bluuebunny/crossref_metadata_2025 huggingface dataset:
Configural errors on WISC–III block design
Authors: KRAMER JOEL H. , KAPLAN EDITH , SHARE LISA , HUCKEBA WENDY
Published: July 2002

This study describes two experiments undertaken
to explore the clinical significance and cognitive substrates
of Block Design broken configurations in children. Broken
configurations were defined as instances in which the child
placed a block outside the 2 × 2 or 3 × 3 square
matrix. In Experiment 1, 336 normal children between the
ages of 6 and 14 were administered WISC–III Block
Design. Broken configurations were fairly common, but almost
always self-corrected. The tendency to break configurations
was inversely related to overall Block Design performance
and mother's level of education, and directly related
to the perceptual cohesiveness of the design. In Experiment
2, children were administered WISC–III Block Design
and a global–local similarity judgment task. The
frequency of broken configurations was inversely related
to global perceptual bias. Taken together, the results
of these experiments indicate that while broken configurations
are common, particularly on designs with high perceptual
cohesiveness, a high number of broken configurations or
final answers containing broken configuration are associated
with weaker visuospatial skills. Broken configurations
are also made more frequently by children whose perception
is less influenced by the global properties of spatial
stimuli. (JINS, 1999, 5, 518–524.)
Structural adjustment and market imperfections: a stylized village economy-wide model with non-separable farm households
Authors: HOLDEN STEIN T. , TAYLOR J. EDWARD , HAMPTON STEPHEN
Published: July 2002

Village economies and peasant households represent the main link between the economy and the environment in sub-Saharan Africa. The links from the macro level and down to the household level and further to the natural resource base are complex. It may therefore be difficult to predict the impact of macro policies and external shocks on the environment. This paper presents a typology of village economies and village economy-wide models. The framework is applied to a special case where a model is proposed and estimated to examine the impacts of external shocks, including structural adjustment policies, on cash-crop production and chitemene (shifting cultivation) in a remote Zambian village characterized by a missing (or negligible) labour market, input supply constraints, and credit rationing. Our findings indicate that structural adjustment policies, by decreasing the profitability of maize production, may encourage households to increase their chitemene production, resulting in more rapid deforestation.
Are the costs of pollution abatement lower in Central and Eastern Europe? Evidence from Lithuania
Authors: BLUFFSTONE RANDALL
Published: July 2002

It is often claimed that pollution reductions can be achieved at lower cost in Central and Eastern Europe and the former Soviet Union, because more possibilities exist to update production processes and reduce waste. To date, however, there has been little or no systematic evaluation of what the costs actually are in these countries. The main purpose of this paper is to partially fill this research gap using firm-level data from Lithuania. Abatement cost estimates for key air pollutants are presented based on investments made in Lithuania during 1993–4. The paper also attempts to estimate the demand for pollution directly using data on pollution charges from 1994. Using both methods, it is shown that for at least some key pollutants marginal and average abatement costs are probably substantially lower in Lithuania than in western countries.
Holzwege on Mount Fuji: a doctrine of no-aesthetics for computer and electroacoustic music
Authors: RICHARD DOMINIQUE M.
Published: July 2002

In German, the word Holzwege means ‘paths that lead nowhere but that are not inconsequential’. They are paths which, without a goal, facilitate the transforming experience of a journey that can gently, yet profoundly, touch our physical, emotional and intellectual self. In this paper, Holzwege is metaphor for a reflection on aesthetics and computer/electroacoustic music, a reflection that does not seek to demonstrate but to suggest. Thus, rather than considering and refining the abundance of concepts and definitions which seek to circumscribe the aesthetic characteristics of these musical idioms, this reflection goes beyond definitions to outline a path of no-aesthetics which highlights their creative potential.
Composing for an ensemble of atoms: the metamorphosis of scientific experiment into music
Authors: Sturm Bob L.
Published: July 2002

In quantum mechanics a particle can behave like a particle or a wave. Thus, systems of particles can be likened to a superposition of waves. Since sound can be described as a superposition of frequencies, it can also be described in terms of a system of particles manifest as waves. This metaphor between ‘particle physics’ and sound synthesis is quantitatively developed here, suggested initially from some similarities between the two domains. It is applied to a few fundamental physical principles to show how these can be sonified. The author discusses the process of using a simulated ‘atom trap’ to compose a piece that does not require a physicist to appreciate it. This metaphor blurs the distinctions between science and art, where scientific experiment becomes musical composition, and exploring a musical idea involves playing with particle system dynamics. In the future, methods like these could be used with a real system of particles – the particle accelerator will become an expressive musical instrument, and the particle physicist will become the composerscientist.
Lenition inhibition in Liverpool English
Authors: Honeybone Patrick
Published: July 2002

This article integrates aspects of synchronic and diachronic phonological theory with points relevant to the study of a nonreference accent in order to investigate the patterns of consonantal lenition found in the variety of English spoken in Liverpool, England. Points of contact with variationist approaches are addressed, partly because the lenitions are variable processes. An implicational understanding of lenition is developed, thanks to which it is possible to describe the prosodic and melodic environments which inhibit the lenitions. New data from a small corpus investigation into Liverpool English are presented and a theoretical and practical methodology is proposed, which enables the data to be investigated. The descriptive focus is on the segments /t/ and /k/, which are typically realized as affricates or fricatives unless the lenition is inhibited. A notion of ‘melodic lenition inhibition’ is developed to account for some of the inhibitory patterns, whereby the sharing of autosegmental phonological elements gives a segment ‘strength’ in certain environments.
Voter Reactions to ‘Strange Bedfellows’: The Japanese Voter Faces a Kaleidoscope of Changing Coalitions
Authors: Kabashima Ikuo , Reed Steven R.
Published: July 2002

