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PubMedDate not supplied

Influence of substituted 1,4-anthraquinones on the chlorophyll fluorescence and photochemical activity of pea thylakoid membranes.

The effect of substituted 1,4-anthraquinones on the photochemical activity and chlorophyll fluorescence of thylakoid membranes was examined. Both the fluorescence and the photochemical activity depend on the 1,4-anthraquinone substituent. Stronger quinone-induced quenching of the chlorophyll fluorescence than quinone-induced changes in the activity of photosystem II is observed. The type (Cl or Br) and the position (Cl) of the chalogen atom strongly influence the degree of inhibition of PSII electron transport and the quenching of chlorophyll fluorescence. The data suggest that the quenching of chlorophyll fluorescence is due rather to the interaction of the 1,4-anthraquinones and chlorophyll molecules than to an indirect effect caused by stimulation of the photochemistry.

Anthraquinones↗
PubMed2005

Enzymes of the last steps of chlorophyll biosynthesis: modification of the substrate structure helps to understand the topology of the active centers.

Enzymes catalyzing two of the late steps of chlorophyll biosynthesis are NADPH:protochlorophyllide oxidoreductase (POR), responsible for the light-dependent reduction of protochlorophyllide to chlorophyllide, and chlorophyll synthase that catalyses the esterification of chlorophyllide to chlorophyll. Inhibitors of these enzymes are of interest as potential herbicides. Both enzymes presumably form a complex, and the question arose whether chlorophyll synthase can react with chlorophyllide while it is still bound to POR. Here, we describe the chemical modification of protochlorophyllides and chlorophyllides with space-filling substituents at rings A, B, and E of the tetrapyrrole macrocycle and the reactivity of the modified substrates. Both enzymes tolerate the large and flexible phenylamino substituent at ring B, indicating that ring B points toward the enzyme surface while the substrate is bound. On the basis of the standard compound zinc protopheophorbide a (100% activity), the 7(1)-phenylamino derivative shows a comparable activity (83%) with POR that is higher than that of the parent formyl derivative zinc protopheophorbide b (58% activity). In contrast, the 3(1)-phenylamino derivative is less active (12%) than the parent formyl compound zinc protopheophorbide d (49% activity), indicating that the binding pocket leaves less space around ring A than around ring B. Almost no space must be left around ring E because substitution of the 13(2)-carboxymethyl ester (100% activity) by the 13(2)-carboxyethyl ester reduces the activity to 0.2%. Chlorophyll synthase leaves somewhat more space around ring E on the A side of the tetrapyrrole in the binding pocket; substitution of the 13(2)-proton (100% activity) by a methoxy group (53% activity) and an ethoxy group (11% activity) is tolerated to a certain extent, while the carbomethoxy group in this position is not accepted. Opening of ring E to a chlorin e6 dimethylester is tolerated (39% activity), while the large benzylamide residue at this site leads to the loss of activity. We conclude that the tetrapyrroles bind to both enzymes in the same direction: rings C, D, and E are oriented to the interior of the binding cleft, and rings A and B are oriented to the surface of the enzyme; this excludes simultaneous binding to both enzymes.

Bacterial Proteins↗
PubMed2006

Red pool chlorophylls of photosystem I of the cyanobacterium Thermosynechococcus elongatus: a single-molecule study.

Photosystem I reaction centers of the cyanobacterium Thermosynechococcus elongatus have been investigated using single-molecule spectroscopy. Single-molecule fluorescence emission spectra reveal a new fluorescence band located at 745 nm. Fluorescence polarization spectroscopy and fluorescence autocorrelation analysis show that only a few chlorophylls are responsible for the photoemission from the Photosystem I trimer at low temperature. Intersystem crossing parameters of the red pool chlorophylls have been determined via fluorescence autocorrelation measurements. The triplet yield of the red chlorophylls is strongly reduced in comparison to chlorophyll a in solution. Strong quenching of the triplet state indicates that the red chlorophylls are located in close contact to carotenoids.

Chlorophyll↗
PubMed1999

Tryptophan at position 181 of the D2 protein of photosystem II confers quenching of variable fluorescence of chlorophyll: implications for the mechanism of energy-dependent quenching.

