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PubMed2004

The phytochrome-interacting transcription factor, PIF3, acts early, selectively, and positively in light-induced chloroplast development.

The phytochrome (phy) family of sensory photoreceptors transduce informational light signals to selected nuclear genes, inducing plant growth and developmental responses appropriate to the environment. Existing data suggest that one signaling pathway by which this occurs involves direct, intranuclear interaction of the photoactivated phy molecule with PIF3, a basic helix-loop-helix transcription factor. Here, we provide evidence from recently identified pif3 mutant alleles that PIF3 is necessary for early chloroplast greening and rapid phy-induced expression of nuclear genes encoding chloroplast components upon first exposure of seedlings to light. Therefore, these data indicate that PIF3 functions to transduce phy signals to genes involved in a critical facet of the early seedling deetiolation process, the generation of a functional photosynthetic apparatus. When transgenically expressed GUS:PIF3 fusion protein constructs were used, we found that PIF3 protein levels are rapidly and reversibly modulated by the photoreceptor over diurnal cycles in Arabidopsis seedlings. The PIF3 protein declines rapidly to a basal steady-state level upon initial light exposure, but reaccumulates to preirradiation levels in darkness during the subsequent night period. These data suggest that PIF3 may function in early phy signaling at the dark-to-light transition, not only during initial seedling deetiolation, but daily at dawn under diurnal light-dark cycles.

Arabidopsis↗
PubMed2005

Silencing of NbNAP1 encoding a plastidic SufB-like protein affects chloroplast development in Nicotiana benthamiana.

It was previously shown that AtNAP1 is a plastidic SufB protein involved in Fe-S cluster assembly in Arabidopsis. In this study, we investigated the effects of depleting SufB protein from plant cells using virus-induced gene silencing (VIGS). VIGS of NbNAP1 encoding a Nicotiana benthamiana homolog of AtNAP1 resulted in a leaf yellowing phenotype. NbNAP1 was expressed ubiquitously in plant tissues with the highest level in roots. A GFP fusion protein of the N-terminal region (M1-V103) of NbNAP1 was targeted to chloroplasts. Depletion of NbNAP1 resulted in reduced numbers of chloroplasts of reduced size. Mitochondria also seemed to be affected. Despite the reduced number and size of the chloroplasts in the NbNAP1 VIGS lines, the expression of many nuclear genes encoding chloroplast-targeted proteins and chlorophyll biosynthesis genes remained unchanged.

Adenosine Triphosphatases↗
PubMed1970

The effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea on chloroplast development and maintenance in Euglena gracilis. I. Ultrastructural characterization of light-grown cells by the techniques of thin sectioning and freeze-etching.

The ultrastructure of light-grown Euglena gracilis var. bacillaris was examined by the techniques of thin sectioning and freeze-etching. Thin sectioning revealed the typical organelles previously observed in chemically fixed Euglena. In addition to confirming the observations on thin sections, the freeze-etch technique has revealed the presence in E. gracilis of a complex multilaminar pellicle, and an ordered arrangement to the paramylon granule. The chloroplast thylakoids are particulate and similar to those observed in higher plants.

Chloroplasts↗
PubMed1996

Subcellular Visualization of Gene Transcripts Encoding Key Proteins of the Chlorophyll Accumulation Process in Developing Chloroplasts.

The coordination of the synthesis of chlorophyll (Chl) and light-harvesting Chl proteins was determined by observing the sequence of appearance of the specific mRNAs for the nuclear genes CHLH, Por, and Lhcb1*2 (AB180). CHLH encodes a magnesium protoporphyrin chelatase subunit that is involved in the first committed step in Chl biosynthesis; Por encodes protochlorophyllide oxidoreductase, which catalyzes the penultimate and only light-dependent step in Chl biosynthesis; and Lhcb1*2 encodes light-harvesting Chl a/b binding protein of the type-1 light-harvesting complex of photosystem II. Using digoxigenin-labeled antisense and sense RNA probes and a highly sensitive in situ hybridization technique, we have visualized the first appearance of the specific mRNAs in postmitotic mesophyll cells of developing 7-d-old wheat leaves (Triticum aestivum cv Maris dove). The transcripts for CHLH and POR are detectable in the youngest (18 h postmitotic) leaf tissue containing dividing cells; light-harvesting complex of photosystem II transcripts appear 12 h later. This is consistent with a requirement for accumulation of Chl before synthesis of Chl a/b binding protein can proceed at a high rate. All of the transcripts are most abundant in mesophyll cells. In the first leaf the POR message is initially restricted to the palisade, but 12 h later it is also present in the spongy mesophyll cells. All three transcripts aggregated around the surface of the chloroplasts, suggesting that translation may occur preferentially in the vicinity of the target organelle for the primary translation products.

Journal Article↗
PubMed1999

Inter-organellar crosstalk in higher plants: impaired chloroplast development affects mitochondrial gene and transcript levels.

