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At least 127 records · Page 7Linked to original sources
PubMed1983

The light-dependent control of chloroplast development in barley (Hordeum vulgare L).

The light-induced greening of etiolated barley plants is used as a model to study the light-dependent control of plastid development. Upon illumination a rapid transformation of etioplasts to chloroplasts is induced. The effect of illumination does not only include the light-dependent chlorophyll synthesis but also the appearance or decline of specific proteins within the plastid membrane fractions. So far two of these proteins have been studied in detail. The light-harvesting chlorophyll a/b protein (LHCP) is one of the major protein constituents of the thylakoid membrane of chloroplasts. However, this protein is not detectable among the membrane polypeptides of etioplasts. Illumination of dark-grown barley plants induces a massive insertion of the LHCP. The appearance of the protein is controlled by the cooperation of at least two distinct photoreceptors: protochlorophyllide and phytochrome. In dark-grown barley plants not only the LHCP but also its mRNA is not detectable. The light-dependent appearance of mRNA activity for the LHCP is under the control of phytochrome (Pfr). Even though the appearance of mRNA activity is induced via Pfr by a single red light pulse, the assembly of the complete LHCP takes place only under continuous illumination, which allows chlorophyll synthesis. The second protein analyzed so far is the NADPH-protochlorophyllide-oxidoreductase. This enzyme catalyzes the light-dependent reduction of protochlorophyllide to chlorophyllide and thus controls one of the first detectable light-dependent reactions during the greening period. It is generally assumed that this enzyme is responsible for the overall chlorophyll synthesis and accumulation during the greening period.(ABSTRACT TRUNCATED AT 250 WORDS)

Chlorophyll↗
PubMed1978

Interactions between photosystem II components in chloroplast membranes. A correlation between the existence of a low potential species of cytochrome b-559 and low chlorophyll fluorescence in inhibited and developing chloroplasts.

1. Chloroplasts inhibited by incubation with hydroxylamine in the light exhibit a low fluorescence yield upon illumination in the presence of dithionite sufficient to completely reduce the primary acceptor, Q. In the absence of magnesium ions, the fluorescence yield is the same as in control chloroplasts, suggesting that the reason for the low yield is a defect in the mechanism by which Mg2+ enhances the fluorescence. These chloroplasts were previouly shown to contain only low potential (Em7.8 = +80 mV) cytochrome b-559 (Horton, P. and Croze, E (1977) Biochim. Biophys. Acta 462, 86-101). 2. In Photosystem II particles, in heat-treated chloroplasts and in trypsin-digested chloroplasts, high potential cytochrome b-559 is absent and the variable fluorescence yield is again low. 3. Peas grown under intermittent light contain only one-fifth of the content of high potential cytochrome b-559 seen in fully greened plants, yet show high rates of water to methyl viologen electron transport. Aquisition of the high potential cytochrome b-559 accompanies synthesis of chlorophyll b, the onset of Mg-stimulated fluorescence and an increased variable yield of fluorescence. A similar correlation was seen during greening of dark-grown barley. 4. It is proposed that the high potential state of cytochrome b-559 is due to the same membrane properties which allow cation enhanced variable fluorescence, so that the presence of low potential cytochrome b-559 is accompanied by a decrease in variable fluorescence yield.

Cell Membrane↗
PubMed1973

Photophosphorylation during Chloroplast Development in Red Kidney Bean: II. Photophosphorylation and Photoreduction Appear Concomitantly but Initially are Uncoupled.

Cyclic phosphorylation with phenazine methosulfate and noncyclic phosphorylation and reduction with ferricyanide were detected in isolated chloroplasts from greening bean leaves after 3 to 4 hours of illumination. Activity commenced when rapid synthesis of chlorophyll was initiated. Rates of photophosphorylation were comparable to mature levels by 15 to 18 hours of development. Photoreduction of ferricyanide attained a peak value by 12 hours of illumination and subsequently fell to normal levels by 15 to 18 hours. With ferricyanide, the P/e(2) ratios were initially less than 0.1 but were close to 1.0 after 18 hours of illumination. The data suggested that photosystems I and II appeared concomitantly in the chloroplast but were not fully operative until later in development. Proplastids and immature chloroplasts exhibited high capacities to reduce ferricyanide in the dark. The rates of dark reduction rapidly diminished to low levels by 15 hours of illumination when normal rates of photochemical activity were observed. After a 2-to 3-day lag, a rapid increase in leaf fresh weight was noted at the time total chlorophyll content reached steady state values on a fresh weight basis. With fresh weight as an index of growth, primary leaves completed their development after 6 to 7 days of illumination.

