SEARCH · PubMed Health

Results for “Chloroplasts”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources

PubMed2005

Origin and evolution of the chloroplast division machinery.

Chloroplasts were originally established in eukaryotes by the endosymbiosis of a cyanobacterium; they then spread through diversification of the eukaryotic hosts and subsequent engulfment of eukaryotic algae by previously nonphotosynthetic eukaryotes. The continuity of chloroplasts is maintained by division of preexisting chloroplasts. Like their ancestors, chloroplasts use a bacterial division system based on the FtsZ ring and some associated factors, all of which are now encoded in the host nuclear genome. The majority of bacterial division factors are absent from chloroplasts and several new factors have been added by the eukaryotic host. For example, the ftsZ gene has been duplicated and modified, plastid-dividing (PD) rings were most likely added by the eukaryotic host, and a member of the dynamin family of proteins evolved to regulate chloroplast division. The identification of several additional proteins involved in the division process, along with data from diverse lineages of organisms, our current knowledge of mitochondrial division, and the mining of genomic sequence data have enabled us to begin to understand the universality and evolution of the division system. The principal features of the chloroplast division system thus far identified are conserved across several lineages, including those with secondary chloroplasts, and may reflect primeval features of mitochondrial division.

Biological Evolution↗

PubMed1990

Amino acid sequence of spinach chloroplast fructose-1,6-bisphosphatase.

The amino acid sequence of the spinach chloroplast fructose-1,6-bisphosphatase (FBPase) subunit has been determined. Placement of the 358 residues in the polypeptide chain was based on automated Edman degradation of the intact protein and of peptides obtained by enzymatic or chemical cleavage. The sequence of spinach chloroplast FBPase shows clear homology (ca. 40%) to gluconeogenic (mammalian, yeast, and Escherichia coli) fructose-1,6-bisphosphatases and 80% homology with the wheat chloroplast enzyme. The two chloroplast enzymes show near the middle of the structure a unique sequence insert probably involved in light-dependent regulation of the chloroplast FBPase enzyme activity. This sequence insert contains two cysteines separated by only 4 amino acid residues, a characteristic feature of some enzymes containing redox-active cysteines. The recent X-ray crystallographic resolution of pig kidney FBPase (H. Ke, C. M. Thorpe, B. A. Seaton, F. Marcus, and W. N. Lipscomb, 1989, Proc. Natl. Acad. Sci. USA 86, 1475-1479) has allowed the discussion of the amino acid sequence of spinach chloroplast FBPase in structural terms. It is to be noted that most of pig kidney FBPase residues shown to be either at (or close to) the sugar bisphosphate binding site or located at the negatively charged metal binding pocket are conserved in the chloroplast enzyme. The unique chloroplast FBPase insert presumably involved in light-dependent activation of the enzyme via a thioredoxin-linked mechanism can be accommodated in the surface of the FBPase molecule.

Amino Acid Sequence↗

PubMed1979

Primary and secondary electron donors in photosystem II of chloroplasts. Rates of electron transfer and location in the membrane.

Absorption changes at 820 or 515 nm after a short laser flash were studied comparatively in untreated chloroplasts and in chloroplasts in which oxygen evolution is inhibited. In chloroplasts pre-treated with Tris, the primary donor of Photosystem II (P-680) is oxidized by the flash it is re-reduced in a biphasic manner with half-times of 6 microseconds (major phase) and 22 microseconds. After the second flash, the 6 microseconds phase is nearly absent and P-680+ decays with half-times of 130 microseconds (major phase) and 22 microseconds. Exogenous electron donors (MnCl2 or reduced phenylenediamine) have no direct influence on the kinetics of P-680+. In untreated chloroplasts the 6 and 22 microseconds phases are of very small amplitude, either at the 1st, 2nd or 3rd flash given after dark-adaptation. They are observed, however, after incubation with 10 mM hydroxylamine. These results are interpreted in terms of multiple pathways for the reduction of P-680+: a rapid reduction (less than 1 microseconds) by the physiological donor D1; a slower reduction (6 and 22 microseconds) by donor D'1, operative when O2 evolution is inhibited; a back-reaction (130 microseconds) when D'1 is oxidized by the pre-illumination in inhibited chloroplasts. In Tris-treated chloroplasts the donor system to P-680+ has the capacity to deliver only one electron. The absorption change at 515 nm (electrochromic absorption shift) has been measured in parallel. It is shown that the change linked to Photosystem II activity has nearly the same magnitude in untreated chloroplasts or in chloroplasts treated with hydroxylamine or with Tris (first and subsequent flashes). Thus we conclude that all the donors (P-680, D1, D'1) are located at the internal side of the thylakoid membrane.

