bluuebunny/crossref_metadata_2025 huggingface dataset:
Diabetes, Hemoglobin A1C, and Regional Alzheimer Disease and Infarct Pathology
Authors: Pruzin Jeremy J. , Schneider Julie A. , Capuano Ana W. , Leurgans Sue E. , Barnes Lisa L. , Ahima Rexford S. , Arnold Steven E. , Bennett David A. , Arvanitakis Zoe
Published: October 2016

We examined the relationship of diabetes and hemoglobin A1C (A1C) to 2 common causes of dementia. The study included 1228 subjects who underwent annual clinical evaluations and a brain autopsy at death, as part of a Rush longitudinal cohort study of aging. A total of 433 subjects had A1C data available. Neuropathologic evaluations documented the size and location of infarcts. Modified silver stain-based Alzheimer disease (AD) measures included global and regional scores. We used regression analyses to examine associations of diabetes and A1C with overall and regional neuropathology. Diabetes [odds ratio (OR)=0.94; 95% confidence interval (CI), 0.73-1.20) and A1C (OR=0.83; 95% CI, 0.62-1.10) were not associated with global AD pathology across the brain, nor with overall or individual measures of neuropathology in mesial temporal or neocortical regions separately (all P>0.05). Diabetes was associated with a higher odds of any infarct (OR=1.43; 95% CI, 1.07-1.90), and particularly with gross (OR=1.53; 95% CI, 1.14-2.06) but not microinfarcts (P=0.06), and subcortical (OR=1.79; 95% CI, 1.34-2.39) but not cortical infarcts (P=0.83). In summary, we found no relationship of diabetes or A1C with global or regional AD pathology, including in the mesial temporal lobe. Diabetes is associated with gross subcortical infarcts. Our results suggest that the diabetes-dementia link is based on subcortical vascular pathology and not on regional AD pathology.
Overview of the mechanisms that could explain the ‘Boundary Exchange’ at the land–ocean contact
Authors: Jeandel Catherine
Published: October 2016

Land to ocean transfer of material largely controls the chemical composition of seawater and the global element cycles. Oceanic isotopic budgets of chemical species, macro- and micronutrients (e.g. Nd, Sr, Si, Mg, Zn, Mo and Ni) have revealed an imbalance between their sources and sinks. Radiogenic isotope budgets underlined the importance of taking into account continental margins as a source of elements to oceans. They also highlighted that the net land–ocean inputs of chemical species probably result from particle-dissolved exchange processes, named ‘Boundary Exchange’. Yet, locations where ‘Boundary Exchange’ occurs are not clearly identified and reviewed here: discharge of huge amount of freshly weathered particles at the river mouths, submarine weathering of deposited sediments along the margins, submarine groundwater discharges and subterranean estuaries. As a whole, we conclude that all of them might contribute to ‘Boundary Exchange’. Highlighting their specific roles and the processes at play is a key scientific issue for the second half of GEOTRACES.

This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
Southern Ocean biological iron cycling in the pre-whaling and present ecosystems
Authors: Maldonado Maria T. , Surma Szymon , Pakhomov Evgeny A.
Published: October 2016

This study aimed to create the first model of biological iron (Fe) cycling in the Southern Ocean food web. Two biomass mass-balanced Ecopath models were built to represent pre- and post-whaling ecosystem states (1900 and 2008). Functional group biomasses (tonnes wet weight km
−2
) were converted to biogenic Fe pools (kg Fe km
−2
) using published Fe content ranges. In both models, biogenic Fe pools and consumption in the pelagic Southern Ocean were highest for plankton and small nektonic groups. The production of plankton biomass, particularly unicellular groups, accounted for the highest annual Fe demand. Microzooplankton contributed most to biological Fe recycling, followed by carnivorous zooplankton and krill. Biological Fe recycling matched previous estimates, and, under most conditions, could entirely meet the Fe demand of bacterioplankton and phytoplankton. Iron recycling by large baleen whales was reduced 10-fold by whaling between 1900 and 2008. However, even under the 1900 scenario, the contribution of whales to biological Fe recycling was negligible compared with that of planktonic consumers. These models are a first step in examining oceanic-scale biological Fe cycling, highlighting gaps in our present knowledge and key questions for future research on the role of marine food webs in the cycling of trace elements in the sea.

This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
The effect of acidification on the bioavailability and electrochemical lability of zinc in seawater
Authors: Kim Ja-Myung , Baars Oliver , Morel François M. M.
Published: October 2016

A poorly studied but potentially important consequence of the CO
2
-induced acidification of the surface ocean is a possible change in the bioavailability of trace metals, which play a critical role in the productivity and population dynamics of marine ecosystems. We report laboratory and field experiments designed to compare quantitatively the effects of acidification on the bioavailability of Zn, a metal essential to the growth of phytoplankton and on the extent of its complexation by model and natural ligands. We observed a good correspondence between the effects of pH on the rate of Zn uptake by a model diatom and the chemical lability of Zn measured by anodic stripping voltammetry (ASV). In model laboratory systems, the chemical lability and the bioavailability of Zn could either increase or decrease at low pH depending on the mix of complexing ligands. In a sample of coastal surface water, we observed similar increases in the ASV-labile and bioavailable Zn concentrations upon acidification, a result contrary to previous observations. These results, which can likely be generalized to other bioactive trace metals,
mutatis mutandis
, demonstrate the intricacy of the effects of ocean acidification on the chemistry and the ecology of surface seawater.

