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PubMed2000

A vibrational study of various K2PdCl(4-x)Br(x) solid solutions.

Infrared and Raman vibrational spectra (700-30 cm(-1)) have been recorded on various K2PdCl(4-x)Br(x) (0 < or = x < or = 4) powdered samples at 300 K, including both K2PdCl4 and K2PdBr4 compounds and ten solid solutions with a bromide content varying from 5-95%. Characteristic variations of the sectra clearly demonstrate a wide domain of existence of the solid solutions and the only possible additional existence, due to no IR-Raman coincidence, of the 'trans' planar PdCl4Br2 centrosymmetric anion. A comparison of the vibrational data with results of valence force field calculations allows us to characterize this new anion, in Raman by two signals at 286 and 225 cm(-1) (v sym., Ag, PdCl2 and PdBr2, respectively), in Infrared by not only the two bands at 309 and 200 cm(-1) (v asym. B3u + B2u, of PdCl2 and PdBr2) but also intense deformation modes in the 178-140 cm(-1) wavenumber range. These results suggest slight modifications in the internal f(Pd-Cl) and f(Pd-Br) force constans on going from the PdCl4(2-) or PdBr4(2-) anions to the 'trans' PdCl2Br2(2-) anonic species.

Bromine↗

PubMed1975

Anion binding properties of human serum albumin from halide ion quadrupole relaxation.

The nuclear magnetic quadrupole relaxation enhancement of 35Cl-, 81Br-, and 12I- anions on binding to human serum albumin has been studied under conditions of variable protein and anion concentration and also in the presence of simple inorganic, amphiphilic, and complex anions which compete with the halide ions for the protein anion binding sites. Two classes of anion binding sites with greatly different binding constans were identified. Experiments at variable halide ion concentration were employed to determin the Cl- and I- binding constants. By means of 35 Cl nuclear magnetic resonance (NMR) the relative affinity for different anions was determined by competition experiments for both the strong and the weak anion binding sites. Anion binding follows the sequence SO42- smaller than F- smaller than CH3COO- smaller than Ci- smaller Br- smaller than NO3- smaller than I- smaller than ClO4- smaller than SCN- smaller than Pt(CN)42- smaller than Au(CN)2- smaller than CH3(CH2)11OSO3- for the high affinity sites, and the sequence SO42- congruent to F- congruent to Cl- smaller CH3COO- smaller than NO3- smaller than Br- smaller than I- smaller than ClO4- smaller than SCN- for the low affinity sites. These series are nearly identical with the well-known lyotropic series. Consequently, those effects of anions on proteins described by the lyotropic series can be correlated with the affinities of the anions for binding to the protein. The data suggest that the physical nature of the interaction is the same for both types of biding sites, and that the differences in affinity between different binding sites must be explained in terms of tertiary structure. Analogous experiments performed using 127I- quadrupole relaxation gave results very similar to those obtained with 35Cl-. A comparison between the Cl-, Br- and I- ions revealed that, as a result of the increasing affinity for the weak anion binding sites in the series Cl- smaller than Br- smaller than I-, Cl- is much more useful as a probe for the specific anion binding sites than the other two halide ions. The findings with human serum albumin in this and other respects are probably of general relevance in studies of protein-anion interactions. In addition to competition experiments, the magnitude of the relaxation rate is also discussed. Line broadening not related to anion binding to the protein is found to be small. A comparison of transverse and longitudinal 35Cl relaxation rates gives a value for the quadrupole coupling constant of the high affinity sites in good agreement with a calculated coupling constant assuming anion binding to arginine.

Anions↗

PubMed1996

Activation of floral meristem identity genes in Arabidopsis.

The Arabidopsis floral meristem-identity genes APETALA1 (AP1) and LEAFY (LFY) confer floral identity on developing floral primordia, whereas TERMINAL FLOWER (TFL) is required to repress their expression within shoot and inflorescence meristems. LFY and AP1 are expressed in floral primordia in response to environmental conditions, such as day length, which regulate the onset of flowering, and presumably also in response to the action of genes that influence flowering time. However, the relationship between these flowering-time genes and the floral meristem-identity genes has been difficult to assess because flowering time is determined by several interacting genetic pathways. Here we describe a method to regulate expression of the flowering-time gene CONSTANS (CO) and demonstrate that CO expression is sufficient to trigger flowering, irrespective of day length. In response to CO expression, transcription of LFY and TFL is initiated rapidly, whereas transcription of AP1 occurs much later. We propose that CO acts within a genetic pathway that is sufficient to activate LFY and TFL transcription, but that rapid activation of AP1 requires an additional pathway.