On 30 June 1994 the Social Democratic Party of Japan (SDPJ, formerly the Japan Socialist Party) joined its historic enemy, the Liberal Democratic Party (LDP), to form a coalition government in a Japanese equivalent of Italy's ‘historic compromise’. Competition between the conservative LDP and the progressive socialists had defined the Japanese party system since 1955. In this paper we analyze voter reactions to this and other confusing events surrounding the end of the LDP's 38-year dominance. We find, first, that the Japanese electorate was able to make sense of these events. The political space reflected in public opinion mapped the political space reflected in the mass media remarkably well. Secondly, our findings support the idea that attitudes toward political parties are endogenous to the political process: strategic moves by political actors alter the political space within which they maneuver. Coalitions of strange bedfellows force voters to revise their perceptions of political space and reevaluate their attitudes toward the actors involved. Strange bedfellows seemed less strange, friendlier after they had been seen in bed together.
Order-consistent programs are cautiously monotonic
Authors: TURNER HUDSON
Published: July 2002

Some normal logic programs under the answer set (or stable model) semantics lack the
appealing property of ‘cautious monotonicity.’ That is, augmenting a program with one of
its consequences may cause it to lose another of its consequences. The syntactic condition of
‘order-consistency’ was shown by Fages to guarantee existence of an answer set. This note
establishes that order-consistent programs are not only consistent, but cautiously monotonic.
From this it follows that they are also ‘cumulative’. That is, augmenting an order-consistent
program with some of its consequences does not alter its consequences. In fact, as we show,
its answer sets remain unchanged.
Seed development in Camellia sinensis (L.) O. Kuntze
Authors: Bhattacharya Amita , Nagar P.K. , Ahuja P.S.
Published: July 2002

Seed development of tea was studied to identify the maturity index and the optimal time of seed collection. After harvest, the moisture content (28–30%fresh weight basis) of mature seeds, which germinated 100%, declined progressively (19% moisture content) after shedding, with a decrease in seed germination and viability. However, this viability loss could be prevented to some extent by storing seeds within intact fruits. The maximum rate of seed dry matter accumulation coincided with the accumulation of starch in the embryos and seeds at stage 8, the embryo maturation phase. Although the embryo abscisic acid (ABA) content was highest at stage 8, free ABA declined in the tea embryos throughout the remainder of the seed maturation cycle.
Raf induces TGFβ production while blocking its apoptotic but not invasive responses: a mechanism leading to increased malignancy in epithelial cells
Authors: Lehmann Kerstin , Janda Elzbieta , Pierreux Christophe E. , Rytömaa Marjatta , Schulze Almut , McMahon Martin , Hill Caroline S. , Beug Hartmut , Downward Julian
Published: July 2002

c-Raf-1 is a major effector of Ras proteins, responsible for activation of the ERK MAP kinase pathway and a critical regulator of both normal growth and oncogenic transformation. Using an inducible form of Raf in MDCK cells, we have shown that sustained activation of Raf alone is able to induce the transition from an epithelial to a mesenchymal phenotype. Raf promoted invasive growth in collagen gels, a characteristic of malignant cells; this was dependent on the operation of an autocrine loop involving TGFβ, whose secretion was induced by Raf. TGFβ induced growth inhibition and apoptosis in normal MDCK cells: Activation of Raf led to inhibition of the ability of TGFβ to induce apoptosis but not growth retardation. ERK has been reported previously to inhibit TGFβ signaling via phosphorylation of the linker region of Smads, which prevents their translocation to the nucleus. However, we found no evidence in this system that ERK can significantly influence the function of Smad2, Smad3, and Smad4 at the level of nuclear translocation, DNA binding, or transcriptional activation. Instead, strong activation of Raf caused a broad protection of these cells from various apoptotic stimuli, allowing them to respond to TGFβ with increased invasiveness while avoiding cell death. The Raf–MAP kinase pathway thus synergizes with TGFβ in promoting malignancy but does not directly impair TGFβ-induced Smad signaling.
High-resolution localization of Drosophila Spt5 and Spt6 at heat shock genes in vivo: roles in promoter proximal pausing and transcription elongation
Authors: Andrulis Erik D. , Guzmán Ernesto , Döring Pascal , Werner Janis , Lis John T.
Published: July 2002

Recent studies have demonstrated roles for Spt4, Spt5, and Spt6 in the regulation of transcriptional elongation in both yeast and humans. Here, we show that Drosophila Spt5 and Spt6 colocalize at a large number of transcriptionally active chromosomal sites on polytene chromosomes and are rapidly recruited to endogenous and transgenic heat shock loci upon heat shock. Costaining with antibodies to Spt6 and to either the largest subunit of RNA polymerase II or cyclin T, a subunit of the elongation factor P-TEFb, reveals that all three factors have a similar distribution at sites of active transcription. Crosslinking and immunoprecipitation experiments show that Spt5 is present at uninduced heat shock gene promoters, and that upon heat shock, Spt5 and Spt6 associate with the 5′ and 3′ ends of heat shock genes. Spt6 is recruited within 2 minutes of a heat shock, similar to heat shock factor (HSF); moreover, this recruitment is dependent on HSF. These findings provide support for the roles of Spt5 in promoter-associated pausing and of Spt5 and Spt6 in transcriptional elongation in vivo.
The Plexin-B1/Rac interaction inhibits PAK activation and enhances Sema4D ligand binding
Authors: Vikis Haris G. , Li Weiquan , Guan Kun-Liang
Published: July 2002