This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
Lead isotope exchange between dissolved and fluvial particulate matter: a laboratory study from the Johor River estuary
Authors: Chen Mengli , Boyle Edward A. , Lee Jong-Mi , Nurhati Intan , Zurbrick Cheryl , Switzer Adam D. , Carrasco Gonzalo
Published: October 2016

Atmospheric aerosols are the dominant source of Pb to the modern marine environment, and as a result, in most regions of the ocean the Pb isotopic composition of dissolved Pb in the surface ocean (and in corals) matches that of the regional aerosols. In the Singapore Strait, however, there is a large offset between seawater dissolved and coral Pb isotopes and that of the regional aerosols. We propose that this difference results from isotope exchange between dissolved Pb supplied by anthropogenic aerosol deposition and adsorbed natural crustal Pb on weathered particles delivered to the ocean by coastal rivers. To investigate this issue, Pb isotope exchange was assessed through a closed-system exchange experiment using estuarine waters collected at the Johor River mouth (which discharges to the Singapore Strait). During the experiment, a known amount of dissolved Pb with the isotopic composition of NBS-981 (
206
Pb/
207
Pb = 1.093) was spiked into the unfiltered Johor water (dissolved and particulate
206
Pb/
207
Pb = 1.199) and the changing isotopic composition of the dissolved Pb was monitored. The mixing ratio of the estuarine and spike Pb should have produced a dissolved
206
Pb/
207
Pb isotopic composition of 1.161, but within a week, the
206
Pb/
207
Pb in the water increased to 1.190 and continued to increase to 1.197 during the next two months without significant changes of the dissolved Pb concentration. The kinetics of isotope exchange was assessed using a simple
K
d
model, which assumes multiple sub-reservoirs within the particulate matter with different exchange rate constants. The
K
d
model reproduced 56% of the observed Pb isotope variance. Both the closed-system experiment and field measurements imply that isotope exchange can be an important mechanism for controlling Pb and Pb isotopes in coastal waters. A similar process may occur for other trace elements.

This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
Trace element and isotope deposition across the air–sea interface: progress and research needs
Authors: Baker A. R. , Landing W. M. , Bucciarelli E. , Cheize M. , Fietz S. , Hayes C. T. , Kadko D. , Morton P. L. , Rogan N. , Sarthou G. , Shelley R. U. , Shi Z. , Shiller A. , van Hulten M. M. P.
Published: October 2016

The importance of the atmospheric deposition of biologically essential trace elements, especially iron, is widely recognized, as are the difficulties of accurately quantifying the rates of trace element wet and dry deposition and their fractional solubility. This paper summarizes some of the recent progress in this field, particularly that driven by the GEOTRACES, and other, international research programmes. The utility and limitations of models used to estimate atmospheric deposition flux, for example, from the surface ocean distribution of tracers such as dissolved aluminium, are discussed and a relatively new technique for quantifying atmospheric deposition using the short-lived radionuclide beryllium-7 is highlighted. It is proposed that this field will advance more rapidly by using a multi-tracer approach, and that aerosol deposition models should be ground-truthed against observed aerosol concentration data. It is also important to improve our understanding of the mechanisms and rates that control the fractional solubility of these tracers. Aerosol provenance and chemistry (humidity, acidity and organic ligand characteristics) play important roles in governing tracer solubility. Many of these factors are likely to be influenced by changes in atmospheric composition in the future. Intercalibration exercises for aerosol chemistry and fractional solubility are an essential component of the GEOTRACES programme.

This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
Quantifying trace element and isotope fluxes at the ocean–sediment boundary: a review
Authors: Homoky William B. , Weber Thomas , Berelson William M. , Conway Tim M. , Henderson Gideon M. , van Hulten Marco , Jeandel Catherine , Severmann Silke , Tagliabue Alessandro
Published: October 2016

Quantifying fluxes of trace elements and their isotopes (TEIs) at the ocean's sediment–water boundary is a pre-eminent challenge to understand their role in the present, past and future ocean. There are multiple processes that drive the uptake and release of TEIs, and properties that determine their rates are unevenly distributed (e.g. sediment composition, redox conditions and (bio)physical dynamics). These factors complicate our efforts to find, measure and extrapolate TEI fluxes across ocean basins. GEOTRACES observations are unveiling the oceanic distributions of many TEIs for the first time. These data evidence the influence of the sediment–water boundary on many TEI cycles, and underline the fact that our knowledge of the source–sink fluxes that sustain oceanic distributions is largely missing. Present flux measurements provide low spatial coverage and only part of the empirical basis needed to predict TEI flux variations. Many of the advances and present challenges facing TEI flux measurements are linked to process studies that collect sediment cores, pore waters, sinking material or seawater in close contact with sediments. However, such sampling has not routinely been viable on GEOTRACES expeditions. In this article, we recommend approaches to address these issues: firstly, with an interrogation of emergent data using isotopic mass-balance and inverse modelling techniques; and secondly, by innovating pursuits of direct TEI flux measurements. We exemplify the value of GEOTRACES data with a new inverse model estimate of benthic Al flux in the North Atlantic Ocean. Furthermore, we review viable flux measurement techniques tailored to the sediment–water boundary. We propose that such activities are aimed at regions that intersect the GEOTRACES Science Plan on the basis of seven criteria that may influence TEI fluxes: sediment provenance, composition, organic carbon supply, redox conditions, sedimentation rate, bathymetry and the benthic nepheloid inventory.

