bluuebunny/crossref_metadata_2025 huggingface dataset:
Putrescine Aminopropyltransferase Is Responsible for Biosynthesis of Spermidine, Spermine, and Multiple Uncommon Polyamines in Osmotic Stress-Tolerant Alfalfa
Authors: Bagga S. , Rochford J. , Klaene Z. , Kuehn G. D. , Phillips G. C.
Published: October 2016

The biosynthesis of polyamines from the diamine putrescine is not fully understood in higher plants. A putrescine aminopropyltransferase (PAPT) enzyme activity was characterized in alfalfa (Medicago sativa L.). This enzyme activity was highly specific for putrescine as the initial substrate and did not recognize another common diamine, 1,3-diaminopropane, or higher-molecular-weight polyamines such as spermidine and spermine as alternative initial substrates. The enzyme activity was inhibited by a general inhibitor of aminopropyltransferases, 5[prime]-methylthioadenosine, and by a specific inhibitor of PAPTs, cyclohexylammonium sulfate. The initial substrate specificity and inhibition characteristics of the enzyme activity suggested that it is a classical example of a PAPT. However, this enzyme activity yielded multiple polyamine products, which is uncharacteristic of PAPTs. The major reaction product of PAPT activity in alfalfa was spermidine. The next most abundant products of the enzyme reaction using putrescine as the initial substrate included the tetramines spermine and thermospermine. These two tetramines were distinguished by thin-layer chromatography to be distinct reaction products exhibiting differential rates of formation. In addition, the uncommon polyamines homocaldopentamine and homocaldohexamine were tentatively identified as minor enzymatic reaction products but only in extracts prepared from osmotic stresstolerant alfalfa cultivars. PAPT activity from alfalfa was highest in meristematic shoot tip and floral bud tissues and was not detected in older, nonmeristematic tissues. Product inhibition of the enzyme activity was observed after spermidine was added into the in vitro assay for alfalfa PAPT activity. A biosynthetic pathway is proposed that accounts for the characteristics of this PAPT activity and accommodates a novel scheme by which certain uncommon polyamines are produced in plants.
Cold Acclimation and Freezing Tolerance (A Complex Interaction of Light and Temperature)
Authors: Gray G. R. , Chauvin L. P. , Sarhan F. , Huner NPA.
Published: October 2016

By comparing growth under five different temperature and irradiance regimes (20[deg]C and 800, 250, and 50[mu]mol m-2 s-1 and 5[deg]C and 250 and 50 [mu]mul m-2 s-1), we have examined the effects of light, temperature, and the relative reduction state of photosystem II on plant morphology, freezing tolerance (lethal temperature at which freezing injury occurs [LT50]), transcript levels of Lhcb and two cold-stimulated genes (Wcs19 and Wcs120), and photosynthetic adjustment in winter rye (Secale cereale L. cv Musketeer). We show, for the first time to our knowledge, that in addition to adjustments in photosynthetic capacity, nonphotochemical quenching capacity and tolerance to photoinhibition, the accumulation of the cold-induced transcript Wcs19, and the compact plant morphology usually associated with cold-hardening are correlated with the relative reduction state of photosystem II rather than with growth temperature or growth irradiance per se. In contrast, the acquisition of maximal LT50, as well as Lhcb and Wcs120 mRNA accumulation, appears to be dependent on both growth temperature and growth irradiance but in an independent, additive manner. The results are discussed with respect to the possible role of the modulation of chloroplastic redox poise in photosynthetic acclimation to cold-hardening temperatures and the attainment of maximal LT50.
Decreased Growth-Induced Water Potential (A Primary Cause of Growth Inhibition at Low Water Potentials)
Authors: Nonami H. , Wu Y. , Boyer J. S.
Published: October 2016

Cell enlargement depends on a growth-induced difference in water potential to move water into the cells. Water deficits decrease this potential difference and inhibit growth. To investigate whether the decrease causes the growth inhibition, pressure was applied to the roots of soybean (Glycine max L. Merr.) seedlings and the growth and potential difference were monitored in the stems. In water-limited plants, the inhibited stem growth increased when the roots were pressurized and it reverted to the previous rate when the pressure was released. The pressure around the roots was perceived as an increased turgor in the stem in small cells next to the xylem, but not in outlying cortical cells. This local effect implied that water transport was impeded by the small cells. The diffusivity for water was much less in the small cells than in the outlying cells. The small cells thus were a barrier that caused the growth-induced potential difference to be large during rapid growth, but to reverse locally during the early part of a water deficit. Such a barrier may be a frequent property of meristems. Because stem growth responded to the pressure-induced recovery of the potential difference across this barrier, we conclude that a decrease in the growth-induced potential difference was a primary cause of the inhibition.
Physiological and Biochemical Response of the Photosynthetic Apparatus of Two Marine Diatoms to Fe Stress
Authors: McKay R. M. L. , Geider R. J. , LaRoche J.
Published: October 2016