The small GTPase Rac has been implicated in growth cone guidance mediated by semaphorins and their receptors. Here we demonstrate that plexin-B1, a receptor for Semaphorin4D (Sema4D), and p21-activated kinase (PAK) can compete for the interaction with active Rac and plexin-B1 can inhibit Rac-induced PAK activation. We have also demonstrated that expression of active Rac enhances the ability of plexin-B1 to interact with Sema4D. Active Rac stimulates the localization of plexin-B1 to the cell surface. The enhancement in Sema4D binding depends on the ability of Rac to bind plexin-B1. These observations support a model where signaling between Rac and plexin-B1 is bidirectional; Rac modulates plexin-B1 activity and plexin-B1 modulates Rac function.
ASK1 is essential for endoplasmic reticulum stress-induced neuronal cell death triggered by expanded polyglutamine repeats
Authors: Nishitoh Hideki , Matsuzawa Atsushi , Tobiume Kei , Saegusa Kaoru , Takeda Kohsuke , Inoue Kiyoshi , Hori Seiji , Kakizuka Akira , Ichijo Hidenori
Published: July 2002

Expansion of CAG trinucleotide repeats that encode polyglutamine is the underlying cause of at least nine inherited human neurodegenerative disorders, including Huntington's disease and spinocerebellar ataxias. PolyQ fragments accumulate as aggregates in the cytoplasm and/or in the nucleus, and induce neuronal cell death. However, the molecular mechanism of polyQ-induced cell death is controversial. Here, we show the following: (1) polyQ with pathogenic repeat length triggers ER stress through proteasomal dysfunction; (2) ER stress activates ASK 1 through formation of an IRE1–TRAF2–ASK1 complex; and (3)ASK1−/− primary neurons are defective in polyQ-, proteasome inhibitor-, and ER stress-induced JNK activation and cell death. These findings suggest that ASK1 is a key element in ER stress-induced cell death that plays an important role in the neuropathological alterations in polyQ diseases.
Distribution of Hammerhead and Hammerhead-like RNA Motifs Through the GenBank
Authors: Ferbeyre Gerardo , Bourdeau Véronique , Pageau Marie , Miramontes Pedro , Cedergren Robert
Published: July 2002

Hammerhead ribozymes previously were found in satellite RNAs from plant viroids and in repetitive DNA from certain species of newts and schistosomes. To determine if this catalytic RNA motif has a wider distribution, we decided to scrutinize the GenBank database for RNAs that contain hammerhead or hammerhead-like motifs. The search shows a widespread distribution of this kind of RNA motif in different sequences suggesting that they might have a more general role in RNA biology. The frequency of the hammerhead motif is half of that expected from a random distribution, but this fact comes from the low CpG representation in vertebrate sequences and the bias of the GenBank for those sequences. Intriguing motifs include those found in several families of repetitive sequences, in the satellite RNA from the carrot red leaf luteovirus, in plant viruses like the spinach latent virus and the elm mottle virus, in animal viruses like the hepatitis E virus and the caprine encephalitis virus, and in mRNAs such as those coding for cytochrome P450 oxidoreductase in the rat and the hamster.
CAGGG Repeats and the Pericentromeric Duplication of the Hominoid Genome
Authors: Eichler Evan E. , Archidiacono Nicoletta , Rocchi Mariano
Published: July 2002

Gene duplication is one of the primary forces of evolutionary change. We present data from three different pericentromeric regions of human chromosomes, which indicate that such regions of the genome have been sites of recent genomic duplication. This form of duplication has involved the evolutionary movement of segments of genomic material, including both intronic and exonic sequence, from diverse regions of the genome toward the pericentromeric regions. Sequence analyses of the target sites of duplication have identified a novel class of interspersed GC-rich repeats located precisely at the boundaries of duplication. Estimates of the evolutionary age of these duplications indicate that they have occurred between 10 and 25 mya. In contrast, comparative analyses confirm that the GC-rich pericentromeric repeats have existed within the pericentromeric regions of primate chromosomes before the divergence of the cercopithecoid and hominoid lineages (∼30 mya). These data provide molecular evidence for considerable interchromosomal duplication of genic segments during the evolution of the hominoid genome and strongly implicate GC-rich repeat elements as playing a direct role in the pericentromeric localization of these events
Differential Effects of Damage within the Hippocampal Region on Memory for a Natural, Nonspatial Odor–Odor Association
Authors: Alvarez Pablo , Lipton Paul A. , Melrose Rebecca , Eichenbaum Howard
Published: July 2002

