bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth strains and creep in thermally grown alumina: Oxide growth mechanisms
Authors: Veal B. W. , Paulikas A. P.
Published: November 2008

In situ measurements of growth strains and creep relaxation in α-Al2O3 films, isothermally grown on β-NiAl alloys at 1100 °C, are reported and analyzed. Samples containing the reactive element Zr, and Zr-free samples, are examined. For Zr-free samples, steady state growth strains are compressive, whereas the growth strains are tensile when the reactive element (RE) is added to the alloy. This behavior is attributed to the counterflow of oxygen and aluminum interstitials, and to simultaneous counterflow of oxygen and aluminum vacancies, all moving through the grain boundaries. Cross diffusing oxygen and aluminum interstitials may merge and combine within the film, forming new oxide along grain boundary walls, a mechanism that leads to an in-plane compressive stress. Cross diffusing oxygen and aluminum vacancies will also merge and combine within the film; in this case material is removed from grain boundary walls, a mechanism that leads to an in-plane tensile stress. When no RE is present, the interstitial mechanism dominates and the resultant stress is compressive. Consistent with the “dynamic segregation model,” the RE slows the outdiffusion of Al interstitials permitting the tensile mechanism to dominate. This interpretation invokes the unconventional view that oxygen and aluminum interstitials and vacancies, created in and driven by the strong chemical gradient, all participate meaningfully in the scale growth process. Grain boundary diffusion measurements were obtained from low stress creep data, interpreted using the Coble model of grain boundary diffusion. Reported diffusion measurements of oxygen through grain boundaries of α-Al2O3, which are known to be inconsistent with oxide scale growth, are critically examined. A simple picture, a “balanced defect model,” emerges that is consistent with the dynamic segregation model, observed growth stresses and their dependence on the presence of a reactive element, sequential oxidation experiments, and our best knowledge about grain boundary diffusion coefficients.
Effect of electric fields on the rest time of coalescing drops
Authors: Lukyanets A. S. , Kavehpour H. P.
Published: November 2008

The rest time of drops coalescing at a fluid interface under ac/dc electric fields is investigated with high-speed photography. We show that the rest time consists of two stages dominated by deformation and drainage. Previous models predict a single stage process, dependent only on the electric field magnitude; our experiments show that frequency is also important. Initially, the drop begins to deform once the electric field in the gap between the drop and fluid bulk reaches a critical value; afterward, the rest time depends only on the interfacial fluid film drainage and is inversely proportional to electric field strength.
Direct observations of Ca ordering in Ca0.33CoO2 thin films with different superstructures
Authors: Huang Rong , Mizoguchi Teruyasu , Sugiura Kenji , Ohta Hiromichi , Koumoto Kunihito , Hirayama Tsukasa , Ikuhara Yuichi
Published: November 2008

Ca-ion superstructures such as 3a×3a (hexagonal) and 2a×3a (orthorhombic) in layered Ca0.33CoO2 crystalline film, which were prepared by the reactive solid-phase epitaxy and the subsequent ion-exchange treatment, were directly distinguished by using spherical-aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The fluctuation of Ca intensities in the HAADF-STEM image indicates the existence of many Ca vacancies in the 2a×3a orthorhombic superstructure, which is consistent with the partial occupation of Ca (x=0.33) in the cation sites of x=0.5.
Management of beneficial invertebrates and their potential role in integrated pest management for Australian grain systems
Authors: Holloway Joanne C. , Furlong Michael J. , Bowden Philip I.
Published: November 2008

Beneficial invertebrates (predators and parasitoids) can make significant contributions to the suppression of insect pest populations in many cropping systems. In Australia, natural enemies are incorporated into integrated pest management programs in cotton and horticultural agroecosystems. They are also often key components of effective programs for the management of insect pests of grain crops in other parts of the world. However, few studies have examined the contribution of endemic natural enemies to insect pest suppression in the diverse grain agroecosystems of Australia. The potential of these organisms is assessed by reviewing the role that natural enemies play in the suppression of the major pests of Australian grain crops when they occur in overseas grain systems or other local agroecosystems. The principal methods by which the efficacy of biological control agents may be enhanced are examined and possible methods to determine the impact of natural enemies on key insect pest species are described. The financial and environmental benefits of practices that encourage the establishment and improve the efficacy of natural enemies are considered and the constraints to adoption of these practices by the Australian grains industry are discussed.
The population dynamics of the mediterranean snails Cernuella virgata, Cochlicella acuta (Hygromiidae) and Theba pisana (Helicidae) in pasture - cereal rotations in South Australia: a 20-year study
Authors: Baker G. H.
Published: November 2008