Absorption↗

PubMed1980

Photosynthetic apparatus in chilling-sensitive plants. VII. Comparison of the effect of galactolipase treatment of chloroplasts and cold-dark storage of leaves on photosynthetic electron flow.

1. Both galactolipase treatment of tomato chloroplasts and the cold and dark storage of leaves induce a large degradation of chloroplast monogalactosyl diacylglycerol and digalactosyl diacylglycerol as well as an accumulatwon of free fatty acids accompanied by the inhibition of Hill reaction activity with water as electron donor. All these changes are reversed upon illumination of the leaves. 2. Inhibition of diphenylcarbazide (DPC) leads to dichlorophenolindophenol (DCIP) activity by free fatty acids released following galactolipase treatment of chloroplasts isolated from either fresh or cold and dark-stored and illuminated leaves is almost completely reversed by either bovine serum albumin or Mn2+, while that in chloroplasts from the cold and dark-stored leaves is reversed by bovine serum albumin and Mn2+ only up to about 60 and 25%, respectively. 3. Fatty acids released during the treatment of chloroplasts with galactolipase affect the electron transport mainly in the same site as exogenous unsaturated fatty acids do, while those released due to endogenous galactolipase activity appear to affect also in the region damaged by either Tris washing of chloroplasts or the cold and dark treatment of leaves. 4. The loss of manganese from chloroplasts (Kaniuga, Z., Zabek, J. and Sochanowicz, B. (1978) Planta 144, 49-56) seems to be the main reason of cold and dark-induced inactivation of Hill reaction activity in chloroplasts of chilling-sensitive plants, while both the degradation of galactolipids and the accumulation of fatty acids are of secondary importance.

Chloroplasts↗

PubMed1975

Aminoacylation of tRNA-Leu species from Escherichia coli and from the cytoplasm, chloroplasts and mitochondria of Phaseolus vulgaris by homologous and heterologous enzymes.

Leucyl-tRNA synthetase from Phaseolus vulgaris chloroplasts could be separated from its cytoplasmic counterpart upon chromatography on hydroxyapatite, but the cytoplasmic and mitochondrial leucyl-tRNA synthetases could not be distinguished. The tRNALeu species from the various plant cell compartments and from Escherichia coli were aminoacylated using either homologous or heterologous enzymes; the levels of aminoacylation and the profiles of the leucyl-tRNAs upon reverse-phase chromatography were studied. Cytoplasmic tRNALeu species could be aminoacylated by the cytoplasmic or by the mitochondrial enzymes and in both cases yielded two peaks upon reverse-phase chromatography (RPC-5). But they could not be charged by the chloroplast-specific or by the E. coli enzynes. Mitochondrial tRNALeu species could be charged by the mitochondrial or by the cytoplasmic enzymes and in both cases yielded four peaks upon reverse phase (RPC-5) chromatography. But they could not be aminoacylated using the chloroplast-specific or the E. coli leucyl-tRNA synthetases. Chloroplastic tRNALeu species can be divided into two classes: the first class contains four isoacceptor species which can be charged by the cytoplasmic or mitochondrial enzymes, but not by the chloroplast-specific or the E. coli enzymes; the second class contains three chloroplast-specific tRNALeu species which can be charged by the chloroplast-specific or the E. coli enzymes but not by the cytoplasmic or the mitochondrial enzymes. There are five isoacceptor tRNALeu species in E. coli; all are charged by the E. coli or the chloroplast-specific enzymes, while only one is aminoacylated by the plant cytoplasmic or mitochondrial enzymes.