Debate continues on whether the role of rodent hippocampus in memory is limited to the spatial domain. Recently, this controversy has been addressed with studies on the social transmission of food preference, an odor–odor association task with no spatial requirements. Multiple reports have concluded that damage to the hippocampal region impairs memory in this task, but there remain questions about the extent of damage essential to produce an impairment. Furthermore, a recent study (Burton et al. 2000) found no effect of hippocampal lesions on memory in this task. We tested animals with complete lesions of the hippocampus (H) lesions of the hippocampus plus subiculum (HS), and lesions of the adjacent, anatomically related cortices of the parahippocampal region (PHR). H lesions produced an impairment on spatial delayed alternation, but not on memory for the social transmission of food preference, whereas HS and PHR lesions produced severe and equivalent impairments on memory for the socially acquired food preference. We discuss possible explanations for the discrepancy with the results of Burton et al. (2000) and conclude that the hippocampus and subiculum together play a critical role in the formation of this form of nonspatial, relational memory.
Identification of Genes Expressed in the Amygdala During the Formation of Fear Memory
Authors: Stork Oliver , Stork Simone , Pape Hans-Christian , Obata Kunihiko
Published: July 2002

In this study we describe changes of gene expression that occur in the basolateral complex of the mouse amygdala (BLA) during the formation of fear memory. Through the combination of a behavioral training scheme with polymerase chain reaction-based expression analysis (subtractive hybridization and virtual Northern analysis) we were able to identify various gene products that are increased in expression after Pavlovian fear conditioning and are of potential significance for neural plasticity and information storage in the amygdala. In particular, a key enzyme of monoamine metabolism, aldehyde reductase, and the protein sorting and ubiquitination factor Praja1, showed pronounced and learning-specific induction six hours after fear conditioning training. Aldehyde reductase and Praja1, including a novel alternatively spliced isoform termed Praja1a, were induced in the BLA depending on the emotional stimulus presented and showed different expression levels in response to associative conditioning, training stress, and experience of conditioned fear. Stress and fear were further found to induce various signal transduction factors (transthyretin, phosphodiesterase1, protein kinase inhibitor-α) and structural reorganization factors (e.g., E2-ubiquitin conjugating enzyme, neuroligin1, actin, UDP-galactose transporter) during training. Our results show that the formation of Pavlovian fear memory is associated with changes of gene expression in the BLA, which may contribute to neural plasticity and the processing of information about both conditioned and unconditioned fear stimuli. [The Praja1a sequence has been deposited in GenBank data base under accession no. AF335250.]
Computer-Assisted Behavioral Assessment of Pavlovian Fear Conditioning in Mice
Authors: Anagnostaras Stephan G. , Josselyn Sheena A. , Frankland Paul W. , Silva Alcino J.
Published: July 2002

In Pavlovian fear conditioning, a conditional stimulus (CS, usually a tone) is paired with an aversive unconditional stimulus (US, usually a foot shock) in a novel context. After even a single pairing, the animal comes to exhibit a long-lasting fear to the CS and the conditioning context, which can be measured as freezing, an adaptive defense reaction in mice. Both context and tone conditioning depend on the integrity of the amygdala, and context conditioning further depends on the hippocampus. The reliability and efficiency of the fear conditioning assay makes it an excellent candidate for the screening of learning and memory deficits in mutant mice. One obstacle is that freezing in mice has been accurately quantified only by human observers, using a tedious method that can be subject to bias. In the present study we generated a simple, high-speed, and highly accurate algorithm that scores freezing of four mice simultaneously using NIH Image on an ordinary Macintosh computer. The algorithm yielded a high correlation and excellent linear fit between computer and human scores across a broad range of conditions. This included the ability to score low pretraining baseline scores and accurately mimic the effects of two independent variables (shock intensity and test modality) on fear. Because we used a computer and digital video, we were able to acquire a secondary index of fear, activity suppression, as well as baseline activity scores. Moreover, we measured the unconditional response to shock. These additional measures can enhance the sensitivity of the assay to detect interesting memory phenotypes and control for possible confounds. Thus, this computer-assisted system for measuring behavior during fear conditioning allows for the standardized and carefully controlled assessment of multiple aspects of the fear conditioning experience.
Operant Conditioning in Lymnaea: Evidence for Intermediate- and Long-term Memory
Authors: Lukowiak Ken , Adatia Nimet , Krygier Darin , Syed Naweed
Published: July 2002

Aerial respiration of the pond snail, Lymnaea stagnalis, can be operantly conditioned; however, the parameters necessary to produce long-term (LTM) or intermediate term memory (ITM) have not previously been investigated. We conducted training using procedures that varied in the duration of the training session, the number of training sessions per day or the amount of time between subsequent training sessions (SI). We found that by varying the duration and frequency of the training session learning could be differentially produced. Furthermore, the ability to form LTM was dependent not only on the duration of the training session was also the interval between training sessions, the SI. Thus it was possible to produce ITM, which persists for up to 3 hr, and not form LTM, which persists at least 18 hr. Learning, ITM, and LTM can be differentially produced by altering the SI, the duration of the training session, or the number of training sessions per day. These findings may allow us to begin to elucidate the underlying neural mechanisms of learning, ITM, and LTM.
The Biophysics of Leaf Growth in Salt-Stressed Barley. A Study at the Cell Level
Authors: Fricke Wieland , Peters Winfried S.
Published: July 2002