Flavodoxin is a small electron-transfer protein capable of replacing ferredoxin during periods of Fe deficiency. When evaluating the suitability of flavodoxin as a diagnostic indicator for Fe limitation of phytoplankton growth, we examined its expression in two marine diatoms we cultured using trace-metal-buffered medium. Thalassio-sira weissflogii and Phaeodactylum tricornutum were cultured in ethylenediaminetetraacetic acid-buffered Sargasso Sea water containing from 10 to 1000 nM added Fe. Trace-metal-buffered cultures of each diatom maintained high growth rates across the entire range of Fe additions. Similarly, declines in chlorophyll/cell and in the ratio of photosystem II variable-to-maximum fluorescence were negligible (P. tricornutum) to moderate (T. weissflogii; 54% decline in chlorophyll/cell and 22% decrease in variable-to-maximum fluorescence). Moreover, only minor variations in photosynthetic parameters were observed across the range of additions. In contrast, flavodoxin was expressed to high levels in low-Fe cultures. Despite the inverse relationship between flavodoxin expression and Fe content of the medium, its expression was seemingly independent of any of the indicators of cell physiology that were assayed. It appears that flavodoxin is expressed as an early-stage response to Fe stress and that its accumulation need not be intimately connected to limitations imposed by Fe on the growth rate of these diatoms.
Differential Induction of Lipoxygenase Isoforms in Wheat upon Treatment with Rust Fungus Elicitor, Chitin Oligosaccharides, Chitosan, and Methyl Jasmonate
Authors: Bohland C. , Balkenhohl T. , Loers G. , Feussner I. , Grambow H. J.
Published: October 2016

A glycopeptide elicitor prepared from germ tubes of the rust fungus Puccinia graminis Pers. f. sp. tritici Erikss. & Henn (Pgt), as well as chitin oligosaccharides, chitosan, and methyl jasmonate (MJ) stimulated lipoxygenase (LOX) activity (E.C. 1.13.11.12) in wheat (Triticum aestivum) leaves. Immunoblot analysis using anti-LOX antibodies revealed the induction of 92- and 103-kD LOX species after Pgt elicitor treatment. In contrast, MJ treatment led to a significant increase of a 100-kD LOX species, which was also detected at lower levels in control plants. The effects of chitin oligomers and chitosan resembled those caused by MJ. In conjunction with other observations the results suggest that separate reaction cascades exist, and that jasmonates may not be involved in Pgt elicitor action. LOX-92 appears to be mainly responsible for the increase in LOX activity after Pgt elicitor treatment because its appearance on western blots coincided with high LOX activity in distinct anion-exchange chromatography fractions. It is most active at pH 5.5 to 6.0, and product formation from linoleic and α--linolenic acid is clearly in favor of the 9-LOOHs. It is interesting that a 92-kD LOX species, which seems to correspond to the Pgt elicitor-induced LOX species, was also detected in rust-inoculated leaves.
Evidence That a Malate/Inorganic Phosphate Exchange Translocator Imports Carbon across the Leucoplast Envelope for Fatty Acid Synthesis in Developing Castor Seed Endosperm
Authors: Eastmond P. J. , Dennis D. T. , Rawsthorne S.
Published: October 2016

In this study we examined the processes by which malate and pyruvate are taken up across the leucoplast envelope for fatty acid synthesis in developing castor (Ricinus communis L.) seed endosperm. Malate was taken up by isolated leucoplasts with a concentration dependence indicative of protein-mediated transport. The maximum rate of malate uptake was 704 [plus or minus] 41 nmol mg-1 protein h-1 and the Km was 0.62 [plus or minus] 0.08 mM. In contrast, the rate of pyruvate uptake increased linearly with respect to the substrate concentration and was 5-fold less than malate at a concentration of 5 mM. Malate uptake was inhibited by inorganic phosphate (Pi), glutamate, malonate, succinate, 2-oxoglutarate, and n-butyl malonate, an inhibitor of the mitochondrial malate/Pi-exchange translocator. Back-exchange experiments confirmed that malate was taken up by leucoplasts in counterexchange for Pi. The exchange stoichiometry was 1:1. The rate of malate-dependent fatty acid synthesis by isolated leucoplasts was 3-fold greater than from pyruvate at a concentration of 5 mM and was inhibited by n-butyl malonate. It is proposed that leucoplasts from developing castor endosperm contain a malate/Pi translocator that imports malate for fatty acid synthesis. This type of dicarboxylate transport activity has not been identified previously in plastids.
Biochemical Characterization and Subcellular Localization of the Red Kidney Bean Purple Acid Phosphatase
Authors: Cashikar A. G. , Kumaresan R. , Rao N. M.
Published: October 2016

Phosphatases are known to play a crucial role in phosphate turnover in plants. However, the exact role of acid phosphatases in plants has been elusive because of insufficient knowledge of their in vivo substrate and subcellular localization. We investigated the biochemical properties of a purple acid phosphatase isolated from red kidney bean (Phaseolus vulgaris) (KBPAP) with respect to its substrate and inhibitor profiles. The kinetic parameters were estimated for five substrates. We used 31P nuclear magnetic resonance to investigate the in vivo substrate of KBPAP. Chemical and enzymological estimation of polyphosphates and ATP, respectively, indicated the absence of polyphosphates and the presence of ATP in trace amounts in the seed extracts. Immunolocalization using antibodies raised against KBPAP was unsuccessful because of the non-specificity of the antiserum toward glycoproteins. Using histoenzymological methods with ATP as a substrate, we could localize KBPAP exclusively in the cell walls of the peripheral two to three rows of cells in the cotyledons. KBPAP activity was not detected in the embryo. In vitro experiments indicated that pectin, a major component of the cell wall, significantly altered the kinetic properties of KBPAP. The substrate profile and localization suggest that KBPAP may have a role in mobilizing organic phosphates in the soil during germination.
Characterization of Antisense Transformed Plants Deficient in the Tobacco Anionic Peroxidase
Authors: Lagrimini L. M. , Gingas V. , Finger F. , Rothstein S. , Liu TTY.
Published: October 2016