Amino Acyl-tRNA Synthetases↗

PubMed1975

Aminoacylation of Phaseolus vulgaris cytoplasmic, chloroplastic and mitochondrial tRNAsMet and of Escherichia coli tRNAsMet by homologous and heterologous enzymes.

Met-tRNA synthetase from Paseolus vulgaris cytoplasm could be separated from its chloroplastic or mitochondrial counterpart by DEAE-cellulose chromatography, but the Met-tRNA synthetase from the two latter organelles could not be distinguished using DEAE-cellulose, hydroxyapatite or CM-Sephadex chromatography. As revealed by reverse-phase chromatography, bean cytoplasm contains 2 tRNAsMet; only one is charged by chloroplast, mitochondrial or Escherichia coli Met-tRNA synthetase. Mitochondria contain, in addition to the 2 cytoplasmic tRNAsMet, 3 mitochondria-spedific tRNAsMet; 2 can be formylated by the mitochondrial or the E. coli transformylase; all 3 are charged by mitochondrial, chloroplastic or E, coli Met-tRNA synthetase; none is charged by the cytoplasmic enzyme. Chloroplasts contain, in addition to the 2 cytoplasmic tRNAsMet, 3 chloroplast-specific tRNAsMet, different from the mitochondrial tRNAsMet; one is formylatable by the chloroplastic or the E. coli transformylase; all 3 are charged by chloroplastic, mitochondrial or E. coli Met-tRNA synthetase; only one is charged by the cytoplasmic enzyme. Of the 3 E. coli tRNAsMet, only the formylatable species can be charged by bean cytoplasmic, chloroplastic or mitochondrial Met-tRNA synthetase.

Amino Acyl-tRNA Synthetases↗

PubMed1976

Counting the genes for stabel RNA in the nucleus and chloroplasts of Euglena.

Improved procedures for counting the genes for ribosomal and 4 S RNA in the nucleus and chloroplasts of Euglena are described. These procedures exploit (a) the chloroplast-free strain ZHB, (b) the flotation method for purifying chloroplasts, (c) Hg2+/Cs2SO4 density gradients to fractionate large quantities of DNA and (d) more efficient conditions of DNA - RNA hybridization particularly for 4 S RNA. We find that the average Euglena cell in an exponentially growing culture contains 800 nuclear genes for each cytoplasmic rRNA and 800-880 chloroplast genes for chloroplast rRNA. Each chloroplast chromosome of molecular weight 92 - 10(6) contains two genes for each rRNA. The number of nuclear genes for 4 S RNA is approx. 760. The total number of chloroplast genes for 4S RNA is approx. 10 000, or 22-25 on each chloroplast chromosome.

Animals↗

PubMed1979

Sedimentation behavior of chloroplast ribosomes from Chlamydomonas reinhardtii.

The identity of peaks generated by chloroplast ribosomes of Chlamydomonas reinhardtii were determined by zone velocity sedimentation on sucrose density gradients, and analysis of distribution of ribosomal RNAs in the gradients. The sedimentagion coefficient of the principal peak was 66-70 S (usually 69 S), in good agreement with previously reported values for chloroplast ribosomes of C. reinhardtii, and other organisms. The fast sedimenting side of the 69 S peak contained an excess of chloroplast large subunit. When ribosome dissociation was prevented by sedimentation at low velocity, by aldehyde fixation, or by the presence of nascent polypeptide chains, the principal peak had a sedimentation coefficient of about 75 S. Thus the 69 S peak was an artifact caused by dissociation during centrifugation. Peaks that contained chloroplast ribosomal RNAs were also observed at '60 S' and '45 S' when chloroplast ribosomes were centrifuged unfixed at high velocity. The amounts of '60 S' and '45 S' components were decreased by centrifugation at low speed, or fixation, but sedimentation coefficients remained unchanged. The '60 S', and '45 S' components were identified as large, and small subunits of chloroplast ribosomes, respectively. The artifacts produced by centrifugation of chloroplast ribosomes, are similar to the artifacts produced by centrifuging ribosomes of Escherichia coli. Similar explanations appear to apply to both. We concluded that the 69 S chloroplast ribosome peak occurs because of dissociation of 'tight' couples, and incomplete separation of subunits. Subunit peaks (60 S and 45 S) arise from free subunits, and/or from dissociation of 'loose' couples.