Arabidopsis↗

PubMed2002

The ELF4 gene controls circadian rhythms and flowering time in Arabidopsis thaliana.

Many plants use day length as an environmental cue to ensure proper timing of the switch from vegetative to reproductive growth. Day-length sensing involves an interaction between the relative length of day and night, and endogenous rhythms that are controlled by the plant circadian clock. Thus, plants with defects in circadian regulation cannot properly regulate the timing of the floral transition. Here we describe the gene EARLY FLOWERING 4 (ELF4), which is involved in photoperiod perception and circadian regulation. ELF4 promotes clock accuracy and is required for sustained rhythms in the absence of daily light/dark cycles. elf4 mutants show attenuated expression of CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), a gene that is thought to function as a central oscillator component. In addition, elf4 plants transiently show output rhythms with highly variable period lengths before becoming arrhythmic. Mutations in elf4 result in early flowering in non-inductive photoperiods, which is probably caused by elevated amounts of CONSTANS (CO), a gene that promotes floral induction.

Arabidopsis↗

PubMed2002

Molecular basis of seasonal time measurement in Arabidopsis.

Several organisms have evolved the ability to measure daylength, or photoperiod, allowing them to adjust their development in anticipation of annual seasonal changes. Daylength measurement requires the integration of temporal information, provided by the circadian system, with light/dark discrimination, initiated by specific photoreceptors. Here we demonstrate that in Arabidopsis this integration takes place at the level of CONSTANS (CO) function. CO is a transcriptional activator that accelerates flowering time in long days, at least in part by inducing the expression of FLOWERING LOCUS T (FT). First, we show that precise clock control of the timing of CO expression, such that it is high during daytime only in long days, is critical for daylength discrimination. We then provide evidence that CO activation of FT expression requires the presence of light perceived through cryptochrome 2 (cry2) or phytochrome A (phyA). We conclude that an external coincidence mechanism, based on the endogenous circadian control of CO messenger RNA levels, and the modulation of CO function by light, constitutes the molecular basis for the regulation of flowering time by daylength in Arabidopsis.

Arabidopsis↗

PubMed2003

Adaptation of photoperiodic control pathways produces short-day flowering in rice.

The photoperiodic control of flowering is one of the important developmental processes of plants because it is directly related to successful reproduction. Although the molecular genetic analysis of Arabidopsis thaliana, a long-day (LD) plant, has provided models to explain the control of flowering time in this species, very little is known about its molecular mechanisms for short-day (SD) plants. Here we show how the photoperiodic control of flowering is regulated in rice, a SD plant. Overexpression of OsGI, an orthologue of the Arabidopsis GIGANTEA (GI) gene in transgenic rice, caused late flowering under both SD and LD conditions. Expression of the rice orthologue of the Arabidopsis CONSTANS (CO) gene was increased in the transgenic rice, whereas expression of the rice orthologue of FLOWERING LOCUS T (FT) was suppressed. Our results indicate that three key regulatory genes for the photoperiodic control of flowering are conserved between Arabidopsis, a LD plant, and rice, a SD plant, but regulation of the FT gene by CO was reversed, resulting in the suppression of flowering in rice under LD conditions.

Arabidopsis↗

PubMed2003

FKF1 is essential for photoperiodic-specific light signalling in Arabidopsis.

Adaptation to seasonal change is a crucial component of an organism's survival strategy. To monitor seasonal variation, organisms have developed the capacity to measure day length (photoperiodism). Day-length assessment involves the photoperiodic control of flowering in Arabidopsis thaliana, whereby the coincidence of light and high expression of CONSTANS (CO) induces the expression of FLOWERING LOCUS T (FT), leading to flowering in long-day conditions. Although controlling CO expression is clearly a key step in day-length discrimination, the mechanism that generates day-length-dependent CO expression remains unknown. Here we show that the clock-controlled FLAVIN-BINDING, KELCH REPEAT, F-BOX (FKF1) protein has an essential role in generating the diurnal CO peak and that this function is dependent on light. We show that a recombinant FKF1 LIGHT, OXYGEN OR VOLTAGE (LOV) domain binds the chromophore flavin mononucleotide and undergoes light-induced photochemistry, indicating that FKF1 may function as a photoperiodic blue-light receptor. It is likely that the circadian control of FKF1 expression and the light regulation of FKF1 function coincide to control the daytime CO waveform precisely, which in turn is crucial for day-length discrimination by Arabidopsis.

