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191.
192.
Traditionally the intensity discontinuities in an image are detected as zero-crossings of the second derivative with the help
of a Laplacian of Gaussian (LOG) operator that models the receptive field of retinal Ganglion cells. Such zero-crossings supposedly
form a raw primal sketch edge map of the external world in the primary visual cortex of the brain. Based on a new operator
which is a linear combination of the LOG and a Dirac-delta function that models the extra-classical receptive field of the
ganglion cells, we find that zero-crossing points thus generated, store in presence of noise, apart from the edge information,
the shading information of the image in the form of density variation of these points. We have also shown that an optimal
image contrast produces best mapping of the shading information to such zero-crossing density variation for a given amount
of noise contamination. Furthermore, we have observed that an optimal amount of noise contamination reproduces the minimum
optimal contrast and hence gives rise to the best representation of the original image. We show that this phenomenon is similar
in nature to that of stochastic resonance phenomenon observed in psychophysical experiments. 相似文献
193.
Vega-Sánchez ME Verhertbruggen Y Christensen U Chen X Sharma V Varanasi P Jobling SA Talbot M White RG Joo M Singh S Auer M Scheller HV Ronald PC 《Plant physiology》2012,159(1):56-69
Mixed-linkage glucan (MLG) is a cell wall polysaccharide containing a backbone of unbranched (1,3)- and (1,4)-linked β-glucosyl residues. Based on its occurrence in plants and chemical characteristics, MLG has primarily been associated with the regulation of cell wall expansion due to its high and transient accumulation in young, expanding tissues. The Cellulose synthase-like F (CslF) subfamily of glycosyltransferases has previously been implicated in mediating the biosynthesis of this polymer. We confirmed that the rice (Oryza sativa) CslF6 gene mediates the biosynthesis of MLG by overexpressing it in Nicotiana benthamiana. Rice cslf6 knockout mutants show a slight decrease in height and stem diameter but otherwise grew normally during vegetative development. However, cslf6 mutants display a drastic decrease in MLG content (97% reduction in coleoptiles and virtually undetectable in other tissues). Immunodetection with an anti-MLG monoclonal antibody revealed that the coleoptiles and leaves retain trace amounts of MLG only in specific cell types such as sclerenchyma fibers. These results correlate with the absence of endogenous MLG synthase activity in mutant seedlings and 4-week-old sheaths. Mutant cell walls are weaker in mature stems but not seedlings, and more brittle in both stems and seedlings, compared to wild type. Mutants also display lesion mimic phenotypes in leaves, which correlates with enhanced defense-related gene expression and enhanced disease resistance. Taken together, our results underline a weaker role of MLG in cell expansion than previously thought, and highlight a structural role for MLG in nonexpanding, mature stem tissues in rice. 相似文献
194.
Polyamines are nitrogenous compounds found in all eukaryotic and prokaryotic cells and absolutely essential for cell viability.
In plants, they regulate several growth and developmental processes and the levels of polyamines are also correlated with
the plant responses to various biotic and abiotic stresses. In plant cells, polyamines are synthesized in plastids and cytosol.
This biosynthetic compartmentation indicates that the specific transporters are essential to transport polyamines between
the cellular compartments. In the present study, a phylogenetic analysis was used to identify candidate polyamine transporters
in rice. A full-length cDNA rice clone AK068055 was heterologously expressed in the Saccharomyces cerevisiae spermidine uptake mutant, agp2∆. Radiological uptake and competitive inhibition studies with putrescine indicated that rice gene encodes a protein that
functioned as a spermidine-preferential transporter. In competition experiments with several amino acids at 25-fold higher
levels than spermidine, only methionine, asparagine, and glutamine were effective in reducing uptake of spermidine to 60%
of control rates. Based on those observations, this rice gene was named polyamine uptake transporter 1 (OsPUT1). Tissue-specific expression of OsPUT1 by semiquantitative RT-PCR showed that the gene was expressed in all tissues except seeds and roots. Transient expression
assays in onion epidermal cells and rice protoplasts failed to localize to a cellular compartment. The characterization of
the first plant polyamine transporter sets the stage for a systems approach that can be used to build a model to fully define
how the biosynthesis, degradation, and transport of polyamines in plants mediate developmental and biotic responses. 相似文献
195.
196.
We have recently demonstrated the formation of an atypical histone H2A-H2B dimer-enriched chromatin at the coding sequence of the active gene in the absence of Rad26p in vivo. However, the mechanisms for such a surprising observation remain unknown. Here, using a ChIP assay, we demonstrate that Rad26p promotes the eviction of histone H2A-H2B dimer and prevents the reassociation of the dimer with naked DNA in the wake of elongating RNA polymerase II at the coding sequence of the active GAL1 gene. Thus, the absence of Rad26p leads to the generation of an atypical histone H2A-H2B dimer-enriched chromatin at the active coding sequence in vivo. 相似文献
197.
198.
Chad A. Van Huis Agustin Casimiro-Garcia Christopher F. Bigge Wayne L. Cody Danette A. Dudley Kevin J. Filipski Ronald J. Heemstra Jeffrey T. Kohrt Robert J. Leadley Lakshmi S. Narasimhan Thomas McClanahan Igor Mochalkin Michael Pamment J. Thomas Peterson Vaishali Sahasrabudhe Robert P. Schaum Jeremy J. Edmunds 《Bioorganic & medicinal chemistry》2009,17(6):2501-2511
Aiming to improve upon previously disclosed Factor Xa inhibitors, a series of 4,4-disubstituted pyrrolidine-1,2-dicarboxamides were explored with the intent of increasing the projected human half-life versus 5 (projected human t1/2 = 6 h). A stereospecific route to compounds containing a 4-aryl-4-hydroxypyrrolidine scaffold was developed, resulting in several compounds that demonstrated an increase in the half-life as well as an increase in the in vitro potency compared to 5. Reported herein is the discovery of 26, containing a (2R,4S)-4-hydroxy-4-(2,4-difluorophenyl)-pyrrolidine scaffold, which is a selective, orally bioavailable, efficacious Factor Xa inhibitor that appears suitable for a once-daily dosing (projected human t1/2 = 23 h). 相似文献
199.
Vimlesh Yadav Satya Prakash Shipra Srivastava Praveen Chandra Verma Vijayta Gupta Vaishali Basu Anil Kumar Rawat 《Bioinformation》2009,3(9):381-383
A bacterial strain Bz02 was isolated from a water sample collected from river Gomti at the Indian city of Lucknow. We
characterized the strain using 16S rRNA sequence. Phylogenetic analysis showed that the strain formed a monophyletic
clade with members of the genus Comamonas. The closest phylogenetic relative was Comamonas testosteroni with 95% 16S
rRNA gene sequence similarity. It is proposed that the identified strain Bz02 be assigned as the type strain of a species of the
genus Comamonas (Comamonas sp Bz02) based on 16S rRNA gene sequence search in Ribosomal Database Project, small
subunit rRNA and large subunit rRNA databases together with the phylogenetic tree analysis. The sequence is deposted in
GenBank with the accession number . FJ211417相似文献
200.