Centrifugation, Density Gradient↗

PubMed1993

Interaction of homologues of Hsp70 and Cpn60 with ferredoxin-NADP+ reductase upon its import into chloroplasts.

A homologue of the 70-kDa heat-shock protein (Hsp70) was purified from pumpkin chloroplasts. The molecular mass of the purified protein was approximately 75 kDa and its N-terminal amino acid sequence was very similar to those of homologues of Hsp70 from bacterial cells and from the mitochondrial matrix and stroma of pea chloroplasts. The purified homologue of Hsp70 was found in the stroma of chloroplasts. To investigate the role(s) of the homologue of Hsp70 in the chloroplast stroma, we examined the possibility that the homologue of Hsp70 might interact with newly imported proteins to assist in their maturation (for example, in their folding and assembly). Ferredoxin NADP+ reductase (FNR) imported into chloroplasts in vitro could be immunoprecipitated with antisera raised against the homologue of Hsp70 from pumpkin chloroplasts and against GroEL from Escherichia coli, which is a bacterial homologue of chaperonin 60 (Cpn60), in an ATP-dependent manner, an indication that newly imported FNR interacts physically with homologues of Hsp70 and Cpn60 in chloroplasts. Time-course analysis of the import of FNR showed that imported FNR interacts transiently with the homologue of Hsp70 and that the association of FNR with the homologue of Hsp70 precedes that with the homologue of Cpn60. These results suggest that homologues of Hsp70 and Cpn60 in chloroplasts might sequentially assist in the maturation of newly imported FNR in an ATP-dependent manner.

Adenosine Triphosphate↗

PubMed1995

Analysis of the primary structure of the chloroplast isozyme of triosephosphate isomerase from rye leaves by protein and cDNA sequencing indicates a eukaryotic origin of its gene.

The primary structure of the chloroplast isozyme of triosephosphate isomerase from rye leaves was identified by protein and cDNA sequencing and compared to the deduced amino acid sequence of a cDNA for the cytosolic isozyme. The mature cytosolic and chloroplast isozyme proteins share 64% amino acid sequence identity. The cDNA for the chloroplast isozyme codes for a precursor protein consisting of an N-terminal transit peptide of Mr 4351 and a mature subunit of Mr 27,282. Southern blot analysis indicates that the two rye isozymes are encoded by two independent single genes. Amino acid residues or sequence regions of basic functional relevance in known triosephosphate isomerases are strictly conserved in the chloroplast isozyme. The chloroplast isozyme contains 6 cysteine residues, instead of 4 in the cytosolic isozyme. A cysteine at position 143 of the chloroplast isozyme appears to be modified. Phylogenetic trees constructed on the basis of sequence comparisons for triosephosphate isomerases from different species of all major taxonomic groups indicate that the chloroplast isozyme is much more closely related to eukaryotic cytosolic enzymes than to eubacterial enzymes. The results indicate that the nuclear gene for the chloroplast isozyme originated with that for the cytosolic isozyme through duplication of an ancestral eukaryotic gene, rather than through gene transfer from a prokaryotic endosymbiont.

Amino Acid Sequence↗

PubMed1995

Nucleotides of tRNA (Glu) involved in recognition by barley chloroplast glutamyl-tRNA synthetase and glutamyl-tRNA reductase.

