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PubMed1982

The participation of the Shemin and C5 pathways in 5-aminolaevulinate and chlorophyll formation in higher plants and facultative photosynthetic bacteria.

Chlorophyll and bacteriochlorophyll formation from 14C-labelled precursors was studied during the illumination of etiolated maize leaves excised from dark-grown seedlings and in cell suspensions of respiring, dark-, aerobically-grown Rhodopseudomonas spheroides adapting to the photosynthetic state in the light under anaerobic conditions. It was found that 1-14C-labelled glutamate and 2-oxoglutarate were incorporated into the tetrapyrrole moieties of chlorophyll and bacteriochlorophyll. This suggests that the C5 pathway of tetrapyrrole biosynthesis operates in both Zea mays and R. spheroides since in the alternative Shemin pathway the label would have been lost as 14CO2 during the formation of succinyl-CoA prior to the condensation with glycine to form 5-aminolaevulinate. It was also found that 5(-14)C-labelled glutamate and 2-oxoglutarate were incorporated into these chlorophylls which is consistent with the operation of both the C5 and Shemin pathways. That the Shemin pathway is also involved was confirmed by the incorporation of [2(-14)C]glycine into both chlorophylls. None of these substrates were incorporated into the phytol moieties of either plant or bacterial chlorophyll or into the carotenoids. However, when [1(-14)C]acetate was added to greening maize leaves not only the tetrapyrrole and phytol moieties were labelled but also the carotenoids: the labelling of these lipids is consistent with their formation from acetate via the isopentenyl pyrophosphate pathway. By comparing the incorporation of [1(-14)C]2-oxoglutarate with that of [5(-14)C]2-oxoglutarate the approximate relative contribution of each pathway to chlorophyll biosynthesis was determined. In maize leaves both pathways contributed almost equally but in R. spheroides the contribution by the Shemin and C5 pathways was 90 and 10%, respectively.

Amino Acids↗
PubMedDate not supplied

Enzymic capacities for chlorophyll biosynthesis. Activation and de novo synthesis of enzymes.

A previously published working model for the regulation of chlorophyll formation has been tested studying early steps of chlorophyll and porphyrin biosynthesis in developing cotyledons of Helianthus annuus. The activities of delta-aminolevulinate synthetase (ALAS), delta-aminolevulinate dehydratase (ALAD), and the porphobilinogenase complex (PBGase) at any given time have been found to be strongly associated with endogenous developmental processes. Highest activities in darkness have been observed at times when maximum chlorophyll formation would have occurred had the plants been exposed to light. Only in the case of ALAS was the maximum activity in light much greater than that observed in the dark. Density labeling experiments and other data suggest that enzyme synthesis is mediated both by development and by illumination. Moreover, ALAS activity appears to be subject to inhibition, presumably by products of the porphyrin biosynthesis, as indicated by halflife experiments. Rapid enzyme degradation in the absence of light seems to be less probable. Slight ALAS activity in darkness is present as long as the plastids are not fully developed. In contrast to findings with cell cultures of tobacco, in Helianthus cotyledons ALAS certainly plays the main role in the regulation of chlorophyll biosynthesis. Nevertheless, increasing activities of the succeeding enzymes, located in the plastids, ensure that increased concentrations of delta-aminolevulinate (ALA) are drawn into the chlorophyll biosynthetic pathway. The experiments corroborate the suggestion that chlorophyll biosynthesis is controlled by different but interdependent mechanisms. The dominant regulatory mechanism is dependent on the stage of development.

5-Aminolevulinate Synthetase↗
PubMedDate not supplied

[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.

Chlorophyll↗
PubMedDate not supplied

[Effect of the spectral composition of light on the mechanism of reaction of chlorophyll oxidation].

