The composition and structure of photosystem I‐associated antenna from Cyanidioschyzon merolae

Red algae contain two types of light‐harvesting antenna systems, the phycobilisomes and chlorophyll a binding polypeptides (termed Lhcr), which expand the light‐harvesting capacity of the photosynthetic reaction centers. In this study, photosystem I (PSI) and its associated light‐harvesting proteins were isolated from the red alga Cyanidioschyzon merolae. The structural and functional properties of the largest PSI particles observed were investigated by biochemical characterization, mass spectrometry, fluorescence emission and excitation spectroscopy, and transmission electron microscopy. Our data provide strong evidence for a stable PSI complex in red algae that possesses two distinct types of functional peripheral light‐harvesting antenna complex, comprising both Lhcr and a PSI‐linked phycobilisome sub‐complex. We conclude that the PSI antennae system of red algae represents an evolutionary intermediate between the prokaryotic cyanobacteria and other eukaryotes, such as green algae and vascular plants.     

Optimization and evolution of light harvesting in photosynthesis: the role of antenna chlorophyll conserved between photosystem II and photosystem I

The efficiency of oxygenic photosynthesis depends on the presence of core antenna chlorophyll closely associated with the photochemical reaction centers of both photosystem II (PSII) and photosystem I (PSI). Although the number and overall arrangement of these chlorophylls in PSII and PSI differ, structural comparison reveals a cluster of 26 conserved chlorophylls in nearly identical positions and orientations. To explore the role of these conserved chlorophylls within PSII and PSI we studied the influence of their orientation on the efficiency of photochemistry in computer simulations. We found that the native orientations of the conserved chlorophylls were not optimal for light harvesting in either photosystem. However, PSII and PSI each contain two highly orientationally optimized antenna chlorophylls, located close to their respective reaction centers, in positions unique to each photosystem. In both photosystems the orientation of these optimized bridging chlorophylls had a much larger impact on photochemical efficiency than the orientation of any of the conserved chlorophylls. The differential optimization of antenna chlorophyll is discussed in the context of competing selection pressures for the evolution of light harvesting in photosynthesis.     

Plasticity in the composition of the light harvesting antenna of higher plants preserves structural integrity and biological function

Arabidopsis plants in which the major trimeric light harvesting complex (LHCIIb) is eliminated by antisense expression still exhibit the typical macrostructure of photosystem II in the granal membranes. Here the detailed analysis of the composition and the functional state of the light harvesting antennae of both photosystem I and II of these plants is presented. Two new populations of trimers were found, both functional in energy transfer to the PSII reaction center, a homotrimer of CP26 and a heterotrimer of CP26 and Lhcb3. These trimers possess characteristic features thought to be specific for the native LHCIIb trimers they are replacing: the long wavelength form of lutein and at least one extra chlorophyll b, but they were less stable. A new population of loosely bound LHCI was also found, contributing to an increased antenna size for photosystem I, which may in part compensate for the loss of the phosphorylated LHCIIb that can associate with this photosystem. Thus, the loss of LHCIIb has triggered concerted compensatory responses in the composition of antennae of both photosystems. These responses clearly show the importance of LHCIIb in the structure and assembly of the photosynthetic membrane and illustrate the extreme plasticity at the level of the composition of the light harvesting system.     

Adaptation of the Photosynthetic Apparatus to Irradiance in Dunaliella tertiolecta: A Kinetic Study