The lumenal CD loop region of the D2 protein of photosystem II contains residues that interact with a reaction center chlorophyll and the redox-active Tyr(D). Using combinatorial mutagenesis, photoautotrophic mutants of Synechocystis sp. PCC 6803 have been generated with multiple amino acid changes in this region. The CD loop mutations were transferred into a photosystem I-less Synechocystis strain to facilitate characterization of photosystem II properties in the mutants. Most of the combinatorial photosystem I-less mutants obtained had a high yield of variable fluorescence, F(V). However, in three mutants, which shared a replacement of Phe181 by Trp, the F(V) yield was dramatically reduced although a high rate of oxygen evolution was maintained. A site-directed F181W D2 mutant shared similar properties. Picosecond time-resolved fluorescence measurements revealed that in the combinatorial F181W mutants the fluorescence lifetimes in closed and open photosystem II centers were essentially identical and were similar to the fluorescence lifetime in open centers of the control strain. These results are explained by quenching of variable fluorescence in the mutants by charge separation between Trp181 and excited reaction center chlorophyll. This reaction competes efficiently with fluorescence and nonradiative decay in closed photosystem II centers, where the lifetime of the excitation in the chlorophyll antenna is long. Thermodynamic considerations favor the formation of oxidized tryptophan and reduced chlorophyll in the quenching reaction, presumably followed by charge recombination. A possible role of tryptophan-chlorophyll charge separation in the mechanism of energy-dependent quenching of excitations in photosynthesis is discussed.

Amino Acid Sequence↗
PubMed2002

Effect of maturity on chlorophyll, tannin, color, and polyphenol oxidase (PPO) activity of sugarcane juice (Saccharum officinarum Var. Yellow Cane).

A study was conducted to determine the effect of sugarcane maturation on the contents of chlorophyll, tannin, and polyphenol oxidase (PPO) activity and on color change of sugarcane juice. The maturation period of the cane studied was between 3 and 10 months after planting. Different parts of the cane, namely, the top, middle, and bottom portions, were analyzed. Results obtained indicated that there were significant (P < 0.01) decreases in total chlorophyll a and b and tannin contents during maturity followed by slower rates of decrease of both parameters at the end of maturity stages. There were no significant differences (P > 0.05) in chlorophyll and tannin contents between the middle and bottom portions. On the other hand, the top portion of the stem had a significantly (P < 0.01) lower concentration of chlorophyll and a significantly (P < 0.01) higher content of tannin. PPO activity of sugarcane juice was determined using chlorogenic acid as a substrate. There was a highly significant difference (P < 0.01) in PPO activity of cane juice during maturity. PPO activity was high at the early development stage, decreased during maturation, and then remained relatively constant at the end of maturity. PPO activity was higher when chlorogenic acid was used as substrate. There were also significant differences (P < 0.01) in juice color (L*, a*, b* values) from different portions at different maturity stages. At the early stages, the color of extracted juice was dark, and then the juice turned to yellowish green during maturity. The decrease in green color or the increase in the yellow color could be associated with the decline in chlorophyll. The overall color change (DeltaE) at maturity indicated that the color of the middle and bottom portions was lower than that of the top portion.

Catechol Oxidase↗
PubMed2005

Genotypic differences in chlorophyll, lutein, and beta-carotene contents in the fruits of actinidia species.

Chlorophyll, lutein, and beta-carotene contents in Actinidia fruits were determined by high-performance liquid chromatography in various genotypes, including five Actinidia deliciosa, seven Actinidia chinensis, two Actinidia rufa, five Actinidia arguta, and three interspecific hybrids. The concentrations of chlorophyll, lutein, and beta-carotene in the fruit of A. deliciosa Hayward were 1.65, 0.418, and 0.088 mg/100 g fresh weight, respectively. Of A. deliciosa cultivars, Koryoku showed significantly higher concentrations in chlorophyll, lutein, and beta-carotene than Hayward. In most cultivars of A. chinensis, although both chlorophyll and lutein contents were significantly lower than in Hayward, the beta-carotene content tended to be slightly higher. In A. rufa, A. arguta, and their interspecific hybrids, the contents of chlorophyll, lutein, and beta-carotene were much higher than in Hayward. In particular, these fruits were found to be the richest dietary source of lutein among commonly consumed fruits.