Journal Article↗
PubMed2006

Rice Chlorina-1 and Chlorina-9 encode ChlD and ChlI subunits of Mg-chelatase, a key enzyme for chlorophyll synthesis and chloroplast development.

Photosynthetic organisms exhibit a green color due to the accumulation of chlorophyll pigments in chloroplasts. Mg-protoporphyrin IX chelatase (Mg-chelatase) comprises three subunits (ChlH, ChlD and ChlI) and catalyzes the insertion of Mg(2+) into protoporphyrin IX, the last common intermediate precursor in both chlorophyll and heme biosyntheses, to produce Mg-protoporphyrin IX (MgProto). Chlorophyll deficiency in higher plants results in chlorina (yellowish-green) phenotype. To date, 10 chlorina (chl) mutants have been isolated in rice, but the corresponding genes have not yet been identified. Rice Chl1 and Chl9 genes were mapped to chromosome 3 and isolated by map-based cloning. A missense mutation occurred in a highly conserved amino acid of ChlD in the chl1 mutant and ChlI in the chl9 mutant. Ultrastructural analyses have revealed that the grana are poorly stacked, resulting in the underdevelopment of chloroplasts. In the seedlings fed with aminolevulinate-dipyridyl in darkness, MgProto levels in the chl1 and chl9 mutants decreased up to 25% and 31% of that in wild-type, respectively, indicating that the Mg-chelatase activity is significantly reduced, causing the eventual decrease in chlorophyll synthesis. Furthermore, Northern blot analysis indicated that the nuclear genes encoding the three subunits of Mg-chelatase and LhcpII in chl1 mutant are expressed about 2-fold higher than those in WT, but are not altered in the chl9 mutant. This result indicates that the ChlD subunit participates in negative feedback regulation of plastid-to-nucleus in the expression of nuclear genes encoding chloroplast proteins, but not the ChlI subunit.

Alleles↗
PubMed2003

cor Gene expression in barley mutants affected in chloroplast development and photosynthetic electron transport.

The expression of several barley (Hordeum vulgare) cold-regulated (cor) genes during cold acclimation was blocked in the albino mutant a(n), implying a chloroplast control on mRNAs accumulation. By using albino and xantha mutants ordered according to the step in chloroplast biogenesis affected, we show that the cold-dependent accumulation of cor14b, tmc-ap3, and blt14 mRNAs depends on plastid developmental stage. Plants acquire the ability to fully express cor genes only after the development of primary thylakoid membranes in their chloroplasts. To investigate the chloroplast-dependent mechanism involved in cor gene expression, the activity of a 643-bp cor14b promoter fragment was assayed in wild-type and albino mutant a(n) leaf explants using transient beta-glucuronidase reporter expression assay. Deletion analysis identified a 27-bp region between nucleotides -274 and -247 with respect to the transcription start point, encompassing a boundary of some element that contributes to the cold-induced expression of cor14b. However, cor14b promoter was equally active in green and in albino a(n) leaves, suggesting that chloroplast controls cor14b expression by posttranscriptional mechanisms. Barley mutants lacking either photosystem I or II reaction center complexes were then used to evaluate the effects of redox state of electron transport chain components on COR14b accumulation. In the mutants analyzed, the amount of COR14b protein, but not the steady-state level of the corresponding mRNA, was dependent on the redox state of the electron transport chain. Treatments of the vir-zb63 mutant with electron transport chain inhibitors showed that oxidized plastoquinone promotes COR14b accumulation, thus suggesting a molecular relationship between plastoquinone/plastoquinol pool and COR14b.

Acclimatization↗
PubMed1975

Ultrastructural Effects of Water Stress on Chloroplast Development in Jack Bean (Canavalia ensiformis [L.] DC).

