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PubMed1993

Plastid Genes Encoding the Transcription/Translation Apparatus Are Differentially Transcribed Early in Barley (Hordeum vulgare) Chloroplast Development (Evidence for Selective Stabilization of psbA mRNA).

Chloroplast genomes encode rRNAs, tRNAs, and proteins involved in transcription, translation, and photosynthesis. The expression of 15 plastid genes representing each of these functions was quantitated during chloroplast development in barley (Hordeum vulgare). The transcription of all plastid genes increased during the initial phase of chloroplast development and then declined during chloroplast maturation. RNAs corresponding to rpoB- rpoC1-rpoC2, which encode subunits of a plastid RNA polymerase, and rps16, which encodes a ribosomal protein, reached maximal abundance early in chloroplast development prior to genes encoding subunits of the photosynthetic apparatus (rbcL, atpB, psaA, petB). Transcription of rpoB as well as 16S rRNA, trnfM-trnG, and trnK was high early in chloroplast development and declined 10-fold relative to rbcL transcription during chloroplast maturation. RNA hybridizing to psbA and psbD, genes encoding reaction center proteins of photosystem II, was differentially maintained in mature chloroplasts of illuminated barley. Differential accumulation of psbD mRNA relative to rbcL mRNA was due to light-stimulated transcription of psbD. In contrast, enhanced levels of psbA mRNA in mature chloroplasts were due primarily to selective stabilization of the psbA mRNA. These data document dynamic modulation of plastid gene transcription and mRNA stability during barley chloroplast development.

Journal Article↗

PubMed1993

Respiration of Sugars in Spinach (Spinacia oleracea), Maize (Zea mays), and Chlamydomonas reinhardtii F-60 Chloroplasts with Emphasis on the Hexose Kinases.

The role of hexokinase in carbohydrate degradation in isolated, intact chloroplasts was evaluated. This was accomplished by monitoring the evolution of 14CO2 from darkened spinach (Spinacia oleracea), maize (Zea mays) mesophyll, and Chlamydomonas reinhardtii chloroplasts externally supplied with 14C-labeled fructose, glucose, mannose, galactose, maltose, and ribose. Glucose and ribose were the preferred substrates with the Chlamydomonas and maize chloroplasts, respectively. The rate of CO2 release from fructose was about twice that from glucose in the spinach chloroplast. Externally supplied ATP stimulated the rate of CO2 release. The pH optimum for CO2 release was 7.5 with ribose and fructose and 8.5 with glucose as substrates. Probing the outer membrane polypeptides of the intact spinach chloroplast with two proteases, trypsin and thermolysin, decreased 14CO2 release from glucose about 50% but had little effect when fructose was the substrate. Tryptic digestion decreased CO2 release from glucose in the Chlamydomonas chloroplast about 70%. 14CO2 evolution from [1-14C]-glucose-6-phosphate in both chloroplasts was unaffected by treatment with trypsin. Enzymic analysis of the supernatant (stroma) of the lysed spinach chloroplast indicated a hexokinase active primarily with fructose but with some affinity for glucose. The pellet (membranal fraction) contained a hexokinase utilizing both glucose and fructose but with considerably less total activity than the stromal enzyme. Treatment with trypsin and thermolysin eliminated more than 50% of the glucokinase activity but had little effect on fructokinase activity in the spinach chloroplast. Tryptic digestion of the Chlamydomonas chloroplast resulted in a loss of about 90% of glucokinase activity.

Journal Article↗

PubMed1998

Manipulation of glutathione and amino acid biosynthesis in the chloroplast

Poplars (Populus tremula x Populus alba) were transformed to overexpress Escherichia coli gamma-glutamylcysteine synthetase (gamma-ECS) or glutathione synthetase in the chloroplast. Five independent lines of each transformant strongly expressed the introduced gene and possessed markedly enhanced activity of the gene product. Glutathione (GSH) contents were unaffected by high chloroplastic glutathione synthetase activity. Enhanced chloroplastic gamma-ECS activity markedly increased gamma-glutamylcysteine and GSH levels. These effects are similar to those previously observed in poplars overexpressing these enzymes in the cytosol. Similar to cytosolic gamma-ECS overexpression, chloroplastic overexpression did not deplete foliar cysteine or methionine pools and did not lead to morphological changes. Light was required for maximal accumulation of GSH in poplars overexpressing gamma-ECS in the chloroplast. High chloroplastic, but not cytosolic, gamma-ECS activities were accompanied by increases in amino acids synthesized in the chloroplast. We conclude that (a) GSH synthesis can occur in the chloroplast and the cytosol and may be up-regulated in both compartments by increased gamma-ECS activity, (b) interactions between GSH synthesis and the pathways supplying the necessary substrates are similar in both compartments, and (c) chloroplastic up-regulation of GSH synthesis is associated with an activating effect on the synthesis of specific amino acids formed in the chloroplast.