Actinidia↗
PubMed2003

Chlorophyll reduction in the seed of Brassica napus with a glutamate 1-semialdehyde aminotransferase antisense gene.

Chlorophyll reduction in the seed of Brassica can be achieved by downregulating its synthesis. To reduce chlorophyll synthesis, we have used a cDNA clone of Brassica napus encoding glutamate 1-semialdehyde aminotransferase (GSA-AT) to make an antisense construct for gene manipulation. Antisense glutamate 1-semialdehyde aminotransferase gene (Gsa) expression, directed by a Brassica napin promoter, was targeted specifically to the embryo of the developing seed. Transformants expressing antisense Gsa showed varying degrees of inhibition resulting in a range of chlorophyll reduction in the seeds. Seed growth and development were not affected by reduction of chlorophyll. Seeds from selfed transgenic plants germinated with high efficiency and growth of seedlings was vigorous. Seedlings from T2 transgenic lines segregated into three distinctive phenotypes: dark green, light green and yellow, indicating the dominant inheritance of Gsa antisense gene. These transgenic lines have provided useful materials for the development of a low chlorophyll seed variety of B. napus.

Amino Acid Sequence↗
PubMed1975

Some observations on chlorophyll(ide) synthesis by isolated etioplasts.

1. A modified procedure for the isolation of etioplasts from dark-grown barley is described and the regeneration of phototransformable protchlorophyll(ide) was demonstrated in the isolated plastids. 2. On exposure of the etioplasts to a long-term flash illumination, chlorophyll(ide) synthesis from a precursor pool, which includes all the protochlorophyllide, was demonstrated. 3. Added delta-aminolaevulinic acid failed to be significantly incorporated into chlorophyll(ide) in the etioplasts despite its extensive incorporation into porphyrin precursors of chlorophyll and haem compounds. The findings are discussed in terms of the inability of etioplasts to carry out the metal-insertion step in chlorophyll synthesis. 4. An elevated chlorophyll(ide) concentration was attained in the etioplasts by increasing the size of the utilizable precursor pool by pre-feeding whole plants with delta-aminolaevulinic acid, isolating the etioplasts and subjecting them to the flash illumination.

Aminolevulinic Acid↗
PubMed1977

The oxidation-reduction potential of the reaction-centre chlorophyll (P700) in Photosystem I. Evidence for multiple components in electron-paramagnetic-resonance signal 1 at low temperature.

The oxidation-reduction potential of the reaction-centre chlorophyll of Photosystem I (P700) in spinach chloroplasts was determined by using the ability of the reaction centre to photoreduce the bound ferredoxin and to photo-oxidize P700 on illumination at 20K as an indicator of the oxidation state of P700. This procedure shows that P700 is oxidized with Em (pH8.0)(mid-point redox potential at pH8.0)congruent to +375mV. Further oxidation of the chloroplast preparations by high concentrations of K3Fe(CN)6(10mM) in the presence of mediating dyes leads to the appearance of a large radical signal with an apparent Em congruent to +470mVA second, light-inducible, radical also appears over the same potential range. We propose that these signals are due to bulk chlorophyll oxidation and not, as was previously thought [Knaff & Malkin (1973) Arch. Biochem. Biophys. 159, 555-562], to reaction-centre oxidation. A number of optical techniques were used to determine Em of P700. Dual-wavelength spectroscopy (697-720nm) indicates Em congruent to +460-+480mV. The spectrum of the sample during the titration showed a large contribution to the signal by bulk chlorophyll oxidation, in agreement with the electron-paramagnetic-resonance results and those of Ke, Sugahara & Shaw [(1975) Biochim. Biophys. Acta 408, 12-25]. The light-induced absorbance change at 435 nm, usually attributed to P700, showed a potential dependence similar to that of bulk chlorophyll oxidation. Determination of Em of P700 on the basis of the appearance of the P700 signal in oxidized-versus-reduced difference spectra showed Em (pH8.0) congruent to +360mV. Measurements of the effect of potential on the irreversible photo-oxidation of P700 at 77K showed that P700 became oxidized in this potential range. We conclude that the reaction-centre chlorophyll of Photosystem I has Em (pH8.0) congruent to +375mV.