On the basis of the biological compounds that they metabolize, plant peroxidases have long been implicated in plant growth, cell wall biogenesis, lignification, and host defenses. Transgenic tobacco (Nicotiana tabacum L.) plants that underexpress anionic peroxidase were generated using antisense RNA. The antisense RNA was found to be specific for the anionic isoenzyme and highly effective, reducing endogenous transcript levels and total peroxidase activity by as much as 1600-fold. Antisense-transformed plants appeared normal at initial observation; however, growth studies showed that plants with reduced peroxidase activity grow taller and flower sooner than control plants. In contrast, previously transformed plants overproducing anionic peroxidase were shorter and flowered later than controls. Axillary buds were more developed in antisense-transformed plants and less developed in plants overproducing this enzyme. It was found that the lignin content in leaf, stem, and root was unchanged in antisense-transformed plants, which does not support a role for anionic peroxidase in the lignification of secondary xylem vessels. However, studies of wounded tissue show some reduction in wound-induced deposition of lignin-like polymers. The data support a possible role for tobacco anionic peroxidase in host defenses but not without a reduction in growth potential.
Role of Catalase in Inducing Chilling Tolerance in Pre-Emergent Maize Seedlings
Authors: Prasad T. K.
Published: October 2016

The mechanisms of chilling acclimation and the role of antioxidant enzymes, catalase in particular, in inducing chilling tolerance in pre-emergent maize (Zea mays L.) seedlings have been investigated. Seedlings were acclimated to chilling stress in two different ways. Three-day-old seedlings did not survive 7 d of 4[deg]C stress unless acclimated by exposure to either 14[deg]C for 1 d or 4[deg]C for 1 d followed by recovery at 27[deg]C for 1 d. Although no changes in superoxide dismutase and ascorbate peroxidase activities were observed, both kinds of acclimated seedlings had higher catalase (CAT), glutathione reductase, and guaiacol peroxidase activities compared with nonacclimated seedlings during low-temperature stress and recovery conditions. To study the role of CAT in chilling tolerance, aminotriazole (AT) was used as a tool to artificially inhibit CAT activity and to initiate oxidative stress in the seedlings. Treatment of acclimating seedlings with 3 mM AT for 18 h abolished the acclimation phenomenon. AT treatment was found to be specific to CAT inhibition, because the total activities or isozyme profiles of the other investigated antioxidant enzymes were not altered in AT-treated seedlings. Protein carbonyl content, an indication of oxidative damage, was increased 2-fold in nonacclimated and AT-treated acclimated seedlings. These results collectively indicate that acclimation to prolonged chilling stress can be achieved by briefly pre-exposing the seedlings to 4[deg]C chilling stress and that acclimation-induced (oxidative stress-induced) CAT seems to play a major role, probably along with other antioxidant enzymes, in inducing chilling tolerance in pre-emergent maize seedlings.
Cell Wall Metabolism in Ripening Fruit (IX. Synthesis of Pectic and Hemicellulosic Cell Wall Polymers in the Outer Pericarp of Mature Green Tomatoes (cv XMT-22)
Authors: Huysamer M. , Greve L. C. , Labavitch J. M.
Published: October 2016

Discs of outer pericarp were excised from mature green tomato (Lycopersicon esculentum Mill.) fruit and kept in sterile tissue culture plates for 4 d, including 2 d of incubation with D-[U-13C]glucose. Cell walls were prepared and the water-soluble, pectic, and hemicellulosic polymers were extracted. Cell wall synthetic capacity was determined by gas chromatography-mass spectrometry analysis of incorporation of the heavy isotope label. The $#x201C;outer$#x201D; 2-mm pericarp region, which included the cuticle, had a lower cell wall synthetic capacity than the $#x201C;inner$#x201D; 2-mm region immediately below it (closer to the locules), based on the percentage of labeling of the neutral sugars. There were no significant differences in relative abundance of glycosidic linkages in the two tissue regions. Label was incorporated into neutral sugars and linkages typical for each polysaccharide class were identified in the cell wall preparations. Galacturonic acid and glucuronic acid were labeled to an extent similar to that of the neutral sugars in each tissue region.
Seed and Hormonal Regulation of Gibberellin 20-Oxidase Expression in Pea Pericarp
Authors: van Huizen R. , Ozga J. A. , Reinecke D. M.
Published: October 2016

To understand further how seeds, auxin (4-chloroindole-3-acetic acid [4-Cl-IAA]), and gibberellins (GAs) regulate GA biosynthesis in pea (Pisum sativum L.) pericarp at the molecular level, we studied the expression of GA 20-oxidase in this tissue using northern-blot analysis. Pericarp GA 20-oxidase mRNA levels were highest from prepollination (-2 d after anthesis [DAA]) through anthesis (0 DAA), then decreased 3-fold by 2 DAA, and remained at these levels through 6 DAA. The effects of seeds and hormones (4-Cl-IAA and GA3) on the expression of GA 20-oxidase in pea pericarp were investigated over a 36-h treatment period. GA 20-oxidase mRNA levels in 2 DAA pericarp with seeds remained relatively stable throughout the treatment period; however, when the seeds were removed the pericarp transcript levels declined. When 2 DAA deseeded pericarps were treated with 4-Cl-IAA, a significant increase in GA 20-oxidase mRNA levels was detected within 2 h and transcript levels remained elevated for up to 12 h after 4-Cl-IAA application. GA3 significantly decreased GA 20-oxidase mRNA levels in deseeded pericarp within 2 h of application. These data suggest that the previously reported conversion of GA19 to GA20 in pea pericarp is controlled by seeds, 4-Cl-IAA, and GA3 at least in part by regulating GA 20-oxidase mRNA levels in this tissue.
Physical and Kinetic Evidence for an Association between Sucrose-Phosphate Synthase and Sucrose-Phosphate Phosphatase
Authors: Echeverria E. , Salvucci M. E. , Gonzalez P. , Paris G. , Salerno G.
Published: October 2016