Photochemical oxidation of chlorophyll "a" on excitation of the pigment in different spectrum region (400-800 nm) was studied by flash photolysis. The absorption spectrum of chlorophyll cation-radical Chl+ was obtained and the values of extinction coefficient found. An attempt was made of photochemical generation of dication form of chlorophyll. Thermodynamical calculation supporting the possibility of the following reaction is presented: (Chl+)*+Ae -- Chl2""Ae. The absence of Chl2+ is explained by a short life time of the excited cation-radical of chlorophyll (Chl+)*. The effect of the wave length of excited light on the kinetics of the decay of chlorophyll cation-radical is studied. It is shown that on excitation of chlorophyll "a" with white light the life time of Chl+ decreases and its death is described by an equation of first order, which is explained by the formation of ion-radical of the electron acceptor resulting from the direct excitation of Ae.

Chlorophyll↗
PubMedDate not supplied

[Pigment-protein complexes nd the number of the reaction photosystem centers in pea chlorophyll mutants].

We studied fluorescent and absorption properties of the chloroplasts and pigment-protein complexes isolated by gel electrophoresis from the leaves of pea, the initial cultivar Torsdag and mutants chlorotica 2004 and 2014. Specific maxima of fluorescence and chlorophyll forms in individual complexes have been determined from the absorption and fluorescence spectra of the chloroplast chlorophyll and their secondary derivatives at 23 and -196 degrees C. Chlorotica 2004 mutant proved to have an increased intensity of a long-wave band at both 23 degrees C (745 nm) and -196 degrees C (728 nm) of the light-harvesting complex I. At the same time, this mutant featured a decreased accumulation of chlorophyll forms at 690, 697, and 708 nm forming the nearest-neighbor antenna of PSI reaction center. No spectral differences have been revealed between chlorotica 2014 mutant and the initial cultivar. Gel electrophoresis demonstrated synthesis of all chlorophyll-protein complexes in both mutants. At the same time, analysis of photochemical activity of PSI and PSII reaction centers and evaluation of the light-harvesting antenna as well as the number of reaction centers of the photosystems suggest that chlorotica 2004 mutant has 1.7 times less PSI reaction centers due to a mutation-disturbed chlorophyll a-protein complex of PSI. The primary effect of chlorotica 2014 mutation remains unclear. The proportional changes in the photosystem complexes in this mutant suggest that they are secondary and result from a 50% decrease in chlorophyll content.

Chlorophyll↗
PubMed2006

[Effects of NO3- stress and recovery on chlorophyll fluorescence parameters and Atpase activities of cucumber seedling leaves].

With water culture, this paper studied the effects of NO3- stress and recovery on the chlorophyll contents, chlorophyll fluorescence parameters, and ATPase activities of cucumber seedling leaves. The results showed that under stress for 7 days, the chlorophyll a, chlorophyll b, total chlorophyll and carotenoid contents, intrinsic fluorescence (Fo), and Mg-ATPase and Ca-ATPase activities were increased significantly when the NO3- concentration was high (168 mmol x L(-1)), while the intrinsic photochemical efficiency (Fv/Fm), potential activities (Fv/Fo) and quantum yield (phiPS II) of PSII were decreased with increasing NO3- concentration. After recovery for 7 days, the chlorophyll and carotenoid contents of all treatments with NO3- were lower than CK, while the intrinsic fluorescence, intrinsic photochemical efficiency and quantum yield of PS II were similar to CK when the NO3- concentration was < or = 84 mmol x L((-1), and the Fv/Fm and phiPS II were significantly lower than CK when the NO3-concentration was > 84 mmol x L(-1). The potential activity of PS II was similar to CK when the NO3- concentration was 42 and 126 mmol x L(-1), but significantly lower than CK in other treatments. The activities of Mg-ATPase and Ca-ATPase were decreased firstly but increased then when the NO3- concentration was > 84 mmol x L(-1).

Adenosine Triphosphatases↗
PubMedDate not supplied

[Absorption spectra of chlorophyll a adsorbed on aerosil].