An ultrastructural study has been made to determine to what degree chloroplast differentiation is retarded in leaves of young jack bean (Canavalia ensiformis [L.] DC.) seedlings when they are subjected to mild water stress. Rapid chloroplast differentiation occurred when etiolated seedlings were allowed to green at relative humidities above 85% but not at a relative humidity of 25%. Response to a drop in humidity was rapid. Germination and early development in the dark occurred at 100% relative humidity. At the time of exposure to light, the etioplasts contained well formed prolamellar bodies. Under high relative humidity conditions, transformation of the prolamellar body was well advanced within 2 hours. Under low relative humidity conditions, however, prolamellar body differentiation was extremely retarded for more than 24 hours following the beginning of illumination.

Journal Article↗
PubMed1990

Regulation of 5-Aminolevulinic Acid (ALA) Synthesis in Developing Chloroplasts : III. Evidence for Functional Heterogeneity of the ALA Pool.

Gabaculine and 4-amino-5-hexynoic acid (AHA) up to 3.0 millimolar concentration strongly inhibited 5-aminolevulinic acid (ALA) synthesis in developing cucumber (Cucumis sativus L. var Beit Alpha) chloroplasts, while they hardly affected protochlorophyllide (Pchlide) synthesis. Exogenous protoheme up to 1.0 micromolar had a similar effect. Exogenous glutathione also exhibited a strong inhibitory effect on ALA synthesis in organello but hardly inhibited Pchlide synthesis. Pchlide synthesis in organello was highly sensitive to inhibition by levulinic acid, both in the presence and in the absence of gabaculine, indicating that the Pchlide was indeed formed from precursor(s) before the ALA dehydratase step. The synthesis of Pchlide in the presence of saturating concentrations of glutamate was stimulated by exogenous ALA, confirming that Pchlide synthesis was limited at the formation of ALA. The gabaculine inhibition of ALA accumulation occurred whether levulinic acid or 4,6-dioxohepatonic acid was used in the ALA assay system. ALA overproduction was also observed in the absence of added glutamate and was noticeable after 10-minute incubation. These observations suggest that although Pchlide synthesis in organello is limited by ALA formation, it does not utilize all the ALA that is made in the in organello assay system. Gabaculine, AHA, and probably also protoheme, inhibit preferentially the formation of that portion of ALA that is not destined for Pchlide. A model proposing a heterogenous ALA pool is described.

Journal Article↗
PubMed2000

Galactolipid deficiency and abnormal chloroplast development in the Arabidopsis MGD synthase 1 mutant.

The lipid monogalactosyl diacylglycerol (MGD) is a major structural component of photosynthetic membranes in chloroplasts. Its formation is catalyzed by the enzyme MGD synthase. In many plants, MGD derives from two different biosynthetic pathways: the prokaryotic pathway, which operates entirely within the plastid, and the eukaryotic pathway, which involves steps in the endoplasmic reticulum. Here, we describe the identification and characterization of an Arabidopsis mutant with a defective MGD synthase gene (MGD1). The mutant was identified in a screen of T-DNA lines for individuals with defects in chloroplast biogenesis. It has a yellow-green phenotype that correlates with a approximately 50% deficiency in total chlorophyll per plant. A single T-DNA insertion is located adjacent to the transcription initiation site of the MGD1 gene, and the abundance of MGD1 mRNA is reduced by 75% compared with wild type. Correlation between steady-state MGD1 transcript levels and MGD synthase activity (also reduced by 75% in mgd1) suggests that MGD1 is the most important MGD synthase in green tissues. The amount of MGD in mutant leaves is reduced by 42% compared with wild type. MGD from the mutant contains 23% less 16:3 fatty acid and 10% more 18:3 fatty acid. Because 16:3 is a characteristic feature of MGD from the prokaryotic pathway, it is possible that MGD1 operates with some preference in the prokaryotic pathway. Finally, the MGD-deficiency of mgd1 is correlated with striking defects in chloroplast ultrastructure, strongly suggesting a unique role for MGD in the structural organization of plastidic membranes.

Amino Acid Sequence↗