The possible formation of a multienzyme complex between sucrose (Suc)-phosphate synthase (SPS) and Suc-phosphate phosphatase (SPP) was examined by measuring the rates of Suc-6-phosphate (Suc-6-P) synthesis and hydrolysis in mixing experiments with partially purified enzymes from spinach (Spinacia oleracea) and rice (Oryza sativa) leaves. The addition of SPP to SPS stimulated the rate of Suc-6-P synthesis. SPS inhibited the hydrolysis of exogenous Suc-6-P by SPP when added in the absence of its substrate (i.e. UDP-glucose) but stimulated SPP activity when the SPS substrates were present and used to generate Suc-6-P directly in the reaction. Results from isotope-dilution experiments suggest that Suc-6-P was channeled between SPS and SPP. A portion of the SPS activity comigrated with SPP during native polyacrylamide gel electrophoresis, providing physical evidence for an enzyme-enzyme interaction. Taken together, these results strongly suggest that SPS and SPP associate to form a multienzyme complex.
Reduced Lignin Content and Altered Lignin Composition in Transgenic Tobacco Down-Regulated in Expression of L-Phenylalanine Ammonia-Lyase or Cinnamate 4-Hydroxylase
Authors: Sewalt VJH. , Ni W. , Blount J. W. , Jung H. G. , Masoud S. A. , Howles P. A. , Lamb C. , Dixon R. A.
Published: October 2016

We analyzed lignin content and composition in transgenic tobacco (Nicotiana tabacum) lines altered in the expression of the early phenylpropanoid biosynthetic enzymes L-phenylalanine ammonia-lyase and cinnamate 4-hydroxylase (C4H). The reduction of C4H activity by antisense expression or sense suppression resulted in reduced levels of Klason lignin, accompanied by a decreased syringyl/guaiacyl monomer ratio as determined by pyrolysis gas chromatography/mass spectrometry Similar reduction of lignin levels by down -regulation of L-phenylalanine ammonia-lyase, the enzyme preceding C4H in the central phenylpropanoid pathway, did not result in a decreased syringyl/guaiacyl ratio. Rather, analysis of lignin methoxyl content and pyrolysis suggested an increased syringyl/guaiacyl ratio. One possible explanation of these results is that monolignol biosynthesis from L-phenylalanine might occur by more than one route, even at the early stages of the core phenylpropanoid pathway, prior to the formation of specific monolignol precursors.
Antisense Repression of Both ADP-Glucose Pyrophosphorylase and Triose Phosphate Translocator Modifies Carbohydrate Partitioning in Potato Leaves
Authors: Hattenbach A. , Muller-Rober B. , Nast G. , Heineke D.
Published: October 2016

Previous experiments have shown that carbohydrate partitioning in leaves of potato (Solanum tuberosum L.) plants can be modified by antisense repression of the triose phosphate translocator (TPT), favoring starch accumulation during the light period, or by leaf-specific antisense repression of ADP-glucose pyrophosphorylase (AGPase), reducing leaf starch content. These experiments showed that starch and sucrose synthesis can partially replace each other. To determine how leaf metabolism acclimates to an inhibition of both pathways, transgenic potato (S. tuberosum L. cv Desiree) plants, with a 30% reduction of the TPT achieved by antisense repression, were transformed with an antisense cDNA of the small subunit of AGPase, driven by the leaf-specific ST-LS1 promoter. These double-transformed plants were analyzed with respect to their carbohydrate metabolism, and starch accumulation was reduced in all lines of these plants. In one line with a 50% reduction of AGPase activity, the rate of CO2 assimilation was unaltered. In these plants the stromal level of triose phosphate was increased, enabling a high rate of triose phosphate export in spite of the reduction of the TPT protein by antisense repression. In a second line with a 95% reduction of AGPase activity, the amount of chlorophyll was significantly reduced as a consequence of the lowered triose phosphate utilization capacity.
Mannitol Protects against Oxidation by Hydroxyl Radicals
Authors: Shen B. , Jensen R. G. , Bohnert H. J.
Published: October 2016

Hydroxyl radicals may be responsible for oxidative damage during drought or chilling stress. We have shown that the presence of mannitol in chloroplasts can protect plants against oxidative damage by hydroxyl radicals (B. Shen, R.G. Jensen, H.J. Bohnert [1997] Plant Physiol 113: 1177–1183). Here we identify one of the target enzymes that may be protected by mannitol. Isolated thylakoids in the presence of physiological concentrations of Fe2+ generated hydroxyl radicals that were detected by the conversion of phenylalanine into tyrosine. The activity of phosphoribulokinase (PRK), a thiol-regulated enzyme of the Calvin cycle, was reduced by 65% in illuminated thylakoids producing hydroxyl radicals. Mannitol (125 mM) and sodium formate (15 mM), both hydroxyl radical scavengers, and catalase (3000 units mL-1) prevented loss of PRK activity. In contrast, superoxide dismutase (300 units mL-1) and glycine betaine (125 mM) were not effective in protecting PRK against oxidative inactivation. Ribulose-1,5-bisphosphate carboxylase/oxygenase activity was not affected by hydroxyl radicals. We suggest that the stress-protective role of mannitol may be to shield susceptible thiol-regulated enzymes like PRK plus thioredoxin, ferredoxin, and glutathione from inactivation by hydroxyl radicals in plants.
Impacts of CO2 Enrichment on Productivity and Light Requirements of Eelgrass
Authors: Zimmerman R. C. , Kohrs D. G. , Steller D. L. , Alberte R. S.
Published: October 2016