Journal Article↗

PubMed1972

Nicotinamide adenine dinucleotide phosphate photoreduction from water by agranal chloroplasts isolated from bundle sheath cells of maize.

Photoreduction of NADP from water in agranal chloroplasts isolated from the leaf bundle sheath cells of Zea mays (var. DS 606A) or Sorghum bicolor (var. Texas 610) was dependent upon addition of plastocyanin as well as ferredoxin. Activity was further increased by the addition of ferredoxin NADP-reductase. Saturation for plastocyanin was reached at about 6 micromolar. In contrast, grana-containing chloroplasts isolated from leaf mesophyll cells of these plants or from pea (Pisum sativum L.) leaves did not require either plastocyanin or ferredoxin NADP-reductase for NADP photoreduction from water, although with some preparations plastocyanin stimulated the activity.Photosystem I activity, which was low in washed preparations of bundle sheath chloroplasts, was also stimulated by plastocyanin. The effect of plastocyanin on photosystem I activity in the grana-containing chloroplasts was similar to that on NADP photoreduction from water.In the presence of plastocyanin, the rates of NADP photoreduction from water were about the same in the agranal and granal chloroplasts, but photosystem I activity was considerably higher in bundle sheath chloroplasts. In these chloroplasts photosystem II appeared to limit the rate of NADP photoreduction.The results indicated that the agranal bundle sheath chloroplasts reduced plastocyanin via photosystem II and oxidized it via photosystem I. Both types of maize chloroplast photoreduced oxidized plastocyanin, but in the presence of methyl viologen, reduced plastocyanin was photo-oxidized only by the bundle sheath chloroplasts.

Journal Article↗

PubMed1978

Photosynthesis by isolated protoplasts, protoplast extracts, and chloroplasts of wheat: influence of orthophosphate, pyrophosphate, and adenylates.

Protoplasts, protoplast extracts (intact chloroplasts plus extrachloroplastic material), and chloroplasts isolated from protoplasts of wheat (Triticum aestivum) have rates of photosynthesis as measured by light-dependent O(2) evolution of about 100 to 150 micromoles of O(2) per milligram of chlorophyll per hour at 20 C and saturating bicarbonate. The assay conditions sufficient for this activity were 0.4 molar sorbitol, 50 millimolar N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid KOH (pH 7.6), and 10 millimolar NaHCO(3) with protoplast, plus a requirement of 1 to 10 millimolar ethylenediaminetetraacetate (EDTA) and 0.2 to 0.5 millimolar inorganic orthophosphate (Pi) with protoplast extracts and chloroplasts. Protoplast extracts evolved approximately 6 micromoles of O(2) per milligram of chlorophyll before photosynthesis became largely dependent on exogenous Pi while photosynthesis by chloroplasts had a much stronger dependence on exogenous Pi from the outset.Photosynthesis by chloroplasts from 6-day-old wheat plants under optimum levels of Pi was similar to that with the addition of 5 millimolar inorganic pyrophosphate (PPi) plus 0.2 millimolar adenosine-5'-diphosphate (ADP). Either PPi or ADP added separately inhibited photosynthesis. When chloroplasts were incubated in the dark for 2 to 6 minutes, photosynthesis was strongly inhibited by 5 millimolar PPi and this inhibiting was relieved by including adenosine-5'-triphosphate (ATP) or ADP (0.2 to 0.6 millimolar). Chloroplasts from 9-day-old wheat leaves were slightly less sensitive to inhibition by PPi and showed little or no inhibition by ADP.Chloroplasts isolated from protoplasts and assayed with 0.3 millimolar Pi added before illumination have an induction time from less than 1 minute up to 16 minutes depending on the time of the assay after isolation and the components of the medium. In order to obtain maximum rates of photosynthesis and minimum induction time, NaHCO(3) and chelating agents, EDTA or PPi (+ATP), are required in the chloroplast isolation, resuspension and assay medium. With these inclusions in the isolation and resuspension medium the induction time decreased rapidly during the first 20 to 30 minutes storage of chloroplasts on ice. Requirements for isolating intact and photosynthetically functional chloroplasts from wheat protoplasts are discussed.

