bluuebunny/crossref_metadata_2025_split huggingface dataset:
Primary Cell Wall Structure in the Evolution of Land Plants
Authors: Nothnagel Alex L. , Nothnagel Eugene A. 
Published: August 2007

Abstract Investigation of the primary cell walls of lower plants improves our understanding of the cell biology of these organisms but also has the potential to improve our understanding of cell wall structure and function in angiosperms that evolved from lower plants. Cell walls were prepared from eight species, ranging from a moss to advanced gymnosperms, and subjected to sequential chemical extraction to separate the main polysaccharide fractions. The glycosyl compositions of these fractions were then determined by gas chromatography. The results were compared among the eight plants and among data from related studies reported in the existing published reports to identify structural features that have been either highly conserved or clearly modified during evolution. Among the highly conserved features are the presence of a cellulose framework, the presence of certain hemicelluloses such as xyloglucan, and the presence of rhamnogalacturonan II, a domain in pectic polysaccharides. Among the modified features are the abundance of mannosyl‐containing hemicelluloses and the presence of methylated sugars.
Genetic Analyses of Meiotic Recombination in Arabidopsis
Authors: Wijeratne Asela J. , Ma Hong 
Published: August 2007

Abstract Meiosis is essential for sexual reproduction and recombination is a critical step required for normal meiosis. Understanding the underlying molecular mechanisms that regulate recombination is important for medical, agricultural and ecological reasons. Readily available molecular and cytological tools make Arabidopsis an excellent system to study meiosis. Here we review recent developments in molecular genetic analyses on meiotic recombination. These include studies on plant homologs of yeast and animal genes, as well as novel genes that were first identified in plants. The characterizations of these genes have demonstrated essential functions from the initiation of recombination by double‐strand breaks to repair of such breaks, from the formation of double‐Holliday junctions to possible resolution of these junctions, both of which are critical for crossover formation. The recent advances have ushered a new era in plant meiosis, in which the combination of genetics, genomics, and molecular cytology can uncover important gene functions.
Mechanisms of Organelle Inheritance in Dividing Plant Cells
Authors: Sheahan Michael B , Rose Ray J , McCurdy David W 
Published: August 2007

Abstract Organelles form essential compartments of all eukaryotic cells. Mechanisms that ensure the unbiased inheritance of organelles during cell division are therefore necessary to maintain the viability of future cell generations. Although inheritance of organelles represents a fundamental component of the cell cycle, surprisingly little is known about the underlying mechanisms that facilitate unbiased organelle inheritance. Evidence from a select number of studies, however, indicates that ordered organelle inheritance strategies exist in dividing cells of higher plants. The basic requirement for unbiased organelle inheritance is the duplication of organelle volume and distribution of the resulting organelle populations in a manner that facilitates unbiased partitioning of the organelle population to each daughter cell. Often, partitioning strategies are specific to the organelle, being influenced by the functional requirements of the organelle and whether the cells are mitotically active or re‐entering into the cell cycle. Organelle partitioning mechanisms frequently depend on interactions with either the actin or microtubule cytoskeleton. In this focused review, we attempt to summarize key findings regarding organelle partitioning strategies in dividing cells of higher plants. We particularly concentrate on the role of the cytoskeleton in mediating unbiased organelle partitioning.
A Putative Calcium‐Permeable Cyclic Nucleotide‐Gated Channel, CNGC18, Regulates Polarized Pollen Tube Growth
Authors: Chang Fang , Yan An , Zhao Li‐Na , Wu Wei‐Hua , Yang Zhenbiao 
Published: August 2007

Abstract A tip‐focused Ca2+ gradient is tightly coupled to polarized pollen tube growth, and tip‐localized influxes of extracellular Ca2+ are required for this process. However the molecular identity and regulation of the potential Ca2+ channels remains elusive. The present study has implicated CNGC18 (cyclic nucleotide‐gated channel 18) in polarized pollen tube growth, because its overexpression induced wider and shorter pollen tubes. Moreover, CNGC18 overexpression induced depolarization of pollen tube growth was suppressed by lower extracellular calcium ([Ca2+]ex). CNGC18‐yellow fluorescence protein (YFP) was preferentially localized to the apparent post‐Golgi vesicles and the plasma membrane (PM) in the apex of pollen tubes. The PM localization was affected by tip‐localized ROP1 signaling. Expression of wild type
ROP1 or an active form of ROP1 enhanced CNGC18‐YFP localization to the apical region of the PM, whereas expression of RopGAP1 (a ROP1 deactivator) blocked the PM localization. These results support a role for PM‐localized CNGC18 in the regulation of polarized pollen tube growth through its potential function in the modulation of calcium influxes.
The Pleiomorphic Plant MTOC: An Evolutionary Perspective
Authors: Brown Roy C. , Lemmon Betty E. 
Published: August 2007