Seagrasses, although well adapted for submerged existence, are CO2-limited and photosynthetically inefficient in seawater. This leads to high light requirements for growth and survival and makes seagrasses vulnerable to light limitation. We explored the long-term impact of increased CO2 availability on light requirements, productivity, and C allocation in eelgrass (Zostera marina L.). Enrichment of seawater CO2 increased photosynthesis 3-fold, but had no long-term impact on respiration. By tripling the rate of light-saturated photosynthesis, CO2 enrichment reduced the daily period of irradiance-saturated photosynthesis (Hsat) that is required for the maintenance of positive whole-plant C balance from 7 to 2.7 h, allowing plants maintained under 4 h of Hsat to perform like plants growing in unenriched seawater with 12 h of Hsat. Eelgrass grown under 4 h of Hsat without added CO2 consumed internal C reserves as photosynthesis rates and chlorophyll levels dropped. Growth ceased after 30 d. Leaf photosynthesis, respiration, chlorophyll, and sucrose-phosphate synthase activity of CO2-enriched plants showed no acclimation to prolonged enrichment. Thus, the CO2-stimulated improvement in photosynthesis reduced light requirements in the long term, suggesting that globally increasing CO2 may enhance seagrass survival in eutrophic coastal waters, where populations have been devastated by algal proliferation and reduced water-column light transparency.
A Secreted Factor Inducs Cell Expansion and Formation of Metaxylem-Like Tracheary Elements in Xylogenic Suspension Cultures of Zinnia
Authors: Roberts A. W. , Donovan S. G. , Haigler C. H.
Published: October 2016

Conditioned medium from mesophyll cell-suspension cultures of Zinnia elegans L. has striking effects on cell expansion and tracheary element differentiation when applied to cultures of freshly isolated mesophyll cells. These effects include (a) induction of early cell expansion, (b) delay in differentiation by 48 h or more, (c) reduction in the synchrony of differentiation, and (d) early formation of very large, metaxylem-like tracheary elements. Like reduced osmotic potential and buffering at pH 5.5, conditioned medium appears to have its primary effect on cell expansion. Partial characterization of the expansion-inducing factor indicates that it is heat stable, of low molecular mass, and is resistant to protease. It also binds reversibly to concanavalin A but is not adsorbed by charcoal. We suggest that the secreted factor may be an oligosaccharide involved in the coordination of cell expansion and differentiation and the regulation of the protoxylem-like to metaxylem-like transition in xylogenic suspension cultures.
The Effects of Salicylic Acid and Tobacco Mosaic Virus Infection on the Alternative Oxidase of Tobacco
Authors: Lennon A. M. , Neuenschwander U. H. , Ribas-Carbo M. , Giles L. , Ryals J. A. , Siedow J. N.
Published: October 2016

Salicylic acid (SA) is a signal in systemic acquired resistance and an inducer of the alternative oxidase protein in tobacco (Nicotiana tabacum cv Xanthi nc) cell suspensions and during thermogenesis in aroid spadices. The effects of SA on the levels of alternative oxidase protein and the pathogenesis-related 1a mRNA (a marker for systemic acquired resistance), and on the partitioning of electrons between the Cyt and alternative pathways were investigated in tobacco. Leaves were treated with 1.0 mM SA and mitochondria isolated at times between 1 h and 3 d after treatment. Alternative oxidase protein increased 2.5-fold within 5 h, reached a maximum (9-fold) after 12 h, and remained at twice the level of control plants after 3 d. Measurements of isotope fractionation of 18O by intact leaf tissue gave a value of 23% at all times, identical to that of control plants, indicating a constant 27 to 30% of electron-flow partitioning to the alternative oxidase independent of treatment with SA. Transgenic NahG tobacco plants that express bacterial salicylate hydroxylase and possess very low levels of SA gave a fractionation of 23% and showed control levels of alternative oxidase protein, suggesting that steady-state alternative oxidase accumulates in an SA-independent manner. Infection of plants with tobacco mosaic virus resulted in an increase in alternative oxidase protein in both infected and systemic leaves, but no increase was observed in comparably infected NahG plants. Total respiration rate and partitioning of electrons to the alternative pathway in virus-infected plants was comparable to that in uninfected controls.
Quantum Yields and Rate Constants of Photochemical and Nonphotochemical Excitation Quenching (Experiment and Model)
Authors: Laisk A. , Oja V. , Rasulov B. , Eichelmann H. , Sumberg A.
Published: October 2016

Sunflower (Helianthus annuus L.), cotton (Gossypium hirsutum L.), tobacco (Nicotiana tabacum L.), sorghum (Sorghum bicolor Moench.), amaranth (Amaranthus cruentus L.), and cytochrome b6f complex-deficient transgenic tobacco leaves were used to test the response of plants exposed to differnt light intensities and CO2 concentrations before and after photoinhibition at 4000 [mu]mol photons m-2 s-1 and to thermoinhibition up to 45[deg]C. Quantum yields of photochemical and nonphotochemical excitation quenching (YP and YN) and the corresponding relative rate constants for excitation capture from the antenna-primary radical pair equilibrium system (k[prime]P and k[prime]N) were calculated from measured fluorescence parameters. The above treatments resulted in decreases in YP and K[prime]P and in approximately complementary increases in YN and K[prime]N under normal and inhibitory conditions. The results were reproduced by a mathematical model of electron/proton transport and O2 evolution/CO2 assimilation in photosynthesis based on budget equations for the intermediates of photosynthesis. Quantitative differences between model predictions and experiments are explainable, assuming that electron transport is organized into domains that contain relatively complete electron and proton transport chains (e.g. thylakoids). With the complementation that occurs between the photochemical and nonphotochemical excitation quenching, the regulatory system can constantly maintain the shortest lifetime of excitation necessary to avoid the formation of chlorophyll triplet states and singlet oxygen.
Flavonoid-Peroxidase Reaction as a Detoxification Mechanism of Plant Cells against H2O2
Authors: Yamasaki H. , Sakihama Y. , Ikehara N.
Published: October 2016