The biosynthesis of delta-aminolevulinate (ALA), via the C-5 pathway, requires tRNA(Glu) as a cofactor for the glutamyl tRNA(Glu) synthetase and the glutamyl tRNA(Glu) reductase which are the first two enzymes in this three step pathway. These two enzymes form a ternary complex with the tRNA(Glu) in Chlamydomonas reinhardtii suggesting that the recognition elements on the tRNA cofactor are different for each enzyme. Chemical modification and comparative studies with tRNA(Glu)s from a number of species were used to determine the nucleotides involved in the recognition of the barley chloroplast tRNA(Glu) by the barley enzymes. The barley chloroplast tRNA(Glu) is chemically modified both before and after ligation to glutamate with monobromobimane or CNBr. The chemically modified tRNA(Glu) is a poor substrate for the glutamyl-tRNA synthetase and the chemically modified glutamyl-tRNA(Glu) is used as a substrate for glutamyl-tRNA(Glu) reductase. The tRNA(Glu) from the chloroplasts if barley, Chlamydomonas reinhardtii, tobacco, cucumber, wheat and spinach and tRNA(Glu) from Synechocystis PCC6803, Escherichia coli, barley germ and bakers yeast and the barley chloroplast tRNA(Gln) are all effective substrates for the barley chloroplast glutamyl-tRNA synthetase. A comparison of the sequences of these tRNAs shows 19 conserved bases and five of these bases, G10, A26, U34, U35 and A37 are suggested as recognition elements of barley glutamyl tRNA(Glu) synthetase by assuming a similar binding orientation as in the crystal structure of the E. coli tRNA(Gln) GlnRS complex. The glutamyl-tRNA(Glu) from E. coli, bakers yeast and barley germ and the barley chloroplast glutamyl-tRNA(Gln) are not effective substrates for the barley chloroplast glutamyl-tRNA(Glu) reductase. A comparison of the sequences of these four tRNA species with the sequences of the tRNA(Glu) species that can be used as substrate by the glutamyl-tRNA(Glu) reductase yields seven common differences in the primary sequence. These 7 nucleotides, A7-U66, U29-A41, A53-U61, and U72 are expected to be required for recognition by the barley chloroplast glutamyl-tRNA(Glu) reductase.

Aldehyde Oxidoreductases↗

PubMed2004

The involvement of cytosolic lipases in converting phosphatidyl choline to substrate for galactolipid synthesis in the chloroplast envelope.

Here we report that cytosolic phospholipases are involved in the utilization of phosphatidylcholine (PC) as substrate for chloroplast-localized synthesis of monogalactosyldiacylglycerol (MGDG). Isolated chloroplasts were pre-incubated with lysoPC and [14C]18:0-CoA to form [14C]PC. When soluble plant proteins (cytosol) and UDP-galactose were added, [14C] MGDG was formed. An inhibitor of phospholipase D markedly lowered the formation of [14C]MGDG, whereas thermolysin pretreatment of the chloroplasts was without effect. The cytosolic activity resided in the >100-kDa fraction. In a second approach, [14C]PC-containing lipid mixtures were incubated with cytosol. Degradation of [14C]PC to [14C]diacylglycerol was highest when the lipid composition of the mixture mimicked that of the outer chloroplast envelope. We also investigated whether PC of extraplastidic origin could function as substrate for MGDG synthesis. Isolated chloroplasts were incubated with enriched endoplasmic reticulum containing radiolabelled acyl lipids. In the presence of cytosol and UDP-galactose, there was a time-dependent transfer of [14C]PC from this fraction to chloroplasts, where [14C]MGDG was formed. We conclude that chloroplasts recruit cytosolic phospholipase D and phosphatidic acid phosphatase to convert PC to diacylglycerol. Apparently, these lipases do not interact with chloroplast surface proteins, but rather with outer membrane lipids, either for association to the envelope or for substrate presentation.