The time course of adaptation from a high to a low photon flux density was studied in the marine chlorophyte Dunaliella tertiolecta. A one-step transition from 700 to 70 micromole quanta per square meter per second resulted in a reduction of doubling rate from 1.1 to 0.4 per day within 24 hours, followed by a slower accumulation of photosynthetic pigments, light harvesting antenna complexes, Photosystem II reaction centers and structural lipids that constitute the thylakoid membranes. Photoregulated changes in the biochemical composition of the thylakoid proteins and lipids were functionally accompanied by decreases in the minimal photosynthetic quantum requirement and photosynthetic capacity, and an increase in the minimal turnover time for in vivo electron transport from water to CO₂. Analysis of de novo synthesis of thylakoid membranes and proteins indicates that a high light to low light transition leads to a transient in carbon metabolism away from lipid biosynthesis toward the synthesis of the light harvesting antenna protein complexes, accompanied by a slower restoration rate of reaction centers and thylakoid membranes. This pattern of sequential synthesis of light harvesting complexes followed by reaction centers and membranes, appears to optimize light harvesting capabilities as cells adapt to low photon flux densities.     

Functional and Structural Organization of Chlorophyll in the Developing Photosynthetic Membranes of Euglena gracilis Z: III. SEQUENCE OF EVENTS LEADING TO THE FORMATION OF FUNCTIONAL PHOTOSYSTEM II PHOTOSYNTHETIC UNITS

Greening cells of Euglena were transferred back to darkness at different stages of chloroplast development in the presence or absence of specific inhibitors of protein synthesis. The analysis of chloroplast components showed that: (a) cycloheximide or streptomycin does not significantly inhibit the formation in darkness of active photosystem II (PSII) reaction centers if added after the lag phase for chloroplast development; (b) a limited number of active reaction centers are formed in the dark, sufficient to increase PSII reaction center to chlorophyll ratios to values close to those found in fully greened cells; (c) these dark-formed reaction centers appear to be inserted in already constituted and complete light-harvesting antennae. These results complement previous ones and lead us to propose a model for a sequential formation of PSII photosynthetic units during greening of Euglena, whereby conformational changes requiring time would allow already synthesized components of PSII reaction centers to be inserted or reorganized as active photochemical complexes in association with previously formed light-harvesting antennae.     

Biogenesis and light regulation of the major light harvesting chlorophyll-protein of diatoms

The apoprotein of the major light harvesting pigment-protein complex from the diatom Phaeodactylum tricornutum (UTEX 646) is composed of two similar polypeptides of 17.5 and 18.0 kilodaltons (kD). The in vivo synthesis of these polypeptides is inhibited by the 80s protein synthesis inhibitor cycloheximide, but not by the 70s ribosome inhibitor chloramphenicol. When total poly(A)⁺ RNA was used in in vitro protein synthesis, a number of polypeptides were synthesized with a dominant product at 22 kD. When the polypeptides were immunoprecipitated with monospecific antibodies to the 17.5 and 18.0 polypeptides, a single protein zone of 22 kD was detected. Immunoprecipitation with preimmune serum failed to precipitate detectable levels of protein at any relative molecular weight (M_r). These findings indicate that the two apoprotein polypeptides of the diatom light harvesting pigment-protein are translated from polyadenylated message on cytoplasmic ribosomes as either a single or two (or more) similar M_r precursor proteins. These findings also suggest that this protein is encoded in the nucleus.

Photosynthetic light adaptation features of P. tricornutum UTEX 646 indicate that it responds to low light by increasing cell size and numbers of photosystem I and II reaction centers per cell, but does not change photosynthetic rate per cell or photosynthetic unit sizes significantly. When low light cells are exposed to higher photon flux densities, the in vivo incorporation of label into the apoprotein of the light harvesting complex decreases. In contrast, high light grown cells show rapid (<3 hour) increases in apoprotein synthesis when exposed to low light levels. This is the first demonstration of a specific role of photon flux density in regulating the synthesis of a major light harvesting pigment-protein during photosynthetic light adaptation.

