chlorophyll-a and norflurazone

Topics: Arabidopsis; Arabidopsis Proteins; Cell Nucleus; Chlorophyll; Chloroplasts; DNA-Binding Proteins; Gene Expression Regulation, Plant; Herbicides; Mutation; Oxidative Stress; Phenotype; Photosynthesis; Pyridazines; Seedlings; Signal Transduction; Tetrapyrroles

Synechocystis sp. PCC 6803 possesses only one sod gene, sodB, encoding iron superoxide dismutase (FeSOD). It could not be knocked out completely by direct insertion of the kanamycin resistance cassette. When the promoter of sodB in WT Synechocystis was replaced with the copper-regulated promoter PpetE, a completely segregated PpetE-sodB strain could be obtained. When this strain was cultured in copper-starved BG11 medium, the chlorophyll a content was greatly reduced, growth was seriously inhibited and the strain was nearly dead during the 8 days of growth, whilst the WT strain grew well under the same growth conditions. These results indicated that sodB was essential for photoautotrophic growth of Synechocystis. The reduction of sodB gene copies in the Synechocystis genome rendered the cells more sensitive to oxidative stress produced by methyl viologen and norflurazon. sodB still could not be knocked out completely after active expression of sodC (encoding Cu/ZnSOD) from Synechococcus sp. CC9311 in the neutral site slr0168 under the control of the psbAII promoter, which means the function of FeSOD could not be complemented completely by Cu/ZnSOD. Heterogeneously expressed sodC increased the oxidation and photoinhibition tolerance of the Synechocystis sodB knockdown mutant. Membrane fractionation followed by immunoblotting revealed that FeSOD was localized in the cytoplasm, and Cu/ZnSOD was localized in the soluble and thylakoid membrane fractions of the transformed Synechocystis. Cu/ZnSOD has a predicted N-terminal signal peptide, so it is probably a lumen protein. The different subcellular localization of these two SODs may have resulted in the failure of substitution of sodC for sodB.

Topics: Bacterial Proteins; Chlorophyll; Chlorophyll A; Cloning, Molecular; Culture Media; Gene Knockout Techniques; Microbial Viability; Oxidative Stress; Paraquat; Pyridazines; Recombinant Proteins; Superoxide Dismutase; Synechococcus; Synechocystis

Interactions between β-carotene (β-C) and Chl a turnover were investigated in relation to photoinhibition and D1 protein turnover in mature leaves of Arabidopsis (Arabidopsis thaliana) by ¹⁴CO₂ pulse-chase labeling. Following a 2 h treatment of leaves with water, lincomycin (Linco; an inhibitor of chloroplast protein synthesis) or norflurazon (NF; an inhibitor of carotenoid biosynthesis at phytoene desaturation) in the dark, ¹⁴CO₂ was applied to the leaves for 30 min under control light (CL; 130 μmol photons m⁻² s⁻¹) conditions, followed by exposure to either CL or high light (HL; 1,100 μmol photons m⁻² s⁻¹) in ambient CO₂ for up to 6 h. Under both light conditions, ¹⁴C incorporation was strongly decreased for Chl a and moderately suppressed for β-C in Linco-treated leaves, showing a marked decline of PSII efficiency (F(v)/F(m)) and β-C content compared with water-treated leaves. Partial inhibition of carotenoid biosynthesis by NF caused no or only a minor decrease in F(v)/F(m) and Chl a turnover under both conditions, while the β-C content significantly declined and high ¹⁴C labeling was found for phytoene, the substrate of phytoene desaturase. Together, the results suggest coordinated turnover of Chl a and D1, but somewhat different regulation for β-C turnover, in Arabidopsis leaves. Inhibition of carotenoid biosynthesis by NF may initially enhance metabolic flux in the pathway upstream of phytoene, presumably compensating for short supply of β-C. Our observations are also in line with the notion that HL-induced accumulation of xanthophylls may involve a precursor pool which is distinct from that for β-C turnover.