Recent studies have revealed that dietary flavonoids are potent radical scavengers, acting in a manner similar to ascorbate and α--tocopherol. However, it is still not clear whether flavonoids have a similar antioxidative function in plants. We examined the possibility that flavonoids could function as stress protectants in plant cells by scavenging H2O2. Two major flavonoids, quercetin and kaempferol glycosides, were isolated from leaves of the tropical tree Schefflera arboricola Hayata. Both glycosides and aglycones of isolated flavonols were oxidized by H2O2 in the presence of horse-radish peroxidase and/or in a soluble fraction of S. arboricola leaf extract. The rates of oxidation were in the order quercetin> kaempferol> quercetin glycoside>> kaempferol glycoside. Judging from the effects of inhibitors such as KCN, p-chloromercuribenzoate, and 3-amino-1H-1,2,4-triazole, we conclude that guaiacol peroxidase in the soluble fraction catalyzes H2O2-dependent oxidation of flavonols. In the flavonol-guaiacol peroxidase reaction, ascorbate had the potential to regenerate flavonols by reducing the oxidized product. These results provide further evidence that the flavonoid-peroxidase reaction can function as a mechanism for H2O2 scavenging in plants.
Isoprene Increases Thermotolerance of Isoprene-Emitting Species
Authors: Singsaas E. L. , Lerdau M. , Winter K. , Sharkey T. D.
Published: October 2016

Isoprene-emitting plants lose a large portion of their assimilated C as isoprene. Because isoprene synthesis can be regulated, it has been assumed that isoprene benefits the plant. Since the rate of isoprene emission from leaves is highly responsive to temperature, we hypothesized that isoprene benefits plants by increasing their thermotolerance. We used three methods to measure isopreneinduced thermotolerance in leaves. Each technique assayed thermotolerance under conditions that suppressed endogenous isoprene synthesis. When measured by chlorophyll fluorescence, thermotolerance of kudzu (Pueraria lobata [Willd.] Ohwi.) leaves increased as much as 4[deg]C in very low light. With higher light, isoprene increased thermotolerance of kudzu leaves by as much as 10[deg]C. When measured as the temperature at which photosynthesis declined to zero, thermotolerance increased with added isoprene by 2.5[deg]C. All three measures of thermotolerance were dose dependent. Both fluorescence techniques also showed isoprene-induced thermotolerance in white oak (Quercus alba L.). Thermotolerance was not observed in bean (Phaseolus vulgaris var Linden), a species that does not emit isoprene. None of the experiments was designed to determine the mechanism of thermotolerance, but we theorize that isoprene functions by enhancing hydrophobic interactions in membranes.
Sugar-Starvation-Induced Changes of Carbon Metabolism in Excised Maize Root Tips
Authors: Dieuaide-Noubhani M. , Canioni P. , Raymond P.
Published: October 2016

Excised maize (Zea mays L.) root tips were used to study the early metabolic effects of glucose (Glc) starvation. Root tips were prelabeled with [1-13C]Glc so that carbohydrates and metabolic intermediates were close to steady-state labeling, but lipids and proteins were scarcely labeled. They were then incubated in a sugar-deprived medium for carbon starvation. Changes in the level of soluble sugars, the respiratory quotient, and the 13C enrichment of intermediates, as measured by 13C and 1H nuclear magnetic resonance, were studied to detect changes in carbon fluxes through glycolysis and the tricarboxylic acid cycle. Labeling of glutamate carbons revealed two major changes in carbon input into the tricarboxylic acid cycle: (a) the phosphoenolpyruvate carboxylase flux stopped early after the start of Glc starvation, and (b) the contribution of glycolysis as the source of acetyl-coenzyme A for respiration decreased progressively, indicating an increasing contribution of the catabolism of protein amino acids, fatty acids, or both. The enrichment of glutamate carbons gave no evidence for proteolysis in the early steps of starvation, indicating that the catabolism of proteins was delayed compared with that of fatty acids. Labeling of carbohydrates showed that sucrose turnover continues during sugar starvation, but gave no indication for any significant flux through gluconeogenesis.
Phloem-Specific Expression of the Tobacco Mosaic Virus Movement Protein Alters Carbon Metabolism and Partitioning in Transgenic Potato Plants
Authors: Almon E. , Horowitz M. , Wang H. L. , Lucas W. J. , Zamski E. , Wolf S.
Published: October 2016

The tobacco mosaic virus movement protein (TMV-MP) has pleiotropic effects when expressed in transgenic tobacco (Nicotiana tabacum) plants. In addition to its ability to increase the plasmodesmal size-exclusion limit, the TMV-MP alters carbohydrate metabolism in source leaves and dry matter partitioning between the various plant organs. In the present study the TMV-MP was expressed under the control of a phloem-specific promoter (rolC), and this system was employed to further explore the potential sites at which the TMV-MP exerts its influence over carbon metabolism and transport in transgenic potato (Solanum tuberosum) plants. Immunohistochemical analyses indicated that the TMV-MP was localized mainly to phloem parenchyma and companion cells. Starch and sucrose accumulated in source leaves of these plants to significantly higher levels compared with control potato lines. In addition, the rate of sucrose efflux from excised petioles was lower compared with control plants. Furthermore, under short-day conditions, carbon partitioning was lower to the roots and higher to tubers in rolC plants compared with controls. These results are discussed in terms of the mode(s) by which the TMV-MP exerts its influence over carbon metabolism and photoassimilate translocation.
Dynamics of Xanthophyll-Cycle Activity in Different Antenna Subcomplexes in the Photosynthetic Membranes of Higher Plants (The Relationship between Zeaxanthin Conversion and Nonphotochemical Fluorescence Quenching)
Authors: Farber A. , Young A. J. , Ruban A. V. , Horton P. , Jahns P.
Published: October 2016