     

Energy transfers from Photosystem II to Photosystem I in Cryptomonas rufescens (Cryptophyceae)

In Cryptomonas rufescens (Cryptophyceae), phycoerythrin located in the thylakoid lumen is the major accessory pigment. Oxygen action spectra prove phycoerythrin to be efficient in trapping light energy.The fluorescence excitation spectra at ?196°C obtained by the method of Butler and Kitajima (Butler, W.L. and Kitajima, M. (1975) Biochim. Biophys. Acta 396, 72–85) indicate that like in Rhodophycease, chlorophyll a is the exclusive light-harvesting pigment for Photosystem I.For Photosystem II we can observe two types of antennae: (1) a light-harvesting chlorophyll complex connected to Photosystem II reaction centers, which transfers excitation energy to Photosystem I reaction centers when all the Photosystem II traps are closed. (2) A light-harvesting phycoerythrin complex, which transfers excitation energy exclusively to the Photosystem II reaction complexes responsible for fluorescence at 690 nm.We conclude that in Cryptophyceae, phycoerythrin is an efficient light-harvesting pigment, organized as an antenna connected to Photosystem II centers, antenna situated in the lumen of the thylakoid. However, we cannot afford to exclude that a few parts of phycobilin pigments could be connected to inactive chlorophylls fluorescing at 690 nm.     

Effects of light quality on chlorophyll-forms Ca 684, Ca 690 and Ca 699 of the diatom Phaeodactylum tricornutum

Colored light modifies the relative concentration of chlorophyll-forms of the diatom Phaeodactylum tricornutum compared to white-light control. No change in the ratio carotenoids/chlorophylls was observed after 4 days exposure to green light (max: 530 nm), blue light (max: 470 nm) or red light ( > 650 nm) of same intensity.However, the absorption spectra were modified, the content in Ca 684, Ca 690, Ca 699 forms increased in red and green light cultures and photosynthetic unit size of PS II decreased by 30% in green and blue light cultures.Fluorescence emission and fluorescence excitation spectra according to the Butler and Kitajima method (1975) were carried out for each culture. Ca 669 form was predominant in the two photosystems. The newly appeared far red forms fluoresce at 715 nm like PS I forms.We conclude that these new forms originated in a rearrangement of PS II forms. They do not transmit excitation energy to reaction center of PS I and are disconnected from the other chlorophyll-forms of the photosynthetic antennae.Abbreviations ABS absorption - Ca chlorophyll-complex - chla chlorophyll a - chl c chlorophyll c - chl t total chlorophylls - D.C.M.U. 3-(3, 4 dichlorophenyl) 1-diméthyl-urea - d^v division - F fluorescence - PS I and PS II photosystem I and photosystem II     

A Cyanobacterial Chlorophyll Synthase-HliD Complex Associates with the Ycf39 Protein and the YidC/Alb3 Insertase

Macromolecular membrane assemblies of chlorophyll-protein complexes efficiently harvest and trap light energy for photosynthesis. To investigate the delivery of chlorophylls to the newly synthesized photosystem apoproteins, a terminal enzyme of chlorophyll biosynthesis, chlorophyll synthase (ChlG), was tagged in the cyanobacterium Synechocystis PCC 6803 (Synechocystis) and used as bait in pull-down experiments. We retrieved an enzymatically active complex comprising ChlG and the high-light-inducible protein HliD, which associates with the Ycf39 protein, a putative assembly factor for photosystem II, and with the YidC/Alb3 insertase. 2D electrophoresis and immunoblotting also provided evidence for the presence of SecY and ribosome subunits. The isolated complex contained chlorophyll, chlorophyllide, and carotenoid pigments. Deletion of hliD elevated the level of the ChlG substrate, chlorophyllide, more than 6-fold; HliD is apparently required for assembly of FLAG-ChlG into larger complexes with other proteins such as Ycf39. These data reveal a link between chlorophyll biosynthesis and the Sec/YidC-dependent cotranslational insertion of nascent photosystem polypeptides into membranes. We expect that this close physical linkage coordinates the arrival of pigments and nascent apoproteins to produce photosynthetic pigment-protein complexes with minimal risk of accumulating phototoxic unbound chlorophylls.     