The adsorption spectra of chlorophyll a adsorbed on aerosil surface have been studied. It has been supposed that the spectral properties of adsorbed chlorophyll a layers are mainly due to the interactions between the pigment molecules. The derivative absorption spectra of adsorbed chlorophyll a have been obtained. It has been determined that descrete absorption maxima of adsorbed chlorophyll a aggregates are characteristic of the native chlorophyll a. It has been supposed that the fundamental spectral forms of chlorophyll a in vivo are reproduced in adsorbed layers of the pigment.

Adsorption↗
PubMedDate not supplied

[Chlorophyll phosphorescence in chloroplasts and their fragments].

Spectral parameters, decay time and quantum yield of low temperature (--196 degrees) delayed luminescence of chloroplasts and chloroplasts fragments have been investigated. It has been shown that the fragments enriched in photosystem 2, photosystem 1 of stroma or grana, obtained by differential centrifugation after digitonin treatment produce a delayed emission with components similar to that of initial chloroplasts, normal leaves and alga; i. e. phosphorescence (maximum 960--980 nm) and delayed fluorescence (maxima at 690 and 740 nm) of chlorophyll and phosphorescence of pigments of different nature (780--820 nm). Excitation spectra of chlorophyll phosphorescence have the maximum at 669 +/- 1 nm and shoulder at 650 nm. The quantum yield of chlorophyll phosphorescence in chloroplast is found to be lower than that of chlorophyll in ethanol by the factor of 200. It increases with destruction of initial structures reaching the maximal value in the most light fragments. The data suggest that the luminescence studied accompanies desactivation of the triplet states of the chlorophyll molecules involved in the photosynthetic pigment complex. On the basis of previous studies it has been proposed that the increase of phosphorescence intensity in the light particles is due to disturbances in the pigment complex leading to a decrease of triplet-triplet energy transfer from chlorophyll to carotenoids.

Carotenoids↗
PubMed1991

Protein and chlorophyll in photosystem II probed by infrared spectroscopy.

The infrared spectra of photosystem II (PS II) enriched submembrane fractions isolated from spinach are obtained in water and in heavy water suspension Other spectra are obtained after a photooxidation reaction was performed on PS II to bleach the pigments. The water bands are removed by computer subtraction and the amide bands (A, B, I, II, and III) of the protein are identified. Computer enhancement techniques are used to narrow the bandwidth of the bands that the weak chlorophyll bands, buried in the much stronger protein bands, can be observed. Comparing the spectra of native and photooxidized PS II pr in water and in heavy water, we determine that three polypeptide domains are present in the native material. The first domain, which contains 22% of th is situated in the peripheral region of the PS II system. The polypeptides in this region are unfolded and devoid of chlorophyll. The second domain con of the polypeptides, is more organized, and contains the chlorophylls. The third domain has an alpha-helix configuration, does not contain chlorophyll, a affected by the photooxidation reaction or by the proton/deuteron exchange. Three different types of chlorophyll organisation are identified: two have carbonyl groups non-bonded, differing from one another only in their hydrophobic milieux; the third is weakly bonded to another unidentified group. Other forms of chlorophyll organisation are present but could not be observed because their absorption is buried in the protein amide I band.

Journal Article↗
PubMed2006

Association of fucoxanthin chlorophyll a/c-binding polypeptides with photosystems and phosphorylation in the centric diatom Cyclotella cryptica.