Biological Transport↗

PubMed2004

Expression of non-toxic mutant of Escherichia coli heat-labile enterotoxin in tobacco chloroplasts.

Chloroplast transformation systems offer unique advantages in biotechnology, including high level of foreign gene expression, maternal inheritance, and polycistronic expression. We studied chloroplast expression of LTK63 (change Ser-->Lys at position 63 in the A subunit) which is the mutant of Escherichia coli heat-labile toxin. LTK63 is devoid of any toxic activity, but still retains its mucosal adjuvanticity. The LTK63 was cloned into chloroplast targeting vector and transformed to tobacco chloroplasts by particle bombardment. PCR and Southern blot analyses confirmed stable homologous recombination of the LTK63 gene into the chloroplast genome. The amount of LTK63 protein detected in tobacco chloroplasts was approximately 3.7% of the total soluble protein. The GM1-ganglioside binding assay confirmed that chloroplast-synthesized LTB of LTK63 binds to the intestinal membrane GM1-ganglioside receptor. Thus, the expression of LTK63 in chloroplasts provides a potential route toward the development of a plant-based edible vaccine for high expression system and environmentally friendly approach.

Bacterial Toxins↗

PubMed2000

A homologue of the bacterial cell division site-determining factor MinD mediates placement of the chloroplast division apparatus.

BACKGROUND: Chloroplast division in plant cells occurs by binary fission, yielding two daughter plastids of equal size. Previously, we reported that two Arabidopsis homologues of FtsZ, a bacterial protein that forms a cytokinetic ring during cell division, are essential for plastid division in plants, and may be involved in the formation of plastid-dividing rings on both the stromal and cytosolic surfaces of the chloroplast envelope membranes. In bacteria, positioning of the FtsZ ring at the center of the cell is mediated in part by the protein MinD. Here, we identified AtMinD1, an Arabidopsis homologue of MinD, and investigated whether positioning of the plastid-division apparatus at the plastid midpoint might involve a mechanism similar to that in bacteria. RESULTS: Sequence analysis and in vitro chloroplast import experiments indicated that AtMinD1 contains a transit peptide that targets it to the chloroplast. Transgenic Arabidopsis plants with reduced AtMinD1 expression exhibited variability in chloroplast size and number and asymmetrically constricted chloroplasts, strongly suggesting that the plastid-division machinery is misplaced. Overexpression of AtMinD1 inhibited chloroplast division. These phenotypes resemble those of bacterial mutants with altered minD expression. CONCLUSIONS: Placement of the plastid-division machinery at the organelle midpoint requires a plastid-targeted form of MinD. The results are consistent with a model whereby assembly of the division apparatus is initiated inside the chloroplast by the plastidic form of FtsZ, and suggest that positioning of the cytosolic components of the apparatus is specified by the position of the plastidic components.

Amino Acid Sequence↗

PubMed1999

Cultured green cells of tobacco as a useful material for the study of chloroplast replication.

Chloroplast replication in cultured cells of tobacco (Nicotiana tabacum cv. Samsun NN) was investigated by electron microscopy in comparison with that of green leaves. The structure of chloroplasts in cultured cells changed conspicuously during cell growth especially in photoautotrophic cells. The frequency of dumbbell-shaped chloroplasts (intermediate of chloroplast division) was the maximum (about 23% of total chloroplast) in photoautotrophic cells at 3 days after inoculation, before the cells had started to grow. By contrast, in photomixotrophically cultured cells, the highest frequency of dividing chloroplasts was observed at the early exponential phase (about 7 days after inoculation). The dividing chloroplast was hardly detected in green leaves even at a young stage. The advantages of cultured cells for the study of chloroplast replication and ultrastructural development are discussed.

Cell Culture Techniques↗

PubMed1982

Epifluorescent microscopic evidence for maternal inheritance of chloroplast DNA.