This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
Conditioned object preference: an alternative approach to measuring reward learning in rats
Authors: Kennedy Bruce C. , Kohli Maulika , Maertens Jamie J. , Marell Paulina S. , Gewirtz Jonathan C.
Published: October 2016

Pavlovian conditioned approach behavior can be directed as much toward discrete cues as it is toward the environmental contexts in which those cues are encountered. The current experiments characterized a tendency of rats to approach object cues whose prior exposure had been paired with reward (conditioned object preference, COP). To demonstrate the phenomenon, rats were conditioned to associate cocaine or saline with two different objects. Rats acquired a preference, assessed using investigation times directed toward each object, for the cocaine-paired object following conditioning. Furthermore, high levels of object investigation during cocaine conditioning predicted stronger preferences for the cocaine-paired object in the test phase. Conditioned approach diminished across extinction but was reinstated through a priming injection of cocaine. To determine whether preferences are affected by reward value, rats were conditioned using three objects paired with 0, 5, or 20 mg/kg of cocaine. This produced object preferences in the post-test that scaled with cocaine dose used for conditioning. Finally, we explored whether contextual cues modulate expression of COP by testing rats for renewal of cocaine seeking. When conditioning was conducted in one context and extinction training in a second context, COP was renewed when the rats were retested in the original context. Thus, conditioned object preferences are readily acquired, easily measured, and amenable to a number of standard Pavlovian conditioning manipulations. This task promises to become a valuable addition to the panoply of behavioral tools available to test mechanisms underlying adaptive and maladaptive reward processing.
Context specificity of both acquisition and extinction of a Pavlovian conditioned response
Authors: Starosta Sarah , Uengoer Metin , Bartetzko Isabelle , Lucke Sara , Güntürkün Onur , Stüttgen Maik C.
Published: October 2016

It is widely held that the extinction of a conditioned response is more context specific than its initial acquisition. One proposed explanation is that context serves to disambiguate the meaning of a stimulus. Using a procedure that equated the learning histories of the contexts, we show that the memory of an appetitive Pavlovian association can be highly context specific despite being unambiguous. This result is inconsistent with predictions of the Rescorla–Wagner model of learning but in line with configural accounts of contextual control of behavior. We propose an explanatory model in which context serves to modulate the gain of associative strength and which expands upon the configural idea of unitary representations of context and conditioned stimuli.
Photosystem II Excitation Pressure and Photosynthetic Carbon Metabolism in Chlorella vulgaris
Authors: Savitch L. V. , Maxwell D. P. , Huner NPA.
Published: October 2016

Chlorella vulgaris grown at 5[deg]C/150 [mu]mol m-2 s-1 mimics cells grown under high irradiance (27[deg]C/2200 [mu]mol m-2 s-1). This has been rationalized through the suggestion that both populations of cells were exposed to comparable photosystem II (PSII) excitation pressures measured as the chlorophyll a fluorescence quenching parameter, 1 - qP (D.P. Maxwell, S. Falk, N.P.A. Huner [1995] Plant Physiol 107: 687–694). To assess the possible role(s) of feed-back mechanisms on PSII excitation pressure, stromal and cytosolic carbon metabolism were examined. Sucrose phosphate synthase and fructose-1,6-bisphosphatase activities as well as the ratios of fructose-1,6-bisphosphate/fructose-6-phosphate and sucrose/starch indicated that cells grown at 27[deg]C/2200 [mu]mol m-2 s-1 appeared to exhibit a restriction in starch metabolism. In contrast, cells grown at 5[deg]C/150 [mu]mol m-2 s-1 appeared to exhibit a restriction in the sucrose metabolism based on decreased cytosolic fructose-1,6- bisphosphatase and sucrose phosphate synthase activities as well as a low sucrose/starch ratio. These metabolic restrictions may feed-back on photosynthetic electron transport and, thus, contribute to the observed PSII excitation pressure. We conclude that, although PSII excitation pressure may reflect redox regulation of photosynthetic acclimation to light and temperature in C. vulgaris, it cannot be considered the primary redox signal. Alternative metabolic sensing/signaling mechanisms are discussed.
The Refined Three-Dimensional Structure of Pectate Lyase E from Erwinia chrysanthemi at 2.2 A Resolution
Authors: Lietzke S. E. , Scavetta R. D. , Yoder M. D. , Jurnak F.
Published: October 2016

The crystal structure of pectate lyase E (PelE; EC 4.2.2.2) from the enterobacteria Erwinia chrysanthemi has been refined by molecular dynamics techniques to a resolution of 2.2 A and an R factor (an agreement factor between observed structure factor amplitudes) of 16.1%. The final model consists of all 355 amino acids and 157 water molecules. The root-mean-square deviation from ideality is 0.009 A for bond lengths and 1.721[deg] for bond angles. The structure of PelE bound to a lanthanum ion, which inhibits the enzymatic activity, has also been refined and compared to the metal-free protein. In addition, the structures of pectate lyase C (PelC) in the presence and absence of a lutetium ion have been refined further using an improved algorithm for identifying waters and other solvent molecules. The two putative active site regions of PelE have been compared to those in the refined structure of PelC. The analysis of the atomic details of PelE and PelC in the presence and absence of lanthanide ions provides insight into the enzymatic mechanism of pectate lyases.
Inhibition of Blue Light-Dependent H+ Pumping by Abscisic Acid in Vicia Guard-Cell Protoplasts
Authors: Goh C. H. , Kinoshita T. , Oku T. , Shimazaki Ki.
Published: October 2016

