Inhibitor Of Carotenoid Biosynthesis Research Articles

Light-harvesting complexes from purple sulfur bacteria Allochromatium minutissimum assembled without carotenoids

Effect of carotenoid (Car) biosynthesis inhibitor diphenylamine (DPA) on purple sulfur bacteria Allochromatium (Alc) minutissimum cell growth has been investigated. Cell growth in the presence of maximum concentration of DPA results in practically complete suppression (∼99%) of carotenoids (Cars) according to the spectrophotometric, HPLC and CD data. Phytoene does not replace the colored carotenoids in these cells. Also Phytoene does not accumulate in large amounts in the cells treated with DPA. A new method for calculating the content of Cars in the complexes from the cells with inhibited Car synthesis including the number of empty Car’s “pockets” has been used. Our results together with published data devoted to DPA action on the cell growth of purple bacteria revealed that Phytoene was not accumulated in the cells treated with DPA. We have concluded that (i) DPA completely inhibits or strongly reduces synthesis of the colored Cars in the cells of purple bacteria, (ii) Phytoene is the main one among the trace amounts of the other Cars in the case of significant inhibition of Car biosynthesis (80–90% or higher).The amount of the LH2 complexes presented in the membranes of Alc minutissimum was found to be little dependent on DPA. From DPA-grown cultures it was possible to isolate Car-less both the LH1 (as LH1–RC complex) and the LH2 complexes. Electronic absorption properties of BChl’s were very similar to those isolated from the control cells. It is shown by HPLC data that the 100 LH2 complexes from cells of Alc minutissimum, in which the synthesis of Car was depressed, contained ∼9 Car molecules and 5 Phytoene molecules. Thus, only nine (with 1 Car molecule per a complex) or less (if more than one Car molecule per a complex) of the 100 LH2 complexes contain molecules of Cars. It means that 90 or more LH2 complexes from each 100 ones are assembled without any Cars. This is in strong contrast with the previous results obtained with purple non-sulfur bacterium Rhodobacter sphaeroides, where the amount of LH2 presented in the membrane was directly correlated to the amount of the carotenoids synthesized (H.P. Lang, C.N. Hunter, The relationship between carotenoid biosynthesis and the assembly of the light harvesting LH2 complex in Rhodobacter sphaeroides, Biochem. J. 298 (1994) 197–205). Our results show that although the presence of Car molecules is important for the stability of the LH2 complexes the overall native structure can be maintained without any Cars at least in the case of purple sulfur bacteria.

Development of the Casparian strip is delayed by blue light in pea stems.

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.

The Arabidopsis translocator protein (AtTSPO) is regulated at multiple levels in response to salt stress and perturbations in tetrapyrrole metabolism

BackgroundThe translocator protein 18 kDa (TSPO), previously known as the peripheral-type benzodiazepine receptor (PBR), is important for many cellular functions in mammals and bacteria, such as steroid biosynthesis, cellular respiration, cell proliferation, apoptosis, immunomodulation, transport of porphyrins and anions. Arabidopsis thaliana contains a single TSPO/PBR-related gene with a 40 amino acid N-terminal extension compared to its homologs in bacteria or mammals suggesting it might be chloroplast or mitochondrial localized.ResultsTo test if the TSPO N-terminal extension targets it to organelles, we fused three potential translational start sites in the TSPO cDNA to the N-terminus of GFP (AtTSPO:eGFP). The location of the AtTSPO:eGFP fusion protein was found to depend on the translational start position and the conditions under which plants were grown. Full-length AtTSPO:eGFP fusion protein was found in the endoplasmic reticulum and in vesicles of unknown identity when plants were grown in standard conditions. However, full length AtTSPO:eGFP localized to chloroplasts when grown in the presence of 150 mM NaCl, conditions of salt stress. In contrast, when AtTSPO:eGFP was truncated to the second or third start codon at amino acid position 21 or 42, the fusion protein co-localized with a mitochondrial marker in standard conditions. Using promoter GUS fusions, qRT-PCR, fluorescent protein tagging, and chloroplast fractionation approaches, we demonstrate that AtTSPO levels are regulated at the transcriptional, post-transcriptional and post-translational levels in response to abiotic stress conditions. Salt-responsive genes are increased in a tspo-1 knock-down mutant compared to wild type under conditions of salt stress, while they are decreased when AtTSPO is overexpressed. Mutations in tetrapyrrole biosynthesis genes and the application of chlorophyll or carotenoid biosynthesis inhibitors also affect AtTSPO expression.ConclusionOur data suggest that AtTSPO plays a role in the response of Arabidopsis to high salt stress. Salt stress leads to re-localization of the AtTSPO from the ER to chloroplasts through its N-terminal extension. In addition, our results show that AtTSPO is regulated at the transcriptional level in tetrapyrrole biosynthetic mutants. Thus, we propose that AtTSPO may play a role in transporting tetrapyrrole intermediates during salt stress and other conditions in which tetrapyrrole metabolism is compromised.