Solubilization of thylakoid membranes of Cyclotella cryptica with dodecyl-beta maltoside followed by sucrose density gradient centrifugation or deriphate polyacrylamide gel electrophoresis resulted in the isolation of pigment protein complexes. These complexes were characterized by absorption and fluorescence spectroscopy, sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western immunoblotting using antisera against fucoxanthin chlorophyll a/c-binding proteins and the reaction center protein D2 of photosystem II. Sucrose density gradient centrifugation yielded four bands. Band 1 consisted of free pigments with minor amounts of fucoxanthin chlorophyll a/c-binding proteins. Bands 2, 3, and 4 represented a major fucoxanthin chlorophyll a/c-binding protein fraction, photosystem II, and photosystem I, respectively. Deriphate polyacrylamide gel electrophoresis gave rise to five bands, representing photosystem I, photosystem II, two fucoxanthin chlorophyll a/c-binding protein complexes, and a band mostly consisting of free pigments. In the Western immunoblotting experiments, the specific association of two fucoxanthin chlorophyll a/c-binding proteins, Fcp2 and Fcp4, to the photosystems could be demonstrated. In vivo experiments using antibodies against phosphothreonine residues and in vitro studies using [gamma-32P]ATP showed that fucoxanthin chlorophyll a/c binding-proteins of 22 kDa became phosphorylated.

Centrifugation, Density Gradient↗
PubMed2006

Density functional theory for charge transfer: the nature of the N-bands of porphyrins and chlorophylls revealed through CAM-B3LYP, CASPT2, and SAC-CI calculations.

While density functional theory (DFT) has been proven to be extremely useful for the prediction of thermodynamic and spectroscopic properties of molecules, to date most functionals used in common implementations of DFT display a systematic failure to predict the properties of charge-transfer processes. While this is explicitly manifest in Rydberg transitions of atoms and molecules and in molecular charge-transfer spectroscopy, it also becomes critical for systems containing extended conjugation such as polyenes and other conducting polymers, porphyrins, chlorophylls, etc. A new density functional, a Coulomb-attenuated hybrid exchange-correlation functional (CAM-B3LYP), has recently been developed specifically to overcome these limitations, and it has been shown to properly predict molecular charge-transfer spectra. Here, we demonstrate that it predicts qualitatively reasonable spectra for porphyrin, some oligoporphyrins, and chlorophyll. However, alternate density functionals developed to overcome the same limitations such as current-density functional theory are shown, in their present implementation, to remain inadequate. The CAM-B3LYP results are shown to be in excellent agreement with complete-active-space plus second-order Møller-Plesset perturbation theory and symmetry-adapted cluster configuration interaction calculations: These depict the N and higher bands of porphyrins and chlorophylls as being charge-transfer bands associated with localization of molecular orbitals on individual pyrrole rings. The validity of the basic Gouterman model for the spectra of porphyrins and chlorophylls is confirmed, rejecting modern suggestions that non-Gouterman transitions lie close in energy to the Q-bands of chlorophylls. As porphyrins and chlorophylls provide useful paradigms for problems involving extended conjugation, the results obtained suggest that many significant areas of nanotechnology and biotechnology may now be realistically treated by cost-effective density-functional-based computational methods.

Journal Article↗
PubMed2000

Absorption spectra of chlorophyll a and b in Lhcb protein environment.

The spectral forms of the two chlorophyll species in higher plant Photosystem II antenna proteins have been experimentally determined within their protein environment. Recombinant CP29 and LHC II antenna proteins missing individual chromophores were obtained by over-expression in bacteria without any changing of the primary protein sequence and in vitro reconstitution. Difference absorption spectroscopy with respect to the corresponding proteins binding the complete pigment complement yielded the spectral shape and extinction of single chlorophyll a and b. A functional relation of their absorption was given by Gaussian subband decomposition covering the entire Q(x) and Q(y) optical region together with the absolute value of the molar extinction coefficient. With respect to analogous determinations reported in the literature for organic solvents, this information is valuable for further understanding the in-protein chlorophyll excited states and excited state dynamics: in particular, for the calculation of Förster transfer rates by means of chlorophyll-chlorophyll overlap integral employing the Stepanov relation for emission and single chromophore transition energies according to the results of mutational analysis of chlorophyll binding sites [Bassi et al. (1999) Proc Natl Acad Sci USA 96: 10056-10061; Remelli et al. (1999) J Biol Chem 274: 33510-33521].

Journal Article↗
PubMed1976

New proposal for structure of special-pair chlorophyll.

