1,045 research outputs found

    Light-regulated plant growth and development.

    Get PDF
    Plants are sessile and photo-autotrophic; their entire life cycle is thus strongly influenced by the ever-changing light environment. In order to sense and respond to those fluctuating conditions higher plants possess several families of photoreceptors that can monitor light from UV-B to the near infrared (far-red). The molecular nature of UV-B sensors remains unknown, red (R) and far-red (FR) light is sensed by the phytochromes (phyA-phyE in Arabidopsis) while three classes of UV-A/blue photoreceptors have been identified: cryptochromes, phototropins, and members of the Zeitlupe family (cry1, cry2, phot1, phot2, ZTL, FKF1, and LKP2 in Arabidopsis). Functional specialization within photoreceptor families gave rise to members optimized for a wide range of light intensities. Genetic and photobiological studies performed in Arabidopsis have shown that these light sensors mediate numerous adaptive responses (e.g., phototropism and shade avoidance) and developmental transitions (e.g., germination and flowering). Some physiological responses are specifically triggered by a single photoreceptor but in many cases multiple light sensors ensure a coordinated response. Recent studies also provide examples of crosstalk between the responses of Arabidopsis to different external factors, in particular among light, temperature, and pathogens. Although the different photoreceptors are unrelated in structure, in many cases they trigger similar signaling mechanisms including light-regulated protein-protein interactions or light-regulated stability of several transcription factors. The breath and complexity of this topic forced us to concentrate on specific aspects of photomorphogenesis and we point the readers to recent reviews for some aspects of light-mediated signaling (e.g., transition to flowering)

    Fluiddynamik des Kammerwassers beim chronischen einfachen Glaukom: Mechanismen der Drucknormalisierung durch ein künstliches Abflusssystem

    Get PDF
    Zusammenfassung: Die Wechselwirkung zwischen Kräften, Verteilung und Absorption des Kammerwassers im subkonjunktivalen Gewebe wird anhand eines kürzlich publizierten theoretischen Modells untersucht, das die Produktion von Flüssigkeit im Auge und deren Eliminierung durch das Trabekelwerk, das uveosklerale Gewebe und einen Shunt beschreibt. Zielgröße dabei ist der intraokulare Druck. Die Mechanismen von neu geschaffenen Abflusswegen werden mithilfe der Theorie der porösen Medien dargestellt, die sich auf ein Sickerkissen beziehen, das unter dem subkonjunktivalen Gewebe liegt. Die rechnerische Analyse basiert auf der Geometrie und den Parametern, die das Zu- und Abflusssystem charakterisieren. Diese sind durch die Produktion von Kammerwasser, den chirurgisch angelegten Abflusskanal, sodann durch die Resorption in den episkleralen Gefäßen und durch die hydraulischen Eigenschaften des subkonjunktivalen Gewebes und des Sickerkissens sowie durch dessen Geometrie gegeben. Anhand parametrischer Untersuchungen können klinische Befunde physikalisch begründet werde

    Confirmatory Factor Analysis of the French Version of the Savoring Beliefs Inventory.

    Get PDF
    The Savoring Beliefs Inventory (SBI) is a measure designed to assess attitudes toward savoring positive experience within three temporal orientations: the past (reminiscence), the present moment (present enjoyment), and the future (anticipation). The aim of this study was to validate the structure of the SBI-French version. The scale was tested with 335 French-speaking participants. Two models were estimated: a one-factor model representing a general construct of savoring and a three-factor model differentiating between anticipation, present enjoyment, and reminiscence. Several indicators of model fit were used: the root mean square error of approximation (RMSEA), the comparison fit index (CFI), the Tucker-Lewis fit index (TLI), and the standardized root mean residual (SRMR). A chi-square difference test was used to compare the two models. The model fit of the three-factor model assessed by the SRMR showed to be excellent, while it could be considered as satisfactory according to the CFI and TLI coefficients. RMSEA, however, was slightly less adequate. The model fit for the one-factor model seemed less adequate than the three-factor solution. Further, the chi-square difference test revealed that the three-factor model had significantly better fit than the one-factor model. Finally, the reliability of the four scores (anticipating pleasure, present moment pleasure, reminiscing pleasure, and total score) was very good. These results show that the French version of the SBI is a valid and valuable scale to measure attitudes regarding the ability to savor positive experience, whether it be in anticipation, reminiscence, or the present moment

    Inhibition of the shade avoidance response by formation of non-DNA binding bHLH heterodimers.

    Get PDF
    In shade-intolerant plants such as Arabidopsis, a reduction in the red/far-red (R/FR) ratio, indicative of competition from other plants, triggers a suite of responses known as the shade avoidance syndrome (SAS). The phytochrome photoreceptors measure the R/FR ratio and control the SAS. The phytochrome-interacting factors 4 and 5 (PIF4 and PIF5) are stabilized in the shade and are required for a full SAS, whereas the related bHLH factor HFR1 (long hypocotyl in FR light) is transcriptionally induced by shade and inhibits this response. Here we show that HFR1 interacts with PIF4 and PIF5 and limits their capacity to induce the expression of shade marker genes and to promote elongation growth. HFR1 directly inhibits these PIFs by forming non-DNA-binding heterodimers with PIF4 and PIF5. Our data indicate that PIF4 and PIF5 promote SAS by directly binding to G-boxes present in the promoter of shade marker genes, but their action is limited later in the shade when HFR1 accumulates and forms non-DNA-binding heterodimers. This negative feedback loop is important to limit the response of plants to shade

    The Arabidopsis PHYTOCHROME KINASE SUBSTRATE2 protein is a phototropin signaling element that regulates leaf flattening and leaf positioning.

