171,419 research outputs found
Regulation of fructan metabolism in barley leaves
No full textFructans, the polymers of fructose (Fru), are major non-structural storage carbohydrates in the vegetative tissues of many higher plants including temperate forage grasses and cereals, as well as major crop plants such as wheat and barley. Fructans play an important role in assimilate partitioning, plant development, environmental stress tolerance etc. Fructans also have a vast application potential in nutrition and medicine. The main focus of this dissertation is the fructan biosynthetic pathway in barley leaves. Its major aspects are the identification of sucrose:sucrose 1-fructosyltransferase (1-SST) as a pacemaker enzyme, regulation of the promoter of sucrose:fructan 6-fructosyltransferase (6-SFT) - one of the main fructosyltransferases (FTs) and the role of vacuolar invertases during fructan metabolism.
Excised barley leaves exposed to continuous light accumulate large amounts of fructans containing β(2-6) linkages with β(2-1) branches, the so-called graminans. The pathway for graminan biosynthesis has not been well characterised, but it has been proposed that the successive action of two main enzymes, 1-SST and 6-SFT is involved (1-SST/6-SFT model). To demonstrate the validity of this model, excised leaves were subjected to a light-dark regime known to sequentially induce fructan accumulation and mobilization. The pattern of accumulation of soluble carbohydrates, the level of 1-SST and 6-SFT activities, and the expression of the corresponding genes, all indicate that the diversion of sucrose (Suc) into the pathway fructan synthesis is initiated by 1-SST induction. The stability of transcripts and enzyme activities of 1-SST and 6-SFT were compared, using appropriate inhibitors. The transcripts of 1-SST and enzymatic activity are subject to a rapid turnover and respond more quickly than 6-SFT. The much higher responsiveness of 1-SST to regulatory processes clearly indicates that it plays the role of the pacemaker enzyme of fructan synthesis in barley leaves.
Plants regulate fructan synthesis in response to several internal and external stimuli primarily through the modulation of gene expression of FTs. Little is known about signal perception and transduction events that control the expression of FT genes. The regulatory sequences of FT genes are valuable tools to decipher the underlying signaling events. Using PCR-based genome walking procedures, the promoter of 6-SFT gene corresponding to 1.6 kb of the upstream region of the coding sequence, was cloned. The promoter activity of the cloned sequence was investigated in transient assays by fusing it to a reporter gene [uidA encoding β-glucuronidase, (GUS)] and by microprojectile bombardment of excised barley leaves. Strong expression of the GUS gene was observed in leaves induced for fructan biosynthesis by Suc and light, indicating that the cloned sequence contains the necessary cis acting elements conferring Suc and light induction of 6-SFT transcription.
Arabidopsis thaliana has been extensively used to study the sugar induced signal transduction pathways in plants. In order to investigate the signaling events involved in the activation of the 6-SFT promoter, stably transformed Arabidopsis plants harboring the 6-SFT promoter driving the expression of the GUS reporter gene, were obtained. Though Arabidopsis is a non-fructan producing plant, the sugar-regulated activation of the barley 6-SFT promoter is maintained in Arabidopsis. The inhibitors of protein phosphatases and protein kinases, and a chelator of calcium, known to block Suc induction of 6-SFT gene expression in wheat, were effective in Arabidopsis too, suggesting that this signal transmission process seems to be conserved between cereals and Arabidopsis. These transgenic plants are valuable to study the activity of the barley 6-SFT promoter further and identify the transcription factors that interact with the key promoter elements.
Invertases play a central role in the metabolism of Suc, the main product of photosynthesis and substrate for the synthesis of the fructans. Soluble acid invertase (SAI) isoforms are present in the vacuoles and are believed to be the ancestors of fructosyltransferases FTs. No SAI sequences are available from barley yet. In the present work, a soluble acid invertase cDNA was cloned from barley (HvSAI) and functionally characterized by heterologous expression in Pichia pastoris. Furthermore, the expression of HvSAI gene was studied in excised leaves and roots. The recombinant HvSAI cleaves Suc efficiently, but despite very high amino acid sequence similarity to FTs, is devoid of FT or fructan hydrolase like side activities. Compared to the FTs, the activity of the recombinant HvSAI is relatively easily saturable (Km of 13.5 mM for Suc) and possesses a higher temperature optimum (10°C more that 1-SST). The mRNA levels of HvSAI are constitutive and not affected much by enhanced sugar levels in excised leaves and roots, by Suc supply or continuous illumination of cut leaves. The cloning of SAIs will help to investigate their role in the regulation of fructan metabolism and decipher the structure-function relationship between SAI and FTs
Northwestern Mediterranean Pliocene Pollen Database (NWMPPD)
No full textSixty-two well-dated Pliocene pollen locations constitute this database covering six provinces (Catalonia, Roussillon, Languedoc, Provence, Southeastern Alps, and Liguria). They constitute the basis of a paper invited for a special issue of the journal Global and Planetary Change within the frame of the ‘PlioMIP3 Project’ (‘Advances in Paleoclimate Modeling of the Pliocene climate’, edited by Zhang Z., Li X., Chan W.-L. and Stepanek C.). The paper should be published by the end of 2025, coinciding with the date of free access to these pollen data.