A new model is proposed for the structure of the special pair of chlorophyll a molecules believed to correspond to the P700 species in green plants and algae. The proposed model, although admittedly speculative, is based upon exciton-theoretical considerations and on in vitro infrared and visible absorption spectra of a 700 nm absorbing ethanol adduct of chlorophyll a. In the new model, two chlorophyll a molecules are held together by (a) two strong ring V keto C[unk]O[unk]H[unk]O (or keto C[unk]O[unk]H[unk]N, or keto C[unk]O[unk]H[unk]S) hydrogen bonds and by (b) pi-pi van der Waals stacking interactions between the two chlorophyll a macrocycles. Macrocycle stacking provides the intermolecular pi-pi overlap necessary to promote the (experimentally observed) delocalization of the unpaired electron of the in vivo radical over two chlorophyll pi systems. The new model provides an explicit role for the participation of protein in the formation of the chlorophyll special pair. The in vitro system yields an electron spin resonance signal indistinguishable from that of oxidized P700 in Chlorella vulgaris.

Journal Article↗
PubMed1978

Coherent stimulated light emission (lasing) in covalently linked chlorophyll dimers.

The covalently linked chlorophyll a dimer exhibits remarkably different properties in the folded and open configurations. In the folded configuration the absorption maximum is at 695 nm and the fluorescence maximum is at 730 nm. Laser output at 733 and 735 nm is obtained for solutions in wet benzene and 0.1 M ethanol/toluene, respectively. Measurements of fluorescence lineshapes, made with a transverse excited atmospheric (TEA) nitrogen laser for excitation, show the lifetime shortening associated with stimulated emission resulting from appreciable concentrations of molecules in S(1) excited states. In contrast, the open dimer has absorption and fluorescence spectra essentially the same as those of chlorophyll a monomer. Unlike either the folded dimer or chlorophyll a monomer, the open dimer shows no laser emission or fluorescene lifetime shortening. It does not appear that the behavior of the open dimer can be explained in terms of excimer or triplet formation or by nonradiative decay processes. It is suggested that absorption of the exciting radiation by S(1), leading to the formation of an exciplex or charge transfer state, may be involved. Significantly, no large changes in fluorescence quantum yield or fluorescence lifetime are observed for these dimers as compared to monomer chlorophyll. This suggests that concentration quenching and lifetime shortening in condensed chlorophyll systems involve more than the simple proximity of two chlorophyll molecules.

Journal Article↗
PubMed1987

Chlorophyll catabolism in senescing plant tissues: In vivo breakdown intermediates suggest different degradative pathways for Citrus fruit and parsley leaves.

High-pressure liquid chromatography was used to separate chlorophyll derivatives in acetone extracts from senescing Citrus fruit peel, autumnal Melia azedarach L. leaves, and dark-held detached parsley (Petroselinum sativum L.) leaves. Chlorophyllide a and another polar, dephytylated derivative accumulated in large amounts in senescing Citrus peel, particularly in fruit treated with ethylene. Ethylene also induced a 4-fold increase in the specific activity of Citrus chlorophyllase (chlorophyll chlorophyllidohydrolase, EC 3.1.1.14). Detailed kinetics based on a hexane/acetone solvent partition system showed that the in vivo increase in dephytylated derivatives coincided with the decrease in total chlorophyll. Polar, dephytylated derivatives accumulated also in senescing Melia leaves. Senescing parsley leaves revealed a very different picture. The gradual disappearance of chlorophyll a was accompanied by an increase in pheophytin a and by the transient appearance of several phytylated derivatives. Only pheophytin a and an adjacent peak were left when all the chlorophyll a had disappeared. The pathways for breakdown of chlorophyll in the Citrus and parsley senescence systems are discussed.

Journal Article↗
PubMed1996

Lhcb Transcription Is Coordinated with Cell Size and Chlorophyll Accumulation (Studies on Fluorescence-Activated, Cell-Sorter-Purified Single Cells from Wild-Type and immutans Arabidopsis thaliana).