Blue-light (BL)-dependent H+ pumping in guard-cell protoplasts (GCPs) from Vicia faba was inhibited by 65% in the presence of abscisic acid (ABA). The inhibition increased with the time after application of ABA and was concentration dependent with a saturating concentration of 1 [mu]M at pH 6.2. The inhibition was nearly independent of the pH of the medium in the range 5.4 to 7.2 when ABA was applied at 10 [mu]M, whereas it was dependent on pH when the ABA concentration was decreased. The protonated form of ABA was saturating at 40 nM in inhibiting BL-dependent H+ pumping under various experimental conditions, whereas the dissociated form at 500 nM had no inhibitory effect on the pumping, suggesting that the protonated form of ABA is the form active in inhibiting the pumping. Fusicoccin (10 [mu]M), an activator of plasma membrane H+-ATPase, induced H+ pumping from GCPs, and the rate of H+ pumping was decreased to 70% by ABA. In contrast, ABA did not inhibit H+ pumping in isolated microsome vesicles from GCPs. These results suggest that the inhibition of BL-dependent H+ pumping by ABA in GCPs may be due to indirect inactivation of plasma membrane H+-ATPase and/or inhibition of the BL-signaling pathway. The pump inhibition by ABA causes membrane depolarization and can be an initial step to induce stomatal closure and reduces the transpirational water loss under drought stress in the daytime.
Phosphoenolpyruvate Carboxylase Kinase in Tobacco Leaves Is Activated by Light in a Similar but Not Identical Way as in Maize
Authors: Li B. , Zhang X. Q. , Chollet R.
Published: October 2016

We have previously reported the partial purification of a Ca2+- independent phosphoenolpyruvate carboxylase (PEPC) protein-serine/threonine kinase (PEPC-PK) from illuminated leaves of N-sufficient tobacco (Nicotiana tabacum L.) plants (Y.-H. Wang, R. Chollet [1993] FEBS Lett 328: 215–218). We now report that this C3 PEPC-kinase is reversibly light activated in vivo in a time-dependent manner. As the kinase becomes light activated, the activity and L-malate sensitivity of its target protein increases and decreases, respectively. The light activation of tobacco PEPC-PK is prevented by pretreatment of detached leaves with various photosynthesis and cytosolic protein-synthesis inhibitors. Similarly, specific inhibitors of glutamine synthetase block the light activation of tobacco leaf PEPC-kinase under both photorespiratory and nonphotorespiratory conditions. This striking effect is partially and specifically reversed by exogenous glutamine, whereas it has no apparent effect on the light activation of the maize (Zea mays L.) leaf kinase. Using an in situ “activity-gel” phosphorylation assay, we have identified two major Ca2+-independent PEPC-kinase catalytic polypeptides in illuminated tobacco leaves that have the same molecular masses (approximately 30 and 37 kD) as found in illuminated maize leaves. Collectively, these results indicate that the phosphorylation of PEPC in N-sufficient leaves of tobacco (C3) and maize (C4) is regulated through similar but not identical light-signal transduction pathways.
Association of Plant p40 Protein with Ribosomes Is Enhanced When Polyribosomes Form during Periods of Active Tissue Growth
Authors: Garcia-Hernandez M. , Davies E. , Baskin T. I. , Staswick P. E.
Published: October 2016

p40s are acidic proteins of eukaryotic cells occurring either free in the cytoplasm or in association with ribosomes, the latter occurring in both monosomes and polysomes. p40s may play a role in the regulation of protein synthesis, although the exact mechanism is not known. Leaves of all 10 plant species examined here, including both monocots and dicots, contained proteins detected on immunoblots with Arabidopsis thaliana p40 antiserum. The number and apparent size of the protein bands were variable even among closely related species. Abundance of p40 relative to ribosomal content during soybean (Glycine max L.) seed germination and during seed and leaf development was examined. p40 abundance correlated with periods of active tissue growth and high polysome content. The plant growth regulator indole acetic acid caused an increase in polysome formation in etiolated pea (Pisum sativum L.) plants and a concomitant recruitment of p40 into polysomes. Subcellular localization at the microscopy level indicated that the pattern of p40 staining is very similar to that for RNA, except that p40 is excluded from the nucleus. These data suggest that p40 is an accessory protein of the ribosome that might play a role in plant growth and development.
Freezing Characteristics of Rigid Plant Tissues (Development of Cell Tension during Extracellular Freezing)
Authors: Rajashekar C. B. , Burke M. J.
Published: October 2016

The freezing characteristics and development of cell tension during extracellular freezing were examined in supercooling stem tissues of riverbank grapes (Vitis riparia) and cold-hardened leaves of live oak (Quercus virginiana) and mountain cranberry (Vaccinium vitis-idaea). Dormant stem xylem and pith tissues of river-bank grapes were resistant to freeze-induced dehydration above the homogeneous nucleation temperature, and they developed cell tension reaching a maximum of 27 MPa. Similarly, extracellular freezing induced cell tension in the leaves of live oak and mountain cranberry. Maximum cell tension in the leaves of live oak was 16.8 MPa and 8.3 MPa in the leaves of mountain cranberry. Following peak tensions in the leaves, a decline in the pressure was observed with progressive freezing. The results suggest that resistance to cell deformation during extracellular freezing due to cell-wall rigidity can lead to reduced cell dehydration and increased cell tension. A relationship to predict freezing behavior in plant tissues based on cell rigidity is presented. Based on cell-water relations and ice nucleation rates, cell-wall rigidity has been shown to effect the freezing characteristics of plant tissues, including freeze-induced dehydration, supercooling, and homogeneous nucleation temperatures.
Specificity of the Organic Acid Activation of Alternative Oxidase in Plant Mitochondria
Authors: Millar A. H. , Hoefnagel MHN. , Day D. A. , Wiskich J. T.
Published: October 2016

