bluuebunny/crossref_metadata_2025_split huggingface dataset:
Purification and Characterization of a β-D-Xylosidase and an Endo-Xylanase from Wheat Flour
Authors: Cleemput G. , Hessing M. , van Oort M. , Deconynck M. , Delcour J. A. 
Published: October 2016

Abstract
A β-D-xylosidase and an endo-xylanase were purified from European wheat (Triticum aestivum) flour. The β-D-xylosidase had a molecular weight of approximately 64,000 and an isoelectric point of 5.5. It hydrolyzed p-nitrophenyl-β-D-xylopyranoside and xylo-oligosaccharides and released D-xylose units from wheat arabinoxylan and oat spelts xylan. An endo-xylanase with a molecular weight of approximately 55,000 was also obtained and it consisted of a number of isoforms with isoelectric points between 4.0 and 5.0. The action of the isolated endo-xylanase depended on the degree of substitution of the polysaccharide. Unbranched polymers were preferentially hydrolyzed. Since xylo-oligosaccharides were not hydrolyzed, the enzyme appeared to need at least five or more consecutive unsubstituted xylose units. Finally, an α--L-arabinofuranosidase that hydrolyzed p-nitrophenyl-α--L-arabinofuranoside was partially purified.
Differential Ammonia-Elicited Changes of Cytosolic pH in Root Hair Cells of Rice and Maize as Monitored by 2[prime],7[prime]-bis-(2-Carboxyethyl)-5 (and -6)-Carboxyfluorescein-Fluorescence Ratio
Authors: Kosegarten H. , Grolig F. , Wieneke J. , Wilson G. , Hoffmann B. 
Published: October 2016

Abstract
Intact hair cells of young rice (Oryza sativa L.) and maize roots (Zea mays L.), grown without external nitrogen, were specifically loaded with 2[prime],7[prime]-bis-(2-carboxyethyl)-5 (and -6)-carboxyfluorescein acetoxymethyl ester to monitor fluorescence ratio cytosolic pH changes in response to external ammonia (NH4+/NH3) application. In neutral media, cytosolic pH of root hairs was 7.15 [plus or minus] 0.13 (O. sativa) and 7.08 [plus or minus] 0.11 (Z. mays). Application of 2 mM ammonia at external pH 7.0 caused a transient cytosolic alkalization (7.5 [plus or minus] 0.15 in rice; 7.23 [plus or minus] 0.13 in maize). Alkalization increased with an increase of external pH; no pH changes occurred at external pH 5.0. The influx of 13N-labeled ammonia in both plant species did not differ between external pH 5.0 and 7.0 but increased significantly with higher pH. Pretreatment with 1 mM 1-methionine sulfoximine significantly reduced the ammonia-elicited pH increase in rice but not in maize. Application of 2 mM methylammonia only caused a cytosolic pH increase at high external pH; the increase in both species compared with the ammonia-elicited alkalization in 1-methionine sulfoximine-treated roots. The differential effects indicate that cytosolic alkalization derived from (a) NH3 protonation after passive permeation of the plasma membrane and, particularly in rice, (b) additional proton consumption via the glutamine synthetase/glutamate synthase cycle.
Reduction of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase by Antisense RNA in the C4 Plant Flaveria bidentis Leads to Reduced Assimilation Rates and Increased Carbon Isotope Discrimination
Authors: von Caemmerer S. , Millgate A. , Farquhar G. D. , Furbank R. T. 
Published: October 2016

Abstract
Transgenic Flaveria bidentis (a C4 species) plants with an antisense gene directed against the mRNA of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were used to examine the relationship between the CO2 assimilation rate, Rubisco content, and carbon isotope discrimination. Reduction in the amount of Rubisco in the transgenic plants resulted in reduced CO2 assimilation rates and increased carbon isotope discrimination of leaf dry matter. The H2O exchange was similar in transgenic and wild-type plants, resulting in higher ratios of intercellular to ambient CO2 partial pressures. Carbon isotope discrimination was measured concurrently with CO2 and H2O exchange on leaves of the control plants and T1 progeny with a 40% reduction in Rubisco. From the theory of carbon isotope discrimination in the C4 species, we conclude that the reduction in the Rubisco content in the transgenic plants has led to an increase in bundle-sheath CO2 concentration and CO2 leakage from the bundle sheath; however, some down-regulation of the C4 cycle also occurred.
Al Partitioning Patterns and Root Growth as Related to Al Sensitivity and Al Tolerance in Wheat
Authors: Samuels T. D. , Kucukakyuz K. , Rincon-Zachary M. 
Published: October 2016