Chlorophyll↗
PubMed2002

Unravelling chlorophyll catabolism in higher plants.

Chlorophyll metabolism is probably the most visible manifestation of life. In spite of this, chlorophyll catabolism has remained something of a mystery until about 10 years ago. At that time, the first non-green tetrapyrrolic chlorophyll breakdown products from higher plants were discovered, and the structure of the first one of them was elucidated by modern spectroscopic methods. In the meantime, the essential structural features of chlorophyll catabolites and some of the biochemistry of chlorophyll breakdown in higher plants have been uncovered, as outlined in this article.

Chlorophyll↗
PubMed1999

Chlorophyll breakdown by chlorophyllase: isolation and functional expression of the Chlase1 gene from ethylene-treated Citrus fruit and its regulation during development.

We report on the isolation, functional expression and characterization of a cDNA encoding chlorophyllase, the enzyme catalyzing the first step in the chlorophyll breakdown pathway. The Chlase1 cDNA from Valencia Orange (Citrus sinensis cv. Valencia) was obtained by RT-PCR using degenerate primers based on the amino acid sequence of the previously purified protein. Chlase1 encodes a protein of 329 amino acids, including a sequence domain characterizing serine-lipases and a putative chloroplast-directing transit peptide. The Chlase1 gene encodes an active chlorophyllase enzyme which catalyzes the dephytylation of chlorophyll as shown by in vitro recombinant enzyme assays. Chlorophyllase expression at the transcript level in Valencia orange peel was found to be low and constitutive during natural fruit development without significant increase towards color-break and ripening. However, ethylene treatment induced an increase in chlorophyllase transcript at all stages of development. An enhanced response to ethylene treatment was observed during the months of October and November, corresponding to the time of natural color-break. The senescence-delaying regulator gibberellin-A3 (GA3) inhibited the effect of ethylene on chlorophyllase transcript accumulation. The data presented suggest that chlorophyllase may not be the regulator of chlorophyll breakdown during natural fruit ripening but is consistent with the notion that chlorophyll is gradually degraded during ripening due to a negative balance between synthesis and breakdown. According to this model, exogenous application of ethylene accelerates chlorophyll breakdown due to increased de novo synthesis of chlorophyllase. Further experimentation on the regulation and role of chlorophyllase in planta will be facilitated by the gene tools established in this work.

Amino Acid Sequence↗
PubMed1998

Association of His117 in the D2 protein of photosystem II with a chlorophyll that affects excitation-energy transfer efficiency to the reaction center.

His117 of the D2 protein of photosystem II (PS II) is a conserved residue in the second transmembrane region of the protein and has been suggested to bind chlorophyll. Nine site-directed mutations were introduced at residue 117, using both photosystem I (PS I)-containing and PS I-less background strains of the cyanobacterium Synechocystis sp. PCC 6803. Of these nine, four (H117C, H117M, H117N, and H117T) were photoautotrophic in the PS I-containing background. The other mutants (H117F, H117L, H117P, H117R, and H117Y) did not accumulate appreciable amounts of PS II in their thylakoids. The type of residues that can functionally replace His117 support the notion of His117 serving as a chlorophyll ligand. The properties of the H117N and H117T mutants were characterized in more detail. Whereas the properties of the H117N mutant were close to those of wild type, in the H117T mutant the 77-K fluorescence emission spectrum shows a much smaller amplitude at 695 nm than expected on the basis of the amount of PS II that is present. Moreover, in H117T, the amount of light needed to half-saturate O2-evolution rates was twofold higher than in the control strain, and the variable fluorescence yield was quenched. However, O2 evolution rates at saturating light intensity and electron-transport kinetics were normal in the mutant. Also, the radical accessory chlorophyll (Chlz+) formed by donation of an electron to the PS-II reaction center could be generated normally by illumination at low temperature in the H117T mutant. We conclude that the chlorophyll associated with residue 117 of the D2 protein is important for efficient excitation transfer between the proximal antenna and the PS II reaction center. A possible mechanism involving a chlorophyll cation to explain the quenching in the H117T mutant is discussed.

