Polarization of PIN3-dependent auxin transport for hypocotyl gravitropic response in Arabidopsis thaliana

Gravitropism aligns plant growth with gravity. It involves gravity perception and the asymmetric distribution of the phytohormone auxin. Here we provide insights into the mechanism for hypocotyl gravitropic growth. We show that the Arabidopsis thaliana PIN3 auxin transporter is required for the asymmetric auxin distribution for the gravitropic response. Gravistimulation polarizes PIN3 to the bottom side of hypocotyl endodermal cells, which correlates with an increased auxin response at the lower hypocotyl side. Both PIN3 polarization and hypocotyl bending require the activity of the trafficking regulator GNOM and the protein kinase PINOID. Our data suggest that gravity-induced PIN3 polarization diverts the auxin flow to mediate the asymmetric distribution of auxin for gravitropic shoot bending.     

Comparison of Doppler flow Tei-indexes with pulmonary artery thermodilution measurement of cardiac output in an experimental porcine model

The objective of our study was to compare Doppler echocardiography imaging with pulmonary artery thermodilution measurement during mechanical ventilation. Total 78 piglets (6 weeks old, average weight 24 kg, under general anesthesia) were divided into 4 groups under different cardiac loading conditions (at rest, with increased left ventricular afterload, with increased right ventricular preload, and with increased afterload of both heart ventricles). At 60 and 120 min the animals were examined by echocardiography and simultaneously pulmonary artery thermodilution was used to measure cardiac output. Tei-indexes data were compared with invasively monitored hemodynamic data and cardiac output values together with calculated vascular resistance indices. A total of 224 parallel measurements were obtained. Correlation was found between values of right Tei-index of myocardial performance and changes in right ventricular preload (p<0.05) and afterload (p<0.01). Significant correlation was also found between left index values and changes of left ventricular preload (p<0.001), afterload (p<0.001), stroke volume (p<0.01), and cardiac output (p<0.01). In conclusion, echocardiographic examination and determination of the global performance selectively for the right and left ventricle can be recommended as a suitable non-invasive supplement to the whole set of methods used for monitoring of circulation and cardiac performance.     

In situ assessment of the brain microcirculation in mechanically-ventilated rabbits using sidestream dark-field (SDF) imaging

Assessment of the cerebral microcirculation by on-line visualization has been impossible for a long time. Sidestream dark-field (SDF) imaging is a relatively new method allowing direct visualization of cerebral surface layer microcirculation using hand-held probe for direct contact with target tissue. The aim of this study was to elucidate the feasibility of studying the cerebral microcirculation in situ by SDF imaging and to assess the basic cerebral microcirculatory parameters in mechanically ventilated rabbits. Images were obtained using SDF imaging from the surface of the brain via craniotomy. Clear high contrast SDF images were successfully obtained. Total small-vessel density was 14.6+/-1.8 mm/mm(2), total all-vessel density was 17.9+/-1.7 mm/mm(2), DeBacker score was 12.0+/-1.6 mm(-1) and microvascular flow index was 3.0+/-0.0. This method seems to be applicable in animal studies with possibility to use SDF imaging also intraoperatively, providing unique opportunity to study cerebral microcirculation during various experimental and clinical settings.     

Study of stereoselective interactions of carbamoylated quinine and quinidine with 3,5-dinitrobenzoyl α-amino acids using VCD spectroscopy in the region of C−H stretching vibrations

The stereoselective complexation of tert‐butylcarbamoyl quinine and tert‐butylcarbamoyl quinidine selectors (SOs) with 3,5‐dinitrobenzoyl (DNB) derivatives of D ‐ and L ‐alpha amino acids (DNB‐Ala, DNB‐Val, DNB‐Leu, and DNB‐Ile) as well as achiral DNB‐Gly has been studied by vibrational circular dichroism (VCD) spectroscopy in the spectral region of C H stretching vibrations. All the complexes of SOs and sterically compatible enantiomers of derivatized amino acid selectands (SAs) showed induced circular dichroism (ICD) bands in the region of aromatic C H stretching vibrations, indicating the occurrence of a π–π interaction between the aromatic moieties of SA and SO. To our knowledge, this is the first report in which a π–π interaction was observed by VCD spectroscopy in this spectral region. No ICD bands were disclosed in the spectra of the sterically incompatible SA and SO complexes. The spectral pattern in the region of aliphatic C H stretching vibrations showed interaction‐induced conformational adaptations in sterically favorable SA and SO complexes. No such spectral changes were observed for any of the sterically incompatible complexes. The DNB‐Gly complexes exhibited spectral patterns similar to those observed for sterically favorable pairs of SOs and chiral SAs. Chirality, 2011. © 2010 Wiley‐Liss, Inc.     