Abstract
Studies of Al partitioning and accumulation and of the effect of Al on the growth of intact wheat (Triticum aestivum L.) roots of cultivars that show differential Al sensitivity were conducted. The effects of various Al concentrations on root growth and Al accumulation in the tissue were followed for 24 h. At low external Al concentrations, Al accumulation in the root tips was low and root growth was either unaffected or stimulated. Calculations based on regression analysis of growth and Al accumulation in the root tips predicted that 50% root growth inhibition in the Al-tolerant cv Atlas 66 would be attained when the Al concentrations were 105 [mu]M in the nutrient solution and 376.7 [mu]g Al g-1 dry weight in the tissue. In contrast, in the Al-sensitive cv Tam 105, 50% root growth inhibition would be attained when the Al concentrations were 11 [mu]M in the nutrient solution and 546.2 [mu]g Al g-1 dry weight in the tissue. The data support the hypotheses that differential Al sensitivity correlates with differential Al accumulation in the growing root tissue, and that mechanisms of Al tolerance may be based on strategies to exclude Al from the root meristems.
Molecular Genetic Evidence of the Ability of Alternative Oxidase to Support Respiratory Carbon Metabolism
Authors: Vanlerberghe G. C. , Vanlerberghe A. E. , McIntosh L. 
Published: October 2016

Abstract
With the cytochrome pathway inhibited, AOX was able to support considerable growth of cultured tobacco (Nicotiana tabacum cv Petit Havana SR1) cells but the efficiency of carbon utilization decreased dramatically. Antisense cells with decreased AOX protein did not grow, whereas sense cells with elevated AOX protein had higher growth and respiration rates than the wild type. In antisense cells a large accumulation of pyruvate resulted in aerobic ethanolic fermentation.
Expression of an Aspartate Kinase Homoserine Dehydrogenase Gene Is Subject to Specific Spatial and Temporal Regulation in Vegetative Tissues, Flowers, and Developing Seeds
Authors: Zhu-Shimoni J. X. , Lev-Yadun S. , Matthews B. , Galili G. 
Published: October 2016

Abstract
Although the regulation of amino acid synthesis has been studied extensively at the biochemical level, it is still not known how genes encoding amino acid biosynthesis enzymes are regulated during plant development. In the present report, we have used the β-glucuronidase (GUS) reporter gene to study the regulation of expression of an Arabidopsis thaliana aspartate kinase-homoserine dehydrogenase (AK/HSD) gene in transgenic tobacco plants. The polypeptide encoded by the AK/HSD gene comprises two linked key enzymes in the biosynthesis of aspartate-family amino acids. AK/HSD-GUS gene expression was highly stimulated in apical and lateral meristems, lateral buds, young leaves, trichomes, vascular and cortical tissues of growing stems, tapetum and other tissues of anthers, pollen grains, various parts of the developing gynoecium, developing seeds, and, in some transgenic plants, also in stem and leaf epidermal trichomes. AK/HSD-GUS gene expression gradually dimished upon maturation of leaves, stems, floral tissues, and embryos. GUS expression was relatively low in roots. During seed development, expression of the AK/HSD gene in the embryo was coordinated with the initiation and onset of storage protein synthesis, whereas in the endosperm it was coordinated with the onset of seed desiccation. Upon germination, AK/HSD-GUS gene expression in the hypocotyl and the cotyledons was significantly affected by light. The expression pattern of the A. thaliana AK/HSD-GUS reporter gene positively correlated with the levels of aspartate-family amino acids and was also very similar to the expression pattern of the endogenous tobacco AK/HSD mRNA as determined by in situ hybridization.
Abscisic Acid Activates a 48-Kilodalton Protein Kinase in Guard Cell Protoplasts
Authors: Mori I. C. , Muto S. 
Published: October 2016