Journal Article↗

PubMed1981

Ribulose 1,5-bisphosphate and activation of the carboxylase in the chloroplast.

Ribulose 1,5-bisphosphate in the chloroplast has been suggested to regulate the activity of the ribulose bisphosphate carboxylase/oxygenase. To generate high levels of ribulose bisphosphate, isolated and intact spinach chloroplasts were illuminated in the absence of CO(2). Under these conditions, chloroplasts generate internally up to 300 nanomoles ribulose 1,5-bisphosphate per milligram chlorophyll if O(2) is also absent. This is equivalent to 12 millimolar ribulose bisphosphate, while the enzyme, ribulose bisphosphate carboxylase, offers up to 3.0 millimolar binding sites for the bisphosphate in the chloroplast stroma. During illumination, the ribulose bisphosphate carboxylase is deactivated, due mostly to the absence of CO(2) required for activation. The rate of deactivation of the ribulose bisphosphate carboxylase was not affected by the chloroplast ribulose bisphosphate levels. Upon addition of CO(2), the carboxylase in the chloroplast was completely reactivated. Of interest, addition of 3-phosphoglycerate stopped deactivation of the carboxylase in the chloroplast while ribulose bisphosphate accumulated. With intact chloroplasts in light, no correlation between deactivation of the carboxylase and ribulose bisphosphate levels could be shown.In contrast, incubation of purified ribulose bisphosphate carboxylase with ribulose bisphosphate irreversibly inhibited activation, especially in the absence of CO(2). Addition of the same amount of ribulose bisphosphate to lysed chloroplasts did cause some deactivation of the carboxylase in the extract, but full activation returned when the ribulose bisphosphate was consumed. The ribulose bisphosphate carboxylase in the chloroplast is not irreversibly inhibited by high levels of ribulose bisphosphate.

Journal Article↗

PubMed1984

Lack of ATP requirement for light stimulation of glycerate transport into intact isolated chloroplasts.

Light increased the initial rate and the extent of glycerate uptake by intact isolated chloroplasts. Half-maximum stimulation occurred with 10 to 20 watts per square meter of red light. Preillumination of chloroplasts enhanced uptake in a subsequent dark period. The light effect was abolished by DCMU and also by uncoupling agents such as nigericin and carbonyl cyanide p-trifluoromethoxyphenyl hydrazone.Arsenate and phlorizin only inhibited glycerate uptake to the extent that metabolism in the chloroplast was decreased by insufficient ATP. The concentration of glycerate accumulated in the chloroplast stroma was not significantly decreased. Chloroplasts isolated from young pea shoots (Pisum sativum, L. cv Massey Gem) were depleted of ATP by incubation with inorganic pyrophosphate or with ATP analogs. These treatments also decreased metabolism of glycerate but the actual concentration of glycerate accumulated in the chloroplast stroma was not decreased.The results indicate that glycerate uptake is driven by ion gradients established across the chloroplast envelope in the light. ATP is not involved in the transport of glycerate into chloroplasts, being required only for the subsequent metabolism of glycerate in the chloroplast stroma. It is proposed that glycerate transport may be coupled to the proton gradient established in the light across the chloroplast envelope.

Journal Article↗

PubMed1985

Characterization of 4,4'-Diisothiocyano-2,2'-disulfonic Acid Stilbene Inhibition of 3-Phosphoglycerate-Dependent O(2) Evolution in Isolated Chloroplasts : Evidence for a Common Binding Site on the C(4) Phosphate Translocator for 3-Phosphoglycerate, Phosphoenolpyruvate, and Inorganic Phosphate.