The snails Cernuella virgata, Cochlicella acuta and Theba pisana are introduced pests of grain crops and pastures in southern Australia. The population dynamics of these three species of snail were studied for 20 years in two adjacent fields where they coexisted on a farm on the Yorke Peninsula in South Australia. The fields were used for pasture–cereal rotations. Surveys were conducted in autumn and spring each year, coinciding respectively with the start of the breeding season and peak abundance of snails (mostly juveniles). Populations varied greatly in abundance between years and between species, but snails were generally most common in spring, in wet years, especially those with wet autumns and wet springs. Rainfall early in a particular year (i.e. at sowing of crops in autumn) can thus be used to predict the likelihood of heavy snail infestations later in spring (i.e. at harvest). In contrast, the abundance of adult snails in autumn was a poor predictor of the subsequent abundance of juvenile snails in spring, especially in crops. There were no significant correlations, at field scale, between the average abundance of the three species of snail in spring, in either pastures or crops. However, at a sampling scale of 0.25 m2, there were consistent, negative relationships between the abundance of all three snail species. Such patterns may reflect either competitive interactions between snails or subtle differences in micro-habitat choice. Patterns in the abundance of snails (e.g. large numbers near field edges) were suggestive of occasional invasion from dense populations in adjacent fields.
An overview of integrated pest management (IPM) in north-eastern Australian grain farming systems: past, present and future prospects
Authors: Brier H. B. , Murray D. A. H. , Wilson L. J. , Nicholas A. H. , Miles M. M. , Grundy P. R. , McLennan A. J.
Published: November 2008

The authors overview integrated pest management (IPM) in grain crops in north-eastern Australia, which is defined as the area north of latitude 32°S. Major grain crops in this region include the coarse grains (winter and summer cereals), oilseeds and pulses. IPM in these systems is complicated by the diversity of crops, pests, market requirements and cropping environments. In general, the pulse crops are at greatest risk, followed by oilseeds and then by cereal grains. Insecticides remain a key grain pest management tool in north-eastern Australia. IPM in grain crops has benefited considerably through the increased adoption of new, more selective insecticides and biopesticides for many caterpillar pests, in particular Helicoverpa spp. and loopers, and the identification of pest–crop scenarios where spraying is unnecessary (e.g. for most Creontiades spp. populations in soybeans). This has favoured the conservation of natural enemies in north-eastern Australia grain crops, and has arguably assisted in the management of silverleaf whitefly in soybeans in coastal Queensland. However, control of sucking pests and podborers such as Maruca vitrata remains a major challenge for IPM in summer pulses. Because these crops have very low pest-damage tolerances and thresholds, intervention with disruptive insecticides is frequently required, particularly during podfill. The threat posed by silverleaf whitefly demands ongoing multi-pest IPM research, development and extension as this pest can flare under favourable seasonal conditions, especially where disruptive insecticides are used injudiciously. The strong links between researchers and industry have facilitated the adoption of IPM practices in north-eastern Australia and augers well for future pest challenges and for the development and promotion of new and improved IPM tactics.
The Birth of the Biotechnology Era: Penicillin in Australia, 1943–80
1
Authors: Mathews John A.
Published: November 2008

As Australia and other countries seek to establish biotechnology industries, it is timely to review successes and failures in this field. One of the most notable stories is the development of penicillin, as a wartime project, to which Australians made major contributions. Australians during and immediately after the war contributed much to the scientific identification and purification of penicillin, and to the industrial scaling up in its production at the Commonwealth Serum Laboratories in Melbourne. This was a classic instance of war accelerating innovations in public administration. Yet the nascent antibiotic industry was never allowed to gain international competitiveness, and was allowed to run down and eventually disappeared by the end of the 1970s. This article is concerned to tease out the puzzle posed by this contrast in aspirations, between the highest levels of scientific and technical achievement in bringing penicillin into widespread use (Australia being the first country in the world to provide penicillin to the civilian population in 1944) and shockingly poor performance in sustaining and developing a national antibiotics industry. As the stirrings of a biotechnology industry may be observed in the first decade of the twenty‐first century, it would be unfortunate to ignore the lessons of this earlier experience at the birth of the biotechnology era.
Towards a Cultural Economy Paradigm for the Australian Wine Industry
Authors: Aylward David
Published: November 2008

The twenty‐first century wine industry is a very different one from that which dominated operations in the 1980s and 1990s. Production, distribution and marketing of wine are now colonised by an array of complex and intersecting dynamics. Primary among these is a growing demand among consumers for value‐added qualities. Particularly in mature markets, standardised, commodity‐style wine is failing to satisfy an increasingly educated consumer base. What is required now among a number of New World producers is an understanding of the way in which wine’s cultural and economic qualities can be woven into a more enriched fabric. This would not simply add cultural elements to an economically oriented product. Rather, it would weave individual and community values, passion, care, identity, and terroir together with the more tangible aspects of production, distribution, price‐points and marketing.

Such an enriched ‘fabric’ will be referred to throughout this paper as the cultural economy of wine. It will be argued that the Australian wine industry, as a case study, must not only reconfigure its operational structure to reflect these qualities, but must change the way it thinks collectively about its product if it is to remain competitive in an increasingly complex environment.
The outer segment serves as a default destination for the trafficking of membrane proteins in photoreceptors
Authors: Baker Sheila A. , Haeri Mohammad , Yoo Peter , Gospe Sidney M. , Skiba Nikolai P. , Knox Barry E. , Arshavsky Vadim Y.
Published: November 2008