Maternal inheritance of chloroplast genes occurs in the isogamous green alga Chlamydomonas reinhardii. It has been shown using biochemical techniques that the chloroplast DNA of male origin is preferentially lost by 6 h after mating. DNAs in the chloroplast are organized by proteins into about 10 chloroplast nucleoids. Therefore, if chloroplast DNA in zygotes is preferentially destroyed, the disappearance of chloroplast nucleoids from male gametes should be observable during zygote formation by high resolution epifluorescent microscopy. Here we present the first fluorescent microscopic evidence that in C. reinhardii, about eight chloroplast nucleoids from the male parent disappear during the first 40-50 min after mating, while those from the female parent persist and finally fuse together to form one large chloroplast nucleoid.

Cell Fusion↗

PubMed1969

Distribution of enzymes in mesophyll and parenchyma-sheath chloroplasts of maize leaves in relation to the C4-dicarboxylic acid pathway of photosynthesis.

1. Mesophyll and parenchyma-sheath chloroplasts of maize leaves were separated by density fractionation in non-aqueous media. 2. An investigation of the distribution of photosynthetic enzymes indicated that the mesophyll chloroplasts probably contain the entire leaf complement of pyruvate,P(i) dikinase, NADP-specific malate dehydrogenase, glycerate kinase and nitrite reductase and most of the adenylate kinase and pyrophosphatase. The fractionation pattern of phosphopyruvate carboxylase suggested that this enzyme may be associated with the bounding membrane of mesophyll chloroplasts. 3. Ribulose diphosphate carboxylase, ribose phosphate isomerase, phosphoribulokinase, fructose diphosphate aldolase, alkaline fructose diphosphatase and NADP-specific ;malic' enzyme appear to be wholly localized in the parenchyma-sheath chloroplasts. Phosphoglycerate kinase and NADP-specific glyceraldehyde phosphate dehydrogenase, on the other hand, are distributed approximately equally between the two types of chloroplast. 4. After exposure of illuminated leaves to (14)CO(2) for 25sec., labelled malate, aspartate and 3-phosphoglycerate had similar fractionation patterns, and a large proportion of each was isolated with mesophyll chloroplasts. Labelled fructose phosphates and ribulose phosphates were mainly isolated in fractions containing parenchyma-sheath chloroplasts, and dihydroxyacetone phosphate had a fractionation pattern intermediate between those of C(4) dicarboxylic acids and sugar phosphates. 6. These results indicate that the mesophyll and parenchyma-sheath chloroplasts have a co-operative function in the operation of the C(4)-dicarboxylic acid pathway. Possible routes for the transfer of carbon from C(4) dicarboxylic acids to sugars are discussed.

Aldehyde-Lyases↗

PubMed1994

A mutant of Arabidopsis thaliana lacking the ability to transport glucose across the chloroplast envelope.

At the end of a 12-h day leaves of the mutant of Arabidopsis thaliana L., TC265, contained 4-5 times more starch than those of the wild type. During a subsequent 12-h night the decline in the starch content of the leaves of the mutant was at least 50% of that of the wild-type leaves. Starch labelled in the light in a 30-min pulse in 14CO2 was rapidly broken down in a subsequent 12-h chase in the dark in air in the leaves of both mutant and wild type. Chloroplasts from leaves of the wild type took up [32P]Pi and [U-14C]glucose at 12 and 1.6 mumol/h per mg of chlorophyll respectively; chloroplasts from the mutant showed a similar rate for [32P]Pi but no uptake of [U-14C]glucose. The glucose content of freshly isolated chloroplasts from the mutant was twice that of chloroplasts from the wild type; this difference was accentuated when the isolated chloroplasts were incubated in the dark. SDS/PAGE of preparations of chloroplast envelopes showed that those from the mutant were deficient in a protein band of approximate molecular mass 40 kDa. It is suggested that in mutant TC265 the primary lesion is in a hexose transporter in the chloroplast envelope, and that this transporter moves the products of starch breakdown that are destined for sucrose synthesis from the chloroplast to the cytosol.

Arabidopsis↗