Biophysical parameters potentially involved in growth regulation were studied at the single-cell level in the third leaf of barley (Hordeum vulgare) after exposure to various degrees of NaCl stress for 3 to 5 d. Gradients of elongation growth were measured, and turgor pressure, osmolality, and water potentials (ψ) were determined (pressure probe and picoliter osmometry) in epidermal cells of the elongation zone and the mature blade. Cells in the elongation zone adjusted to decreasing external ψ through increases in cell osmolality that were accomplished by increased solute loads and reduced water contents. Cell turgor changed only slightly. In contrast, decreases in turgor also contributed significantly to ψ adjustment in the mature blade. Solute deposition rates in the elongation zone increased at moderate stress levels as compared with control conditions, but decreased again at more severe NaCl exposure. Growth-associated ψ gradients between expanding epidermal cells and the xylem were significant under control and moderate stress conditions (75 mm NaCl) but seemed negligible at severe stress (120 mm NaCl). We conclude that leaf cell elongation in NaCl-treated barley is probably limited by the rate at which solutes can be taken up to generate turgor, particularly at high NaCl levels.
Members of the c1/pl1 Regulatory Gene Family Mediate the Response of Maize Aleurone and Mesocotyl to Different Light Qualities and Cytokinins
Authors: Piazza Paolo , Procissi Antonia , Jenkins Gareth I. , Tonelli Chiara
Published: July 2002

We investigated the role of transcription factors (R, SN, C1, and PL) in the regulation of anthocyanin biosynthesis by different light qualities (white, red, blue, and ultraviolet) and by cytokinin in maize (Zea mays). We analyzed anthocyanin accumulation, structural gene expression, and regulatory gene expression in the seed aleurone and the seedling mesocotyl. In the mesocotyl, white, blue, and ultraviolet-B light strongly induced anthocyanin accumulation and expression of two key structural genes. In contrast, red light had little effect. Cytokinin enhanced the response to light but was not sufficient to induce anthocyanin accumulation in darkness. Plants with the pl-bol3 allele showed high levels of anthocyanin accumulation in response to light, whereas those with thepl-W22 allele did not, demonstrating the importance of pl1 in the light response. The expression of the pl-bol3 gene, encoding an MYB-related transcription factor, was induced by light and enhanced by cytokinin in a very similar manner to the structural genes and anthocyanin accumulation. Expression of the bHLH(basic helix-loop-helix) Sn1-bol3 gene was stimulated by several light qualities, but not enhanced by cytokinin, and was less well correlated with the induction of anthocyanin biosynthesis. In the aleurone, white, red, and blue light were effective in stimulating anthocyanin accumulation and expression of the MYB-related gene C1. ThebHLH R gene was constitutively expressed. We conclude that specific members of the MYB-relatedc1/pl1 gene family play important roles in the regulation of anthocyanin synthesis in maize in response to different light qualities and cytokinin.
Starches from A to C (Chlamydomonas reinhardtii as a Model Microbial System to Investigate the Biosynthesis of the Plant Amylopectin Crystal)
Authors: Buleon A. , Gallant D. J. , Bouchet B. , Mouille G. , D'Hulst C. , Kossmann J. , Ball S.
Published: July 2002

Wide-angle powder x-ray diffraction analysis was carried out on starch extracted from wild-type and mutant Chlamydomonas reinhardtii cells. Strains containing no defective starch synthases as well as mutants carrying a disrupted granule-bound starch synthase structural gene displayed the A type of diffraction pattern with a high degree of crystallinity. Mutants carrying a defect for the major soluble starch synthase (SSS), SSS II, were characterized by a switch to the B type of diffraction pattern with very low crystallinity. Mutant strains carrying SSS I as the only glucan elongation enzyme regained some of their crystallinity but switched to the C type of diffraction pattern. Differential scanning calorimetry analysis correlated tightly with the x-ray diffraction results. Together with the electron microscopy analyses, these results establish C. reinhardtii as a microbial model system displaying all aspects of cereal starch synthesis and structure. We further show that SSS II is the major enzyme involved in the synthesis of crystalline structures in starch and demonstrate that SSS I alone builds a new type of amylopectin structure.
The Small, Methionine-Rich Chloroplast Heat-Shock Protein Protects Photosystem II Electron Transport during Heat Stress1
Authors: Heckathorn Scott A. , Downs Craig A. , Sharkey Thomas D. , Coleman James S.
Published: July 2002

Evidence suggests that the small chloroplast heat-shock protein (Hsp) is involved in plant thermotolerance but its site of action is unknown. Functional disruption of this Hsp using anti-Hsp antibodies or addition of purified Hsp to chloroplasts indicated that (a) this Hsp protects thermolabile photosystem II and, consequently, whole-chain electron transport during heat stress; and (b) this Hsp completely accounted for heat acclimation of electron transport in pre-heat-stressed plants. Therefore, this Hsp is a major adaptation to acute heat stress in plants.
Plastid Ontogeny during Petal Development in Arabidopsis1
Authors: Pyke Kevin A. , Page Anton M.
Published: July 2002