Developmental Loss of Photosystem II Activity and Structure in a Chloroplast-Encoded Tobacco Mutant, Lutescens-1

Lutescens-1, a tobacco mutant with a maternally inherited dysfunction, displayed an unusual developmental phenotype. In vivo measurement of chlorophyll fluorescence revealed deterioration in photosystem II (PSII) function as leaves expanded. Analysis of thylakoid membrane proteins by polyacrylamide gel electrophoresis indicated the physical loss of nuclear- and chloroplast-encoded polypeptides comprising the PSII core complex concomitant with loss of activity. Freeze fracture electron micrographs of mutant thylakoids showed a reduced density, compared to wild type, of the EF_s particles which have been shown previously to be the structural entity containing PSII core complexes and associated pigment-proteins. The selective loss of PSII cores from thylakoids resulted in a higher ratio of antenna chlorophyll to reaction centers and an altered 77 K chlorophyll fluorescence emission spectra; these data are interpreted to indicate functional isolation of light-harvesting chlorophyll a/b complexes in the absence of PSII centers. Examination of PSII reaction centers (which were present at lower levels in mutant membranes) by monitoring the light-dependent phosphorylation of PSII polypeptides and flash-induced O₂ evolution patterns demonstrated that the PSII cores which were assembled in mutant thylakoids were functionally identical to those of wild type. We conclude that the lutescens-1 mutation affected the correct stoichiometry of PSII centers, in relation to other membrane constituents, by disrupting the proper assembly and maintenance of PSII complexes in lutescens-1 thylakoid membranes.     

Restriction of Chlorophyll Synthesis Due to Expression of Glutamate 1-Semialdehyde Aminotransferase Antisense RNA Does Not Reduce the Light-Harvesting Antenna Size in Tobacco

The formation of 5-aminolevulinate is a key regulatory step in tetrapyrrole biosynthesis. In higher plants, glutamate 1-semialdehyde aminotransferase (GSA-AT) catalyzes the last step in the sequential conversion of glutamate to 5-aminolevulinate. Antisense RNA synthesis for GSA-AT leads to reduced GSA-AT protein levels in tobacco (Nicotiana tabacum L.) plants. We have used these transgenic plants for studying the significance of chlorophyll (Chl) availability for assembly of the light-harvesting apparatus. To avoid interfering photoinhibitory stress, plants were cultivated under a low photon flux density of 70 [mu]mol photons m-2 s-1. Decreased GSA-AT expression does not seem to suppress other enzymic steps in the Chl pathway, indicating that reduced Chl content in transgenic plants (down to 12% of the wild-type level) is a consequence of reduced GSA-AT activity. Chl deficiency correlated with a drastic reduction in the number of photosystem I and photosystem II reaction centers and their surrounding antenna on a leaf area basis. Different lines of evidence from the transgenic plants indicate that complete assembly of light-harvesting pigment-protein complexes is given preference over synthesis of new reaction center/core complexes, resulting in fully assembled photosynthetic units with no reduction in antenna size. Photosynthetic oxygen evolution rates and in vivo Chl fluorescence showed that GSA-AT antisense plants are photochemically competent. Thus, we suggest that under the growth conditions chosen during this study, plants tend to maintain their light-harvesting antenna size even under limited Chl supply.     

Effects of growth irradiance levels on the ratio of reaction centers in two species of marine phytoplankton

Cells of two species of single-celled marine algae, the diatom Skeletonema costatum (Greve), Cleve, and the chlorophyte Dunaliella tertiolecta Butcher, were cultured in white light of high (500-600 microeinsteins per square meter per second) and low (30 microeinsteins per square meter per second) intensity. For both algal species, cells grown at low light levels contained more chlorophyll a and had a lower ratio of chlorophyll a to chlorophylls b or c than did cells grown at high light levels. When photosynthetic unit sizes were measured on the basis of either oxygen flash yields or P₇₀₀ photooxidation, different results were obtained with the different species. In the chlorophyte, the cellular content of photosystem I (PSI) and photosystem II (PSII) reaction centers increased in tandem as chlorophyll a content increased so that photosynthetic unit sizes changed only slightly and the ratio PSI:PSII reaction centers remained constant at about 1.1. In the diatom, as the chlorophyll content of the cells increased, the number of PSI reaction centers decreased and the number of PSII reaction centers increased so that the ratio of PSI:PSII reaction centers decreased from about unity to 0.44. In neither organism did photosynthetic capacity correlate with changes in cellular content of PSI or PSII reaction centers. The results are discussed in relationship to the physical and biological significance of the photosynthetic unit concept.     