TREATMENTS FOR IMPROVING SEED GERMINATION IN EGGPLANT AND RELATED SPECIES

Orthodox seeds may present ditTerences in germination due to severa] reasons. Poor seed germination Iimits the use of different species for culture or p]ant breeding. In this work, we tested treatments for improving germination in two cultivars of common eggplant (Solanum melongena) and in six accessions of the related species S. macrocarpon, S. aethiopicum, and S. incanum. With the exception of S. incanum MM557, which did not germinate, seeds of the other accessions directly had lower final germination percentages when sown in Petri dishes with deep filter paper than those that were pretreated by surface sterilization and sown in nutrient medium; a further increase in the final germination percentages was achieved by addition of 1 mg L1 GA3 to the medium. The GA3-pretreatment not only increased the final germination percentages but promoted germination also by reducing germination time. Other treatments included stratification of S. macrocarp'on and S. aethiopicum seeds at 4°C for 15 or 30 days, as well as addition of 1 mg L- 1 of TDZ and BAP for the BBS-168 accession, but this did not improve germination. The addition of 0.3 mg L- 1 fluridone, an inhibitor of carotenoid biosynthesis, that is known to prevent ABA biosynthesis, increased the final germination percentages of S. melongena, S. aethiopicum and S. macrocarpon to a similar degree as GA3. Seeds of S. incanum MM-557 did not respond to this treatment but the hybrid derived from this S. incanum accession with eggplant accession ANS-26 showed high germination percentages (70%, 13 days after sowing) in NM medium with GA3, fluridone or both components. These results show that seed treatments can contrihute to improving germination of Solanum accessions with low germination.

Heme synthesis by plastid ferrochelatase I regulates nuclear gene expression in plants.

Chloroplast signals regulate hundreds of nuclear genes during development and in response to stress, but little is known of the signals or signal transduction mechanisms of plastid-to-nucleus (retrograde) signaling. In Arabidopsis thaliana, genetic studies using norflurazon (NF), an inhibitor of carotenoid biosynthesis, have identified five GUN (genomes uncoupled) genes, implicating the tetrapyrrole pathway as a source of a retrograde signal. Loss of function of any of these GUN genes leads to increased expression of photosynthesis-associated nuclear genes (PhANGs) when chloroplast development has been blocked by NF. Here we present a new Arabidopsis gain-of-function mutant, gun6-1D, with a similar phenotype. The gun6-1D mutant overexpresses the conserved plastid ferrochelatase 1 (FC1, heme synthase). Genetic and biochemical experiments demonstrate that increased flux through the heme branch of the plastid tetrapyrrole biosynthetic pathway increases PhANG expression. The second conserved plant ferrochelatase, FC2, colocalizes with FC1, but FC2 activity is unable to increase PhANG expression in undeveloped plastids. These data suggest a model in which heme, specifically produced by FC1, may be used as a retrograde signal to coordinate PhANG expression with chloroplast development.