3-Phosphoglycerate (PGA)-dependent O(2) evolution by mesophyll chloroplasts of the C(4) plant, Digitaria sanguinalis L. Scop. (crabgrass), was inhibited by micromolar levels of 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS). As little as 1.8 micromolar DIDS added to the assay medium (containing 0.7 millimolar PGA) resulted in 80 to 100% inhibition of O(2) evolution. The extent of inhibition of O(2) evolution observed was dependent on various factors including: pH, concentration of DIDS to relative chlorophyll, concentration of PGA, and the time of addition of DIDS to the chloroplasts relative to addition of PGA.Preincubation of crabgrass chloroplasts with micromolar levels of DIDS, followed by washing to remove any nonirreversibly bound DIDS, inhibited PGA-dependent O(2) evolution. Protection against this inhibition was afforded by preincubating the chloroplasts with various substrates before adding DIDS. For example, if the chloroplasts were first incubated with 8.3 millimolar PGA, phosphoenolpyruvate (PEP) or inorganic phosphate before adding 42 micromolar DIDS, the percentage of inhibition was decreased from 100% (without any substrate) to 0, 54, and 67%, respectively. 2-Phosphoglycerate caused a slight decrease in the inhibition (about 10%) and glucose-6-phosphate had no protective effect. If the chloroplasts were pretreated with DIDS initially, the inhibition could not be overcome by PGA, suggesting that DIDS acts as an irreversible inhibitor. Micromolar levels of DIDS also inhibited PGA dependent O(2) evolution by isolated chloroplasts of the C(3) plant barley. As with crabgrass, preincubation with PGA or inorganic phosphate resulted in a decrease in the DIDS inhibition, but PEP was very ineffective compared to the C(4) chloroplasts.Oxalacetate-dependent O(2) evolution and its stimulation by the uncoupler, NH(4)Cl, were unaffected by the addition of DIDS to crabgrass mesophyll chloroplasts. Furthermore, preincubation of the chloroplasts with DIDS (up to 65 micromolar) had no inhibitory effect on the extractable activity of NADP glyceraldehyde-3-P dehydrogenase and phosphoglycerate kinase. Inhibition by DIDS was interpreted to be at the substrate binding site of the phosphate translocator. The data further suggest that in C(4) crabgrass chloroplasts, PEP is transported on a carrier which also transports PGA.

Journal Article↗

PubMed1987

Hill Reaction, Hydrogen Peroxide Scavenging, and Ascorbate Peroxidase Activity of Mesophyll and Bundle Sheath Chloroplasts of NADP-Malic Enzyme Type C(4) Species.

Intact mesophyll and bundle sheath chloroplasts wee isolated from the NADP-malic enzyme type C(4) plants maize, sorghum (monocots), and Flaveria trinervia (dicot) using enzymic digestion and mechanical isolation techniques. Bundle sheath chloroplasts of this C(4) subgroup tend to be agranal and were previously reported to be deficient in photosystem II activity. However, following injection of intact bundle sheath chloroplasts into hypotonic medium, thylakoids had high Hill reaction activity, similar to that of mesophyll chloroplasts with the Hill oxidants dichlorophenolindophenol, p-benzoquinone, and ferricyanide (approximately 200 to 300 micromoles O(2) evolved per mg chlorophyll per hour). In comparison to that of mesophyll chloroplasts, the Hill reaction activity of bundle sheath chloroplasts of maize and sorghum was labile and lost activity during assay. Bundle sheath chloroplasts of maize also exhibited some capacity for 3-phosphoglycerate dependent O(2) evolution (29 to 58 micromoles O(2) evolved per milligram chlorophyll per hour). Both the mesophyll and bundle sheath chloroplasts were equally effective in light dependent scavenging of hydrogen peroxide. The results suggest that both chloroplast types have noncyclic electron transport and the enzymology to reduce hydrogen peroxide to water. The activities of ascorbate peroxidase from these chloroplast types was consistent with their capacity to scavenge hydrogen peroxide.

Journal Article↗

PubMed2001

Molecular biology of chloroplast biogenesis: gene expression, protein import and intraorganellar sorting.