The claim that succinate and malate can directly stimulate the activity of the alternative oxidase in plant mitochondria (A.M. Wagner, C.W.M. van den Bergen, H. Wincencjusz [1995] Plant Physiol 108: 1035–1042) was reinvestigated using sweet potato (Ipomoea batatas L.) mitochondria. In whole mitochondria, succinate (in the presence of malonate) and both L- and D-malate stimulated respiration via alternative oxidase in a pH- (and NAD+)-dependent manner. Solubilized malic enzyme catalyzed the oxidation of both L- and D-malate, although the latter at only a low rate and only at acid pH. In submitochondrial particle preparations with negligible malic enzyme activity, neither L- nor D-malate stimulated alternative oxidase activity. However, even in the presence of high malonate concentrations, some succinate oxidation was observed via the alternative oxidase, giving the impression of stimulation of the oxidase. Neither L-malate nor succinate (in the presence of malonate) changed the dependence of alternative oxidase activity on ubiquinone reduction state in submitochondrial particles. In contrast, a large change in this dependence was observed upon addition of pyruvate. Half-maximal stimulation of alternative oxidase by pyruvate occurred at less than 5 [mu]M in submitochondrial particles, one-twentieth of that reported for whole mitochondria, suggesting that pyruvate acts on the inside of the mitochondrion. We suggest that malate and succinate do not directly stimulate alternative oxidase, and that reports to the contrary reflect intra-mitochondrial generation of pyruvate via malic enzyme.
Ecotype-Specific Expression of a Flowering Mutant Phenotype in Arabidopsis thaliana
Authors: Sanda S. L. , Amasino R. M.
Published: October 2016

The majority of mutations that delay flowering in Arabidopsis thaliana have been identified in studies of the Landsberg erecta (Ler) ecotype. In this report we describe a gene (referred to as FLD) that, when mutated, delays flowering in the Columbia ecotype but has a minimal phenotype in the Ler genetic background. The late-flowering phenotype of fld mutants requires a non-Ler allele of another gene involved in the control of flowering time, Flowering Locus C. fld mutants retain a photoperiod response, and the flowering time of fld mutants can be reduced by cold treatment and low red/far-red light ratios.
PIP1 Aquaporins Are Concentrated in Plasmalemmasomes of Arabidopsis thaliana Mesophyll
Authors: Robinson D. G. , Sieber H. , Kammerloher W. , Schaffner A. R.
Published: October 2016

The PIP1 subfamily of water channel proteins (aquaporins) constitute about 1% of the plasma membrane (PM) proteins from Arabidopsis thaliana leaves. Immunogold electron microscopy has confirmed their localization at the PM of mesophyll cells. Very high labeling density at PM invaginations known as plasmalemmasomes was observed. Therefore, we suggest that these subcellular structures are involved in water transport between the apoplast and the vacuole.
Effect of Cold Hardening on the Components of Respiratory Decarboxylation in the Light and in the Dark in Leaves of Winter Rye
Authors: Hurry V. , Keerberg O. , Parnik T. , Oquist G. , Gardestrom P.
Published: October 2016

In the dark, all decarboxylation reactions are associated with the oxidase reactions of mitochondrial electron transport. In the light, photorespiration is also active in photosynthetic cells. In winter rye (Secale cereale L.), cold hardening resulted in a 2-fold increase in the rate of dark respiratory CO2 release from leaves compared with nonhardened (NH) controls. However, in the light, NH and cold-hardened (CH) leaves had comparable rates of oxidase decarboxylation and total intracellular decarboxylation. Furthermore, whereas CH leaves showed similar rates of total oxidase decarboxylation in the dark and light, NH leaves showed a 2-fold increase in total oxidase activity in the light compared with the dark. Light suppressed oxidase decarboxylation of end products of photosynthesis 2-fold in NH leaves and 3-fold in CH leaves in air. However, in high-CO2, light did not suppress the oxidase decarboxylation of end products. Thus, the decrease in oxidase decarboxylation of end products observed in the light and in air reflected glycolate-cycle-related inhibition of tricarboxylic acid cycle activity. We also showed that the glycolate cycle was involved in the decarboxylation of the end products of photosynthesis in both NH and CH leaves, suggesting a flow of fixed carbon out of the starch pool in the light.
Identification of Antheridiogens in Lygodium circinnatum and Lygodium flexuosum
Authors: Yamauchi T. , Oyama N. , Yamane H. , Murofushi N. , Schraudolf H. , Pour M. , Furber M. , Mander L. N.
Published: October 2016

Antheridiogens in two species of Schizaeaceous ferns, Lygodium circinnatum and Lygodium flexuosum, were analyzed by gas chromatography-mass spectrometry. In L. circinnatum, gibberellin A73 (GA73) methyl ester (GA73-Me), which had originally been identified in L. japonicum, was identified as a principal antheridiogen, and the methyl esters of five known GAs (GA9, GA20, GA70, GA88, and 3-epi-GA88) were also identified as minor antheridiogens. In addition, four compounds corresponding to isomers of monohydroxy-GA73-Me were detected. One of these was shown to be 12β-hydroxy-GA73-Me, the parent acid of which has been allocated the GA assignment GA96. The other three compounds, tentatively named X1, X2, and X3, have not been fully characterized. In L. flexuosum, GA73-Me was also identified as a major antheridiogen, with X2 being detected as a minor one. The total antheridium-formation activity in the culture medium of 7-week-old prothallia of L. circinnatum and L. flexuosum was more than 1000 times higher than that of L. japonicum. On the other hand, the response of gametophytes of the former two Lygodium ferns to GA73-Me was more than 100 times lower than that of L. japonicum.
Oxidative Stress Induces Partial Degradation of the Large Subunit of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase in Isolated Chloroplasts of Barley
Authors: Desimone M. , Henke A. , Wagner E.
Published: October 2016