To study the mechanisms that integrate pigment and chlorophyll a/b-binding apoprotein biosynthesis during light-harvesting complex II assembly, we have examined [beta]-glucuronidase (GUS) enzyme activities, chlorophyll contents, and cell sizes in fluorescence-activated, cell-sorting-separated single cells from transgenic Arabidopsis thaliana wild-type and immutans variegation mutant plants that express an Lhcb (photosystem II chlorophyll a/b-binding polypeptide gene)/GUS promoter fusion. We found that GUS activities are positively correlated with chlorophyll content and cell size in green cells from the control and immutans plants, indicating that Lhcb gene transcription is coordinated with cell size in this species. Compared with the control plants, however, chlorophyll production is enhanced in the green cells of immutans; this may represent part of a strategy to maximize photosynthesis in the green sectors to compensate for a lack of photosynthesis in the white sectors of the mutant. Lhcb transcription is significantly higher in pure-white cells of the transgenic immutans plants than in pure-white cells from norflurazon-treated, photooxidized A. thaliana leaves. This suggests that immutans partially uncouples Lhcb transcription from its normal dependence on chlorophyll accumulation and chloroplast development. We conclude that immutans may play a role in regulating Lhcb transcription, and may be a key component in the signal transduction pathways that control chloroplast biogenesis.

Journal Article↗
PubMed1969

Photosynthetic Studies on a Pea-mutant Deficient in Chlorophyll.

A chlorophyll-deficient mutant of pea (Pisum sativum) was found as a spontaneous mutation of the variety Greenfeast. Total chlorophyll of the mutant leaves was about one-half that of normal pea leaves per mg dry weight, and the ratio of chl a:chl b ranged from 10 to 18, compared with 3 for normal pea. In each generation the mutant plants gave rise to normal and mutant plants and lethal plants with yellow leaves.For a normal pea plant, CO(2) uptake was saturated at about 60,000 lux, whereas with mutant leaves, the rate of CO(2) uptake was still increasing at 113,000 lux. At 113,000 lux the mutant and normal leaves showed similar rates of CO(2) fixation per unit area of leaf surface, but on a chlorophyll basis the mutant leaves were twice as active. Hill reaction measurements on isolated chloroplasts also showed that the mutant chloroplasts were saturated at higher intensities than the normal, and that the activity of the mutant was at least double that of the normal on a chlorophyll basis.It is suggested that the photosynthetic units of the mutant chloroplasts contain about half the number of chlorophyll molecules as compared to the normal photosynthetic units.Electron microscopy of leaf sections of normal and mutant leaves showed that the mutant chloroplasts contain fewer lamellae per chloroplast and fewer lamellae per granum. The lethal chloroplasts, which were virtually devoid of chlorophyll, were characterized by an absence of grana.

Journal Article↗
PubMed1979

Chlorophyll Turnover in Skeletonema costatum, a Marine Plankton Diatom.

[(3)H]- and delta-[(14)C]Aminolevulinic acids were incorporated into the chlorophylls of Skeletonema costatum, a marine plankton diatom. In the stationary phase of growth, the tetrapyrrole-based pigments reached steady-state labeling after 10 hours. Under conditions of exponential cell division and chlorophyll accumulation, (3)H was rapidly lost from the labeled chlorophylls and was replaced with (14)C derived from delta-[4-(14)C]aminolevulinic acid. The kinetics of isotope dilution suggests recycling of tetrapyrrole precursors and/or two pigment pools, containing both chlorophyll a and chlorophyllide c, one which turns over rapidly (10 hours) and another which turns over more slowly (100 hours). Calculation of turnover times varied from 3 to 10 hours for chlorophyll a and from 7 to 26 hours for chlorophyllide c. The data suggest the dynamics of chlorophyll metabolism in S. costatum and explain the diatom's ability to undergo light-shade adaptation within a generation time.

Journal Article↗