Arabidopsis↗

PubMed2003

Living by the calendar: how plants know when to flower.

Reproductive processes in plants and animals are usually synchronized with favourable seasons of the year. It has been known for 80 years that organisms anticipate seasonal changes by adjusting developmental programmes in response to daylength. Recent studies indicate that plants perceive daylength through the degree of coincidence of light with the expression of CONSTANS, which encodes a clock-regulated transcription factor that controls the expression of floral-inductive genes in a light-dependent manner.

Circadian Rhythm↗

PubMed2004

Salicylic acid regulates flowering time and links defence responses and reproductive development.

Flowering relies on signaling networks that integrate endogenous and external cues. Normally, plants flower at a particular season, reflecting day length and/or temperature cues. However, plants can surpass this seasonal regulation and show precocious flowering under stress environmental conditions. Here, we show that UV-C light stress activates the transition to flowering in Arabidopsis thaliana through salicylic acid (SA). Moreover, SA also regulates flowering time in non-stressed plants, as SA-deficient plants are late flowering. The regulation of flowering time by SA seems to involve the photoperiod and autonomous pathways, but it does not require the function of the flowering time genes CONSTANS (CO), FCA, or FLOWERING LOCUS C (FLC).

Arabidopsis↗

PubMed2006

New screening test to predict the potential impact of ivermectin-contaminated cattle dung on dung beetles.

According to European Union recommendations, a test method has been developed to evaluate the effects of veterinary pharmaceuticals on dung feeding insects. This test method was evaluated with the dung beetle Aphodius constans by using fecal residues of ivermectin after a pour-on administration. Dung of different age (and thus containing different concentrations of ivermectin) as well as mixtures of highly-contaminated spiked dung with untreated control dung were studied in five test runs in two laboratories. The concentration of ivermectin (active substance; a.s.) in the dung samples was verified analytically. The main test endpoint was the survival of first instar larvae. The LC50 using dung directly obtained from treated cattle ranged from 470 to 692 microg a.s. kg(-1) dung (dry weight; d.w.) and 67 to 97 microg a.s. kg(-1) dung (fresh weight; f.w.). Using mixtures, the outcome of two tests was almost identical: 770 to 781 microg a.s. kg(-1) dung (d.w.); 109 to 132 microg a.s. kg(-1) dung (f.w.). In comparison to the LC50 values obtained when ivermectin was spiked in control dung at several concentrations (LC50 880-985 microg a.s. kg(-1) dung (d.w.)), the LC50 values were again very similar. Three conclusions can be drawn from these results. The proposed test method seems to be robust and allows for the initiation of an international validation process (including ringtesting). Because of only small differences found in tests in which the test substance was spiked into control dung and those in which dung from treated cattle was applied, the use of a standard test method is proposed. The effects of ivermectin on ecologically relevant dung beetles obtained in a standardised test method reflect the results from field studies and are in the range of environmentally relevant concentrations.

Animals↗

PubMed2006

Earlier flowering induced by over-expression of CO gene does not accompany increase of artemisinin biosynthesis in Artemisia annua.

The early flowering gene CONSTANS (CO) from Arabidopsis thaliana was transferred into Artemisia annua using the Agrobacterium tumefaciens-mediated transformation system. The plant expression vector pBI CO was constructed by inserting the CO gene into the binary vector pBI121 under the control of CaMV 35S promoter. Analyses of PCR, PCR Southern blot, and Southern blot revealed that the transgenic plants contained the foreign CO gene. The results of RT-PCT and RT-PCR Southern blot suggested that the foreign CO gene had expressed at the transcriptional level. Although the flowering time of the CO transgenic plant was about 2 weeks earlier than that of the non-transgenic plant under short-day conditions, no significant difference in artemisinin content was found between the flowering transgenic plant and the non-flowering non-transgenic plant. These results show that the usually observed increase of artemisinin content before plant flowering under natural conditions is not a direct consequence of flowering itself, perhaps there is even no direct linkage between flowering and artemisinin biosynthesis.

Agrobacterium tumefaciens↗

PubMed2002

Floral responses to photoperiod are correlated with the timing of rhythmic expression relative to dawn and dusk in Arabidopsis.