Imaging of chlorophyll autofluorescence by confocal microscopy in intact whole petals ofArabidopsis thaliana has been used to analyze chloroplast development and redifferentiation during petal development. Young petals dissected from unopened buds contained green chloroplasts throughout their structure, but as the upper part of the petal lamina developed and expanded, plastids lost their chlorophyll and redifferentiated into leukoplasts, resulting in a white petal blade. Normal green chloroplasts remained in the stalk of the mature petal. In epidermal cells the chloroplasts were normal and green, in stark contrast with leaf epidermal cell plastids. In addition, the majority of these chloroplasts had dumbbell shapes, typical of dividing chloroplasts, and we suggest that the rapid expansion of petal epidermal cells may be a trigger for the initiation of chloroplast division. In petals of the Arabidopsis plastid division mutantarc6, the conversion of chloroplasts into leukoplasts was unaffected in spite of the greatly enlarged size and reduced number of arc6 chloroplasts in cells in the petal base, resulting in few enlarged leukoplasts in cells from the white lamina ofarc6 petals.
Comparative Biochemistry of the Oxidative Burst Produced by Rose and French Bean Cells Reveals Two Distinct Mechanisms1
Authors: Bolwell G. Paul , Davies Dewi R. , Gerrish Chris , Auh Chung-Kyoon , Murphy Terence M.
Published: July 2002

Cultured cells of rose (Rosa damascena) treated with an elicitor derived from Phytophthora spp. and suspension-cultured cells of French bean (Phaseolus vulgaris) treated with an elicitor derived from the cell walls of Colletotrichum lindemuthianum both produced H2O2. It has been hypothesized that in rose cells H2O2is produced by a plasma membrane NAD(P)H oxidase (superoxide synthase), whereas in bean cells H2O2 is derived directly from cell wall peroxidases following extracellular alkalinization and the appearance of a reductant. In the rose/Phytophthoraspp. system treated with N,N-diethyldithiocarbamate, superoxide was detected by a N,N′-dimethyl-9,9′-biacridium dinitrate-dependent chemiluminescence; in contrast, in the bean/C. lindemuthianum system, no superoxide was detected, with or withoutN,N-diethyldithiocarbamate. When rose cells were washed free of medium (containing cell wall peroxidase) and then treated with Phytophthora spp. elicitor, they accumulated a higher maximum concentration of H2O2 than when treated without the washing procedure. In contrast, a washing treatment reduced the H2O2 accumulated by French bean cells treated with C. lindemuthianum elicitor. Rose cells produced reductant capable of stimulating horseradish (Armoracia lapathifolia) peroxidase to form H2O2but did not have a peroxidase capable of forming H2O2 in the presence of reductant. Rose and French bean cells thus appear to be responding by different mechanisms to generate the oxidative burst.
The Never ripe Mutant Provides Evidence That Tumor-Induced Ethylene Controls the Morphogenesis ofAgrobacterium tumefaciens-Induced Crown Galls on Tomato Stems1,2
Authors: Aloni Roni , Wolf Asnat , Feigenbaum Pua , Avni Adi , Klee Harry J.
Published: July 2002

We confirm the hypothesis thatAgrobacterium tumefaciens-induced galls produce ethylene that controls vessel differentiation in the host stem of tomato (Lycopersicon esculentum Mill.). Using an ethylene-insensitive mutant, Never ripe(Nr), and its isogenic wild-type parent we show that infection by A. tumefaciens results in high rates of ethylene evolution from the developing crown galls. Ethylene evolution from isolated internodes carrying galls was up to 50-fold greater than from isolated internodes of control plants when measured 21 and 28 d after infection. Tumor-induced ethylene substantially decreased vessel diameter in the host tissues beside the tumor in wild-type stems but had a very limited effect in the Nr stems. Ethylene promoted the typical unorganized callus shape of the gall, which maximized the tumor surface in wild-type stems, whereas the galls on the Nr stems had a smooth surface. The combination of decreased vessel diameter in the host and increased tumor surface ensured water-supply priority to the growing gall over the host shoot. These results indicate that in addition to the well-defined roles of auxin and cytokinin, there is a critical role for ethylene in determining crown-gall morphogenesis.
Characterization of Starch-Debranching Enzymes in Pea Embryos
Authors: Zhu Zhi-Ping , Hylton Christopher M. , Rössner Ute , Smith Alison M.
Published: July 2002

Two distinct types of debranching enzymes have been identified in developing pea (Pisum sativum L.) embryos using native gel analysis and tests of substrate preference on purified or partially purified activities. An isoamylase-like activity capable of hydrolyzing amylopectin and glycogen but not pullulan is present throughout development and is largely or entirely confined to the plastid. Activities capable of hydrolyzing pullulan are present both inside and outside of the plastid, and extraplastidial activity increases relative to the plastidial activity during development. Both types of debranching enzyme are also present in germinating embryos. We argue that debranching enzymes are likely to have a role in starch metabolism in the plastid of the developing embryo and in starch degradation during germination.
Domains of a Transit Sequence Required for in Vivo Import in Arabidopsis Chloroplasts
Authors: Rensink Willem Albert , Pilon Marinus , Weisbeek Peter
Published: July 2002

Nuclear-encoded precursors of chloroplast proteins are synthesized with an amino-terminal cleavable transit sequence, which contains the information for chloroplastic targeting. To determine which regions of the transit sequence are most important for its function, the chloroplast uptake and processing of a full-length ferredoxin precursor and four mutants with deletions in adjacent regions of the transit sequence were analyzed. Arabidopsis was used as an experimental system for both in vitro and in vivo import. The full-length wild-type precursor translocated efficiently into isolated Arabidopsis chloroplasts, and upon expression in transgenic Arabidopsis plants only mature-sized protein was detected, which was localized inside the chloroplast. None of the deletion mutants was imported in vitro. By analyzing transgenic plants, more subtle effects on import were observed. The most N-terminal deletion resulted in a fully defective transit sequence. Two deletions in the middle region of the transit sequence allowed translocation into the chloroplast, although with reduced efficiencies. One deletion in this region strongly reduced mature protein accumulation in older plants. The most C-terminal deletion was translocated but resulted in defective processing. These results allow the dissection of the transit sequence into separate functional regions and give an in vivo basis for a domain-like structure of the ferredoxin transit sequence.
The Sensitivity of Barley Aleurone Tissue to Gibberellin Is Heterogeneous and May Be Spatially Determined1
Authors: Ritchie Sian , McCubbin Andrew , Ambrose Genevieve , Kao Teh-hui , Gilroy Simon
Published: July 2002