Abstractγ‐Tubulin is an essential component of the microtubule organizing center (MTOC) responsible for nucleating microtubules in both plants and animals. Whereas γ‐tubulin is tightly associated with centrosomes that are inheritable organelles in cells of animals and most algae, it appears at different times and places to organize the myriad specialized microtubule systems that characterize plant cells. We have traced the distribution of γ‐tubulin through the cell cycle in representative land plants (embryophytes) and herein present data that have led to a concept of the pleiomorphic and migratory MTOC. The many forms of the plant MTOC at spindle organization constitute pleiomorphism, and stage‐specific “migration” is suggested by the consistent pattern of redistribution of γ‐tubulin during mitosis. Mitotic spindles may be organized at centriolar centrosomes (only in final divisions of spermatogenesis), polar organizers (POs), plastid MTOCs, or nuclear envelope MTOCs (NE‐MTOCs). In all cases, with the possible exception of centrosomes in spermatogenesis, the γ‐tubulin migrates to broad polar regions and along the spindle fibers, even when it is initially a discrete polar entity. At anaphase it moves poleward, and subsequently migrates from polar regions (distal nuclear surfaces) into the interzone (proximal nuclear surfaces) where interzonal microtubule arrays and phragmoplasts are organized. Following cytokinesis, γ‐tubulin becomes associated with nuclear envelopes and organizes radial microtubule systems (RMSs). These may exist only briefly, before establishment of hoop‐like cortical arrays in vegetative tissues, or they may be characteristic of interphase in syncytial systems where they serve to organize the common cytoplasm into nuclear cytoplasmic domains (NCDs).
Transformations of the Pleiomorphic Plant MTOC during Sporogenesis in the Hepatic Marchantia polymorpha
Authors: Brown Roy C. , Lemmon Betty E. , Shimamura Masaki 
Published: August 2007

Abstract Sporogenesis in the hepatic Marchantia polymorpha L. provides an outstanding example of the pleiomorphic nature of the plant microtubule organizing center (MTOC). Microtubules are nucleated from γ‐tubulin in MTOCs that change form during mitosis and meiosis. Following entry of cells into the reproductive pathway of sporogenesis, successive rounds of mitosis give rise to packets of 4–16 sporocytes. Mitotic spindles are organized at discrete polar organizers (POs), a type of MTOC that is unique to this group of early divergent land plants. An abrupt and radical transformation in microtubule organization occurs when sporocytes enter meiosis: POs are lost and γ‐tubulin is closely associated with surfaces of two large elongated plastids that subsequently divide into four. Migration of the four plastid MTOCs into a tetrahedral arrangement establishes the future spore domains and the division polarity of meiosis. As is typical of many bryophytes, cones of microtubules from the four plastid MTOCs initiate a quadripolar microtubule system (QMS) in meiotic prophase. At this point a transformation in the organization of the MTOCs occurs. The γ‐tubulin detaches from plastids and forms a diffuse spheroidal pole in each of the spore domains. The plastids, which are no longer MTOCs, continue to divide. The diffuse MTOCs continue to nucleate cones of microtubules during transformation of the QMS to a bipolar spindle. Following meiosis I, γ‐tubulin is associated with nuclear envelopes, and the spindles of meiosis II are organized from diffuse MTOCs at the tetrad poles. At simultaneous cytokinesis, radial microtubule systems are organized at nuclear envelope MTOCs in each of the tetrad members.
Control of Directional Macromolecular Trafficking Across Specific Cellular Boundaries: A Key to Integrative Plant Biology
Authors: Ding Biao , Itaya Asuka 
Published: August 2007