The effects of oxidative stress on the degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were studied in isolated chloroplasts from barley (Hordeum vulgare L. cv Angora). Active oxygen (AO) was generated by varying the light intensity, the oxygen concentration, or the addition of herbicides or ADP-FeCl3-ascorbate to the medium. Oxidative treatments stimulated association of Rubisco with the insoluble fraction of chloroplasts and partial proteolysis of the large subunit (LSU). The most prominent degradation product of the LSU of Rubisco showed an apparent molecular mass of 36 kD. The data suggest that an increase in the amount of AO photogenerated by O2 reduction at photosystem I triggers Rubisco degradation. A possible relationship between AO-mediated denaturation of Rubisco and proteolysis of the LSU is discussed.
Chloroplast Movement in the Shade Plant Tradescantia albiflora Helps Protect Photosystem II against Light Stress
Authors: Park Y. I. , Chow W. S. , Anderson J. M.
Published: October 2016

The role of high-light-induced chloroplast movement in the photoprotection of the facultative shade plant Tradescantia albiflora was investigated by comparison with pea (Pisum sativum L.) leaves, both grown in 50 [mu]mol photons m-2 s-1. Photoinactivation of photosystem II (PSII) in vivo was induced in 1.1% CO2 by varying either duration (0–2 h) of illumination (fixed at 1800 [mu]mol m-2 s-1) or irradiance (0–3000 [mu]mol m-2 s-1) at a fixed duration (1 h) after infiltration of leaves with water or lincomycin (an inhibitor of chloroplast-encoded protein synthesis). At all photon exposures, PSII of T. albiflora leaves showed a greater resistance to light stress than pea leaves, although both utilization of absorbed light by photosynthesis and psbA gene product synthesis were smaller than for pea leaves. This greater tolerance was not due to differences in PSII antenna size or the index of susceptibility of PSII to light stress, because these two parameters were comparable in both plants. However, the transmittance increase mediated by chloroplast movement was greater in T. albiflora than pea, resulting in a 10% decrease of absorbed light at high light. We suggest that the greater tolerance of PSII against light stress in T. albiflora may be partly ascribed to its light-induced chloroplast rearrangement.
Relationship between Active Oxygen Species, Lipid Peroxidation, Necrosis, and Phytoalexin Production Induced by Elicitins in Nicotiana
Authors: Rusterucci C. , Stallaert V. , Milat M. L. , Pugin A. , Ricci P. , Blein J. P.
Published: October 2016

Excised leaves of Nicotiana tabacum var Xanthi and Nicotiana rustica were treated with cryptogein and capsicein, basic and acidic elicitins, respectively. Both compounds induced leaf necrosis, the intensity of which depended on concentration and duration of treatment. N. tabacum var Xanthi was the most sensitive species and cryptogein was the most active elicitin. Lipid peroxidation in elicitin-treated Nicotiana leaves was closely correlated with the appearance of necrosis. Elicitin treatments induced a rapid and transient burst of active oxygen species (AOS) in cell cultures of both Nicotiana species, with the production by Xanthi cells being 6-fold greater than that by N. rustica. Similar maximum AOS production levels were observed with both elicitins, but capsicein required 10-fold higher concentrations than those of cryptogein. Phytoalexin production was lower in response to both elicitins in N. tabacum var Xanthi cells than in N. rustica cells, and capsicein was the most efficient elicitor of this response. In cryptogein-treated cell suspensions, phytoalexin synthesis was unaffected by diphenyleneiodonium, which inhibited AOS generation, nor was it affected by tiron or catalase, which suppressed AOS accumulation in the extracellular medium. These results suggest that AOS production, lipid peroxidation, and necrosis are directly related, whereas phytoalexin production depends on neither the presence nor the intensity of these responses.
Changes in Dehydrodiferulic Acids and Peroxidase Activity against Ferulic Acid Associated with Cell Walls during Growth of Pinus pinaster Hypocotyl
Authors: Sanchez M. , Pena M. J. , Revilla G. , Zarra I.
Published: October 2016

Hydroxycinnamic acids associated with hypocotyl cell walls of dark-grown seedlings of Pinus pinaster Aiton were extracted with 1 N NaOH and identified by gas chromatography-mass spectrometry. The main hydroxycinnamic acid found was ferulic acid. Diferulic acid dehydrodimers were also found, with the 8,8-coupled isomer (compound 11) being the dehydrodiferulate present in the highest amount. However, the 5,5-coupled isomer, commonly referred to referred to as diferulic acid, was not detected. Two truxillic acids, 4–4[prime]-dihydroxy-3–3[prime]-dimethoxy-α--truxillic acids I and II, were tentatively identified. The 8,8-coupled dehydrodiferulic acid (compound 11) was the phenolic acid that showed the most conspicuous changes with hypocotyl age as well as along the hypocotyl axis. Peroxidase activity against ferulic acid was found in the apoplastic fluid as well as being ionically and covalently bound to the cell walls. The peroxidase activity increased with hypocotyl age as well as from the subapical toward the basal region of the hypocotyls. A key role in the cell-wall stiffening of 8,8 but not 5,5 dimerization of ferulic acid catalyzed by cell-wall peroxidases is proposed.
Biphasic Temporal and Spatial Induction Patterns of Defense-Related mRNAs and Proteins in Fungus-Infected Parsley Leaves
Authors: Reinold S. , Hahlbrock K.
Published: October 2016