Topics: Arabidopsis; beta Carotene; Carbon Dioxide; Carotenoids; Chlorophyll; Chlorophyll A; Isotope Labeling; Light; Lincomycin; Photosystem II Protein Complex; Plant Leaves; Pyridazines

Pentatricopeptide repeat (PPR) proteins (PPRPs) are encoded by a large gene family in Arabidopsis (Arabidopsis thaliana), and their functions are largely unknown. The few studied PPRPs are implicated in different developmental processes through their function in RNA metabolism and posttranscriptional regulation in plant organelles. Here, we studied the functions of Arabidopsis PENTATRICOPEPTIDE REPEAT PROTEIN FOR GERMINATION ON NaCl (PGN) in plant defense and abiotic stress responses. Inactivation of PGN results in susceptibility to necrotrophic fungal pathogens as well as hypersensitivity to abscisic acid (ABA), glucose, and salinity. Interestingly, ectopic expression of PGN results in the same phenotypes as the pgn null allele, indicating that a tight regulation of the PGN transcript is required for normal function. Loss of PGN function dramatically enhanced reactive oxygen species accumulation in seedlings in response to salt stress. Inhibition of ABA synthesis and signaling partially alleviates the glucose sensitivity of pgn, suggesting that the mutant accumulates high endogenous ABA. Accordingly, induction of NCED3, encoding the rate-limiting enzyme in stress-induced ABA biosynthesis, is significantly higher in pgn, and the mutant has higher basal ABA levels, which may underlie its phenotypes. The pgn mutant has altered expression of other ABA-related genes as well as mitochondria-associated transcripts, most notably elevated levels of ABI4 and ALTERNATIVE OXIDASE1a, which are known for their roles in retrograde signaling induced by changes in or inhibition of mitochondrial function. These data, coupled with its mitochondrial localization, suggest that PGN functions in regulation of reactive oxygen species homeostasis in mitochondria during abiotic and biotic stress responses, likely through involvement in retrograde signaling.

Topics: Abscisic Acid; Adaptation, Physiological; Amino Acid Sequence; Arabidopsis; Arabidopsis Proteins; Botrytis; Cell Nucleus; Chlorophyll; Chloroplasts; Ethylenes; Gene Expression Regulation, Plant; Genes, Plant; Germination; Glucose; Mitochondria; Mitochondrial Proteins; Molecular Sequence Data; Mutation; Oxidative Stress; Phenotype; Protein Transport; Pyridazines; Reactive Oxygen Species; Repetitive Sequences, Amino Acid; Seedlings; Sodium Chloride; Stress, Physiological

To understand the regulatory mechanisms involved in tissue development by light, the kinetics of regulation of Casparian strip (CS) development in garden pea stems was studied. We found that short-term irradiation with white light delayed the development of the CS and used this delay to assess the quantitative effect of light on CS development. We examined the effect of the duration and fluence rates of white light treatment on CS development and observed a significant relationship between fluence and the delay in CS development indicating that the Bunsen-Roscoe law of reciprocity holds for this response. The effect of white light irradiation was not inhibited in the presence of a photosynthetic inhibitor, DCMU, or a carotenoid biosynthesis inhibitor, Norflurazon, indicating that the delay in CS development by light is a photomorphogenetic response rather than a subsidiary effect mediated by photosynthetic activity. An action spectrum for the response displayed a major peak in the blue-light region, suggesting a dominant role for blue-light receptors. A minor peak in the red-light region also suggested the possible involvement of phytochromes. Although phytochromes are known to contribute to blue-light responses, phytochrome-deficient mutants showed a normal delay of CS development in response to blue light, indicating that the response is not mediated by phytochrome and suggesting a role for one or more specific blue-light receptors.