Daylength, or photoperiod, is perceived as a seasonal signal for the control of flowering of many plants. The measurement of daylength is thought to be mediated through the interaction of phototransduction pathways with a circadian rhythm, so that flowering is induced (in long-day plants) or repressed (in short-day plants) when light coincides with a sensitive phase of the circadian cycle. To test this hypothesis in the facultative long-day plant, Arabidopsis thaliana, we used varying, non-24-hr light/dark cycles to alter the timing of circadian rhythms of gene expression relative to dawn and dusk. Effects on circadian rhythms were correlated with those on flowering times. We show that conditions that displaced subjective night events, such as expression of the flowering time regulator CONSTANS into the light portion of the cycle, were perceived as longer days. This work demonstrates that the perception of daylength in Arabidopsis relies on adjustments of the phase angle of circadian rhythms relative to the light/dark cycle, rather than on the measurement of the absolute duration of light and darkness.

Arabidopsis↗

PubMed1996

Two classes of plant cDNA clones differentially complement yeast calcineurin mutants and increase salt tolerance of wild-type yeast.

The salt-sensitive phenotype of yeast cells deficient in the phosphoprotein phosphatase, calcineurin, was used to identify genes from the higher plant Arabidopsis thaliana that complement this phenotype. cDNA clones corresponding to two different sequences, designated STO (salt tolerance) and STZ (salt tolerance zinc finger), were found to increased tolerance of calcineurin mutants and of wild-type yeast to both Li+ and Na+ ions. STZ is related to Cys2/His2-type zinc-finger proteins found in higher plants, and STO is similar to the Arabidopsis CONSTANS protein in regions that may also be zinc fingers. Although neither protein has sequence similarity to any protein phosphatase, STO was able to at least partially compensate for all tested additional phenotypic effects of calcineurin deficiency, and STZ compensated for a subset of these effects. Salt tolerance produced by STZ appeared to be partially dependent on ENA1/PMR2, a P-type ATPase required for Li+ and Na+ efflux in yeast, whereas the effect of STO on salt tolerance was independent of ENA1/PMR2. STZ and STO were found to be expressed in Arabidopsis roots and leaves, whereas only STO message was detectable in flowers. An apparent increase in the level of STZ mRNA was observed in response NaCl exposure in Arabidopsis seedlings, but the level of STO mRNA was not altered by this treatment.

Adaptation, Physiological↗

PubMed1998

Isolation and mapping of a family of putative zinc-finger protein cDNAs from rice.

To understand the functions of rice homologues of the Arabidopsis flowering-time gene CONSTANS (CO) and salt-tolerance gene STO, we performed a similarity search of the single-run sequence data of cDNA clones accumulated by the Rice Genome Research Program, and isolated seven rice cDNA clones (S3574, C60910, S12569, R2931, R1479, R1577, and E10707) coding for proteins containing one of two zinc-finger-like motifs. Comparison of the deduced amino acid sequences between these cDNAs and the CO gene revealed significant similarities (46%-61%) in the region of zinc-finger motifs. A domain having a high content of basic amino acids at the C-terminus of the CO protein was found in the corresponding region of proteins predicted by from cDNAs S3574, C60910, and S12569. Two amino acid sequences, "CCADEAAL" and "FCV(L)EDRA," which were present inside each zinc-finger in the Arabidposis regulatory protein STO, were also found in each of the two zinc-finger regions of proteins predicted from cDNAs R2931, R1479, R1577, and E10707. Using restriction fragment length polymorphism (RFLP) linkage analysis, we determined the chromosomal location of the seven cDNA clones. The position of R2931 on the RFLP linkage map was closely linked to Hd-3, one of the putative quantitative trait loci (QTL) controlling heading date in rice.

Amino Acid Sequence↗

PubMed2006

Light signals and flowering.

Physiological studies over a long period have shown that light acts to regulate flowering through the three main variables of quality, quantity, and duration. Intensive molecular genetic and genomic studies with the model plant Arabidopsis have given considerable insight into the mechanisms involved, particularly with regard to quality and photoperiod. For photoperiodism light, acting through phytochromes and cryptochromes, the main photomorphogenetic photoreceptors, acts to entrain and interact with a circadian rhythm of CONSTANS (CO) expression leading to transcription of the mobile floral integrator, FLOWERING LOCUS T (FT). The action of phytochromes and cryptochromes in photoperiodism is augmented by ZEITLUPE (ZTL) and FLAVIN-BINDING, KELCH REPEAT, F-BOX (FKF1) acting as accessory photoreceptors on entrainment and interaction, respectively. Light quality acts independently of the circadian system through Phytochromes B, D, and E to regulate FT. Light quantity effects, on the other hand, are still incompletely understood but are likely to be linked either directly or indirectly to patterns of assimilate partitioning and resource utilization within the plant.