Co-ordination of gene expression between the three genomes present in plastids, mitochondria and nucleus is of crucial importance for plant cells. Previous studies revealed that in white leaves of the albostrians (Hordeum vulgare cv. Haisa) mutant, photosynthesis-related plastid and nuclear genes are expressed only at an extremely low level. The plastids of this mutant lack ribosomes, photosynthetic activity and have only rudimentary membrane systems. Here we report on the expression of mitochondrial genes in albostrians barley. Steady-state RNA levels of the mitochondrial genes encoding cytochrome oxidase or ATPase subunits, coxII, coxIII, atpA, atp6, atp9 and cob, were observed to be consistently elevated in the white leaves but not in roots. Investigation of mitochondrial DNA revealed an about three-fold enhanced mitochondrial gene copy number in white compared to green leaf cells, but no differential amplification of mitochondrial genes. Analysis of plants in which the white albostrians plastids were combined with a new nuclear background showed that the enhanced transcript levels were a consequence of the impaired plastids and not of the nuclear albostrians allele. Furthermore, plants bleached by the carotenoid biosynthesis inhibitor norflurazon also showed an enhanced mitochondrial transcript level. These findings allow the conclusion that lack of chloroplast activity in an otherwise fully differentiated leaf leads to an increase in mitochondrial gene copy number and an elevated level of mitochondrial transcripts. Our results indicate an influence of plastids on the genetic apparatus of mitochondria in leaves but not in roots.

Chloroplasts↗
PubMed1966

Studies of chloroplast development in Euglena. XIV. Sequential interactions of ultraviolet light and photoreactivating light in green colony formation.

Photoreactivation (PR) of green colony-forming ability in Euglena is pH-insensitive from pH 6.0 to 8.0 and temperature-sensitive with a maximum rate at 35 degrees C. There is no PR at 0 degrees C. The rate of PR varies with the growth stage of the cells; PR of exponential phase cells is slower than that of stationary phase cells. The reciprocity rule holds for PR over a 6-fold range of intensity. The shape of PR curves is a function of the UV dose; there appears to be a progressive increase in multiplicity until a limiting multiplicity is reached as indicated by the fact that curves for high doses are superposable. Dark-grown and light-grown cells give the same PR response for comparable UV doses. UV inactivation of cells which have been treated with UV and then with PR light shows that, if the PR dose is sufficiently large, the same UV-inactivation curve is obtained as for nonpretreated control cells. Doses of PR lower than the saturating dose produce UV-inactivation curves, the ultimate slopes of which are parallel to the slope of the control curve, but which show reduced multiplicity. The multiplicity of these curves increases with increasing PR dose. The UV inactivation of green colony-forming ability in Euglena is completely photoreactivable at the doses studied, in contrast with the UV inactivation of colony-forming ability, which occurs at considerably higher UV doses and behaves like most other photoreactivable systems, showing a photoreactivable sector of 0.32.

Cell Division↗
PubMed2002

Light-signalling pathways leading to the co-ordinated expression of HEMA1 and Lhcb during chloroplast development in Arabidopsis thaliana.

During de-etiolation, the co-ordinated synthesis of chlorophyll and the chlorophyll a/b-binding proteins is critical to the development of functional light-harvesting complexes. To understand how this co-ordination is achieved, we have made a detailed study of the light-regulated signalling pathways mediating the expression of the HEMA1 and Lhcb genes encoding glutamyl-tRNA reductase, the first committed enzyme of 5-aminolaevulinic acid formation, and chlorophyll a/b-binding proteins, respectively. To do this, we have screened 7 photoreceptor and 12 light-signalling mutants of Arabidopsis thaliana L. for induction of HEMA1 and Lhcb expression in continuous red, far-red and blue light and following a red pulse. We have categorised these mutants into two groups. The phyA, phyB, phyAphyB, cry1, cry2, cop1, det1, poc1, eid1, and far1 mutations lead to diverse effects on the light regulation of HEMA1, but affect Lhcb expression to a similar degree. The hy1, hy2, hy5, fin219, fhy1, fhy3, spa1, ndpk2, and pat1 mutants also affect light regulation of both HEMA1 and Lhcb expression, but with differences in the relative magnitude of the two responses. The fhy1 and fhy3 mutants show the most significant differences in light regulation between the two genes, with both showing a strong inhibition of HEMA1 expression under continuous red light. These results demonstrate that co-ordinated regulation of HEMA1 and Lhcb is largely achieved through parallel light regulation mediated by shared phytochrome- and cryptochrome-signalling pathways. However, glutamyl-tRNA reductase is also required for the synthesis of other tetrapyrroles and this dual role may account for the observed differences in these light-signalling pathways.

Aldehyde Oxidoreductases↗
PubMed1993

The Circadian Oscillator Coordinates the Synthesis of Apoproteins and Their Pigments during Chloroplast Development.