Functional and structural organization of chlorophyll in the developing photosynthetic membranes of Euglena gracilis Z. I. Formation of System II photosynthetic units during greening under optimal light intensity

The relationships between light-harvesting chlorophyll and reaction centers in Photosystem II were analyzed during the chloroplast development of dark-grown, non-dividing Euglena gracilis Z. Comparative measurements included light saturation of photosynthesis, oxygen evolution under flashing-light and fluorescence induction. The results obtained can be summarized as follows: (1) Photosystem II photocenters are formed in parallel with chlorophyll synthesis, but after a longer lag phase. (2) As a consequence, the chlorophyll: reaction center ratio (Emerson's type photosynthetic unit) decreases during greening. (3) This decrease is accompanied by considerable changes in the energy transfer and trapping properties of Photosystem II. Most of the initially synthesized chlorophylls are inactive in the transfer of excitations to active photochemical centers and are shared among newly formed Photosystem II photocenters; as a consequence, the number of chlorophylls functionally connected to each Photosystem II photocenter decreases and cooperativity between these centers appears. Results are discussed in terms of chlorophyll organization in developing photosynthetic membranes with reference to the lake or puddle models of photosynthetic unit organization.     

The causes of altered chlorophyll fluorescence quenching induction in the Arabidopsis mutant lacking all minor antenna complexes

Non-photochemical quenching (NPQ) of chlorophyll fluorescence is the process by which excess light energy is harmlessly dissipated within the photosynthetic membrane. The fastest component of NPQ, known as energy-dependent quenching (qE), occurs within minutes, but the site and mechanism of qE remain of great debate. Here, the chlorophyll fluorescence of Arabidopsis thaliana wild type (WT) plants was compared to mutants lacking all minor antenna complexes (NoM). Upon illumination, NoM exhibits altered chlorophyll fluorescence quenching induction (i.e. from the dark-adapted state) characterised by three different stages: (i) a fast quenching component, (ii) transient fluorescence recovery and (iii) a second quenching component. The initial fast quenching component originates in light harvesting complex II (LHCII) trimers and is dependent upon PsbS and the formation of a proton gradient across the thylakoid membrane (ΔpH). Transient fluorescence recovery is likely to occur in both WT and NoM plants, but it cannot be overcome in NoM due to impaired ΔpH formation and a reduced zeaxanthin synthesis rate. Moreover, an enhanced fluorescence emission peak at ~679?nm in NoM plants indicates detachment of LHCII trimers from the bulk antenna system, which could also contribute to the transient fluorescence recovery. Finally, the second quenching component is triggered by both ΔpH and PsbS and enhanced by zeaxanthin synthesis. This study indicates that minor antenna complexes are not essential for qE, but reveals their importance in electron stransport, ΔpH formation and zeaxanthin synthesis.     