The chloroplast is the hallmark organelle of plants. It performs photosynthesis and is therefore required for photoautotrophic plant growth. The chloroplast is the most prominent member of a family of related organelles termed plastids which are ubiquitous in plant cells. Biogenesis of the chloroplast from undifferentiated proplastids is induced by light. The generally accepted endosymbiont hypothesis states that chloroplasts have arisen from an internalized cyanobacterial ancestor. Although chloroplasts have maintained remnants of the ancestral genome (plastome), the vast majority of the genes encoding chloroplast proteins have been transferred to the nucleus. This poses two major challenges to the plant cell during chloroplast biogenesis: First, light and developmental signals must be interpreted to coordinately express genetic information contained in two distinct compartments. This is to ensure supply and stoichiometry of abundant chloroplast components. Second, developing chloroplasts must efficiently import nuclear encoded and cytosolically synthesized proteins. A subset of proteins, including such encoded by the plastome, must further be sorted to the thylakoid compartments for assembly into the photosynthetic apparatus.

Biological Transport↗

PubMed2026

Phytochrome-interacting factor 1b (SlPIF1b) affects the fruit quality of tomato by regulating chloroplast development.

The increased abundance and functionality of fruit chloroplasts could promote the accumulation of nutrients and flavor in the fruit. Tomato fruit has fully developed fruit chloroplasts, whose abundance and functionality have much untapped potential in improving fruit quality by controlling fruit chloroplast development. Previous studies have identified many regulatory factors that specifically regulate fruit chloroplast development in tomatoes, but there are fewer reports on tomato phytochrome-interacting factors (SlPIFs). Arabidopsis AtPIFs have been implicated in chloroplast development and chlorophyll biosynthesis. In this study, we identified and characterized an SlPIF1b mutant in tomato, named GS, which exhibited a dark green fruit shoulder with enhanced chloroplast development. RNA-seq and genotyping analysis identified a - 21 bp (A → T) mutation in the promoter of SlPIF1b, resulting in the absence of the TATA-box core transcriptional element and inhibiting SlPIF1b transcription. The overexpression of SlPIF1b in GS inhibited chloroplast development of fruits, leading to a lighter green shoulder color, decreased chlorophyll content, reduced photosynthetic activity, diminished starch accumulation, and compromised fruit quality upon ripening. Conversely, the down expression of SlPIF1b significantly enhanced fruit chloroplast development and functionality in fruits, resulting in increased chlorophyll and carotenoid accumulation. Further analysis of expression profile and transcriptional activity indicated that SlPIF1b could bind to G/PBE-box elements present in SlGLK2, SlTKN4, SlCAO1a, SlPOR1, SlPOR3, SlCAB1 and SlCAB1b promoters, thereby inhibiting their expression. This study revealed the specific regulatory mechanism by which SlPIF1b modulates chloroplast development and chlorophyll synthesis in tomato fruit and provided valuable genetic resources and a theoretical basis for tomato quality improvement.

Solanum lycopersicum↗

PubMed1983

Selective in vitro transcription of chloroplast genes.

Transcription of Euglena gracilis chloroplast genes has been investigated by using in vitro transcription systems. A DNA-dependent RNA polymerase responsible for the transcription of rRNA genes has been isolated as a nucleoprotein complex (transcriptionally active chromosome). The RNA polymerase remains tightly bound to the chloroplast DNA template and does not initiate transcription with cloned chloroplast genes. A transcriptionally active extract has been prepared from intact Euglena chloroplasts. The soluble RNA polymerase in this extract recognizes cloned chloroplast tRNA genes and tRNA-sized products have been detected after transcription. The tRNA-sized molecules specifically hybridize to the tRNA genes in the plasmid DNA. At least five tRNA-sized products have been identified from transcription of a trnY1trnH1-trnM1-trnE1-trnW1-trnG1 cluster. Evidence is also presented that processing enzymes in the chloroplast-extract can recognize a polycistronic tRNAVal-tRNAAsn-tRNAArg precursor and process it into tRNA-sized molecules. Truncated templates have been used to demonstrate that the chloroplast tRNA genes are actively transcribed. From a comparison of 5' flanking sequences in chloroplast tRNA genes, a consensus sequence which might function as a promoter, has been identified. The properties of the RNA polymerase involved in the transcription of chloroplast rRNA genes and tRNA genes have been investigated and compared.