Photoreceptors are compartmentalized neurons in which all proteins responsible for evoking visual signals are confined to the outer segment. Yet, the mechanisms responsible for establishing and maintaining photoreceptor compartmentalization are poorly understood. Here we investigated the targeting of two related membrane proteins, R9AP and syntaxin 3, one residing within and the other excluded from the outer segment. Surprisingly, we have found that only syntaxin 3 has targeting information encoded in its sequence and its removal redirects this protein to the outer segment. Furthermore, proteins residing in the endoplasmic reticulum and mitochondria were similarly redirected to the outer segment after removing their targeting signals. This reveals a pattern where membrane proteins lacking specific targeting information are delivered to the outer segment, which is likely to reflect the enormous appetite of this organelle for new material necessitated by its constant renewal. This also implies that every protein residing outside the outer segment must have a means to avoid this “default” trafficking flow.
Sarcospan reduces dystrophic pathology: stabilization of the utrophin–glycoprotein complex
Authors: Peter Angela K. , Marshall Jamie L. , Crosbie Rachelle H.
Published: November 2008

Mutations in the dystrophin gene cause Duchenne muscular dystrophy and result in the loss of dystrophin and the entire dystrophin–glycoprotein complex (DGC) from the sarcolemma. We show that sarcospan (SSPN), a unique tetraspanin-like component of the DGC, ameliorates muscular dystrophy in dystrophin-deficient mdx mice. SSPN stabilizes the sarcolemma by increasing levels of the utrophin–glycoprotein complex (UGC) at the extrasynaptic membrane to compensate for the loss of dystrophin. Utrophin is normally restricted to the neuromuscular junction, where it replaces dystrophin to form a functionally analogous complex. SSPN directly interacts with the UGC and functions to stabilize utrophin protein without increasing utrophin transcription. These findings reveal the importance of protein stability in the prevention of muscular dystrophy and may impact the future design of therapeutics for muscular dystrophies.
Herpes Zoster–Related Hospitalizations and Expenditures Before and After Introduction of the Varicella Vaccine in the United States
Authors: Patel Mitesh S. , Gebremariam Achamyeleh , Davis Matthew M.
Published: November 2008

Objective.

With childhood varicella vaccination in the United States have come concerns that the incidence of herpes zoster may increase, because of diminishing natural exposure to varicella and consequent reactivation of latent varicella zoster virus. We wanted to estimate the rate of herpes zoster-related hospitalizations and the associated hospital charges before and during the promotion of varicella vaccination in the United States.

Design.

A retrospective study of patients from the Nationwide Inpatient Sample for the years 1993–2004 who were hospitalized due to herpes zoster infection.

Methods.

We searched for diagnoses of herpes zoster (using the International Classification of Diseases, Ninth Revison, Clinical Modification codes starting with 053) in all 15 diagnostic-code fields included for hospital discharges in the Nationwide Inpatient Sample during 1993–2004. We designed our analysis to examine the rates of severe illness due to herpes zoster that resulted in hospitalization, as measured by the rates of herpes zoster-related hospital discharges (HZHDs). The annual population-adjusted rate of HZHDs (per 10,000 US population) and the annual inflation-adjusted total charges for HZHDs were the primary outcomes. Secondary outcomes included mean charges for HZHDs and the distribution of total charges for HZHDs by expected primary payer. Varicella-related hospital discharges (VRHDs) were identified by use of similar diagnosis-based methods, which were described in our previous study.

Results.

Population-adjusted rates of HZHDs did not change significantiy from the prevaccination years (1993–1995) through the initial 5 years of the varicella vaccination period. Beginning in 2001, however, the rate of HZHDs overall began to increase, and by 2004 the overall rate was 2.5 HZHDs (95% confidence interval, 2.38–2.62) per 10,000 US population, significantly higher than any of the rates calculated during the years prior to 2002. Hospital charges for HZHDs overall increased by more than $700 million annually by 2004; in particular, we found that the herpes zoster vaccine–eligible population (ie, persons aged 60 years or older) accounted for 74% of the total annual hospital charges in 2004. The annual rate of VRHDs and the associated hospital charges decreased significantly from 1993 through 2004, but the decrease in hospitalizations and charges for VRHDs was less than the increase in hospitalizations and charges for HZHDs.

Conclusions.

AS the rates of VRHDs and the associated charges have decreased, there has been a significant increase in HZHDs and associated charges, disproportionately among older adults. Herpes zoster vaccine may mitigate these trends for HZHDs.
Adaptive plasticity of mammalian sperm production in response to social experience
Authors: Ramm Steven A , Stockley Paula
Published: November 2008

Sperm competition theory predicts that males should invest prudently in ejaculates according to levels of female promiscuity. Males may therefore be sensitive to cues in their social environment associated with sexual competition, and tailor investment in sperm production accordingly. We tested this idea experimentally for the first time, to our knowledge, in a mammal by comparing reproductive traits of male house mice (
Mus musculus domesticus
) that had experienced contrasting encounter regimes with potential sexual competitors. We found that daily sperm production and numbers of sperm in the caput epididymis were significantly higher in subjects that had experienced a high encounter rate of social cues from three other males compared to those that had experienced a low encounter rate of social cues from just one other male. Epididymal sperm counts were negatively correlated with the frequency of scent-marking behaviour across all males in our study, suggesting that investment in ejaculate production may be traded off against traits that function in gaining copulations, although there was no difference in overall levels of scent marking between treatment groups. We conclude that social experience-mediated phenotypic plasticity in mammalian spermatogenesis is likely to be adaptive under sperm competition, enabling males to balance the energetic costs and paternity-enhancing benefits of ejaculate production, and is a potentially widespread explanation for intraspecific variation in ejaculate expenditure.
Molecular Control of Acid Phosphatase Secretion into the Rhizosphere of Proteoid Roots from Phosphorus-Stressed White Lupin
Authors: Miller Susan Stade , Liu Junqi , Allan Deborah L. , Menzhuber Christopher J. , Fedorova Maria , Vance Carroll P.
Published: November 2008