The herbicide aclonifen: The complex theoretical bases of sunflower tolerance

Aclonifen is a diphenylether herbicide in which one ring is unsubstituted and the other is NH 2-1, Cl-2, NO 2-6 substituted. This substitution, especially NH 2-1, is a particular feature in the diphenylether herbicidal family. In contrast with other herbicides of the same family (acifluorfen, oxyfluorfen, bifenox) this compound is not only acting through a phytotoxic protoporphyrin IX accumulation but also through an inhibition of carotenoid biosynthesis. Both biochemical targets are associated to chloroplast structuration in young seedlings under light and the pre-emergence or preplant treatment is consequently an appropriate agronomic strategy. Numerous weeds such as Alopecurus sp., Sinapis sp., Brassica sp., Chenopodium sp. are very sensitive to this herbicide but sunflower culture appears very tolerant. Our results suggest that this tolerance has a complex origin including (1) low root uptake, (2) conjugation in the roots probably with glutathione and (3) low xylem transfer from root to shoot. The low root uptake is associated to aclonifen crystallization on the root surface at high concentrations. The combination of this physico-chemical effect with a sufficient root conjugation rate can explain both the very low amounts of aclonifen or derivatives found in the aerial parts and the strong sunflower tolerance.

Fluridone affects quiescent centre division in the Arabidopsis thaliana root stem cell niche

Plants undergo cell division throughout their life in order to maintain their growth. It is well known that root and shoot tip of plants possess meristems, which contain quiescent cells. Fluridone (1-methyl-3-phenyl-5-(3-trifluoromethyl (phenyl))-4-(1H)-pyridinone) is an established inhibitor of both ABA and carotenoid biosynthesis. However, the other functions of fluridone remain undiscovered. In this report, we provide experimental evidence that fluridone plays a role in the division of the quiescent centre of the Arabidopsis root meristem. This study examined the effects of exogenous fluridone and ABA on the development of the stem cell niche in Arabidopsis root. We show that fluridone promoted the division of stem cells in the quiescent centre, whereas exogenous ABA suppressed quiescent centre division. Furthermore, we established a novel regulatory function for fluridone by demonstrating that it plays an important role in postembryonic development.

In‐depth analysis of the distinctive effects of norflurazon implies that tetrapyrrole biosynthesis, organellar gene expression and ABA cooperate in the GUN‐type of plastid signalling

Application of norflurazon (NF) damages plastids, induces photobleaching and represses expression of the nuclear LHCB1.2 gene encoding a light-harvesting protein. In genomes uncoupled (gun) mutants, LHCB1.2 expression is maintained in the presence of NF. The mutants gun2, gun4 and gun5 exhibit perturbations in tetrapyrrole biosynthesis, but gun1 is defective in organellar gene expression (OGE). How gun mutations affect nuclear gene expression (NGE) and why the signals elicited by the two types evoke the same response remains unknown. Here we show that the carotenoid biosynthesis inhibitors amitrole and flurochloridone can replace NF in gun assays, whereas novel tetrapyrrole pathway mutations do not provoke a gun phenotype. Changes in haem levels also do not account for LHCB1.2 derepression in NF-treated gun mutants. Pigment measurements indicated that gun mutants are not resistant to NF, but gun2, gun4 and gun5 retain low levels of lutein, as well as of neoxanthin and violaxanthin, the precursors of abscisic acid (ABA). This might explain the enhanced ABA sensitivity of gun4 and gun5 plants found in germination assays. Metabolite profiling and analyses of reactive oxygen species and cellular redox state failed to suggest a link between gun mutations and altered LHCB1.2 expression. However, in contrast to NF-treated wild-type plants, gun mutants retain to a marked extent the capability to express the plastome-encoded proteins AtpB and RbcL. This, together with the finding that application of ABA can partially restore LHCB1.2 expression in NF-treated wild-type plants, supports the view that tetrapyrrole, OGE and ABA signalling are interconnected.