The generation of nonphotochemical quenching of chlorophyll fluorescence (qN) in the antenna of photosystem II (PSII) is accompanied by the de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin. The function of zeaxanthin in two mechanisms of qN, energy-dependent quenching (qE) and photoinhibitory quenching (qI), was investigated by measuring the de-epoxidation state in the antenna subcomplexes of PSII during the generation and relaxation of qN under varying conditions. Three different antenna subcomplexes were separated by isoelectric focusing: Lhcb1/2/3, Lhcb5/6, and the Lhcb4/PSII core. Under all conditions, the highest de-epoxidation state was detected in Lhcb1/2/3 and Lhcb5/6. The kinetics of de-epoxidation in these complexes were found to be similar to the formation of qE. The Lhcb4/PSII core showed the most pronounced differences in the de-epoxidation state when illumination with low and high light intensities was compared, correlating roughly with the differences in qI. Furthermore, the epoxidation kinetics in the Lhcb4/PSII core showed the most pronounced differences of all subcomplexes when comparing the epoxidation after either moderate or very strong photoinhibitory preillumination. Our data support the suggestion that zeaxanthin formation/epoxidation in Lhcb1-3 and Lhcb5/6 may be related to qE, and in Lhcb4 (and/or PSII core) to qI.
Correction
Authors: Gallois R. , Prevot J. C. , Clement A. , Jacob J. L.
Published: October 2016

Phosphoribosylpyrophosphate synthetase (PRS; EC 2.7.6.1) from Hevea brasiliensis Mull. Arg. latex was located in the cytosol. After purification, its apparent molecular weight under nondenaturing conditions was estimated at 200,000 [plus or minus] 10,000; a single band at 57,000 [plus or minus] 3,000 was detected after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme seemed to be a homotetramer. Its affinity constants were estimated at 200 [plus or minus] 30 [mu]M for adenosine triphosphate and 40 [plus or minus] 2 [mu]M for ribose-5-phosphate. The purified enzyme proved to be functional in a paraphysiological medium (cytosol deproteinized by ultrafiltration). Optimum pH was 7.5 in buffer and 6.5 in a paraphysiological medium. No PRS activity was detected in the absence of the Mg2+ ion. Of the numerous compounds tested, only Mn2+, phosphoribosylpyrophosphate and inorganic phosphate affected the enzymatic reaction. Mn2+ (inhibitor constant = 20 [mu]M) and phosphoribosylpyrophosphate (inhibitor constant = 30 [mu]M) were inhibitors. PRS responded allosterically (Hill's coefficient = 2.3) to ribose-5-phosphate in the presence of a physiological concentration of inorganic phosphate (10 mM). These results are set in the physiological context of laticifers.
Dynamic Interplay between Nucleoid Segregation and Genome Integrity in Chlamydomonas Chloroplasts
Authors: Odahara Masaki , Kobayashi Yusuke , Shikanai Toshiharu , Nishimura Yoshiki
Published: October 2016

The chloroplast (cp) genome is organized as nucleoids that are dispersed throughout the cp stroma. Previously, a cp homolog of bacterial recombinase RecA (cpRECA) was shown to be involved in the maintenance of cp genome integrity by repairing damaged chloroplast DNA and by suppressing aberrant recombination between short dispersed repeats in the moss Physcomitrella patens. Here, overexpression and knockdown analysis of cpRECA in the green alga Chlamydomonas reinhardtii revealed that cpRECA was involved in cp nucleoid dynamics as well as having a role in maintaining cp genome integrity. Overexpression of cpRECA tagged with yellow fluorescent protein or hemagglutinin resulted in the formation of giant filamentous structures that colocalized exclusively to chloroplast DNA and cpRECA localized to cp nucleoids in a heterogenous manner. Knockdown of cpRECA led to a significant reduction in cp nucleoid number that was accompanied by nucleoid enlargement. This phenotype resembled those of gyrase inhibitor-treated cells and monokaryotic chloroplast mutant cells and suggested that cpRECA was involved in organizing cp nucleoid dynamics. The cp genome also was destabilized by induced recombination between short dispersed repeats in cpRECA-knockdown cells and gyrase inhibitor-treated cells. Taken together, these results suggest that cpRECA and gyrase are both involved in nucleoid dynamics and the maintenance of genome integrity and that the mechanisms underlying these processes may be intimately related in C. reinhardtii  cps.
X-ray analyzer-based phase-contrast computed laminography
Authors: Hirano Keiichi , Takahashi Yumiko , Hyodo Kazuyuki , Kimura Masao
Published: October 2016

X-ray analyzer-based phase-contrast imaging is combined with computed laminography for imaging regions of interest in laterally extended flat specimens of weak absorption contrast. The optics discussed here consist of an asymmetrically cut collimator crystal and a symmetrically cut analyzer crystal arranged in a nondispersive (+, −) diffraction geometry. A generalized algorithm is given for calculating multi-contrast (absorption, refraction and phase contrast) images of a sample. Basic formulae are also presented for laminographic reconstruction. The feasibility of the method discussed was verified at the vertical wiggler beamline BL-14B of the Photon Factory. At a wavelength of 0.0733 nm, phase-contrast sectional images of plastic beads were successfully obtained. Owing to strong circular artifacts caused by a sample holder, the field of view was limited to about 6 mm in diameter.
Fast X-ray microfluorescence imaging with submicrometer-resolution integrating a Maia detector at beamline P06 at PETRA III
Authors: Boesenberg Ulrike , Ryan Christopher G. , Kirkham Robin , Siddons D. Peter , Alfeld Matthias , Garrevoet Jan , Núñez Teresa , Claussen Thorsten , Kracht Thorsten , Falkenberg Gerald
Published: October 2016