On the role of ß-carotene in the reaction center chlorophyll a antennae of photosystem I

Absorption and low temperature fluorescence emission spectra were measured on chloroplast thylakoids and on purified reaction center chlorophyll a-protein complexes of photosystem I, CP-a₁. A clear association between the presence of ß-carotene and the occurrence of far red absorbing and emitting chlorophyll a components of the reaction center antennae of photosystem I was demonstrated. For this study chloroplasts and CP-a₁ were obtained from normal and carotenoid deficient plant material of various sources. The experimental material included 1) lyophilized pea chloroplasts extracted with petroleum ether, 2) the carotenoid deficient mutant C-6E of Scenedesmus obliquus and 3) wheat chloroplasts derived from normal and SAN-9789 treated plants. Removal of carotenoids, most likely principally ß-carotene, caused a loss of long wavelength absorbing chlorophylls in chloroplasts and purified CP-a₁, and the loss or diminution of the long wavelength peak seen in the low temperature fluorescence emission spectrum. This association between ß-carotene and special chlorophyll a forms may explain both the photoprotective and antenna functions ascribed to ß-carotene. In the absence of carotenoids in wheat and in the Scenedesmus mutant, the chlorophyll a antenna of photosystem I was extremely photosensitive. A triplet-triplet resonance energy transfer from chlorophyll a to ß-carotene and a singlet-singlet energy transfer from excited ß-carotene to chlorophyll would explain the photoprotective and antenna functions, respectively. The role of this association in determining some of the fluorescence properties of photosystem I is also discussed.     

Photoprotective energy dissipation involves the reorganization of photosystem II light-harvesting complexes in the grana membranes of spinach chloroplasts

Plants must regulate their use of absorbed light energy on a minute-by-minute basis to maximize the efficiency of photosynthesis and to protect photosystem II (PSII) reaction centers from photooxidative damage. The regulation of light harvesting involves the photoprotective dissipation of excess absorbed light energy in the light-harvesting antenna complexes (LHCs) as heat. Here, we report an investigation into the structural basis of light-harvesting regulation in intact spinach (Spinacia oleracea) chloroplasts using freeze-fracture electron microscopy, combined with laser confocal microscopy employing the fluorescence recovery after photobleaching technique. The results demonstrate that formation of the photoprotective state requires a structural reorganization of the photosynthetic membrane involving dissociation of LHCII from PSII and its aggregation. The structural changes are manifested by a reduced mobility of LHC antenna chlorophyll proteins. It is demonstrated that these changes occur rapidly and reversibly within 5 min of illumination and dark relaxation, are dependent on ΔpH, and are enhanced by the deepoxidation of violaxanthin to zeaxanthin.     

Functional Analysis of the Photosynthetic Apparatus of Prochlorothrix hollandica (Prochlorales), a Chlorophyll b Containing Procaryote

Light-shade adaptation of the chlorophyll a/b containing procaryote Prochlorothrix hollandica was studied in semicontinuous cultures adapted to 8, 80 and 200 μmole quanta per square meter per second. Chlorophyll a contents based on dry weight differed by a factor of 6 and chlorophyll b by a factor of 2.5 between the two extreme light conditions. Light utilization efficiencies determined from photosynthesis response curves were found to decrease in low light grown cultures due to lower light harvesting efficiencies; quantum requirements were constant at limiting and saturating irradiances for growth. At saturating growth irradiances, changes in light saturated oxygen evolution rate originated from changes in chlorophyll a antenna relative to the number of reaction centers II. At light-limiting conditions both the number of reaction centers II and the antenna size changed. The amount of chlorophyll b relative to reaction center II remained constant. As in cyanobacteria, the ratio of reaction center I to reaction center II was modulated during light-shade adaptation. On the other hand, time constants for photosynthetic electron transport (4 milliseconds) were low as observed in green algae and diatoms. The occurrence of state one to two and state two to one transitions is reported here. Another feature linking photosynthetic electron transport in P. hollandica to that in the eucaryotic photosynthetic apparatus was blockage of the state one to two transition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Although chlorophyll b was reported in association with photosystem I, the 630 nanometer light effect does not exclude that chlorophyll b is the photoreceptor for the state one to two transition.     

Changes in the composition of the photosynthetic apparatus in the galactolipid-deficient dgd1 mutant of Arabidopsis thaliana.