Carotenoid Biosynthesis in Intraerythrocytic Stages of Plasmodium falciparum

Carotenoids are widespread lipophilic pigments synthesized by all photosynthetic organisms and some nonphotosynthetic fungi and bacteria. All carotenoids are derived from the C40 isoprenoid precursor geranylgeranyl pyrophosphate, and their chemical and physical properties are associated with light absorption, free radical scavenging, and antioxidant activity. Carotenoids are generally synthesized in well defined subcellular organelles, the plastids, which are also present in the phylum Apicomplexa, which comprises a number of important human parasites, such as Plasmodium and Toxoplasma. Recently, it was demonstrated that Toxoplasma gondii synthesizes abscisic acid. We therefore asked if Plasmodium falciparum is also capable of synthesizing carotenoids. Herein, biochemical findings demonstrated the presence of carotenoid biosynthesis in the intraerythrocytic stages of the apicomplexan parasite P. falciparum. Using metabolic labeling with radioisotopes, in vitro inhibition tests with norflurazon, a specific inhibitor of plant carotenoid biosynthesis, the results showed that intraerythrocytic stages of P. falciparum synthesize carotenoid compounds. A plasmodial enzyme that presented phytoene synthase activity was also identified and characterized. These findings not only contribute to the current understanding of P. falciparum evolution but shed light on a pathway that could serve as a chemotherapeutic target.

Yellow Nutsedge (Cyperus esculentus) and Large Crabgrass (Digitaria sanguinalis) Response to Soil- and Foliar-Applied Mesotrione

Mesotrione, a carotenoid biosynthesis inhibitor, is being evaluated for use in turfgrass systems. It was hypothesized that root absorption of soil-applied mesotrione is necessary for effective weed control. Greenhouse studies were conducted to compare the effects of foliar-, soil-, and soil-plus-foliar–applied mesotrione at 0.14 and 0.28 kg ai/ha on yellow nutsedge and large crabgrass. In general, greatest control of yellow nutsedge and large crabgrass was by treatments that included soil application. In addition, mesotrione applied at 0.28 kg/ha generally controlled both yellow nutsedge and large crabgrass more effectively than mesotrione applied at 0.14 kg/ha. Soil- and soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled yellow nutsedge more than foliar-applied mesotrione 56 d after treatment. Soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled large crabgrass more than any other treatment 28 d after treatment. Soil- and soil-plus-foliar–applied mesotrione at both rates reduced large crabgrass foliar dry weight more effectively than did foliar-applied mesotrione. Results indicate that root absorption of mesotrione from soil is beneficial for the effective control of both yellow nutsedge and large crabgrass. For this reason, methods such as granular or high-volume applications, which enhance delivery of mesotrione to soil, would be potentially beneficial for turfgrass weed control.

Accumulation of prenyl alcohols by terpenoid biosynthesis inhibitors in various microorganisms

Squalene synthase inhibitors significantly accelerate the production of farnesol by various microorganisms. However, farnesol production by Saccharomyces cerevisiae ATCC 64031, in which the squalene synthase gene is deleted, was not affected by the inhibitors, indicating that farnesol accumulation is enhanced in the absence of squalene synthase activity. The combination of diphenylamine as an inhibitor of carotenoid biosynthesis and a squalene synthase inhibitor increases geranylgeraniol production by a yeast, Rhodotorula rubra NBRC 0870. An ent-kauren synthase inhibitor also enhances the production of farnesol and geranylgeraniol by a filamentous fungus, Gibberella fujikuroi NBRC 30336. These results indicate that the inhibition of downstream enzymes from prenyl diphosphate synthase leads to the production of farnesol and geranylgeraniol.

The biosynthetic pathway of carotenoids in the astaxanthin-producing green alga Chlorella zofingiensis