Chlorophyll↗
PubMed1996

Evolution of chlorophyll and bacteriochlorophyll: the problem of invariant sites in sequence analysis.

Competing hypotheses seek to explain the evolution of oxygenic and anoxygenic processes of photosynthesis. Since chlorophyll is less reduced and precedes bacteriochlorophyll on the modern biosynthetic pathway, it has been proposed that chlorophyll preceded bacteriochlorophyll in its evolution. However, recent analyses of nucleotide sequences that encode chlorophyll and bacteriochlorophyll biosynthetic enzymes appear to provide support for an alternative hypothesis. This is that the evolution of bacteriochlorophyll occurred earlier than the evolution of chlorophyll. Here we demonstrate that the presence of invariant sites in sequence datasets leads to inconsistency in tree building (including maximum-likelihood methods). Homologous sequences with different biological functions often share invariant sites at the same nucleotide positions. However, different constraints can also result in additional invariant sites unique to the genes, which have specific and different biological functions. Consequently, the distribution of these sites can be uneven between the different types of homologous genes. The presence of invariant sites, shared by related biosynthetic genes as well as those unique to only some of these genes, has misled the recent evolutionary analysis of oxygenic and anoxygenic photosynthetic pigments. We evaluate an alternative scheme for the evolution of chlorophyll and bacteriochlorophyll.

Bacteriochlorophylls↗
PubMed1996

How plants dispose of chlorophyll catabolites. Directly energized uptake of tetrapyrrolic breakdown products into isolated vacuoles.

During the yellowing of leaves the porphyrin moiety of chlorophyll is cleaved into colorless linear tetrapyrrolic catabolites, which eventually are deposited in the central vacuoles of mesophyll cells. In senescent cotyledons of rape, Brassica napus, three nonfluorescent chlorophyll catabolites (NCCs), accounting for practically all the chlorophyll broken down, were found to be located in the vacuoles (vacuoplasts) prepared from protoplasts. Transport of catabolites across the tonoplast was studied with vacuoles isolated from barley mesophyll protoplasts in conjunction with a radiolabeled NCC, Bn-NCC-1, prepared from senescent rape cotyledons. The uptake of Bn-NCC-1 into vacuoles was against a concentration gradient and strictly dependent on MgATP and it followed saturation kinetics with a Km of approximately 100 microM. Although the hydrolysis of ATP was required, transport was apparently independent of the vacuolar proton pumps: accumulation of the NCC occurred both in the presence of the H+-ATPase inhibitor bafilomycin and after destroying the DeltapH between the vacuolar sap and the medium. ATP could be replaced by GTP or UTP, and the transport was inhibited in the presence of vanadate. Chlorophyll catabolites isolated from senescent barley leaves competed with the rape-specific substrate for uptake into the vacuoles. Compounds such as the glutathione conjugate of N-ethylmaleimide and taurocholate, which are known to be transported across the tonoplast in a primary active mode, did not significantly inhibit uptake of Bn-NCC-1. Although the heme catabolites biliverdin and bilirubin inhibited the uptake of the NCC, this effect is caused by unspecific binding to the vacuolar membrane rather than to the specific inhibition of carrier-mediated transport. Taken together, the results demonstrate that barley mesophyll vacuoles are constitutively equipped with a directly energized carrier that transports tetrapyrrolic catabolites of chlorophyll into the vacuole.

Biological Transport↗
PubMed1999

Chlorophyll binding to monomeric light-harvesting complex. A mutation analysis of chromophore-binding residues.

The chromophore binding properties of the higher plant light-harvesting complex II have been studied by site-directed mutagenesis of pigment-binding residues. Mutant apoproteins were overexpressed in Escherichia coli and then refolded in vitro with purified chromophores to yield holoproteins selectively affected in chlorophyll-binding sites. Biochemical and spectroscopic characterization showed a specific loss of pigments and absorption spectral forms for each mutant, thus allowing identification of the chromophores bound to most of the binding sites. On these bases a map for the occupancy of individual sites by chlorophyll a and chlorophyll b is proposed. In some cases a single mutation led to the loss of more than one chromophore indicating that four chlorophylls and one xanthophyll could be bound by pigment-pigment interactions. Differential absorption spectroscopy allowed identification of the Q(y) transition energy level for each chlorophyll within the complex. It is shown that not only site selectivity is largely conserved between light-harvesting complex II and CP29 but also the distribution of absorption forms among different protein domains, suggesting conservation of energy transfer pathways within the protein and outward to neighbor subunits of the photosystem.