White lupin (Lupinus albus) grown under P deficiency displays a suite of highly coordinated adaptive responses. Included among these is secretion of copious amounts of acid phosphatase (APase). Although numerous reports document that plants secrete APases in response to P deficiency, little is known of the biochemical and molecular events involved in this process. Here we characterize the secreted APase protein, cDNA, and gene from white lupin. The secreted APase enzyme is a glycoprotein with broad substrate specificity. It is synthesized as a preprotein with a deducedM  r of 52,000 containing a 31-amino acid presequence. Analysis of the presequence predicts that the protein is targeted to outside the cell. The processed protein has a predictedM  r of 49,000 but migrates as a protein withM  r of 70,000 on sodium dodecyl sulfate gels. This is likely due to glycosylation. Enhanced expression is fairly specific to proteoid roots of P-stressed plants and involves enhanced synthesis of both enzyme protein and mRNA. Secreted APase appears to be encoded by a single gene containing seven exons interrupted by six introns. The 5′-upstream putative promoter of the white lupin-secreted APase contains a 50-base pair region having 72% identity to an Arabidopsis APase promoter that is responsive to P deficiency. The white lupin-secreted APase promoter and targeting sequence may be useful tools for genetically engineering important proteins from plant roots.
Response of Arabidopsis to Iron Deficiency Stress as Revealed by Microarray Analysis
Authors: Thimm Oliver , Essigmann Bernd , Kloska Sebastian , Altmann Thomas , Buckhout Thomas J.
Published: November 2008

Gene expression in response to Fe deficiency was analyzed in Arabidopsis roots and shoots through the use of a cDNA collection representing at least 6,000 individual gene sequences. Arabidopsis seedlings were grown 1, 3, and 7 d in the absence of Fe, and gene expression in roots and shoots was investigated. Following confirmation of data and normalization methods, expression of several sequences encoding enzymes known to be affected by Fe deficiency was investigated by microarray analysis. Confirmation of literature reports, particularly for changes in enzyme activity, was not always possible, but changes in gene expression could be confirmed. An expression analysis of genes in glycolysis, the tricarboxylic acid cycle, and oxidative pentose phosphate pathway revealed an induction of several enzymes within 3 d of Fe-deficient growth, indicating an increase in respiration in response to Fe deficiency. In roots, transcription of sequences corresponding to enzymes of anaerobic respiration was also induced, whereas in shoots, the induction of several genes in gluconeogenesis, starch degradation, and phloem loading was observed. Thus, it seemed likely that the energy demand in roots required for the Fe deficiency response exceeded the capacity of oxidative phosphorylation, and an increase in carbon import and anaerobic respiration were required to maintain metabolism.
Rapid Deposition of Extensin during the Elicitation of Grapevine Callus Cultures Is Specifically Catalyzed by a 40-Kilodalton Peroxidase
Authors: Jackson Phil A.P. , Galinha Carla I.R. , Pereira Cristina S. , Fortunato Ana , Soares Nelson C. , Amâncio Sara B.Q. , Ricardo Cândido P. Pinto
Published: November 2008

Elicitation or peroxide stimulation of grape (Vitis vinifera L. cv Touriga) vine callus cultures results in the rapid and selective in situ insolubilization of an abundant and ionically bound cell wall protein-denominated GvP1. Surface-enhanced laser desorption/ionization/time of flight-mass spectrometry analysis, the amino acid composition, and the N-terminal sequence of purified GvP1 identified it as an 89.9-kD extensin. Analysis of cell walls following the in situ insolubilization of GvP1 indicates large and specific increases in the major amino acids of GvP1 as compared with the amino acids present in salt-eluted cell walls. We calculate that following deposition, covalently bound GvP1 contributes up to 4% to 5% of the cell wall dry weight. The deposition of GvP1 in situ requires peroxide and endogenous peroxidase activity. Isoelectric focusing of saline eluates of callus revealed only a few basic peroxidases that were all isolated or purified to electrophoretic homogeneity. In vitro and in situ assays of extensin cross-linking activity using GvP1 and peroxidases showed that a 40-kD peroxidase cross-linked GvP1 within minutes, whereas other grapevine peroxidases had no significant activity with GvP1. Internal peptide sequences indicated this extensin peroxidase (EP) is a member of the class III peroxidases. We conclude that we have identified and purified an EP from grapevine callus that is responsible for the catalysis of GvP1 deposition in situ during elicitation. Our results suggest that GvP1 and this EP play an important combined role in grapevine cell wall defense.
Photosystem II Peripheral Accessory Chlorophyll Mutants inChlamydomonas reinhardtii. Biochemical Characterization and Sensitivity to Photo-Inhibition,
Authors: Ruffle Stuart V. , Wang Jun , Johnston Heather G. , Gustafson Terry L. , Hutchison Ronald S. , Minagawa Jun , Crofts Anthony , Sayre Richard T.
Published: November 2008