The carotenoid composition of the astaxanthin-producing green alga Chlorella zofingiensis was investigated using high-performance liquid chromatography. Astaxanthin, adonixanthin, and zeaxanthin are the major carotenoids in this alga. The pigment pattern was characterized during the accumulation period, and in response to diphenylamine (DPA), an inhibitor of carotenoid biosynthesis. An increase in zeaxanthin followed by a decrease in xanthophyll was seen after the induction of astaxanthin biosynthesis by glucose. This biphasic kinetics of zeaxanthin was parallel to the marked increase in adonixanthin (from 0 mg g(-1) to 0.21 mg g(-1)) and astaxanthin (from 0.05 mg g(-1) to 0.35 mg g(-1)) and decrease of beta-carotene (from 0.30 mg g(-1) to 0.03 mg g(-1)). More importantly, unlike the Haematococcus alga, in which there was a high beta-carotene accumulation after DPA treatment, C. zofingiensis showed an accumulation of extra zeaxanthin instead of beta-carotene after treatment of the cells with DPA. All these results observed in vivo studies corroborate the observations in vitro studies at the enzyme level that zeaxanthin is a substrate for the carotenoid oxygenase in C. zofingiensis. It is suggested that zeaxanthin might be an important intermediate and not an end product of the biosynthetic pathway of astaxanthin. Therefore, a new pathway for astaxanthin formation by C. zofingiensis, which is different from that of the other astaxanthin-producing microorganisms, is proposed. An understanding of the astaxanthin biosynthetic pathway may yield important information toward the optimization of astaxanthin production, especially for the improvement of astaxanthin through genetic manipulations.

Tomato strigolactones are derived from carotenoids and their biosynthesis is promoted by phosphate starvation

* Strigolactones are rhizosphere signalling compounds that mediate host location in arbuscular mycorrhizal (AM) fungi and parasitic plants. Here, the regulation of the biosynthesis of strigolactones is studied in tomato (Solanum lycopersicum). * Strigolactone production under phosphate starvation, in the presence of the carotenoid biosynthesis inhibitor fluridone and in the abscisic acid (ABA) mutant notabilis were assessed using a germination bioassay with seeds of Orobanche ramosa; a hyphal branching assay with Gigaspora spp; and by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis. * The root exudates of tomato cv. MoneyMaker induced O. ramosa seed germination and hyphal branching in AM fungi. Phosphate starvation markedly increased, and fluridone strongly decreased, this activity. Exudates of notabilis induced approx. 40% less germination than the wild-type. The LC-MS/MS analysis confirmed that the biological activity and changes therein were due to the presence of several strigolactones; orobanchol, solanacol and two or three didehydro-orobanchol isomers. * These results show that the AM branching factors and parasitic plant germination stimulants in tomato root exudate are strigolactones and that they are biosynthetically derived from carotenoids. The dual activity of these signalling compounds in attracting beneficial AM fungi and detrimental parasitic plants is further strengthened by environmental conditions such as phosphate availability.

Differential Response of Several Carotenoid Biosynthesis Inhibitors in Mixtures with Atrazine

Greenhouse studies were conducted in 2003 at the Stine–Haskell Research Center to determine whether herbicide inhibitors of six specific sites in the carotenoid biosynthesis pathway would elicit synergistic responses when applied postemergence (POST) in combination with the photosystem II (PSII) inhibitor atrazine. Based on data analysis with the Isobole method, synergistic responses were observed on red morningglory, common cocklebur, and giant foxtail when atrazine was applied in mixtures with the deoxy-D-xylulose-5-phosphate reductoisomerase (DOXP reductoisomerase) inhibitor fosmidomycin, thep-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor mesotrione, and the DuPont proprietary zeta-carotene desaturase (ZDS) inhibitor DFPC. Clomazone (its metabolite ketoclomazone is the actual enzyme inhibitor), an inhibitor of 1-deoxy-D-xylulose-5-phosphate synthatase (DOXP synthase), provided synergistic responses on red morningglory, but antagonistic responses on both common cocklebur and giant foxtail when applied in mixtures with atrazine. Combinations of the lycopene cyclase (LC) inhibitor, CPTA, with atrazine produced synergistic responses on both common cocklebur and giant foxtail but were antagonistic on red morningglory. Norflurazon, a phytoene desaturase (PDS) inhibitor, applied in mixtures with atrazine provided synergistic responses on red morningglory, antagonistic responses on giant foxtail, and independent responses on common cocklebur. Because carotenoids have been determined to play a key role in quenching singlet oxygen species in the chloroplast and also assist in the maintenance of the D1 protein in PSII, this might help explain the synergistic responses with atrazine observed in our studies.