Topics: Cell Wall; Chlorophyll; Diuron; Fluorescence; Light; Mannitol; Microscopy, Fluorescence; Photosynthesis; Pisum sativum; Plant Roots; Plant Stems; Pyridazines

Chloroplast biogenesis involves careful coordination of both plastid and nuclear gene expression, which is achieved in part by retrograde signaling from the chloroplast to the nucleus. This can be demonstrated by the fact that the herbicide, Norflurazon (NF), which causes bleaching of chloroplasts, prevents the light induction of photosynthesis-related genes in the nucleus. It has been proposed that the tetrapyrrole pathway intermediate Mg-protoporphyrin IX acts as the signaling molecule in this pathway and accumulates in the chloroplasts and cytosol of the cell after NF treatment. Here we present data that demonstrate that this model is too simplistic. We have developed a sensitive liquid chromatography-mass spectrometry (LC/MS) method to measure tetrapyrrole intermediates and have shown that no Mg-protoporphyrin IX, nor indeed any other chlorophyll-biosynthesis intermediate, can be detected in NF-treated plants under conditions in which nuclear gene expression is repressed. Conversely when endogenous Mg-protoporphyrin IX levels are artificially increased by supplementation with the tetrapyrrole precursor, 5-aminolevulinic acid, the expression of nuclear-encoded photosynthetic genes is induced, not repressed. We also demonstrate that NF-treatment leads to a strong down-regulation of tetrapyrrole biosynthesis genes, consistent with the absence of an accumulation of tetrapyrrole intermediates. Finally, there is no correlation between nuclear-gene expression and any of the chlorophyll biosynthetic intermediates over a range of growth conditions and treatments. Instead, it is possible that a perturbation of tetrapyrrole synthesis may lead to localized ROS production or an altered redox state of the plastid, which could mediate retrograde signaling.

Topics: Arabidopsis; Cell Nucleus; Chlorophyll; Chlorophyll A; Chromatography, Liquid; Gene Expression Regulation, Plant; Herbicides; Mass Spectrometry; Plastids; Protoporphyrins; Pyridazines; Seedlings; Signal Transduction

The pyridazinone-type herbicide norflurazon SAN 9789 inhibiting the biosynthesis of long-chain carotenoids results in significant decrease in PS II core complexes and content of light-harvesting complex (LHC) polypeptides in the 29.5-21 kDa region. The Chl a forms at 668, 676, and 690 nm that belong to LHC and antenna part of PS I disappear completely after treatment. The intensity of the Chl b form at 648 nm is sharply decreased in treated seedlings grown under 30 or 100 lx light intensity. The bands of carotenoid absorption at 421, 448 (Chl a), 452, 480, 492, 496 (beta-carotene), and 508 nm also disappear. The band shift from 740 to 720 nm and decrease in its intensity relative to the 687 nm emission peak in the low-temperature fluorescence spectrum (77 K) suggests a disturbance of energy transfer from LHC to the Chl a form at 710-712 nm.

Topics: Carotenoids; Chlorophyll; Herbicides; Light; Photosystem II Protein Complex; Pyridazines; Triticum

In the present study we have optimized the concentration of the bleaching herbicide norflurazon to obtain Dunaliella bardawil cells able to accumulate phytoene without losing viability. The highest concentration of phytoene 10.4 g/gChl was obtained for a concentration of norflurazon of 10 microg/mL. Norflurazon-treated Dunaliella bardawil cells are able to accumulate high concentrations of phytoene if the carotenogenic pathway is stimulated, but the lack of colored carotenoids make these cells particularly sensitive to high light intensities and to UVB radiation, so other stimuli, such as nitrogen starvation, have to be used to force the accumulation of phytoene. Detailed time-course evolution of the carotenoids lutein, violaxanthin, zeaxanthin, phytene and beta-carotene and the photosynthetic pigment chlorophyll was followed upon transfer of Dunaliella bardawil cells to nitrogen starvation in presence and absence of norflurazon. The combined use of the carotenogenic pathway inhibitor norflurazon and biphasic aqueous/organic systems to force the excretion of phytoene into the culture medium has been investigated. Cells cultured in the biphasic system were viable and able to produce phytoene during 3 days. Futhermore the productivity increased from 0.14 g/gChl . h in the aqueous culture to 0.18 g/gChl . h in the biphasic system. About 15% of the total phytoene produced by Dunaliella bardawil was excreted and immediately partionated into the organic phase. The concentration of phytoene in the decane phase was 2.05 g/gChl after 72 h, this means that about 47 g of phytoene per litre of culture were in the organic phase.