Abstract There is now solid evidence that cell‐to‐cell trafficking of certain proteins and RNAs plays a critical role in trans‐cellular regulation of gene expression to coordinate cellular differentiation and development. Such trafficking also is critical for viral infection and plant defense. The mechanisms of trafficking remain poorly understood. Although some proteins may move between cells by diffusion, many proteins and RNAs move in a highly regulated fashion. Regulation is likely achieved through interactions between distinct protein or RNA motifs and cellular factors. Some motifs and factors have been identified. One of the major focuses for future studies is to identify all motifs and their cognate factors and further elucidate their roles in trafficking between specific cells. With increasing information from such studies, we should be able to develop an understanding of the mechanisms that regulate trafficking of various proteins and RNAs across all and specific cellular boundaries. On the basis of such mechanistic knowledge, we can further investigate how the trafficking machinery has evolved to regulate developmental and physiological processes in a plant, how pathogens have co‐evolved to use this machinery for systemic spread in a plant, and how plants use this machinery for counter‐ defense.
The Katanin Microtubule Severing Protein in Plants
Authors: Burk David H. , Zhong Ruiqin , Ye Zheng‐Hua 
Published: August 2007

Abstract Katanin is a heterodimeric microtubule (MT) severing protein that uses energy from ATP hydrolysis to generate internal breaks along MTs. Katanin p60, one of the two subunits, possesses ATPase and MT‐binding/severing activities, and the p 80 subunit is responsible for targeting of katanin to certain subcellular locations. In animals, katanin plays an important role in the release of MTs from their nucleation sites in the centrosome. It is also involved in severing MTs into smaller fragments which can serve as templates for further polymerization to increase MT number during meiotic and mitotic spindle assembly. Katanin homologs are present in a wide variety of plant species. The Arabidopsis katanin homolog has been shown to possess ATP‐dependent MT severing activity in vitro and exhibit a punctate localization pattern at the cell cortex and the perinuclear region. Disruption of katanin functions by genetic mutations causes a delay in the disappearance of the perinuclear MT array and results in an aberrant organization of cortical MTs in elongating cells. Consequently, katanin mutations lead to defects in cell elongation, cellulose microfibril deposition, and hormonal responses. Studies of katanin in plants provide new insights into our understanding of its roles in cellular functions.
How do Plants Organize Microtubules Without a Centrosome?
Authors: Murata Takashi , Tanahashi Takako , Nishiyama Tomoaki , Yamaguchi Kazuo , Hasebe Mitsuyasu 
Published: August 2007

AbstractA microtubule nucleates from a γ‐tubulin complex, which consists of γ‐tubulin, proteins from the SPC97/SPC98 family, and the WD40 motif protein GCP‐WD. We analyzed the phylogenetic relationships of the genes encoding these proteins and found that the components of this complex are widely conserved among land plants and other eukaryotes. By contrast, the interphase and mitotic arrays of microtubules in land plants differ from those in other eukaryotes. In the interphase cortical array, the majority of microtubules nucleate on existing microtubules in the absence of conspicuous microtubule organizing centers (MTOCs), such as a centrosome. During mitosis, the spindle also forms in the absence of conspicuous MTOCs. Both poles of the spindle are broad, and branched structures of microtubules called microtubule converging centers form at the poles. In this review, we hypothesize that the microtubule converging centers form via microtubule‐dependent microtubule nucleation, as in the case of the interphase arrays. The evolutionary insights arising from the molecular basis of the diversity in microtubule organization are discussed.
The Villin/Gelsolin/Fragmin Superfamily Proteins in Plants
Authors: Su Hui , Wang Ting , Dong Huaijian , Ren Haiyun 
Published: August 2007

Abstract The villin/gelsolin/fragmin superfamily is a conserved Ca2+‐dependent family of actin‐regulating proteins that is widely present both in mammalian and non‐mammalian organisms. They have traditionally been characterized by the same core of three or six tandem gelsolin subdomains. The study in vertebrates and lower eukaryotic cells has revealed that the villin/gelsolin/fragmin superfamily of proteins has versatile functions including severing, capping, nucleating or bundling actin filaments. In plants, encouraging progress has been made in this field of research in recent years. This review will summarize the identified plant homologs of villin/gelsolin/fragmin superfamily, thus providing a basis for reflection on their biochemical activities and functions in plants.
In Silico Identification of Co‐transcribed Core Cell Cycle Regulators and Transcription Factors in Arabidopsis
Authors: Wang Yixing , Yang Ming 
Published: August 2007

Abstract Regulatory networks involving transcription factors and core cell cycle regulators are expected to play crucial roles in plant growth and development. In this report, we describe the identification of two groups of co‐transcribed core cell cycle regulators and transcription factors via a two‐step in silico screening. The core cell cycle regulators include TARDY ASYNCHRONOUS MEIOSIS (CYCA1;2), CYCB1;1, CYCB2;1, CDKB1;2, and CDKB2;2 while the transcription factors include CURLY LEAF, AINTEGUMENTA, a MYB protein, two Forkhead‐associated domain proteins, and a SCARECROW family protein. Promoter analysis revealed a potential web of cross‐ and self‐regulations among the identified proteins. Because one criterion for screening for these genes is that they are predominantly transcribed in young organs but not in mature organs, these genes are likely to be particularly involved in Arabidopsis organ growth.
Toxicity Profile of Lisdexamfetamine Dimesylate in Three Independent Rat Toxicology Studies
Authors: Krishnan Suma , Montcrief Scott 
Published: August 2007