Expression of ASCORBATE PEROXIDASE 8 in roots of rice (Oryza sativa L.) seedlings in response to NaCl

Reactive oxygen species are thought to play an important role in NaCl stress. Therefore, the expression patterns of the gene family encoding the H(2)O(2)-scavenging enzyme ascorbate peroxidase (APx; EC1.11.1.11) were analysed in roots of etiolated rice (Oryza sativa L.) seedlings in response to NaCl stress. Applying semi-quantitative RT-PCR, the mRNA levels were quantified for two cytosolic (OsAPx1 and OsAPx2), two peroxisomal (OsAPx3 and OsAPx4), and four chloroplastic (OsAPx5, OsAPx6, OsAPx7, and OsAPx8) isoforms identified in the rice genome. NaCl at 150 mM and 200 mM increased the expression of OsAPx8 and the activities of APx, but had no effect on the expression of OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, OsAPx6, and OsAPx7 in rice roots. However, NaCl at 300 mM up-regulated OsAPx8 expression, increased APx activity, and down-regulated OsAPx7 expression, but had no effect on the expression of OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, and OsAPx6. The accumulation of abscisic acid (ABA) in response to NaCl was observed in rice roots. Exogenously applied ABA also specifically enhanced the expression of OsAPx8 in rice roots. The accumulation of ABA in rice roots in response to NaCl was inhibited by fluridone (Flu), an inhibitor of carotenoid biosynthesis. Flu treatment also suppressed NaCl-enhanced OsAPx8 expression and APx activity. The effect of Flu on the expression of OsAPx8 and increase in APx activity was reversed by the application of ABA. It appears that NaCl-enhanced expression of OsAPx8 in rice roots is mediated through an accumulation of ABA. Evidence is provided to show that Na(+) but not Cl(-) is required for enhancing OsAPx8 expression, APx activity, and ABA accumulation in rice roots treated with NaCl. H(2)O(2) treatment resulted in an enhancement of OsAPx8 induction but no accumulation of ABA. Diphenylene iodonium treatment, which is known to inhibit NaCl-induced accumulation of H(2)O(2) in rice roots, did not suppress OsAPx8 induction and ABA accumulation by NaCl. It appears that H(2)O(2) is not involved in the regulation of NaCl-induced OsAPx8 expression in rice roots.

Dormancy-break and germination in seeds ofPrunus campanulata(Rosaceae): role of covering layers and changes in concentration of abscisic acid and gibberellins

AbstractIntact seeds (seed+endocarp) from freshly harvested fruits ofPrunus campanulatawere dormant, and required 4–6 weeks of warm followed by 8 weeks of cold stratification for maximum germination percentage. Removing both endocarp and seed coat, however, promoted germination in a high percentage of non-stratified seeds. Treatment of intact, non-stratified seeds with gibberellic acid (GA3) was only partially effective in breaking dormancy. However, GA3promoted germination of non-stratified seeds in which the endocarp (but not the seed coat) had been removed. The order of abscisic acid (ABA) concentration in fresh seeds was endocarp > seed coat > embryo, and its concentration in endocarp plus seed coat was about 6.2-fold higher than that in the embryo. Total ABA contents of seeds subjected to warm and/or cold moist stratification were reduced 6- to 12-fold. A higher concentration of GA4was detected in embryos of non-dormant than in those of dormant seeds. Fluridone, a carotenoid biosynthesis inhibitor, was efficient in breaking dormancy ofPrunusseeds. Paclobutrazol, a GA biosynthesis inhibitor, completely inhibited seed germination, and the inhibitory effect could be partially reversed by GA4, but not by GA3. Thus, dormancy inP. campanulataseeds is imposed by the covering layers. Dormancy break is accompanied by a decrease in ABA content of the covering layers and germination by an increase of embryonic GA4content.