Greening has been studied at circadian times of maximal and minimal levels of mRNA for the light-harvesting chlorophyll a/b binding protein in photosystem II (Cab mRNA) after circadian synchronization of etiolated barley plantlets (Hordeum vulgare cv Apex) by heat-shock treatments. It was found that greening occurs faster and without a lag period when illumination was started at the time of maximal Cab mRNA accumulation. This holds true for the rate of accumulation of Cab and early light-inducible protein mRNAs, the levels of their correspondent proteins, and the levels of chlorophyll a and b. When illumination was started at the time of Cab mRNA minimum, a lag in the appearance of all components mentioned above was observed. Under these conditions, the lag in chlorophyll b accumulation was by far more pronounced than that found for chlorophyll a. The circadian oscillation in the capacity of chlorophyll synthesis appears to be controlled via [delta]-aminolevulinic acid ([delta]-ALA) synthesis. [delta]-ALA accumulation after levulinic acid treatment is itself under circadian control; the maxima in stationary concentrations coincide with those of Cab mRNA levels. The amounts of protochlorophyllide and photoconvertible protochlorophyllide showed only minor differences between circadian minima and maxima, the levels being slightly lower during the time of minimum.

Journal Article↗
PubMed1969

The Formation of Ribulose Diphosphate Carboxylase Protein during Chloroplast Development in Barley.

Ribulose 1,5-diphosphate carboxylase is synthesized in barley leaves growing in the dark. Upon illumination there is a marked increase in the rate of synthesis of the enzyme. The specific activity of the enzyme expressed as cpm incorporated into phosphoglyceric acid per mug of fraction I protein, after isolation shows no change either during dark growth or greening. During early stages of illumination of 7 day dark grown leaves with 320 foot-candles the enzymic activity in the water soluble protein fraction of the leaf shows a short term decline after 15 min which lasts for 30 min. Leaves greening at 2 foot-candles show a similar decline which is shifted to a time between the fourth and eighth hr after the onset of illumination.

Journal Article↗
PubMed1972

Changes in Mitochondrial Properties Associated with Chloroplast Development in Jack Bean (Canavalia ensiformis [L] DC.).

Procedures were developed to isolate actively respiring mitochondria from jack bean (Canavalia ensiformis [L.] DC.) leaves and cotyledons. Consistent respiratory control values of about 2 for succinate oxidation were obtained in preparations from etiolated cotyledons. Jack bean mitochondria oxidized malate with high respiratory control (2 to 5) and ADP/O (up to 2.8).Mitochondria purified from greening leaves and cotyledons exhibited rapid increases in respiratory control for up to 4 hours of light exposure followed by a decrease in activity. ADP/O values remained constant at about 1.2 while oxygen consumption per unit mitochondrial protein increased constantly during the first 14 hours of greening in preparations from cotyledons. The changes in mitochondrial respiratory activity during greening were correlated with the reversible appearance of mitochondria in the condensed conformation observed by electron microscopy. Both isolated mitochondrial pellets and cotyledon mitochondria in situ were shown to exhibit these changes in conformation during greening.

Journal Article↗
PubMed1972

Lipid Composition of Pea and Bean Leaves during Chloroplast Development.

The changes in composition of the complex lipids were followed during the greening of dark-grown pea (Pisum sativum) and bean (Phaseolus vulgaris) seedlings. No significant changes in glycerolipid concentrations in the leaves were observed during the early stages of greening (0-8 hour for peas and 0-12 hour for beans). On further greening, there was an increase in the proportion of galactolipids and a decrease in the phospholipids. The fatty acid composition of the galactolipids remained constant during 24 hours of greening, but there was a slight increase in alpha-linolenic acid at 72 hours in the bean. The percentage of alpha-linolenic acid in the phospholipids and in sulfolipid showed a marked increase between 24 and 72 hours in the bean. Trans-delta(3)-hexadecenoic acid was the major fatty acid of phosphatidyl glycerol in bean leaves at 72 hours, but it was barely detectable at 24 hours. The lipid composition of greening leaves is discussed in relation to the fine structure and photochemical activity of the developing plastids.

Journal Article↗
PubMed1978

Kinetics of Membrane Transport during Chloroplast Development.

In the course of plastid development there are changes in the permeability of the envelope membranes. An investigation of the kinetics of transport with largely uncontaminated and intact etioplast/etiochloroplast preparations from greening Avena sativa laminae demonstrates: (a) that etioplasts already possess specific translocators for the transporation of orthophosphate, dihydroxyacetone phosphate, 3-phosphoglycerate ("phosphate translocator"), and dicarboxylic acids ("dicarboxylate translocator"); (b) that changes in the rates of uptake during development are mainly due to changes in velocity for specific transport and not due to changes in the affinity for transport (K(m)) or nonspecific permeation. The very low competitive inhibition of transport of orthophosphate by dihydroxyacetone phosphate and 3-phosphoglycerate, observed for developmental stages corresponding to up to 3 hours of illumination of etiolated tissue, is discussed with respect to the possibility of an early phosphate transport mechanism that is different from the phosphate translocator of more developed plastids.

Journal Article↗