The glycerolipid digalactosyl diacylglycerol (DGDG) is exclusively associated with photosynthetic membranes and thus may play a role in the proper assembly and maintenance of the photosynthetic apparatus. Here we employ a genetic approach based on the dgd1 mutant of Arabidopsis thaliana to investigate the function of DGDG in thylakoid membranes. The primary defect in the genetically well-characterized dgd1 mutant resulted in a 90% reduction of the DGDG content. The mutant showed a decreased photosystem II (PSII) to photosystem I ratio. In vivo room- and low-temperature (77 K) chlorophyll fluorescence measurements with thylakoid preparations are in agreement with a drastically altered excitation energy allocation to the reaction centers. Quantification of pigment-binding apoproteins and pigments supports an altered stoichiometry of individual pigment-protein complexes in the mutant. Most strikingly, an increase in the amount of peripheral light-harvesting complexes of PSII relative to the inner antenna complexes and the PSII reaction center/core complexes was observed. Regardless of the severe alterations in thylakoid organization, photosynthetic oxygen evolution was virtually not compromised in dgd1 mutant leaves.     

Nuclear Involvement in the Appearance of a Chloroplast-Encoded 32,000 Dalton Thylakoid Membrane Polypeptide Integral to the Photosystem II Complex

The genetic locus for the high chlorophyll fluorescent photosystem II-deficient maize mutant hcf^*-3 has been definitively located to the nuclear genome. Fluorography of lamellar polypeptides labeled with [³⁵S]methionine in vivo revealed the specific loss of a heavily labeled 32,000 dalton thylakoid membrane polypeptide as well as its chloroplast encoded precursor species at 34,000 daltons. Examination of freeze-fractured mesophyll and bundle sheath thylakoids from hcf^*-3 revealed that both plastid types lacked the large EFs particles believed to consist of the photosystem II reaction center-core complex and associated light harvesting chlorophyll-proteins. The present evidence suggests that the synthesis or turnover/integration of the chloroplast-encoded 34,000 to 32,000 dalton polypeptide is under nuclear control, and that these polyipeptides are integral components of photosystem II which may be required for the assembly or structural stabilization of newly formed photosystem II reaction centers in both mesophyll and bundle sheath chloroplasts.     

Fluorescence,chlorophyll shape and number of photosystem reaction centers I and II in chlorotica mutants of Pisum sativum L

The fluorescent and absorbing properties of chloroplasts and pigment-protein complexes isolated by gel electrophoresis from pea leaves of the cultivar Torsdag and the mutants chlorotica 2004 and 2014 were studied. From the absorption and fluorescence spectra of chlorophylls and their 2nd derivatives, the range of their changes in the native state at 23 degrees C and specific maxima of fluorescence and the forms of chlorophyll of individual complexes at -196 degrees C were found. It was found that in mutant chlorotica 2004 the intensity of fluorescence of long-wave band at 745 nm (23 degrees C) and the maximum--at 728 nm (-196 degrees C) belonging to the light-harvesting complex I increased. Nevertheless, the accumulation of the chlorophyll forms in this mutant at 690, 697 and 708 nm, which make an antenna of reaction centers of photosystem (PS) I decreased. No spectral differences from the spectrum of the wild type were found in mutant chlorotica 2014, except for a weakening of interaction between the complexes of PS I and PS II. It was shown by gel electrophoresis that both mutants were capable of synthesizing any chlorophyll-protein complexes. However, the analysis of the photochemical activity of reaction centers of PS I and PS II as well as calculations of the value of the photosynthetic unit and the number of reaction centers of the photosystems enabled us to conclude that the quantity of the reaction centers of PS I in the mutant chlorotica 2004 was 1.7 times lower due to disturbance of mutations in biosynthesis or the formation of the chlorophyll a-protein complex of PS I. No primary effect of mutation of chlorotica 2014 was established. Proportional changes of all parameters in this mutant gave us the ground to consider them as secondary ones, which are caused by a decrease in chlorophyll content by half.