In addition to the four chlorophylls (Chls) involved in primary charge separation, the photosystem II (PSII) reaction center polypeptides, D1 and D2, coordinate a pair of symmetry-related, peripheral accessory Chls. These Chls are axially coordinated by the D1-H118 and D2-H117 residues and are in close association with the proximal Chl antennae proteins, CP43 and CP47. To gain insight into the function(s) of each of the peripheral Chls, we generated site-specific mutations of the amino acid residues that coordinate these Chls and characterized their energy and electron transfer properties. Our results demonstrate that D1-H118 and D2-H117 mutants differ with respect to: (a) their relative numbers of functional PSII complexes, (b) their relative ability to stabilize charge-separated states, (c) light-harvesting efficiency, and (d) their sensitivity to photo-inhibition. The D2-H117N and D2-H117Q mutants had reduced levels of functional PSII complexes and oxygen evolution capacity as well as reduced light-harvesting efficiencies relative to wild-type cells. In contrast, the D1-H118Q mutant was capable of near wild-type rates of oxygen evolution at saturating light intensities. The D1-H118Q mutant also was substantially more resistant to photo-inhibition than wild type. This reduced sensitivity to photo-inhibition is presumably associated with a reduced light-harvesting efficiency in this mutant. Finally, it is noted that the PSII peripheral accessory Chls have similarities to a to a pair of Chls also present in the PSI reaction center complex.
Dissection of the Light Signal Transduction Pathways Regulating the TwoEarly Light-Induced ProteinGenes in Arabidopsis
Authors: Harari-Steinberg Orit , Ohad Itzhak , Chamovitz Daniel A.
Published: November 2008

The expression of light-regulated genes in plants is controlled by different classes of photoreceptors that act through a variety of signaling molecules. During photomorphogenesis, the early light-induced protein (Elip) genes are among the first to be induced. To understand the light signal transduction pathways that regulate Elip expression, the twoElip genes, Elip1 andElip2, in Arabidopsis were studied, taking advantage of the genetic tools available for studying light signaling in Arabidopsis. Using two independent quantitative reverse transcriptase-PCR techniques, we found that red, far-red, and blue lights positively regulate expression of the Elip genes. Phytochrome A and phytochrome B are involved in this signaling. The cryptochrome or phototropin photoreceptors are not required for blue-light induction of either Elip gene, suggesting the involvement of an additional, unidentified, blue-light receptor. Although the COP9 signalosome, a downstream regulator, is involved in dark repression of both Elips, Elip1 andElip2 show different expression patterns in the dark. The transcription factor HY5 promotes the light induction ofElip1, but not Elip2. A defect in photosystem II activity in greening of hy5 seedlings may result from the loss of Elip1. Heat shock positively controlled Elip1 and Elip2 in a light-independent fashion. This induction is independent of HY5, indicating that heat shock and light activate transcription of the Elip genes through independent pathways.
Root Hair Initiation Is Coupled to a Highly Localized Increase of Xyloglucan Endotransglycosylase Action in Arabidopsis Roots
Authors: Vissenberg Kris , Fry Stephen C. , Verbelen Jean-Pierre
Published: November 2008

Root hairs are formed by two separate processes: initiation and subsequent tip growth. Root hair initiation is always accompanied by a highly localized increase in xyloglucan endotransglycosylase (XET) action at the site of future bulge formation, where the trichoblast locally loosens its cell wall. This suggests an important role of XET in the first stages of root hair initiation. The tip of growing root hairs is not marked by localized high XET action. Experiments in which root hair initiation was modulated and observations on root hair mutants support this view. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid shifts both root hair initiation and the local increase in XET action toward the root tip. On the other hand, roots treated with the ethylene inhibitor aminoethoxyvinyl-glycine, as well as roots of mutants affected in root hair initiation (rhl1, rhd6-1, andaxr2-1) revealed no localized increases of XET action at all and consequently did not initiate root hairs. Disruption of actin and microtubules did not prevent the localized increase in XET action. Also, the temporal and spatial pattern of action as the specific pH dependence suggest that different isoforms of XET act in different processes of root development.
Senescence Is Induced in Individually Darkened Arabidopsis Leaves, but Inhibited in Whole Darkened Plants
Authors: Weaver L. Michael , Amasino Richard M.
Published: November 2008

It has long been known that leaf senescence can be induced in many plant species by detaching leaves and placing them in the darkness. It recently has been shown that entire Arabidopsis plants placed in the darkness are not induced to senesce, as judged by visible yellowing and certain molecular markers. Here, we show that when individual Arabidopsis leaves are darkened, but not when entire plants are darkened, senescence is induced in the covered leaves. This induction of senescence is highly localized. The phenomenon is leaf age dependent in that it occurs more rapidly and strongly in older leaves than in younger ones, as is the case with many forms of induced senescence. Whole adult plants placed in darkness, in contrast, show delayed senescence, although seedlings lacking primary leaves do not. These observations imply that the light status of the entire plant affects the senescence of individual leaves. A model summarizing the results is presented.
Cadmium-Induced Changes in Antioxidative Systems, Hydrogen Peroxide Content, and Differentiation in Scots Pine Roots
Authors: Schützendübel Andres , Schwanz Peter , Teichmann Thomas , Gross Kristina , Langenfeld-Heyser Rosemarie , Godbold Douglas L. , Polle Andrea
Published: November 2008