Chloroplasts↗

PubMed1994

Differential transcription of plastome-encoded genes in the mesophyll and bundle-sheath chloroplasts of the monocotyledonous NADP-malic enzyme-type C4 plants maize and Sorghum.

The transcription of plastome-encoded genes in mesophyll and bundle-sheath chloroplasts of the monocotyledonous NADP-malic enzyme-type C4 species Zea mays L. (maize) and Sorghum bicolor (L.) Moench. was investigated. RNA accumulation and transcription were assayed starting from isolated mesophyll and bundle-sheath chloroplasts and using quantitative northern and run-on transcription analysis. Determination of the mesophyll to bundle-sheath ratios of transcript abundance in maize and Sorghum chloroplasts showed that the mRNAs of the plastome-encoded photosystem II genes analysed (psbA, psbB, psbD, psbH and psbE/F) varied from 2.5- to 4.0-fold (maize) and 3.1- to 5.2-fold (Sorghum), respectively. The rbcL transcript, in contrast, was more abundant in bundle-sheath chloroplasts of both species, about 3-fold in maize and more than 10-fold in Sorghum. On the other hand, transcripts of genes encoding the 16S ribosomal RNA (r16) and subunits of photosystem I (psaA) and the cytochrome b/f complex (petB, petA) accumulated to similar levels in both types of chloroplasts. Determination of absolute transcript levels for rbcL and psbA in chloroplasts from maize and Sorghum demonstrated that for both genes, the mesophyll to bundle-sheath differences in transcript abundance were more pronounced in Sorghum. Measurements of the transcriptional activities of rbcL and psbA showed that the transcription rate of rbcL is higher in bundle-sheath chloroplasts while psbA is more actively transcribed in mesophyll chloroplasts. The differences in the transcription rates between the two chloroplast types were again more pronounced in Sorghum, thus reflecting the differences between maize and Sorghum in the relative levels of the rbcL and psbA transcripts. However, although transcription rate and mRNA abundance are correlated, they did not exactly match one another. This indicates additional regulation of transcript abundance at the level of RNA stability.

Chloroplasts↗

PubMed1993

Identification of the entire set of transferred chloroplast DNA sequences in the mitochondrial genome of rice.

The entire set of transferred chloroplast DNA sequences in the mitochondrial genome of rice (Oryza sativa cv. Nipponbare) was identified using clone banks that cover the chloroplast and mitochondrial genomes. The mitochondrial fragments that were homologous to chloroplast DNA were mapped and sequenced. The nucleotide sequences around the termini of integrated chloroplast sequences in the rice mtDNA revealed no common sequences or structures that might enhance the transfer of DNA. Sixteen chloroplast sequences, ranging from 32 bases to 6.8 kb in length, were found to be dispersed throughout the rice mitochondrial genome. The total length of these sequences is equal to approximately 6% (22 kb) of the rice mitochondrial genome and to 19% of the chloroplast genome. The transfer of segments of chloroplast DNA seems to have occurred at different times, both before and after the divergence of rice and maize. The mitochondrial genome appears to have been rearranged after the transfer of chloroplast sequences as a result of recombination at these sequences. The rice mitochondrial DNA contains nine intact tRNA genes and three tRNA pseudogenes derived from the chloroplast genome.

Base Sequence↗

PubMed2006

Evolution of chloroplast mononucleotide microsatellites in Arabidopsis thaliana.

The level of variation and the mutation rate were investigated in an empirical study of 244 chloroplast microsatellites in 15 accessions of Arabidopsis thaliana. In contrast to SNP variation, microsatellite variation in the chloroplast was found to be common, although less common than microsatellite variation in the nucleus. No microsatellite variation was found in coding regions of the chloroplast. To evaluate different models of microsatellite evolution as possible explanations for the observed pattern of variation, the length distribution of microsatellites in the published DNA sequence of the A. thaliana chloroplast was subsequently used. By combining information from these two analyses we found that the mode of evolution of the chloroplast mononucleotide microsatellites was best described by a linear relation between repeat length and mutation rate, when the repeat lengths exceeded about 7 bp. This model can readily predict the variation observed in non-coding chloroplast DNA. It was found that the number of uninterrupted repeat units had a large impact on the level of chloroplast microsatellite variation. No other factors investigated--such as the position of a locus within the chromosome, or imperfect repeats--appeared to affect the variability of chloroplast microsatellites. By fitting the slippage models to the Genbank sequence of chromosome 1, we show that the difference between microsatellite variation in the nucleus and the chloroplast is largely due to differences in slippage rate.