Egg yolk antioxidant deposition as a function of parental ornamentation,age, and environment in great tits Parus major

Females can modify phenotype of their offspring through the deposition of biologically active compounds into eggs, including carotenoids, vitamins and other antioxidants. Understanding patterns of deposition is critical for better insight into the significance of maternal effects. Here we investigated how egg yolk antioxidants (lutein, zeaxanthin, β‐carotene, vitamin A and E) related to environmental conditions and parental characteristics in great tits Parus major using data from three breeding seasons. Male and female traits included condition, age and multiple feather ornaments, both carotenoid‐ and melanin‐based (carotenoid and UV chroma of yellow breast feathers, area of black breast band, white cheek immaculateness). Yolk mass increased with ambient temperature during laying, laying date, and the area of male black breast band. Lutein, zeaxanthin, and vitamin E increased with laying date. Total antioxidants increased with female age, immaculateness of female white cheek patch, and UV chroma of carotenoid‐based yellow breast feathers of the social mate. These patterns were thus consistent with 1) environmental effects on yolk mass and composition, 2) higher quality females depositing more antioxidants, and 3) differential allocation of resources in females in relation to male ornamentation. Overall, environmental factors, female traits, and male traits all had an influence on egg yolk characteristics in this socially monogamous songbird.     

The effect of lignin photodegradation on decomposability of <Emphasis Type="Italic">Calamagrostis epigeios</Emphasis> grass litter

The common grass Calamagrostis epigeions produces a large amount of dead biomass, which remain above the soil surface for many months. In this study, we determined how exposure of dead biomass above the soil affects its subsequent decomposition in soil. Collected dead standing biomass was divided in two parts, the first one (initial litter) was stored in a dark, dry place. The other part was placed in litterbags in the field. The litterbags were located in soil, on the soil surface, or hanging in the air without contact with soil but exposed to the sun and rain. After 1 year of field exposure, litter mass loss and C and N content were measured, and changes in litter chemistry were explored using NMR and thermochemolysis-GC–MS. The potential decomposability of the litter was quantified by burying the litter from the litterbags and the initial litter in soil microcosms and measuring soil respiration. Soil respiration was greater with litter that had been hanging in air than with all other kinds of litter. These finding could not be explained by changes in litter mass or C:N ratio. NMR indicated a decrease in polysaccharides relative to lignin in litter that was buried in soil but not in litter that was placed on soil surface or that was hanging in the air. Thermochemolysis indicated that the syringyl units of the litter lignin were decomposed when the litter was exposed to light. We postulate that photochemical decay of lignin increase decomposability of dead standing biomass.     

Cell plate restricted association of DRP1A and PIN proteins is required for cell polarity establishment in Arabidopsis

The polarized transport of the phytohormone auxin [1], which is crucial for the regulation of different stages of plant development [2, 3], depends on the asymmetric plasma membrane distribution of the PIN-FORMED (PIN) auxin efflux carriers [4,?5]. The PIN polar localization results from clathrin-mediated endocytosis (CME) from the plasma membrane and subsequent polar recycling [6]. The Arabidopsis genome encodes two groups of dynamin-related proteins (DRPs) that show homology to mammalian dynamin-a protein required for fission of endocytic vesicles during CME [7, 8]. Here we show by coimmunoprecipitation (coIP), bimolecular fluorescence complementation (BiFC), and F?rster resonance energy transfer (FRET) that members of the DRP1 group closely associate with PIN proteins at the cell plate. Localization and phenotypic analysis of novel drp1 mutants revealed a requirement for DRP1 function in correct PIN distribution and in auxin-mediated development. We propose that rapid and specific internalization of PIN proteins mediated by the DRP1 proteins and the associated CME machinery from the cell plate membranes during cytokinesis is an important mechanism for proper polar PIN positioning in interphase cells.     

PIN polarity maintenance by the cell wall in Arabidopsis

A central question in developmental biology concerns the mechanism of generation and maintenance of cell polarity, because these processes are essential for many cellular functions and multicellular development. In plants, cell polarity has an additional role in mediating directional transport of the plant hormone auxin that is crucial for multiple developmental processes. In addition, plant cells have a complex extracellular matrix, the cell wall, whose role in regulating cellular processes, including cell polarity, is unexplored. We have found that polar distribution of PIN auxin transporters in plant cells is maintained by connections between polar domains at the plasma membrane and the cell wall. Genetic and pharmacological interference with cellulose, the major component of the cell wall, or mechanical interference with the cell wall disrupts these connections and leads to increased lateral diffusion and loss of polar distribution of PIN transporters for the phytohormone auxin. Our results reveal a plant-specific mechanism for cell polarity maintenance and provide a conceptual framework for modulating cell polarity and plant development via endogenous and environmental manipulations of the cellulose-based extracellular matrix.     

Non-photochemical fluorescence quenching in Chromera velia is enabled by fast violaxanthin de-epoxidation

Non-photochemical quenching (NPQ) is a mechanism protecting photosynthetic organisms against excessive irradiation. Here, we analyze a unique NPQ mechanism in the alga Chromera velia, a recently discovered close relative of apicomplexan parasites. NPQ in C. velia is enabled by an operative and fast violaxanthin de-epoxidation to zeaxanthin without accumulation of antheraxanthin. In C. velia violaxanthin also serves as a main light-harvesting pigment. Therefore, in C. velia violaxanthin acts as a key factor in both light harvesting and photoprotection. This is in contrast to a similar alga, Nannochloropsis limnetica, where violaxanthin has only light-harvesting function.