To investigate whether Cd induces common plant defense pathways or unspecific necrosis, the temporal sequence of physiological reactions, including hydrogen peroxide (H2O2) production, changes in ascorbate-glutathione-related antioxidant systems, secondary metabolism (peroxidases, phenolics, and lignification), and developmental changes, was characterized in roots of hydroponically grown Scots pine (Pinus sylvestris) seedlings. Cd (50 μm, 6 h) initially increased superoxide dismutase, inhibited the systems involved in H2O2 removal (glutathione/glutathione reductase, catalase [CAT], and ascorbate peroxidase [APX]), and caused H2O2accumulation. Elongation of the roots was completely inhibited within 12 h. After 24 h, glutathione reductase activities recovered to control levels; APX and CAT were stimulated by factors of 5.5 and 1.5. Cell death was increased. After 48 h, nonspecific peroxidases and lignification were increased, and APX and CAT activities were decreased. Histochemical analysis showed that soluble phenolics accumulated in the cytosol of Cd-treated roots but lignification was confined to newly formed protoxylem elements, which were found in the region of the root tip that normally constitutes the elongation zone. Roots exposed to 5 μm Cd showed less pronounced responses and only a small decrease in the elongation rate. These results suggest that in cells challenged by Cd at concentrations exceeding the detoxification capacity, H2O2 accumulated because of an imbalance of redox systems. This, in turn, may have triggered the developmental program leading to xylogenesis. In conclusion, Cd did not cause necrotic injury in root tips but appeared to expedite differentiation, thus leading to accelerated aging.
Effect of Temperature on Rates of Alternative and Cytochrome Pathway Respiration and Their Relationship with the Redox Poise of the Quinone Pool
Authors: Atkin Owen K. , Zhang Qisen , Wiskich Joe T.
Published: November 2008

We investigated the effect of short-term changes in temperature on alternative (Alt) and cytochrome (Cyt) pathway respiration, both in intact tissues and isolated mitochondria of 14-d-old cotyledons of soybean (Glycine max L. cv Stevens). We also established the extent to which temperature alters the interaction between the oxidizing pathways and the level of ubiquinone (UQ) reduction (UQr/UQt). No difference was found between the temperature coefficient of respiration (Q  10; proportional change per 10°C) of Alt and Cyt pathway respiration in cotyledon slices (Q  10 = 1.92 and 1.86, respectively). In isolated mitochondria, the Q  10 of the fully activated Alt pathway (Q  10 = 2.24–2.61) was always equal to, or higher than, that of Cytc oxidase (COX) alone (Q  10 = 2.08) and the complete Cyt pathway (Q  10 = 2.40–2.55). This was true regardless of substrate or whether ADP was present. There was little difference in the Q  10 of the Cyt pathway with or without ADP; however, theQ  10 of COX was substantially lower in the presence of an uncoupler (Q  10 = 1.61) than its absence (Q  10 = 2.08). The kinetics of Alt and Cyt pathway activity in relation to UQr/UQt were not affected by temperature. For a given UQr/UQt value, the proportion of maximum flux taking place was similar at all temperatures for both pathways (±ADP). However, the Q  10 of the Alt and the Cyt pathways (+ADP) increased with increasing UQr/UQt. We conclude that the Alt pathway is not less temperature sensitive than the Cyt pathway or COX per se and that changes in the degree of control exerted by individual steps in the respiratory apparatus could result in changes in theQ  10 of mitochondrial O2uptake.
An Off-Line Implementation of the Stable Isotope Technique for Measurements of Alternative Respiratory Pathway Activities
Authors: Nagel Oscar W. , Waldron Susan , Jones Hamlyn G.
Published: November 2008

In situ measurements of alternative respiratory pathway activity are needed to provide insight into the energy efficiency of plant metabolism under various conditions in the field. The only reliable method at present to measure alternative oxidase (AOX) activity is through measurement of changes in δ18O(O2), which to date has only been used in laboratory environments. We have developed a cuvette system to measure partitioning of electrons to AOX that is suitable for off-line use and for field experiments. Plant samples are enclosed in airtight cuvettes and O2 consumption is monitored. Gas samples from the cuvette are stored in evacuated gas containers until measurement of δ18O(O2). We have validated this method using differing plant material to assess AOX activity. Fractionation factors were calculated from δ18O(O2) measurements, which could be measured with an accuracy and precision to 0.1‰ and 0.3‰, respectively. Potential sources of error are discussed and quantified. Our method provides results similar to those obtained with laboratory incubations on-line to a mass spectrometer but greatly increases the potential for adoption of the stable isotope method.
Analysis of the Arabidopsis Mitochondrial Proteome
Authors: Millar A. Harvey , Sweetlove Lee J. , Giegé Philippe , Leaver Christopher J.
Published: November 2008