Topics: Carotenoids; Cell Culture Techniques; Cell Survival; Cells, Cultured; Chlorophyll; Chlorophyta; Chromatography, High Pressure Liquid; Herbicides; Light; Pyridazines

Methyl jasmonate (MeJA) and norflurazon (NF) treatments resulted in a substantial decrease in photosynthetic activities and chlorophylls (Chls) in Arabidopsis thaliana plants, causing a senescence-like yellowing and a bleaching in MeJA- and NF-treated plants, respectively. Non-radiative energy dissipation through q(N) and non-photochemical quenching increased greatly in NF-treated plants in concomitance with an increase in photoprotectants antheraxanthin and zeaxanthin from interconversion of violaxanthin, although they were not changed in MeJA-treated plants. A significant accumulation of anthocyanin was observed only in MeJA-treated plants, not in NF-treated plants. Total activities of catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), superoxide dismutase (EC 1.15.1.1) and glutathione reductase (EC 1.6.4.2) increased greatly in response to MeJA, particularly a 100-fold increase in POD activity 7 days after MeJA treatment. NF application to plants exhibited less increase in antioxidant enzymes than MeJA-treated plants. NF-treated young leaves had a greater decline in Chls and CAT activity, and less zeaxanthin accumulation compared to NF-treated mature leaves, indicating that NF-treated young leaves are more susceptible to excess light exposure and a possible photooxidative stress. Both MeJA- and NF-treated Arabidopsis plants suffered destruction of Chls, however, they developed differential antioxidant responses during the stress, in large part by an increased anthocyanin level in the epidermis and enzymatic antioxidants in MeJA-treated plants and by accumulation of antheraxanthin and zeaxanthin, and enhanced energy dissipation in NF-treated plants.

Topics: Acetates; Antioxidants; Arabidopsis; Catalase; Chlorophyll; Cyclopentanes; Glutathione Reductase; Oxylipins; Peroxidase; Photosynthesis; Plant Leaves; Pyridazines; Superoxide Dismutase

The effects of the bleaching herbicides amitrole (125 micro M) and norflurazon (100 micro M) on etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 degrees C or 30 degrees C in darkness. Total lipid, glycolipid and phospholipid contents of control etioplasts were increased at 30 degrees C in comparison with those at 20 degrees C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 degrees C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 degrees C and norflurazon at 30 degrees C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of etioplasts and the interaction between the pigment-protein complex, protochlorophyllide-NADPH-protochlorophyllide oxidoreductase, and polar lipids are discussed.

Topics: Amitrole; Chlorophyll; Darkness; Diglycerides; Galactolipids; Glycolipids; Herbicides; Hordeum; Light; Lipid Metabolism; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors; Phospholipids; Plant Leaves; Plant Proteins; Plastids; Pyridazines; Temperature

We have examined the expression of the HEMA1 gene, which encodes the key chlorophyll synthesis enzyme glutamyl-tRNA reductase, during the phytochrome A-mediated far-red light (FR) block of greening response in Arabidopsis. Our results demonstrate that the FR block of greening comprises two separate responses: a white light (WL) intensity-independent response that requires 3 d of FR and is associated with a loss of expression of the nuclear genes HEMA1 and Lhcb following the transfer to WL (transcriptionally coupled response) and a WL intensity-dependent response that is induced by 1 d of FR and is transcriptionally uncoupled. Both responses required phytochrome A. The transcriptionally uncoupled response correlated with a deregulation of tetrapyrrole synthesis and potential photooxidative damage and was inhibited by cytokinin. The transcriptionally coupled FR response was additive with the loss of expression following Norflurazon-induced photobleaching and was absent in the presence of sucrose or after lower fluence rate (1 micromol m(-2) s(-1)) FR treatments. Both pathways leading to the loss of nuclear gene expression were inhibited by overexpression of NADPH:protochlorophyllide oxidoreductase, indicating a role for plastid signaling in the FR-mediated pathway. The significance of identifying a distinct phytochrome A-mediated plastid signaling pathway is discussed.