Arabidopsis↗

PubMed2006

The control of flowering in time and space.

The transition to flowering is one of the most important developmental decisions made by plants. Classical studies have highlighted the importance of photoperiod in controlling flowering time. More recently, the identification of mutants specifically affected in the photoperiod pathway in the model system Arabidopsis thaliana has enabled the flowering time pathways to be placed in a molecular context. This review highlights recent advances in understanding how photoperiod signals (perceived in the leaves) act at the apex of the plant where the floral stimulus is perceived. The photoperiod pathway acts predominantly through the gene CONSTANS to activate the small signalling molecule FT. While FT transcription is induced in the leaves, it is essential that FT protein is present at the apex of the plant. FT at the apex interacts with the transcription factor FD to induce flowering.

Arabidopsis↗

PubMed2000

Genes encoding pseudo-response regulators: insight into His-to-Asp phosphorelay and circadian rhythm in Arabidopsis thaliana.

In the higher plant, Arabidopsis thaliana, results from recent intensive studies suggested that His-to-Asp phosphorelay mechanisms are involved presumably in propagation of environmental stimuli, such as phytohormones (e.g. ethylene and cytokinin). Here we identified and characterized a set of novel Arabidopsis genes whose products considerably resemble the authentic response regulators (ARR-series) of Arabidopsis in the sense that they have a phospho-accepting receiver-like domain. However, they should be discriminated from the classical ones in the strict sense that they lack the invariant phospho-accepting aspartate site. They were thus named APRRs (Arabidopsis pseudo-response regulators). Two such representatives, APRR1 and APRR2, were characterized extensively through cloning of the corresponding cDNAs, in terms of their structural designs, biochemical properties, subcellular localization in plant cells, and expression profiles at the transcriptional level. The result of in vitro phosphorylation experiment with the Arabidopsis AHP phosphotransmitter suggested that the pseudo-receivers have no ability to undergo phosphorylation. The result of transient expression assay with onion epidermal cells showed that the GFP-APRR1 fusion protein has an ability to enter into the nuclei. The C-terminal domain of APRR1, termed CONSTANS-motif, appears to be responsible for the nuclear-localization. The most intriguing result was that the accumulation of APRR1 transcript is subjected to a circadian rhythm. The APRR1 protein is identical to the one that was recently suggested to interact with the ABI3 (ABISCISIC ACID INSENSITIVE3) protein. These are discussed with special reference to the His-to-Asp phosphorelay signal transduction and circadian rhythm in Arabidopsis thaliana.

Amino Acid Sequence↗

PubMed2000

Circadian waves of expression of the APRR1/TOC1 family of pseudo-response regulators in Arabidopsis thaliana: insight into the plant circadian clock.

The Arabidopsis pseudo-response regulator, APRR1, has a unique structural design containing a pseudo-receiver domain and a C-terminal CONSTANS motif. This protein was originally characterized as a presumed component of the His-to-Asp phosphorelay systems in Arabidopsis thaliana. Recently, it was reported that APRR1 is identical to the TOC1 gene product, a mutational lesion of which affects the periods of many circadian rhythms in Arabidopsis plants. TOC1 is believed to be a component of the presumed circadian clock (or central oscillator). Based on these facts, in this study four more genes, each encoding a member of the APRR1/TOC1 family of pseudo-response regulators were identified and characterized with special reference to circadian rhythms. It was found that all these members of the APRR1/TOC1 family (APRR1, APRR3, APRR5, APRR7, and APRR9) are subjected to a circadian rhythm at the level of transcription. Furthermore, in a given 24 h period, the APRR-mRNAs started accumulating sequentially after dawn with 2-3 h intervals in the order of APRR9-->APRR7-->APRR5-->APRR3-->APRR1. These sequential events of transcription, termed 'circadian waves of APRR1/TOCI', were not significantly affected by the photoperiod conditions, if any (e.g. both long and short days), and the expression of APRR9 was first boosted always after dawn. Among these APRRs, in fact, only the expression of APRR9 was rapidly and transiently induced also by white light, whereas such light responses of others were very dull, if any. These results collectively support the view that these members of the APRR1/TOC1 family are together all involved in an as yet unknown mechanism underlying the Arabidopsis circadian clock. Here we propose that the circadian waves of the APRR1/TOC1 family members are most likely a molecular basis of such a biological clock in higher plants.

Amino Acid Sequence↗