Amino Acid Sequence↗
PubMed2000

Chlorophyll binding to peptide maquettes containing a retention motif.

The motif Glu-X-X-His/Asn-X-Arg is conserved in the first and third membrane-spanning domains of all light-harvesting chlorophyll a/b- and a/c-binding proteins in chloroplasts. Molecular modeling of synthetic peptides containing the sequence Glu-Ile-Val-His-Ser-Arg, a motif found in the apoprotein of the major light-harvesting complex in plants, generated a loop structure formed by intrapeptide, electrostatic attraction between Glu and Arg. His, Asn, and charge-compensated Glu-Arg pairs are known ligands of the magnesium atom in chlorophyll. The prediction that this structure should bind two molecules of chlorophyll was confirmed experimentally with an assay based on fluorescence resonance energy transfer between peptides and chlorophyll a. Motifs with both potential ligands bound approximately two times the amount of chlorophyll as one in which His was replaced by Ala. These results support the conclusion that formation of this intermediate, within membranes of the envelope, is a crucial step in assembly of light-harvesting complexes and a mechanism that regulates import of the apoproteins into the chloroplast.

Amino Acid Motifs↗
PubMed2000

Effect of imazaquin applications on the growth, leaf chlorophyll and yield of soybean in the Guinea savanna of Nigeria.

Field trials were conducted during the wet seasons of 1989, 1991, 1994 and 1995 to evaluate the effects of pre-emergence and post-emergence applications of four rates of imazaquin (0.00; 0.15; 0.30 and 0.45kg a.i/ha) on the growth, leaf chlorophyll types and grain yield of soybean c.v. SAMSOY 2. Imazaquin applications had no significant effect on the growth of soybean roots on most of the sampling dates, but pre-and post-emergence applications of imazaquin at 0.30 and 0.45kg a.i/ha reduced soybean root nodules at 5 and 7 weeks after planting (WAP). Soybean shoot growth was generally reduced at 5WAP by the pre-emergence and at 7WAP by the higher rates (0.30 & 0.45kg a.i/ha) of post-emergence application of imazaquin. Pre-and post-emergence applications of imazaquin showed a strong tendency to reduce the concentration of chlorophyll a and total chlorophyll at 3 and 5WAP respectively. The concentrations of chlorophyll types in soybean leaves at 9WAP was generally comparable among most treatments especially in 1991. Whole plant fresh weight of soybean at 7WAP was reduced by all rates of post-emergence application of imazaquin. However, there was no significant difference in the whole plant dry weight of soybean at 3 to 7 WAP in 1989 and at 3, 5 and 9WAP in 1991. In each trial, pre-and post-emergence applications of soybean significantly increased the grain yield of soybean compared with the control treatment. This study showed that, inhibition of soybean shoot growth and leaf chlorophyll concentration was transient and that soybean plants require about 6 weeks for complete recovery from imazaquin phytotoxicity.

Chlorophyll↗
PubMed2001

Partial recovery of light-independent chlorophyll biosynthesis in the chlL-deletion mutant of Synechocystis sp. PCC 6803.

A chlL-deletion mutant of Synechocystis sp. PCC 6803 designated as chlL- was unable to make significant amounts of chlorophyll in darkness. However, an apparent pseudorevertant has been generated spontaneously that can synthesize an increased amount of chlorophyll under light-activated heterotrophic growth conditions. Under these conditions, the chlorophyll content in this pseudorevertant was about 20% of that in the wild-type strain and about 4 times more than that in the original and in the recently recreated chlL-deletion mutant. This is paralleled by increased performance of dark-grown cells in terms of chlorophyll fluorescence induction and oxygen evolution rates in the pseudorevertant versus in the original mutant. PCR analysis confirmed that the chlL- -pseudorevertant mutant still lacked the chlL gene. These results imply that the light-independent chlorophyll biosynthesis pathway was partly recovered.

Bacterial Proteins↗