In cereals, gibberellin (GA) enhances the synthesis and secretion of hydrolytic enzymes from aleurone cells. These enzymes then mobilize the endosperm storage reserves that fuel germination. The dose-response curve of aleurone protoplasts to GA extends over a range of concentrations from 10−11 to more than 10−6m. One hypothesis is that subpopulations of cells have different sensitivities to GA, with each cell having a threshold concentration of GA above which it is switched on. The dose-response curve therefore reflects a gradual recruitment of cells to the pool exhibiting a full GA response. Alternatively, all cells may gradually increase their responses as the GA level is increased. In the present study we found that at increasing GA concentrations, increasing numbers of barley (Hordeum vulgare) cells showed the enhanced amylase secretion and vacuolation characteristic of the GA response. We also observed that the region of aleurone tissue closest to the embryo contains the highest proportion of cells activated at the GA concentrations thought to occur naturally in germinating grain. These data indicate that an aleurone layer contains cells of varying sensitivities to GA and that recruitment of these differentially responding pools of cells may explain the broad dose response to GA.
Genetic Analysis of Growth-Regulator-Induced Parthenocarpy in Arabidopsis
Authors: Vivian-Smith Adam , Koltunow Anna M.
Published: July 2002

In Arabidopsis, seedless silique development or parthenocarpy can be induced by the application of various plant growth regulators (PGRs) to unfertilized pistils. Ecotype-specific responses were observed in the Arabidopsis ecotypes Columbia and Landsberg relative to the type of PGR and level applied. The parthenocarpic response was greatest in ecotype Landsberg, and comparisons of fruit growth and morphology were studied primarily in this ecotype. Gibberellic acid application (10 μmol pistil−1) caused development similar to that in pollinated pistils, while benzyladenine (1 μmol pistil−1) and naphthylacetic acid (10 μmol pistil−1) treatment produced shorter siliques. Naphthylacetic acid primarily modified mesocarp cell expansion. Arabidopsis mutants were employed to examine potential dependencies on gibberellin biosynthesis (ga1-3,ga4-1, andga5-1) and perception (spy-4 and gai) during parthenocarpic silique development. Emasculated spy-4 pistils were neither obviously parthenocarpic nor deficient in PGR perception. By contrast, emasculated gai mutants did not produce parthenocarpic siliques following gibberellic acid application, but silique development occurred following pollination or application of auxin and cytokinin. Pollinated gai siliques had decreased cell numbers and morphologically resembled auxin-induced parthenocarpic siliques. This shows that a number of independent and possibly redundant pathways can direct hormone-induced parthenocarpy, and that endogenous gibberellins play a role in regulating cell expansion and promoting cell division in carpels.
Initial Binding of Preproteins Involving the Toc159 Receptor Can Be Bypassed during Protein Import into Chloroplasts
Authors: Chen Kunhua , Chen Xuejun , Schnell Danny J.
Published: July 2002

Two integral outer envelope GTPases, Toc34 and Toc86, are proposed to regulate the recognition and translocation of nuclear-encoded preproteins during the early stages of protein import into chloroplasts. Defining the precise roles of Toc86 and Toc34 has been complicated by the inability to distinguish their GTPase activities. Furthermore, the assignment of Toc86 function is rendered equivocal by recent reports suggesting that the standard protocol for the isolation of chloroplasts results in significant proteolysis of Toc86 (B. Bolter, T. May, J. Soll [1998] FEBS Lett 441: 59–62; G. Schatz [1998] Nature 395: 439–440). We demonstrate that Toc86 corresponds to a native protein of 159 kD in pea (Pisum sativum), designated Toc159. We take advantage of the proteolytic sensitivity of Toc159 to selectively remove its 100-kD cytoplasmic GTPase domain and thereby distinguish its activities from other import components. Proteolysis eliminates detectable binding of preproteins at the chloroplast surface, which is consistent with the proposed role of Toc159 as a receptor component. Remarkably, preprotein translocation across the outer membrane can occur in the absence of the Toc159 cytoplasmic domain, suggesting that binding can be bypassed. Translocation remains sensitive to GTP analogs in the absence of the Toc159 GTP-binding domain, providing evidence that Toc34 plays a key role in the regulation of translocation by GTP.
Cloning and Expression of Cytochrome P450 Enzymes Catalyzing the Conversion of Tyrosine to p-Hydroxyphenylacetaldoxime in the Biosynthesis of Cyanogenic Glucosides in Triglochin maritima
Authors: Nielsen John Strikart , Møller Birger Lindberg
Published: July 2002