Topics: Aldehyde Oxidoreductases; Aminolevulinic Acid; Arabidopsis; Arabidopsis Proteins; Chlorophyll; Chloroplasts; Cytokinins; Gene Expression Regulation, Plant; Light; Light-Harvesting Protein Complexes; NADP; Nuclear Proteins; Oxidative Stress; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors; Photosynthetic Reaction Center Complex Proteins; Phytochrome; Phytochrome A; Promoter Regions, Genetic; Pyridazines; Signal Transduction; Sucrose; Transcriptional Activation

RNA silencing of endogenous plant genes can be achieved by virus-mediated, transient expression of homologous gene fragments. This powerful, reverse genetic approach, known as virus-induced gene silencing (VIGS), has been demonstrated only in dicot plant species, where it has become an important tool for functional genomics. Barley stripe mosaic virus (BSMV) is a tripartite, positive-sense RNA virus that infects many agriculturally important monocot species including barley, oats, wheat and maize. To demonstrate VIGS in a monocot host, we modified BSMV to express untranslatable foreign inserts downstream of the gammab gene, in either sense or antisense orientations. Phytoene desaturase (PDS) is required for synthesizing carotenoids, compounds that protect chlorophyll from photo-bleaching. A partial PDS cDNA amplified from barley was 90, 88 and 74% identical to PDS cDNAs from rice, maize and Nicotiana benthamiana, respectively. Barley infected with BSMV expressing barley, rice or maize PDS fragments became photo-bleached and accumulated phytoene (the substrate for PDS) in a manner similar to plants treated with the chemical inhibitor of PDS, norflurazon. In contrast, barley infected with wild-type BSMV, or BSMV expressing either N. benthamiana PDS or antisense green fluorescent protein (GFP), did not photo-bleach or accumulate phytoene. Thus BSMV silencing of the endogenous PDS was homology-dependent. Deletion of the coat protein enhanced the ability of BSMV to silence PDS. This is the first demonstration of VIGS in a monocot, and suggests that BSMV can be used for functional genomics and studies of RNA-silencing mechanisms in monocot plant species.

Topics: Base Sequence; Carotenoids; Chlorophyll; Cloning, Molecular; DNA, Complementary; Gene Expression Regulation, Plant; Gene Silencing; Hordeum; Molecular Sequence Data; Mosaic Viruses; Nicotiana; Oryza; Oxidoreductases; Plants, Genetically Modified; Poaceae; Pyridazines; RNA Viruses; Sequence Homology, Nucleic Acid; Zea mays

We report here the isolation and characterization of a cotyledon-specific albino locus of Arabidopsis, WHITE COTYLEDONS (WCO). This recessive mutation in the WCO locus, located on the top of Chromosome 1, results in albino cotyledons but green true leaves. An accumulation profile of chlorophylls and ultrastructure of chloroplasts indicate that WCO is necessary for development of functional chloroplasts in cotyledons but is dispensable in true leaves. This was further supported by the fact that the mutants request feeding of sucrose for their survival at the early seedling stage where true leaves have not emerged, but the mutants which have developed true leaves are able to grow autotrophically without sucrose supplementation. The wco mutants accumulate low levels of chloroplast mRNA encoding photosynthesis-related proteins and have a specific defect in 16S rRNA maturation in a cotyledon-specific manner. Although wco mutants exhibited abnormal chloroplasts and chloroplast gene expression in cotyledons, nuclear genes for photosynthetic components are expressed at similar levels to those found in wild-type siblings. This lack of suppression of the nuclear genes is not due to a defect in the signaling of the so-called "plastid factor" to the nucleus since normal suppression of the nuclear genes was observed in response to the photo-oxidative damage due to norflurazon application.