Arabidopsis↗

PubMed2003

Distribution of rare earth elements among chloroplast components of hyperaccumulator Dicranopteris dichotoma.

A rare earth element (REE) hyperaccumulator, Dicranopteris dichotoma, that accumulates more than 0.1% REEs dry leaf mass has been discovered in southern China. The different components of chloroplast were isolated and the concentration of REEs in each component was determined by ICP-MS. The experimental data indicated that about 8% of total leaf REEs was present in the chloroplast of Dicranopteris dichotoma. In order to thoroughly study the distribution of REEs among different components of chloroplast, the membrane of chloroplast, the intact thylakoid and the photosystem II (PS II system) of D. dichotoma were isolated from the chloroplast. It was found that half of total chloroplast REEs was stored at the membrane of the chloroplast and another half was in the thylakoid. And 25% of total chloroplast REEs was bound with PS II system of D.dichotoma. The concentration of REEs in chlorophyll a was only at the level of microg/g on the bases of chlorophylls. These data are useful for understanding of both the storage of REEs in chloroplast and the effect of REEs on the photosynthesis of plants.

Chlorophyll↗

PubMed2004

Causes of size homoplasy among chloroplast microsatellites in closely related Clusia species.

Chloroplast DNA sequences and microsatellites are useful tools for phylogenetic as well as population genetic analyses of plants. Chloroplast microsatellites tend to be less variable than nuclear microsatellites and therefore they may not be as powerful as nuclear microsatellites for within-species population analysis. However, chloroplast microsatellites may be useful for phylogenetic analysis between closely related taxa when more conventional loci, such as ITS or chloroplast sequence data, are not variable enough to resolve phylogenetic relationships in all clades. To determine the limits of chloroplast microsatellites as tools in phylogenetic analyses, we need to understand their evolution. Thus, we examined and compared phylogenetic relationships of species within the genus Clusia, using both chloroplast sequence data and variation at seven chloroplast microsatellite loci. Neither ITS nor chloroplast sequences were variable enough to resolve relationships within some sections of the genus, yet chloroplast microsatellite loci were too variable to provide any useful phylogenetic information. Size homoplasy was apparent, caused by base substitutions within the microsatellite, base substitutions in the flanking regions, indels in the flanking regions, multiple microsatellites within a fragment, and forward/reverse mutations of repeat length resulting in microsatellites of identical base composition that were not identical by descent.

Base Sequence↗

PubMed1983

Localization of photosynthetic electron transport components in mesophyll and bundle sheath chloroplasts of Zea mays.

The organization of the electron transport components in mesophyll and bundle sheath chloroplasts of Zea mays was investigated. Grana-containing mesophyll chloroplasts (chlorophyll a to chlorophyll b ratio of about 3.0) possessed the full complement of the various electron transport components, comparable to chloroplasts from C3 plants. Agranal bundle sheath chloroplasts (Chl a/Chl b greater than 5.0) contained the full complement of photosystem (PS) I and of cytochrome (cyt) f but lacked a major portion of PS II and its associated Chl a/b light-harvesting complex (LHC), and most of the cyt b559. The kinetic analysis of system I photoactivity revealed that the functional photosynthetic unit size of PS I was unchanged and identical in mesophyll and bundle sheath chloroplasts. The results suggest that PS I is contained in stroma-exposed thylakoids and that it does not receive excitation energy from the Chl a/b LHC present in the grana. A stoichiometric parity between PS I and cyt f in mesophyll and bundle sheath chloroplasts indicates that biosynthetic and functional properties of cyt f and P700 are closely coordinated. Thus, it is likely that both cyt f and P700 are located in the membrane of the intergrana thylakoids only. The kinetic analysis of PS II photoactivity revealed the absence of PS II alpha from the bundle sheath chloroplasts and helped identify the small complement of system II in bundle sheath chloroplasts as PS II beta. The distribution of the main electron transport components in grana and stroma thylakoids is presented in a model of the higher plant chloroplast membrane system.

Binding Sites↗