Preliminary reference: Suc, J.-P., Fauquette, S., Cheddadi, R., Tan, N., Ramstein, G., Li, L., Jiménez-Moreno, G., Popescu, S.-M., Zheng, Z. Pliocene contrasted climatic conditions in space and along time: an unique pollen dataset from the NW Mediterranean Region comparable with model.
The peculiarity of these pollen data consists in the botanical identification of pollen grains and detailed pollen counts.
The data are distributed in three sheets of an excel file (NWMPPD) accompanied by this introductive text, a location map, a table of locations (numbers and names of locations, respective latitude and longitude, estimated age, basis of dating, author of pollen analysis, concerned references). The quoted papers can also be provided on request
Relative expression of Suc-inducible and Suc-starvation inducible genes.
No full text(A) Suc-inducible gene expression in flag leaves, (B) Suc starvation-inducible gene expression in flag leaves, (C) Suc-inducible gene expression in grains, (D) Suc starvation-inducible gene expression in grains. Error bars indicate mean ± SE of data from six replicates. *, P P < 0.01.</p
The overlay of elution profiles of T6-L-suc peptide at 0–80 min after incubation.
No full text<p>Column: Shiseido UG 80 3.0×250 mm. Gradient: 17–26.5% acetonitrile/0.1% TFA over 25 min. Flow rate: 0.5 mL/min. Detection: 215 nm. a: elution profile of T6-L-suc peptide at incubation time = 0 min. b: elution profile of T6-L-suc peptide which was incubated at 37°C for 20 min. c: elution profile of T6-L-suc peptide which was incubated at 37°C for 80 min.</p
Proboscis extension reflex (PER) responses to sucrose (SUC) of males pre-exposed to gustatory and olfactory stimuli.
No full text<p><b>A</b>) pre-exposure to SUC and QUI, test with 0.03 M SUC. <b>B</b>) pre-exposure to SUC ipsi- or contralateral antenna, test with 0.03 M SUC. <b>C</b>) pre-exposure to PHE, test with 0.03 M SUC. <b>D</b>) responses of males to SUC after a non-specific mechanical stimulus, test with 0.1 M SUC. Columns show the percentage of males extending the proboscis when one of their antennae was contacted with a toothpick soaked with a SUC solution. Within each frame (A, B, C, D), the percentage of PER responses were significantly different between columns with different letters (Chi-Square, p<0.05). Numbers at the bottom of bars indicate numbers of tested males. Sensitivity to SUC was intra-modally increased by pre-exposure to SUC and QUI, and cross-modally increased by pre-exposure to PHE.</p
The overlay of elution profiles of the purified T6-D-suc, T6-L-suc and the mixture of synthesized T6 Lα, T6 Lβ, T6 Dα, T6 Dβ peptides.
No full text<p>Column: Shiseido UG 80 3.0×250 mm. Gradient: 17–26.5% acetonitrile/0.1% TFA over 25 min. Flow rate: 0.5 mL/min. Detection: 215 nm. a: elution profile of mixture of synthesized T6 Lα, T6 Lβ, T6 Dα and T6 Dβ. b: elution profile of purified T6-L-suc. c: elution profile of purified T6-D-suc.</p
The overlay of elution profiles of incubated T6-D-suc peptide after incubation for 0–80 min.
No full text<p>Column: Shiseido UG 80 3.0×250 mm. Gradient: 17–26.5% acetonitrile/0.1% TFA over 25 min. Flow rate: 0.5 mL/min. Detection: 215 nm. a: elution profile of T6-D-suc peptide at incubation time = 0 min. b: elution profile of T6-D-suc peptide which was incubated at 37°C for 20 min. c: elution profile of T6-D-suc peptide which was incubated at 37°C for 80 min.</p
On the geometry of rank two vector bundles and two-theta divisors on a curve
No full textThis thesis aims at presenting results and remarks concerning the study of subvarieties of the projective space |2Ɵ| associated to a smooth projective curve C of genus at least 3 and its connections to the moduli space SU(_c)(2) of rank 2 semi-stable vector bundles with trivial determinant. In the first part of the thesis, I present a review of Narasimhan and Ramanan's embedding of SU(_C)(2) in |2Ɵ| for non-hyperelliptic curves of genus 3 ([N-R2]). In particular, I clarify some of the points of their construction (2.3.6) and give complete proofs of lemma 5.1 and lemma 5.2 (see 2.3.4 and 2.3.17). Moreover in section 2.3 I show that lemma 5.4 of [N-R2] is false, providing an extensive counterexample (2.4.3).In the second part, I discuss the Abel-Jacobi stratification of |2Ɵ| for non-hyperelliptic curves of genus at least 3 as introduced in [0-P], which generalises classical subvarieties of |2Ɵ| such as the Kummer variety. I show that the top element of these stratifications is always a hypersurface and compute its degree (3.2.5), then I provide insight into the characterisation of the general element of the stratification (§3.3)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
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