Topics: Arabidopsis; Cell Nucleus; Chlorophyll; Chloroplasts; Chromosome Mapping; Cotyledon; DNA, Plant; Gene Expression Regulation, Developmental; Gene Expression Regulation, Plant; Glucuronidase; Light-Harvesting Protein Complexes; Mutation; Oxidation-Reduction; Phenotype; Photochemistry; Photosynthetic Reaction Center Complex Proteins; Plant Development; Plant Leaves; Plants; Plants, Genetically Modified; Pyridazines; Recombinant Fusion Proteins; RNA, Plant; RNA, Ribosomal, 16S; Sucrose

Synthesis of carotenoids in higher plants occurs in the plastids, but all of the required enzymes are coded for in the nuclear genome and are post-transcriptionally imported into the plastid compartment. Regulation of the synthesis of the enzymes is poorly understood. The two-step desaturation of phytoene to zeta-carotene, carried out by the enzyme phytoene desaturase (PDS), is one of the earliest steps in the pathway and has been studied in several systems. Previous analyses of phytoene-accumulating tissue suggested that there may be feedback regulation of PDS gene transcription, with higher expression in white tissue. To investigate this regulation further, we examined phytoene-accumulating tissue in Arabidopsis thaliana (L.) Heynh. Two types of phytoene-accumulating tissue were studied: Norflurazon-bleached plants and white sectors from the immutans variegation mutant. Based on competitive RT-PCR measurements of PDS mRNA and immunochemical detection of PDS protein, we determined that there is no significant induction of PDS gene expression specific to white tissue, indicating that PDS expression is independent of the pigment status of the cells. Reasons why our results differ from those in other systems are discussed.

Topics: Arabidopsis; Carotenoids; Chlorophyll; Feedback; Gene Expression Regulation, Enzymologic; Herbicides; Mutation; Oxidoreductases; Pigments, Biological; Polymerase Chain Reaction; Pyridazines; RNA, Messenger; RNA, Plant

Inhibitors of the phytoene desaturase in carotene biosynthesis were tested in the enhanced rapid turnover of the D1 protein of photosystem II in high light exposure of Chlamydomonas reinhardtii cells. After 1 h high light on heterotrophically grown cells in the presence of norflurazon or fluridone, photosynthesis activity in vivo and PS II activity in vitro is lost. The D1 protein has disappeared. PS I activity is not affected, nor is the D2 protein. It is concluded that beta-carotene is essential for the assembly of the D1 protein into functional photosystem II. It is suspected that bleaching of beta-carotene in the reaction center of PS II by high light destabilizes the structure and triggers the degradation of the D1 protein.

Topics: Animals; beta Carotene; Chlamydomonas reinhardtii; Chlorophyll; Light; Light-Harvesting Protein Complexes; Oxidoreductases; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Pyridazines; Pyridones

Treatment of six-day-old barley leaves with white light of high intensity, 250-2000 W/m2, leads to a linear increase in the steady-state concentrations of early light-inducible protein (ELIP) mRNA followed by an accumulation of the protein. Accumulation of ELIP mRNA, under light stress, is highest in the basal third of the leaf and declines to approximately 50% of this level in the apical segment. The amount of the accumulated protein decreases more steeply towards the tip than would be expected from mRNA levels. This finding, as well as the fact that during greening a massive accumulation of the protein starts only at a time when the steady-state concentrations of ELIP mRNA have declined to 10% of the maximal value, indicate post-transcriptional control. Accumulation is presumably achieved by stabilization of the protein. ELIP mRNA and protein levels, induced by a 2-h period of high-light stress, are lowest in the afternoon and highest at midnight and during the morning. The inducibility of ELIP by high light is therefore under diurnal control. An increase of light stress, due to application of the carotenoid-biosynthesis inhibitor norfluorazon, results in a considerable induction of ELIP mRNA and protein. The plant hormone abscisic acid exerts only a small effect on the mRNA level. In all cases studied, the light-induced increase in the amount of ELIP mRNA was accompanied by a corresponding decline in the mRNA levels for the apoprotein of the chlorophyll-a/b-binding protein. Steady-state concentrations of mRNA for the small subunit of ribulose-1,5-bisphosphate carboxylase were hardly affected under all investigated light intensities.