The complete set of nuclear genes that encode proteins targeted to mitochondria in plants is currently undefined and thus the full range of mitochondrial functions in plants is unknown. Analysis of two-dimensional gel separations of Arabidopsis cell culture mitochondrial protein revealed approximately 100 abundant proteins and 250 low-abundance proteins. Comparison of subfractions of mitochondrial protein on two-dimensional gels provided information on the soluble, membrane, or integral membrane locations of this protein set. A total of 170 protein spots were excised, trypsin-digested, and matrix-assisted laser desorption ionization/time of flight mass spectrometry spectra obtained. Using this dataset, 91 of the proteins were identified by searching translated Arabidopsis genomic databases. Of this set, 81 have defined functions based on sequence comparison. These functions include respiratory electron transport, tricarboxylic acid cycle metabolism, amino acid metabolism, protein import, processing, and assembly, transcription, membrane transport, and antioxidant defense. A total of 10 spectra were matched to Arabidopsis putative open reading frames for which no specific function has been determined. A total of 64 spectra did not match to an identified open reading frame. Analysis of full-length putative protein sequences using bioinformatic tools to predict subcellular targeting (TargetP, Psort, and MitoProt) revealed significant variation in predictions, and also a lack of mitochondrial targeting prediction for several characterized mitochondrial proteins.
A Gene Controlling Variation in Arabidopsis Glucosinolate Composition Is Part of the Methionine Chain Elongation Pathway
Authors: Kroymann Juergen , Textor Susanne , Tokuhisa Jim G. , Falk Kimberly L. , Bartram Stefan , Gershenzon Jonathan , Mitchell-Olds Thomas
Published: November 2008

Arabidopsis and other Brassicaceae produce an enormous diversity of aliphatic glucosinolates, a group of methionine (Met)-derived plant secondary compounds containing a β-thio-glucose moiety, a sulfonated oxime, and a variable side chain. We fine-scale mappedGSL-ELONG, a locus controlling variation in the side-chain length of aliphatic glucosinolates. Within this locus, a polymorphic gene was identified that determines whether Met is extended predominantly by either one or by two methylene groups to produce aliphatic glucosinolates with either three- or four-carbon side chains. Two allelic mutants deficient in four-carbon side-chain glucosinolates were shown to contain independent missense mutations within this gene. In cell-free enzyme assays, a heterologously expressed cDNA from this locus was capable of condensing 2-oxo-4-methylthiobutanoic acid with acetyl-coenzyme A, the initial reaction in Met chain elongation. The gene methylthioalkylmalate synthase1(MAM1) is a member of a gene family sharing approximately 60% amino acid sequence similarity with 2-isopropylmalate synthase, an enzyme of leucine biosynthesis that condenses 2-oxo-3-methylbutanoate with acetyl-coenzyme A.
Dominant Negative Guard Cell K+ Channel Mutants Reduce Inward-Rectifying K+ Currents and Light-Induced Stomatal Opening in Arabidopsis
Authors: Kwak June M. , Murata Yoshiyuki , Baizabal-Aguirre Victor M. , Merrill Jennifer , Wang Michele , Kemper Andrea , Hawke Scott D. , Tallman Gary , Schroeder Julian I.
Published: November 2008

Inward-rectifying potassium (K+  in) channels in guard cells have been suggested to provide a pathway for K+ uptake into guard cells during stomatal opening. To test the proposed role of guard cell K+  in channels in light-induced stomatal opening, transgenic Arabidopsis plants were generated that expressed dominant negative point mutations in the K+  in channel subunit KAT1. Patch-clamp analyses with transgenic guard cells from independent lines showed that K+  in current magnitudes were reduced by approximately 75% compared with vector-transformed controls at −180 mV, which resulted in reduction in light-induced stomatal opening by 38% to 45% compared with vector-transformed controls. Analyses of intracellular K+ content using both sodium hexanitrocobaltate (III) and elemental x-ray microanalyses showed that light-induced K+ uptake was also significantly reduced in guard cells of K+  in channel depressor lines. These findings support the model that K+  inchannels contribute to K+ uptake during light-induced stomatal opening. Furthermore, transpirational water loss from leaves was reduced in the K+  in channel depressor lines. Comparisons of guard cell K+  in current magnitudes among four different transgenic lines with different K+  in current magnitudes show the range of activities of K+  in channels required for guard cell K+ uptake during light-induced stomatal opening.
Phosphoenolpyruvate Carboxykinase Assayed at Physiological Concentrations of Metal Ions Has a High Affinity for CO2
Authors: Chen Zhi-Hui , Walker Robert P. , Acheson Richard M. , Leegood Richard C.
Published: November 2008