Previous experiments using in situ RNA hybridization have shown that the mRNAs encoding phenylalanine ammonia-lyase, 4-coumarate:coenzyme A ligase, and pathogenesis-related protein 1 accumulated transiently around fungal infection sites in parsley (Petroselinum crispum) leaf buds. These studies have now been extended by (a) analyzing different stages of the infection process and (b) monitoring the timing of appearance and the spatial distribution of the proteins as well as the corresponding mRNAs. An early and short period of mRNA induction throughout a large portion of the infected leaf was followed by a longer period, during which the mRNA levels remained high in a more localized area around the site of fungal penetration with sharp borders toward the surrounding tissue. This biphasic pattern of mRNA accumulation was followed after some delay by the same pattern of protein accumulation.
Light-Dependent Isoprene Emission (Characterization of a Thylakoid-Bound Isoprene Synthase in Salix discolor Chloroplasts)
Authors: Wildermuth M. C. , Fall R.
Published: October 2016

Isoprene synthase is an enzyme that is responsible for the production of the volatile C5 hydrocarbon, isoprene, in plant leaves. Isoprene formation in numerous C3 plants is interesting because (a) large quantities of isoprene are emitted, 5 x 1014 g of C annually, (b) a plant may release 1 to 8% of its fixed C as isoprene, and (c) the function of plant isoprene production is unknown. Because of the dependence of foliar isoprene emission on light, the existence of a plastidic isoprene synthase has been postulated. To pursue this idea, a method to isolate chloroplasts from Salix discolor was developed and shows a plastidic isoprene synthase that is tightly bound to the thylakoid membrane and accessible to trypsin inactivation. The thylakoid-bound isoprene synthase has catalytic properties similar to known soluble isoprene synthases; however, the relationship between these enzymes is unknown. The discovery of a thylakoid-bound isoprene synthase with a stromal-facing domain places it in the chloroplast, where it may be subject to numerous direct and indirect light-mediated effects. Implications for the light-dependent regulation of foliar isoprene production and its function are presented.
Aluminum Tolerance Acquired during Phosphate Starvation in Cultured Tobacco Cells
Authors: Yamamoto Y. , Masamoto K. , Rikiishi S. , Hachiya A. , Yamaguchi Y. , Matsumoto H.
Published: October 2016

Al toxicity in cultured tobacco cells (Nicotiana tabacum L. cv Samsun; nonchlorophyllic cell line SL) has been investigated in nutrient medium. In this system, Al and Fe(II) (ferrous ion) in the medium synergistically result in the accumulation of both Al and Fe, the peroxidation of lipids, and eventually death in cells at the logarithmic phase of growth (+P cells). A lipophilic antioxidant, N,N[prime]-diphenyl-p-phenylenediamine, protected +P cells from the peroxidation of lipids and from cell death, suggesting that a relationship exists between the two. Compared with +P cells, cells that had been starved of Pi (-P cells) were more tolerant to Al, accumulated 30 to 40% less Al and 70 to 90% less Fe, and did not show any evidence of the peroxidation of lipids during Al treatment. These results suggest that -P cells exhibit Al tolerance because their plasma membranes are protected from the peroxidation of lipids caused by the combination of Al and Fe(II). It seems likely that the exclusion of Fe from -P cells might suppress directly Fe-mediated peroxidation of lipids. Furthermore, since -P cells accumulated β-carotene, it is proposed that this carotenoid pigment might function as a radical-trapping antioxidant in the plasma membrane of cells starved of Pi.
Stomatal Closure in Flooded Tomato Plants Involves Abscisic Acid and a Chemically Unidentified Anti-Transpirant in Xylem Sap
Authors: Else M. A. , Tiekstra A. E. , Croker S. J. , Davies W. J. , Jackson M. B.
Published: October 2016

We address the question of how soil flooding closes stomata of tomato (Lycopersicon esculentum Mill. cv Ailsa Craig) plants within a few hours in the absence of leaf water deficits. Three hypotheses to explain this were tested, namely that (a) flooding increases abscisic acid (ABA) export in xylem sap from roots, (b) flooding increases ABA synthesis and export from older to younger leaves, and (c) flooding promotes accumulation of ABA within foliage because of reduced export. Hypothesis a was rejected because delivery of ABA from flooded roots in xylem sap decreased. Hypothesis b was rejected because older leaves neither supplied younger leaves with ABA nor influenced their stomata. Limited support was obtained for hypothesis c. Heat girdling of petioles inhibited phloem export and mimicked flooding by decreasing export of [14C]sucrose, increasing bulk ABA, and closing stomata without leaf water deficits. However, in flooded plants bulk leaf ABA did not increase until after stomata began to close. Later, ABA declined, even though stomata remained closed. Commelina communis L. epidermal strip bioassays showed that xylem sap from roots of flooded tomato plants contained an unknown factor that promoted stomatal closure, but it was not ABA. This may be a root-sourced positive message that closes stomata in flooded tomato plants.
Nitrogen and Carbon Flows Estimated by 15N and 13C Pulse-Chase Labeling during Regrowth of Alfalfa
Authors: Avice J. C. , Ourry A. , Lemaire G. , Boucaud J.
Published: October 2016