Two cDNA clones encoding cytochrome P450 enzymes belonging to the CYP79 family have been isolated fromTriglochin maritima. The two proteins show 94% sequence identity and have been designated CYP79E1 and CYP79E2. Heterologous expression of the native and the truncated forms of the two clones inEscherichia coli demonstrated that both encode multifunctional N-hydroxylases catalyzing the conversion of tyrosine to p-hydroxyphenylacetaldoxime in the biosynthesis of the two cyanogenic glucosides taxiphyllin and triglochinin in T. maritima. This renders CYP79E functionally identical to CYP79A1 from Sorghum bicolor, and unambiguously demonstrates that cyanogenic glucoside biosynthesis in T. maritima and S. bicolor is catalyzed by analogous enzyme systems withp-hydroxyphenylacetaldoxime as a free intermediate. This is in contrast to earlier reports stipulatingp-hydroxyphenylacetonitrile as the only free intermediate in T. maritima.l-3,4-Dihydroxyphenyl[3-14C]Ala (DOPA) was not metabolized by CYP79E1, indicating that hydroxylation of the phenol ring at the meta position, as required for triglochinin formation, takes place at a later stage. In S. bicolor, CYP71E1 catalyzes the subsequent conversion ofp-hydroxyphenylacetaldoxime top-hydroxymandelonitrile. When CYP79E1 from T. maritima was reconstituted with CYP71E1 and NADPH-cytochrome P450 oxidoreductase from S. bicolor, efficient conversion of tyrosine to p-hydroxymandelonitrile was observed.
Regulation of Carbonic Anhydrase Expression by Zinc, Cobalt, and Carbon Dioxide in the Marine Diatom Thalassiosira weissflogii
Authors: Lane Todd W. , Morel François M.M.
Published: July 2002

TWCA1 is the major Zn-requiring isoform of carbonic anhydrase (CA) in the marine diatom Thalassiosira weissflogii. We have examined the roles that trace metals and CO2 play in the regulation of TWCA1 expression over ranges of concentrations that bracket those encountered in the marine environment. Both steady-state levels of TWCA1 and the kinetics of induction were measured by western analysis. TWCA1 levels correlated well with cellular CA activity levels. TWCA1 was induced at a low CO2 concentration but the level of induction, as determined by western analysis, was dependent on the availability of Zn. Co effectively substituted for Zn in regulating TWCA1 expression and promoting TWCA1 activity. Upon shift from low to high CO2, the concentration of TWCA1 decreased. The expression of TWCA1 is diel cycle regulated, and cellular TWCA1 decreased during the dark phase. These results provide the basis for studying the expression of CA in field populations and, taken together with previous radiolabeling studies, provide strong evidence of in vivo metal substitution of Co for Zn in a CA. Our data also support the conclusion that TWCA1 plays a central role in carbon acquisition inT. weissflogii.
Ionic and Osmotic Effects of NaCl-Induced Inactivation of Photosystems I and II in Synechococcus sp.
Authors: Allakhverdiev Suleyman I. , Sakamoto Atsushi , Nishiyama Yoshitaka , Inaba Masami , Murata Norio
Published: July 2002

We report here that osmotic effects and ionic effects are both involved in the NaCl-induced inactivation of the photosynthetic machinery in the cyanobacteriumSynechococcus sp. PCC 7942. Incubation of the cyanobacterial cells in 0.5 m NaCl induced a rapid and reversible decline and subsequent slow and irreversible loss of the oxygen-evolving activity of photosystem (PS) II and the electron transport activity of PSI. An Na+-channel blocker protected both PSII and PSI against the slow, but not the rapid, inactivation. The rapid decline resembled the effect of 1.0 m sorbitol. The presence of both an Na+-channel blocker and a water-channel blocker protected PSI and PSII against the short- and long-term effects of NaCl. Salt stress also decreased cytoplasmic volume and this effect was enhanced by the Na+-channel blocker. Our observations suggested that NaCl had both osmotic and ionic effects. The osmotic effect decreased the amount of water in the cytosol, rapidly increasing the intracellular concentration of salts. The ionic effect was caused by an influx of Na+ ions through potassium/Na+ channels that also increased concentrations of salts in the cytosol and irreversibly inactivated PSI and PSII.
The Calcium Rhythms of Different Cell Types Oscillate with Different Circadian Phases
Authors: Wood Nicola T. , Haley Ann , Viry-Moussaı̈d Martine , Johnson Carl H. , van der Luit Arnold H. , Trewavas Anthony J.
Published: July 2002

Transgenic tobacco (Nicotiana plumbaginifolia) seedlings containing the Ca2+-sensitive luminescent protein aequorin have been shown to exhibit circadian variations in cytosolic calcium. Concomitant measurements of cytosolic and nuclear calcium show that circadian variations in the cytoplasm are not expressed in the nucleus. To investigate whether all cells of transgenic seedlings contribute equally to circadian variations in cytosolic calcium, different promoters eliciting different expression patterns have been placed upstream of aequorin and used for transformation. The circadian peak occurred at different times in the three transgenic lines constructed. Luminescence imaging of these transgenic lines indicated that aequorin was differentially accumulated among the main tissues and cells of the seedlings and overcoat technology with applied epidermal strips indicated that the surface cell layers contribute the vast majority of luminescent light. We conclude that the Ca2+rhythmicities of cells and tissues oscillate with distinct differences in phase, that this might represent different underlying cellular control mechanisms and that these observations have significant implications for our understanding and study of Ca2+mediated signal transduction in plant cells.