The high brilliance of third-generation synchrotron sources increases the demand for faster detectors to utilize the available flux. The Maia detector is an advanced imaging scheme for energy-dispersive detection realising dwell times per image-pixel as low as 50 µs and count rates higher than 10 × 106 s−1. In this article the integration of such a Maia detector in the Microprobe setup of beamline P06 at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg, Germany, is described. The analytical performance of the complete system in terms of rate-dependent energy resolution, scanning-speed-dependent spatial resolution and lower limits of detection is characterized. The potential of the Maia-based setup is demonstrated by key applications from materials science and chemistry, as well as environmental science with geological applications and biological questions that have been investigated at the P06 beamline.
Crystal structures of 3,3′-bis(hydroxydimethylsilanyl)azobenzene and 4,4′-bis(hydroxydimethylsilane)azobenzene
Authors: Strüben Jan , Hoffmann Jonas , Presa-Soto David , Näther Christian , Staubitz Anne
Published: October 2016

The title compounds {systematic names (E)-[diazene-1,2-diylbis(3,1-phenylene)]bis(dimethylsilanol) and (E)-[diazene-1,2-diylbis(4,1-phenylene)]bis(dimethylsilanol)}, both of the sum formula C16H22N2O2Si2, were obtained by transmetallation of the respective bis-stannylated azobenzenes with dichlorodimethylsilane and esterification followed by hydrolysis. The asymmetric unit of 3,3′-diazenediylbis[dimethyl(phenyl)silanol] (with the silanol functional group in a meta position) consists of two molecules, of which one occupies a general position, whereas the second is located on a centre of inversion. In 4,4′-diazenediylbis[dimethyl(phenyl)silanol] (with the silanol functional group in a para position) likewise two molecules are present in the asymmetric unit, but in this case both occupy general positions. Differences between all molecules can be found in the torsions about the N=N bond, as well as in the dihedral angles between the benzene rings. In both structures, intermolecular O—H...O hydrogen bonding is observed, leading to the formation of layers parallel to (01-1) for (I) and to chains parallel to the a axis for (II).
4,4′-[(1E,1′E)-(2-Chloropyrimidine-4,6-diyl)bis(ethene-2,1-diyl)]bis(N,N-diethylaniline)
Authors: Hu Lei , Wang Hui , Zhang Qiong
Published: October 2016

In the title molecule, C28H33ClN4, the central pyrimidine ring is twisted with respect to the two benzene rings, making dihedral angles of 13.56 (19) and 23.1 (2)°. In the crystal, weak C—H...π interactions link the molecules into supramolecular chains propagating along the c-axis direction.
Creatinium 4-methylbenzenesulfonate
Authors: Thayanithi V. , Kumar P. Praveen , Gunasekaran B.
Published: October 2016

In the title molecular salt, C4H10N3O2+·C7H7O3S−(systematic name: {amino[(carboxymethyl)(methyl)amino]methylidene}azanium 4-methylbenzenesulfonate), the OH group of the carboxylic acid and central N atom of the cation are close to being eclipsed [N—C—C—O = 11.6 (3)°]. In the crystal, C—H...·O, O—H...O and N—H...O hydrogen bonds link the components into (001) sheets.
Poly[tris{μ-2-[(dimethylamino)methyl]imidazolato-κ3
N
1,N
2:N
3}(nitrato-κO)dizinc(II)]
Authors: Kuramoto Takahiro , Sadakiyo Masaaki , Yamauchi Miho
Published: October 2016

In the title coordination polymer, [Zn2(C6H10N3)3(NO3)]
n
, two independent ZnII ions are tetrahedrally coordinated by the anionic ligands, viz. 2-[(dimethylamino)methyl]imidazolate or nitrate ions. One ZnII ion is coordinated by the imidazolate N atoms of three anions and an O atom of the nitrate ion. The second ZnII ion is coordinated by imidazolate N atoms of three anions and one amino N atom of one such ligand. The 2-[(dimethylamino)methyl]imidazolate anions are bridging the ZnII ions to form a helical chain structure along [001]. The chains are further linked by the bridging ligands into a three-dimensional framework structure. The nitrate anion is disordered over two sets of sites and was refined with two pairs of three O atoms using half-occupancy for each O atom.
Chloride ion entrapment by calcined layered double hydroxides
Authors: K. Karaxi Evangelia , Kartsonakis Ioannis A. , Charitidis Costas A.
Published: October 2016

Purpose

Magnesium-aluminum layered double hydroxides (LDH) with a platelet-like morphology were synthesized through a modified co-precipitation method. The purpose of this paper is to investigate calcined Mg-Al-CO3 LDH (CLDH) as chloride ion traps.

Design/methodology/approach

The morphology and chemical composition of the synthesized materials were studied through UHR-SEM, EDS, FT-IR and XRD. The chloride ion adsorption was confirmed by XRD; the characteristic diffraction peaks of the reconstructed LDH structure were revealed, similar to the one before the thermal treatment process. The effect of varying the experimental conditions on the chloride ion adsorption, such as the initial target-ion concentration, the adsorbent material dosage, the solution temperature and the solution pH was also investigated.

Findings

The experimental data fitting revealed that the Langmuir equation is a better model on the basis of correlation coefficients (R2) and that the pseudo-second kinetic model can satisfactorily describe the chloride ion uptake.

Originality/value

The ability of Mg-Al CLDH to recover their layered structure upon exposure to aqueous sodium chloride solutions with concentrations up to 0.3 M (10,636 mg/L) through the chloride adsorption and the simultaneous rehydration process is clearly demonstrated.