Abstract:  Lisdexamfetamine dimesylate (LDX) is a d‐amphetamine prodrug developed for the treatment of attention‐deficit/hyperactivity disorder. The toxicity profile of orally administered LDX has been evaluated in rats. In an acute study, LDX doses of 60 mg/kg and higher caused increased motor activity. At 1000 mg/kg, one rat died and another was euthanized. In a 7‐day repeat‐dose study, all rats dosed with LDX (14 per dose group for each sex) showed increased activity; 10 male rats and 11 female rats at 300 mg/kg/day and 3 female rats at 100 mg/kg/day were euthanized because of self‐mutilation and 1 male rat at 300 mg/kg/day was found dead. In a 28‐day study, only rats at 80 mg/kg showed signs of self‐mutilation and thin body condition. In both the 7‐ and 28‐day studies, LDX caused significant changes in some blood chemistry parameters (e.g. blood urea nitrogen, alanine aminotransferase, aspartate aminotransferase) and organ weights (e.g. particularly heart, liver, brain, and spleen). Overall, no apparent treatment‐related histopathologic changes were observed. Toxicokinetic assessments indicated that as the dose of LDX was increased, rats were exposed to increasing levels of LDX and d‐amphetamine. The extent of exposure to LDX and d‐amphetamine increased after repeated‐dose in the 28‐day study. The findings of the repeat‐dose studies indicate that the toxicity profile in rats administered LDX orally is comparable to that for d‐amphetamine; however, the apparent lethal dose of LDX in rats is more than five times higher than the LD50 of orally administered d‐amphetamine, supporting a putative protective effect of conjugating amphetamine with lysine.
Oral Supplementation of Majun Baladar Ameliorates Antioxidant Enzyme Activities in Cerebral Ischaemic Damage
Authors: Yousuf Seema , Atif Fahim , Hoda Nasrul , Ahmad Muzamil , Saleem Sofiyan , Ishrat Tauheed , Khan M. Badruzzaman , Ahmad Abdullah Shafique , Islam Fakhrul 
Published: August 2007

Abstract:   Majun Baladar (MB), a traditional herbal formulation of the Unani system of medicine, was studied for its efficacy against cerebral ischaemia‐induced oxidative damage in hippocampus and associated neurobehavioural deficits. Adult male Wistar rats were divided into four groups. The first group was sham, the second group was ischaemic (MCAO: middle cerebral artery occluded) and the third group was a MB pre‐treated ischaemic group (MCAO + MB). The fourth group was given MB (1.05 g/kg) orally for 15 days as a drug control. The middle cerebral artery was occluded for 2 hr and reperfused for 22 hr in the ischaemic as well as the drug pre‐treated group. The activity of the various enzymatic antioxidants like glutathione peroxidase, glutathione reductase, glutathione S‐transferase and non‐enzymatic antioxidants, glutathione along with levels of lipid peroxidation were evaluated. Cerebral ischaemic rats showed elevated level of lipid peroxidation and decreased levels of various antioxidants significantly over sham values. As a result of MB pre‐treatment, the level of lipid peroxidation was found to be significantly depleted as compared to the ischaemic group. Furthermore, depleted levels of glutathione and the activity of glutathione peroxidase, glutathione S‐transferase and glutathione reductase were restored significantly in MB treated group. Majun Baladar exhibited a significant improvement in neurobehavioural activities in the drug pre‐treated animals as compared to the ischaemic group as evidenced by the grip strength test, Rota‐Rod and video path analysis. The results of the present study provide baseline information regarding the neuroprotective efficacy of MB and also open a window for a potent therapeutic use of this traditional herbal Unani medicine.
Pharmacokinetics of Two Randomized Trials Evaluating the Safety and Efficacy of Indinavir, Saquinavir and Lopinavir in Combination with Low‐Dose Ritonavir: The MaxCmin1 and 2 Trials*
Authors: Justesen Ulrik S. , Fox Zoe , Pedersen Court , Cahn Pedro , Gerstoft Jan , Clumeck Nathan , Losso Marcello , Peters Barry , Obel Niels , Castagna Antonella , Dragsted Ulrik B. , Lundgren Jens D. ,   on behalf of the MaxCmin1 and 2 trial groups
Published: August 2007