The flow of 15N and 13C from storage compounds in organs remaining after defoliation (sources) to regrowing tissue (sinks), and 13C losses through root or shoot respiration were assessed by pulse-chase labeling during regrowth of alfalfa (Medicago sativa L.) following shoot removal. A total of 73% of labeled C and 34% of labeled N were mobilized in source organs within 30 d. Although all of the 15N from source organs was recovered in the regrowing tissue, much of the 13C was lost, mainly as CO2 respired from the root (61%) or shoot (8%), and was found to a lesser extent in sink tissue (5%). After 3, 10, or 30 d of regrowth, 87, 66, and 52% of shoot N, respectively, was derived from source tissue storage compounds; the rest resulted from translocation of fixed N2. Overall results suggest that most shoot C was linked to photosynthetic activity rather than being derived from mobilization of stored C in source organs. Furthermore, isotopic analysis of different chemical fractions of plant tissue suggests that between 14 and 58% of the shoot C derived from source tissues was linked to the mobilization of N compounds, not carbohydrates.
Patterns of Carbon Partitioning in Leaves of Crassulacean Acid Metabolism Species during Deacidification
Authors: Christopher J. T. , Holtum JAM.
Published: October 2016

Carbohydrates stored during deacidification in the light were examined in 11 Crassulacean acid metabolism (CAM) species from widely separated taxa grown under uniform conditions. The hypothesis that NAD(P) malic enzyme CAM species store chloroplastic starch and glucans, and phosphoenolpyruvate carboxykinase species store extrachloroplastic sugars or polymers was disproved. Of the six malic enzyme species examined, Kalanchoe tubiflora, Kalanchoe pinnata, Kalanchoe daigremontiana, and Vanilla planifolia stored mainly starch. Sansevieria hahnii stored sucrose and Agave guadalajarana did not store starch, glucose, fructose, or sucrose. Of the five phosphoenolpyruvate carboxykinase species investigated, Ananus comosus stored extrachloroplastic carbohydrate, but Stapelia gigantea, Hoya carnosa, and Portea petropolitana stored starch, whereas Aloe vera stored both starch and glucose. Within families, the major decarboxylase was common for all species examined, whereas storage carbohydrate could differ both between and within genera. In the Bromeliaceae, A. comosus stored mainly fructose, but P. petropolitana stored starch. In the genus Aloe, A. vera stored starch and glucose, but A. arborescens is known to store a galactomannan polymer. We postulate that the observed variation in carbohydrate partitioning between CAM species is the result of two principal components: (a) constraints imposed by the CAM syndrome itself, and (b) diversity in biochemistry resulting from different evolutionary histories.
Leaf Abscission Induced by Ethylene in Water-Stressed Intact Seedlings of Cleopatra Mandarin Requires Previous Abscisic Acid Accumulation in Roots
Authors: Gomez-Cadenas A. , Tadeo F. R. , Talon M. , Primo-Millo E.
Published: October 2016

The involvement of abscisic acid (ABA) in the process of leaf abscission induced by 1-aminocyclopropane-1-carboxylic acid (ACC) transported from roots to shoots in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings grown under water stress was studied using norflurazon (NF). Water stress induced both ABA (24-fold) and ACC (16-fold) accumulation in roots and arrested xylem flow. Leaf bulk ABA also increased (8-fold), although leaf abscission did not occur. Shortly after rehydration, root ABA and ACC returned to their prestress levels, whereas sharp and transitory increases of ACC (17-fold) and ethylene (10-fold) in leaves and high percentages of abscission (up to 47%) were observed. NF suppressed the ABA and ACC accumulation induced by water stress in roots and the sharp increases of ACC and ethylene observed after rewatering in leaves. NF also reduced leaf abscission (7-10%). These results indicate that water stress induces root ABA accumulation and that this is required for the process of leaf abscission to occur. It was also shown that exogenous ABA increases ACC levels in roots but not in leaves. Collectively, the data suggest that ABA, the primary sensitive signal to water stress, modulates the levels of ethylene, which is the hormonal activator of leaf abscission. This assumption implies that root ACC levels are correlated with root ABA amounts in a dependent way, which eventually links water status to an adequate, protective response such as leaf abscission.
Ethoxyzolamide Differentially Inhibits CO2 Uptake and Na+-Independent and Na+-Dependent HCO3- Uptake in the Cyanobacterium Synechococcus sp. UTEX 625
Authors: Tyrrell P. N. , Kandasamy R. A. , Crotty C. M. , Espie G. S.
Published: October 2016

The effects of ethoxyzolamide (EZ), a carbonic anhydrase inhibitor, on the active CO2 and Na+-independent and Na+-dependent HCO3- transport systems of the unicellular cyanobacterium Synechococcus sp. UTEX 625 were examined. Measurements of transport and accumulation using radiochemical, fluorometric, and mass spectrometric assays indicated that active CO2 transport and active Na+-independent HCO3- transport were inhibited by EZ. However, Na+-independent HCO3- transport was about 1 order of magnitude more sensitive to EZ inhibition than was CO2 transport (50% inhibition = 12 [mu]M versus 80 [mu]M). The data suggest that both the active CO2 (G.D. Price, M.R. Badger [1989] Plant Physiol 89: 37–43) and the Na+ -independent HCO3 - transport systems possessed carbonic anhydrase-like activity as part of their mechanism of action. In contrast, Na+-dependent HCO3- transport was only partially (50% inhibition = 230 [mu]M) and noncompetitively inhibited by EZ. The collective evidence suggested that EZ inhibition of Na+ -dependent HCO3- transport was an indirect consequence of the action of EZ on the CO2 transport system, rather than a direct effect on HCO3- transport. A model is presented in which the core of the inorganic carbon translocating system is formed by Na+-dependent HCO3- transport and the CO2 transport system. It is argued that the Na+-independent HCO3 - utilizing system was not directly involved in translocation, but converted HCO3- to CO2 for use in CO2 transport.