The effect of Mn2+/Mg2+ concentration on the activity of intact, homogeneous phosphoenolpyruvate carboxykinase (PEPCK) from leaves of the C4 grass, Guinea grass (Panicum maximum), have been investigated. Assay conditions were optimized so that PEPCK activity could be measured at concentrations of Mn2+/Mg2+ similar to those found in the cytosol (low micromolar Mn2+ and millimolar Mg2+). PEPCK activity was totally dependent on Mn2+ and was activated at low micromolar concentrations of Mn2+ by millimolar concentrations of Mg2+. Therefore, at physiological concentrations of Mn2+, PEPCK has a requirement for Mg2+. Assay at physiological concentrations of Mn2+/Mg2+ led to a marked decrease in its affinity for ATP and a 13-fold increase in its affinity for CO2. The K  m(CO2) was further decreased by assay at physiological ATP to ADP ratios, reaching values as low as 20 μmCO2, comparable with the K  m(CO2) of ribulose 1,5-bisphosphate carboxylase-oxygenase. This means that PEPCK will catalyze a reversible reaction and that it could operate as a carboxylase in vivo, a feature that could be particularly important in algal CO2-concentrating systems.
Antisense Inhibition of Threonine Synthase Leads to High Methionine Content in Transgenic Potato Plants
Authors: Zeh Michaela , Casazza Anna Paola , Kreft Oliver , Roessner Ute , Bieberich Katrin , Willmitzer Lothar , Hoefgen Rainer , Hesse Holger
Published: November 2008

Methionine (Met) and threonine (Thr) are members of the aspartate family of amino acids. In plants, their biosynthetic pathways diverge at the level of O-phosphohomo-serine (Ser). The enzymes cystathionine gamma-synthase and Thr synthase (TS) compete for the common substrate O-phosphohomo-Ser with the notable feature that plant TS is activated through S-adenosyl-Met, a metabolite derived from Met. To investigate the regulation of this branch point, we engineered TS antisense potato (Solanum tuberosum cv Désirée) plants using the constitutive cauliflower mosaic virus 35S promoter. In leaf tissues, these transgenics exhibit a reduction of TS activity down to 6% of wild-type levels. Thr levels are reduced to 45% wild-type controls, whereas Met levels increase up to 239-fold depending on the transgenic line and environmental conditions. Increased levels of homo-Ser and homo-cysteine indicate increased carbon allocation into the aspartate pathway. In contrast to findings in Arabidopsis, increased Met content has no detectable effect on mRNA or protein levels or on the enzymatic activity of cystathionine gamma-synthase in potato. Tubers of TS antisense potato plants contain a Met level increased by a factor of 30 and no reduction in Thr. These plants offer a major biotechnological advance toward the development of crop plants with improved nutritional quality.
A Novel Phospholipase D of Arabidopsis That Is Activated by Oleic Acid and Associated with the Plasma Membrane
Authors: Wang Cunxi , Wang Xuemin
Published: November 2008

Oleate-dependent phospholipase D (PLD; EC 3.1.4.4) has been reported in animal systems, but its molecular nature is unkown. Multiple PLDs have been characterized in plants, but none of the previously cloned PLDs exhibits the oleate-activated activity. Here, we describe the biochemical and molecular identification and characterization of an oleate-activated PLD in Arabidopsis. This PLD, designated PLDδ, was associated tightly with the plasma membrane, and its level of expression was higher in old leaves, stems, flowers, and roots than in young leaves and siliques. A cDNA encoding the oleate-activated PLD was identified, and catalytically active PLDδ was expressed from its cDNA inEscherichia coli. PLDδ was activated by free oleic acid in a dose-dependent manner, with the optimal concentration being 0.5 mm. Other unsaturated fatty acids, linoleic and linolenic acids, were less effective than oleic acid, whereas the saturated fatty acids, stearic and palmitic acids, were totally ineffective. Phosphatidylinositol 4,5-bisphosphate stimulated PLDδ to a lesser extent than oleate. Mutation at arginine (Arg)-611 led to a differential loss of the phosphatidylinositol 4,5-bisphosphate-stimulated activity of PLDδ, indicating that separate sites mediate the oleate regulation of PLDδ. Oleate stimulated PLDδ's binding to phosphatidylcholine. Mutation at Arg-399 resulted in a decrease in oleate binding by PLDδ and a loss of PLDδ activity. However, this mutation bound similar levels of phosphatidylcholine as wild type, suggesting that Arg-399 is not required for PC binding. These results provide the molecular information on oleate-activated PLD and also suggest a mechanism for the oleate stimulation of this enzyme.
Distinct But Conserved Functions for Two Chloroplastic NADP-Malic Enzyme Isoforms in C3 and C4 Flaveria Species
Authors: Lai Lien B. , Wang Lin , Nelson Timothy M.
Published: November 2008

In the most common C4 pathway for carbon fixation, an NADP-malic enzyme (NADP-ME) decarboxylates malate in the chloroplasts of bundle sheath cells. Isoforms of plastidic NADP-ME are encoded by two genes in all species of Flaveria, including C3, C3-C4 intermediate, and C4 types. However, only one of these genes,ChlMe1, encodes the enzyme that functions in the C4 pathway. We compared the expression patterns of theChlMe1 and ChlMe2 genes in developing leaves of Flaveria pringlei (C3) andFlaveria trinervia (C4) and in transgenicFlaveria bidentis (C4).ChlMe1 expression in C4 species increases in leaves with high C4 pathway activity. In the C3species F. pringlei, ChlMe1 expression is transient and limited to early leaf development. In contrast,ChlMe2 is expressed in C3 and C4species concurrent with stages in chloroplast biogenesis. Because previous studies suggest that NADP-ME activities generally reflect the level of its mRNA abundance, we discuss possible roles ofChlMe1 and ChlMe2 based on these expression patterns.