various components of the Photosystem I light-harvesting antenna (LHC I). The isolation time for the LHC I subcomplexes following solubilisation of native Photosystem I was reduced from 50 h using traditional density centrifugation procedures down to only 10–25 min by perfusion chromatography. Within this very short period of isolation, LHC I has been obtained as subfractions highly enriched in Lhca2+3 (LHC I-680) and Lhca1+4 (LHC I-730). Moreover, other highly enriched subfractions of LHC I such as Lhca2, Lhca3 and Lhca1+2+4 were obtained where the later two populations have not previously been obtained in a soluble form and without the use of SDS. These various subfractions of the LHC I antenna have been characterised by absorption spectroscopy, 77 K fluorescence-spectroscopy and SDS-PAGE demonstrating their identities, functional intactness and purity. Furthermore, the analyses located a chlorophyll b pool to preferentially transfer its excitation energy to the low energy F735 chromophore, and located specifically the origin of the 730 nm fluorescence to the Lhca4 component. It was also revealed that Lhca2 and Lhca3 have identical light-harvesting properties. The isolated Photosystem I core complex showed high electron transport capacity (1535 moles O₂ mg Chl^–1 h^–1) and low fluorescence yield (0.4%) demonstrating its high functional integrity. The very rapid isolation procedure based upon perfusion chromatography should in a significant way facilitate the subfractionation of Photosystem I proteins and thereby allow more accurate functional and structural studies of individual components.Abbreviations a.u. arbitrary units - DCIP 2.6-dichlorophenol indophenol - LHC light harvesting 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.     

Assembly of light-harvesting complex II and biogenesis of thylakoid membranes in chloroplasts

A critical review of studies on import of Lhcb (apoproteins of LHC II) by chloroplasts uncovered a mechanism for initiation of assembly of light-harvesting complexes. Manipulation of in vivo systems and mutagenesis of specific residues in the protein showed that accumulation of physiological amounts of Lhcb by the plastid requires interaction of the protein with Chl within the inner membrane of the chloroplast envelope. Retention motifs, commonly -EXXHXR- in the first membrane-spanning region (helix-1) and -EXXNXR- in the third membrane-spanning region (helix-3), occur in the primary sequence of the protein. Mutations in these sequences prevent accumulation of Lhcb by isolated chloroplasts. We propose that the His or Asn sidechain and a transient intrahelix ion-pair with the Glu and Arg residues provide ligands for two molecules of Chl in each motif, which serve as a sensing mechanism for the availability of Chl. Interaction of two Chl molecules with both motifs is required for stable insertion of the protein into the membrane. Chl(ide) is possibly quenched by interaction with xanthophylls immediately after synthesis, and Chl-lutein pairs may initiate folding of Lhcb. Lhcb that does not immediately interact with sufficient Chl molecules is not retained by the organelle and, in vivo, is retracted into the cytosol or shunted to vacuoles for degradation rather than imported into the plastid stroma. The ubiquitous existence of retention motifs from small Lhcb-like polypeptides in cyanobacteria to all nuclear-encoded Chl-binding proteins (the Lhcb and Lhca families and related proteins) testify to the importance of these sequences in assembly of Chl-protein complexes.     

Supramolecular Assembly and Function of Subunits Associated with the Chlorophyll a-b Light-Harvesting Complex II (LHC II) in Soybean Chloroplasts

The chlorophyll (Chl) a-b light harvesting complex II (LHC II)contains more than 80% of the light-harvesting pigments of photosystemII (PS II) in chloroplasts. The supramolecular assembly andfunction of this auxiliary antenna system was investigated inChi b-deficient and Chi b-less mutant chloroplasts from soybeanand barley plants, and in their wild-type counterparts. Fourdistinct LHC II polypeptides were resolved by SDS-PAGE (subunitsa, b, c and d), having apparent molecular masses of 29, 28,27.2 and 26.8 kDa, respectively. The analysis of LHC II subunitcomposition in different developmental stages of the PS II unitin soybean (3>Chla/Chlbb>6), indicated the associationof specific subunits with the LHC H-inner and LHC II-peripheralin the chloroplast. The amount of subunit a in PS II was constantover a broad range of Chl a/Chl b ratios, suggesting that thissubunit is closely associated with the PS II-core complex. Subunitd also appeared to be constant over a wide range of Chl a/Chlb ratios, suggesting close association with the LHC II-inner.The PS II content in subunits b and c increased with the PSII antenna development in soybean but the ratio of b/c remainedconstant in all developmental stages and equal to 2 :1. Subunita was present in the Chl b-less chlorina f2 mutant of barleygrown under continuous illumination but was absent under intermittentillumination. The results suggest that each subunit binds 13-15Chl molecules. A working hypothesis is presented on the PS IIantenna development and LHC II subunit composition in soybeanchloroplasts. (Received October 11, 1988; Accepted January 19, 1989)     

Immunological characterization of chlorophyll a/b-binding proteins of barley thylakoids

Monoclonal antibodies have been raised against the light-harvesting chlorophyll a/b-binding proteins of photosystem I (LHCI) using a photosystem (PS) I preparation (PSI-200) wild-type from barley (Hordeum vulgare L. cv. Svaløf's Bonus) as the antigen. These antibodies cross-reacted with a minor light-harvesting chlorophyll a/b-protein of PSII (Chla/b-P1=CP29), but not with the major one, LHCII (=Chla/b-P2^**). Similarly, a monoclonal antibody to Chla/b-P1, elicited by a PSII preparation as the antigen, cross-reacted with LHCI, but not LHCII. This explains why an antigen consisting of LHCII, free of LHCI, but contaminated with Chla/b-P1, can elicit antibodies which cross-react with LHCI. Immunoblot assays showed that LHCI and Chla/b-P1 have at least two epitopes in common. Immunogold labelling of thin-sectioned wild-type thylakoids confirmed a preferential localisation of Chla/b-P1 in grana partition membranes and LHCI in stroma lamellae. The presence of LHCI was demonstrated in barley mutants lacking the PSI reaction centre (viridis-zb ⁶³) and chlorophyll b (chlorina-f2), and was correlated with the presence of long-wavelength (730 nm) fluorescence emission at 77 K. The mutant viridis-k ²³, which has a 77 K long-wavelength fluorescence peak at 720 nm, was shown by immune-blot assay to lack LHCI, although Chla/b-P1 was present.Abbreviations Chl-P chlorophyll-protein - CM Carlsberg Monoclonal - Da dalton - LHC light-harvesting complex - PAGE polyacrylamide gel electrophoresis - PSI, II photosystem I, II - PSI-200 PSI containing LHCI polypeptides - SDS sodium dodecyl sulphate