Dissecting the biosynthetic pathway for the bypass1 root‐derived signal

The Arabidopsis BYPASS1 (BPS1) gene is required for normal root and shoot development. In bps1 mutants, grafting and root excision experiments have shown that mutant roots produce a transmissible signal that is capable of arresting shoot development. In addition, we previously showed that growth of bps1 mutants on the carotenoid biosynthesis inhibitor fluridone resulted in partial rescue of both leaf and root defects. These observations suggest that a single mobile carotenoid-derived signal affects both root and shoot development. Here, we describe further characterization of the bps1 root-derived signal using genetic and biosynthetic inhibitor approaches. We characterized leaf and root development in double mutants that combined the bps1 mutant with mutants that have known defects in genes encoding carotenoid processing enzymes or defects in responses to carotenoid-derived abscisic acid. Our studies indicate that the mobile signal is neither abscisic acid nor the MAX-dependent hormone that regulates shoot branching, and that production of the signal does not require the activity of any single carotenoid cleavage dioxygenase. In addition, our studies with CPTA, a lycopene cyclase inhibitor, show that signal production requires synthesis of beta-carotene and its derivatives. Furthermore, we show a direct requirement for carotenoids as signal precursors, as the GUN plastid-to-nucleus signaling pathway is not required for phenotypic rescue. Together, our results suggest that bps1 roots produce a novel mobile carotenoid-derived signaling compound.

The Biosynthetic Origin of Germination Stimulants for Orobanche Ramosa (L.) in Tobacco and Arabidopsis

ABSTRACTThe germination of root parasites like Orobanche and Striga depends on chemical products exuded from the roots of the host plant, known as germination stimulants (GS). The predominant part of them has structural similarities with sesquiterpene lactones. It is well known that sesquiterpenes are assembled by the cytosol-localized mevalonate pathway in which the key precursor—isopentenyl diphosphate (IDP) is synthesised from mevalonic acid. Our earlier results however suggested that GS originate from plastid- situated 2-C-Methyl-D-Erythritol-4-Phosphate (MEP pathway). Recently Matusova and co-authors al (18) confirmed this and hypothesized that in maize GS originate from carotenoids.In order to better understand the involvement of the two different isoprenoid biosynthetic pathways in GS formation we have used separately and in combination specific chemical inhibitors for each of biosynthetic pathways. Our results indicate that that indeed in Arabidopsis and tobacco the earliest precursors of GS originate from 1-deoxy-D-xylulose 5 phosphate pathway. However application of carotenoid biosynthesis inhibitor—norflurazon did not influences the GS production. Therefore we concluded that in tobacco and Arabodopsis GS are not derived from carotenoids but from an earlier intermediate of MEP biosynthetic pathway, which is later exported from plastids to the cytosol, to be converted to the final product—GS.

Cadmium-induced ammonium ion accumulation of rice seedlings at high temperature is mediated through abscisic acid

In this study, we examined interaction between cadmium (Cd) and temperature in rice seedlings. Effects of CdCl2 (0.5 mM) simultaneously applied at high (35/30°C day/night), medium (25/20°C) and low (15/13°C) temperatures to rice seedlings were detected by measuring changes in biomass production and NH 4 + content. Results indicated that Cd-induced biomass reduction and NH 4 + accumulation increased in parallel with temperature increases. On treatment with CdCl2, the abscisic acid (ABA) content markedly increased in the leaves of seedlings grown at high temperature but not at medium and low temperatures. Exogenous application of ABA at medium temperature increased ABA and NH 4 + contents in the leaves of rice seedlings. Fluridone (Flu) treatment, an inhibitor of carotenoid biosynthesis, reduced ABA content, as well as Cd-induced NH 4 + accumulation in the leaves of rice seedlings grown at high temperature. These Flu effects can be reversed by application of ABA. Furthermore, Flu treatment did not reduce Cd content in leaves of seedlings grown at high temperature. All these results suggest that Cd-induced NH 4 + accumulation at high temperature is mediated through ABA.

Plant–fungal symbiosis en gros and en détail

Plant–fungal symbiosis <i>en gros</i> and <i>en détail</i>