Topics: Abscisic Acid; Arabidopsis Proteins; Carotenoids; Chlorophyll; Circadian Rhythm; Dose-Response Relationship, Radiation; Gene Expression Regulation; Hordeum; Light-Harvesting Protein Complexes; Photosynthetic Reaction Center Complex Proteins; Plant Proteins; Pyridazines; RNA, Messenger; Transcription, Genetic

Steady-state mRNA levels of the three nuclear genes cab1, rbcS1 and rbcS2 (coding for the light-harvesting chlorophyll-binding protein (LHCP) and the small subunit of ribulose 1,5-bisphosphate carboxylase, respectively) and of the two plastid-encoded genes rbcL and psaA2 (coding for the large subunit of the carboxylase and a member of the P700 chlorophyll a protein, respectively) have been investigated in synchronized Chlamydomonas cells in response to light and inhibitors interfering with chlorophyll synthesis. The accumulation of cab1, rbcS1 and psaA2 transcripts is light-dependent, whereas transcripts from rbcS2 and rbcL genes are present in high amounts in the light and in the dark. Dioxoheptanoic acid, an inhibitor blocking chlorophyll synthesis prior to porphyrin formation, does not affect the accumulation of all five mRNAs. However, inhibition of chlorophyll synthesis by incubating cells with dipyridyl, cycloheximide or nitrogen promotes the accumulation of porphyrin compounds, but specifically prevents the accumulation of light-dependent transcripts. Although functionally unrelated, these inhibitors are known to block an Fe-dependent oxygenase, which is involved in the formation of the isocyclic ring in the chlorophyll molecule. The data are explained as a control by chlorophyll precursors over the accumulation of light-dependent transcripts.

Topics: 2,2'-Dipyridyl; Chlamydomonas; Chloramphenicol; Chlorophyll; Cycloheximide; DNA Probes; Hemin; Heptanoates; Iron; Levulinic Acids; Light; Light-Harvesting Protein Complexes; Nucleic Acid Hybridization; Photochemistry; Photosynthetic Reaction Center Complex Proteins; Plant Proteins; Protein Precursors; Pyridazines; RNA, Messenger; Transcription, Genetic

In carotenoid-deficient albina mutants of barley and in barley plants treated with the herbicide Norflurazon the light-dependent accumulation of the mRNA for the light-harvesting chlorophyll a/b protein (LHCP) is blocked. Thus, the elimination of a functional chloroplast, either as a result of mutation or as a result of herbicide treatment, can lead to the specific suppression of the expression of a nuclear gene encoding a plastid-localized protein. These results confirm and extend earlier observations on maize [Mayfield and Taylor (1984) Eur. J. Biochem. 144, 79-84]. The inhibition of mRNA accumulation appears to be specific for the LHCP; the mRNAs encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and the NADPH: protochlorophyllide oxidoreductase are relatively unaffected. The failure of the albina mutants and of Norflurazon-treated plants to accumulate the LHCP mRNA is not exclusively caused by an instability of the transcript but rather by the inability of the plants to enhance the rate of transcription of the LHCP genes during illumination. Several chlorophyll-deficient xantha mutants of barley, which are blocked after protoporphyrin IX or Mg-protoporphyrin, and the chlorophyll-b-less mutant chlorina f2 accumulate the LHCP mRNA to almost normal levels during illumination. Thus, if any of the reactions leading to chlorophyll formation is involved in the control of LHCP mRNA accumulation it should be one between the formation of protochlorophyllide and the esterification of chlorophyllide a. While the nature of the regulatory factor(s) has not been identified our results suggest that, in addition to phytochrome (Pfr), plastid-dependent factors are required for a continuous light-dependent transcription of nuclear genes encoding the LHCP.

Topics: Carotenoids; Cell Nucleus; Chlorophyll; Chloroplasts; Gene Expression Regulation; Herbicides; Light-Harvesting Protein Complexes; Molecular Weight; Mutation; Photosynthetic Reaction Center Complex Proteins; Plant Proteins; Plants; Proton-Translocating ATPases; Pyridazines; Transcription, Genetic