Abstract:   Our objective was to identify possible differences in protease inhibitor plasma concentrations between and within three protease inhibitor regimens (indinavir, saquinavir and lopinavir all in combination with low‐dose ritonavir) and to relate these differences to safety and efficacy. Data originated from pre‐defined pharmacokinetic substudies within two randomized 48‐week trials evaluating the safety and efficacy of three protease inhibitor regimens. At weeks 4 and 48, plasma was collected and minimum drug plasma concentrations, Cmin, were obtained. Out of 656 randomized patients, 283 patients had available Cmin at week 4. Indinavir, saquinavir and lopinavir Cmin were high when combined with low‐dose ritonavir. No significant difference in the proportion of patients experiencing treatment failure could be found according to the Cmin within any treatment arm. A saquinavir Cmin > 2000 ng/ml was associated with an increased risk of gastrointestinal grade 3 or 4 adverse events and higher total cholesterol. Overall, there were no changes in Cmin from week 4 to week 48 in patients who remained on therapy. No association between treatment failure and the Cmin could be demonstrated. Associations between high Cmin and toxicity were identified in the saquinavir arm; therefore, dose reductions may be appropriate in certain patients with Cmin several times above the minimum effective concentration.
Bursts of Potential Elicited by d‐Amphetamine in Central Snail Neuron: Effect of Sodium Azide
Authors: Lin Pei‐Lin , Lu Kuan‐Ling , Lee Ya‐Ling , Chen Yi‐Hung , Chang Yu‐Chi , Chou Hong‐Nong , Tsai Ming‐Cheng 
Published: August 2007

Abstract:   Effects of sodium azide (NaN3) on spontaneously generated action potential and bursts of potential elicited by d‐amphetamine (d‐amphetamine‐elicited BoP) were studied on the right parietal 4 (RP4) neuron of the snail Achatina fulica Ferussac in vitro. Sodium azide altered the spontaneous action potential of RP4 neuron in a concentration‐dependent manner. In lower concentrations, neither NaN3 (30, 100, 300 µM; 1 and 3 mM) nor d‐amphetamine (135 µM) affect the resting membrane potential, amplitude and frequency of RP4 neurons, while in the higher concentrations NaN3 (30 mM) did abolish the spontaneous action potential on RP4 neurons and depolarized the RP4 neurons reversibly. At lower concentration, NaN3 (30 µM) facilitated the d‐amphetamine‐elicited BoP. The BoP elicited by NaN3 (30 µM) and d‐amphetamine (135 µM) were decreased following treatment with KT5720 (protein kinase A inhibitor), or intracellular injection of EGTA [ethylene glycol‐bis(2‐aminoethyl ether)‐N,N,N′,N′‐tetraacetic acid]. However, the BoP was not affected by applying U73122 (1‐[6‐[((17β)‐3‐methoxyestra‐1,3,5[10]‐trien‐17‐yl)amino]hexyl]‐1H‐pyrrole‐2,5‐dione) or neomycin (phospholipase inhibitors). Voltage clamp studies revealed that NaN3 (30 µM) did not alter the total fast inwards currents (70 msec.) and the steady‐state outwards currents (5 sec.). It appeared that the BoP elicited by NaN3 (30 µM) and d‐amphetamine (135 µM) was mainly due to protein kinase A‐related messenger system and intracellular calcium. It is concluded that d‐amphetamine‐elicited BoP was not mainly due to inhibition of the function of mitochondria in the neuron while the function of mitochondria did alter the BoP elicited by amphetamine.
Four canals in the mesial root of a mandibular first molar. A case report under the operating microscope
Authors: Kontakiotis Evangelos G. , Tzanetakis Giorgos N. 
Published: August 2007

AbstractIn this era of microscope‐assisted endodontics, finding variations in root canal system anatomy is not uncommon. Operating microscopes combined with careful clinical examination and radiographic interpretation can aid the clinician to successfully treat cases with such internal anatomy. The understanding of this view enables the possible location of additional canals in any tooth requiring endodontic treatment. The present clinical article demonstrates a rare anatomical complexity in the mesial root of a mandibular first molar. Four independent root canal orifices were found in this root by clinical detection with the aid of a dental operating microscope. This case shows that additional canals can be located in any root undergoing endodontic treatment and clinicians should always be aware of aberrant internal anatomy.