    Get PDF
    In Arabidopsis (Arabidopsis thaliana), the blue light photoreceptor phototropins (phot1 and phot2) fine-tune the photosynthetic status of the plant by controlling several important adaptive processes in response to environmental light variations. These processes include stem and petiole phototropism (leaf positioning), leaf flattening, stomatal opening, and chloroplast movements. The PHYTOCHROME KINASE SUBSTRATE (PKS) protein family comprises four members in Arabidopsis (PKS1-PKS4). PKS1 is a novel phot1 signaling element during phototropism, as it interacts with phot1 and the important signaling element NONPHOTOTROPIC HYPOCOTYL3 (NPH3) and is required for normal phot1-mediated phototropism. In this study, we have analyzed more globally the role of three PKS members (PKS1, PKS2, and PKS4). Systematic analysis of mutants reveals that PKS2 (and to a lesser extent PKS1) act in the same subset of phototropin-controlled responses as NPH3, namely leaf flattening and positioning. PKS1, PKS2, and NPH3 coimmunoprecipitate with both phot1-green fluorescent protein and phot2-green fluorescent protein in leaf extracts. Genetic experiments position PKS2 within phot1 and phot2 pathways controlling leaf positioning and leaf flattening, respectively. NPH3 can act in both phot1 and phot2 pathways, and synergistic interactions observed between pks2 and nph3 mutants suggest complementary roles of PKS2 and NPH3 during phototropin signaling. Finally, several observations further suggest that PKS2 may regulate leaf flattening and positioning by controlling auxin homeostasis. Together with previous findings, our results indicate that the PKS proteins represent an important family of phototropin signaling proteins

    An adaptive variable order quadrature strategy

    Get PDF
    In this article we propose a new adaptive numerical quadrature procedure which includes both local subdivision of the integration domain, as well as local variation of the number of quadrature points employed on each subinterval. In this way we aim to account for local smoothness properties of the function to be integrated as effectively as possible, and thereby achieve highly accurate results in a very efficient manner. Indeed, this idea originates from so-called hp-version finite element methods which are known to deliver high-order convergence rates, even for nonsmooth functions

    Integration of Phytochrome and Cryptochrome Signals Determines Plant Growth during Competition for Light.

    Get PDF
    Plants in dense vegetation perceive their neighbors primarily through changes in light quality. Initially, the ratio between red (R) and far-red (FR) light decreases due to reflection of FR by plant tissue well before shading occurs. Perception of low R:FR by the phytochrome photoreceptors induces the shade avoidance response [1], of which accelerated elongation growth of leaf-bearing organs is an important feature. Low R:FR-induced phytochrome inactivation leads to the accumulation and activation of the transcription factors PHYTOCHROME-INTERACTING FACTORs (PIFs) 4, 5, and 7 and subsequent expression of their growth-mediating targets [2, 3]. When true shading occurs, transmitted light is especially depleted in red and blue (B) wavelengths, due to absorption by chlorophyll [4]. Although the reduction of blue wavelengths alone does not occur in nature, long-term exposure to low B light induces a shade avoidance-like response that is dependent on the cryptochrome photoreceptors and the transcription factors PIF4 and PIF5 [5-7]. We show in Arabidopsis thaliana that low B in combination with low R:FR enhances petiole elongation similar to vegetation shade, providing functional context for a low B response in plant competition. Low B potentiates the low R:FR response through PIF4, PIF5, and PIF7, and it involves increased PIF5 abundance and transcriptional changes. Low B attenuates a low R:FR-induced negative feedback loop through reduced gene expression of negative regulators and reduced HFR1 levels. The enhanced response to combined phytochrome and cryptochrome inactivation shows how multiple light cues can be integrated to fine-tune the plant's response to a changing environment

    Neighbor Detection Induces Organ-Specific Transcriptomes, Revealing Patterns Underlying Hypocotyl-Specific Growth.

    Get PDF
    In response to neighbor proximity, plants increase the growth of specific organs (e.g., hypocotyls) to enhance access to sunlight. Shade enhances the activity of Phytochrome Interacting Factors (PIFs) by releasing these bHLH transcription factors from phytochrome B-mediated inhibition. PIFs promote elongation by inducing auxin production in cotyledons. In order to elucidate spatiotemporal aspects of the neighbor proximity response, we separately analyzed gene expression patterns in the major light-sensing organ (cotyledons) and in rapidly elongating hypocotyls of Arabidopsis thaliana PIFs initiate transcriptional reprogramming in both organs within 15 min, comprising regulated expression of several early auxin response genes. This suggests that hypocotyl growth is elicited by both local and distal auxin signals. We show that cotyledon-derived auxin is both necessary and sufficient to initiate hypocotyl growth, but we also provide evidence for the functional importance of the local PIF-induced response. With time, the transcriptional response diverges increasingly between organs. We identify genes whose differential expression may underlie organ-specific elongation. Finally, we uncover a growth promotion gene expression signature shared between different developmentally regulated growth processes and responses to the environment in different organs
    corecore