Abstract
A 49- and a 46-kD Ca2+-independent protein kinase and a 53-kD Ca2+-dependent protein kinase were detected in Vicia faba guard cell protoplasts (GCPs) by an in-gel protein kinase assay using myelin basic protein as a substrate. A 48-kD protein kinase designated as abscisic acid (ABA)-responsive protein kinase (ABR kinase) appeared when GCPs were treated with ABA. The activation of ABR kinase was suppressed by the protein kinase inhibitor staurosporine, indicating that a putative activator protein kinase phosphorylates and activates ABR kinase. The treatment of GCPs with 1,2-bis(o-aminophenoxy)ethan-N,N,N′,N′-tetraacetic acid, a calcium chelator, suppressed the activation of ABR kinase, suggesting that an influx of extracellular Ca2+ is required for the activation. Staurosporine and K-252a inhibited both the activity of ABR kinase and the stomatal closure induced by ABA treatment of V. faba epidermal peels. These results suggest that ABR kinase and its activator kinase may consist of a protein kinase cascade in a signal transduction pathway linking ABA perception to stomatal closure. The mobility of the 53-kD Ca2+-dependent protein kinase in sodium dodecyl sulfate-polyacrylamide gel was shifted upon Ca2+ binding to the enzyme, thus exhibiting the characteristics of a Ca2+-dependent or calmodulin-like domain protein kinase. This kinase may be the activator of ABR kinase.
The cdc2Ms Kinase Is Differently Regulated in the Cytoplasm and in the Nucleus
Authors: Bogre L. , Zwerger K. , Meskiene I. , Binarova P. , Csizmadia V. , Planck C. , Wagner E. , Hirt H. , Heberle-Bors E. 
Published: October 2016

Abstract
To study a cyclin-dependent kinase (CDK) from alfalfa (Medicago sativa L.), an antibody was raised against the C-terminal 16 amino acids of the protein cdc2aMs. The cdc2Ms protein was immunopurified with this antibody and its histone kinase activity was measured. The cdc2Ms kinase is activated at the G1/S transition when phosphate-starved cells from the G0 phase re-enter the cell cycle and remain active as cells transit the S, G2, and M phases, indicating that the same CDK regulates all of these phases in alfalfa. In contrast, when cdc2Ms kinase was purified by binding to p13suc1, it was active only in the G2 and M phases. In immunoblots the C-terminal antibody detected an equal amount of the cdc2Ms protein in the cytoplasm and in the nucleus. By indirect immunofluorescence, however, the cytoplasmic form of cdc2Ms could not be found in the S phase of the cells, indicating that the epitope for the cdc2 antibody is not accessible. Binding of putative inhibitor proteins to cdc2 was shown by inactivation of purified plant CDK when cell extracts were added. Furthermore, purified CDK inhibitors, such as the mouse p27kip1 and the yeast p40sic1, blocked the purified plant CDK activity.
Proteinase Activity during Tracheary Element Differentiation in Zinnia Mesophyll Cultures
Authors: Beers E. P. , Freeman T. B. 
Published: October 2016

Abstract
The zinnia (Zinnia elegans) mesophyll cell culture tracheary element (TE) system was used to study proteinases active during developmentally programmed cell death. Substrate-impregnated gels and single-cell assays revealed high levels of proteinase activity in differentiating TEs compared with undifferentiated cultured cells and expanding leaves. Three proteinases (145, 28, and 24 kD) were exclusive to differentiating TEs. A fourth proteinase (59 kD), although detected in extracts from all tissues examined, was most active in differentiating TEs. The 28- and 24-kD proteinases were inhibited by thiol proteinase inhibitors, leupeptin, and N-[N-(L-3-trans-carboxirane-2-carbonyl)-L-leucyl]-agmatine (E-64). The 145- and 59-kD proteinases were inhibited by the serine proteinase inhibitor phenylmethylsulfonyl fluoride (PMSF). Extracts from the TE cultures contained sodium dodecyl sulfate-stimulated proteolytic activity not detected in control cultures. Sodium dodecyl sulfate-stimulated proteolysis was inhibited by leupeptin or E-64, but not by PMSF. Other tissues, sucrose-starved cells and cotyledons, that contain high levels of proteolytic activity did not contain TE-specific proteinases, but did contain higher levels of E-64-sensitive activities migrating as 36- to 31-kD enzymes and as a PMSF-sensitive 66-kD proteinase.
Growth, Water Relations, and Accumulation of Organic and Inorganic Solutes in Roots of Maize Seedlings during Salt Stress
Authors: Rodriguez H. G. , Roberts JKM. , Jordan W. R. , Drew M. C. 
Published: October 2016

Abstract
Seedlings of maize (Zea mays L. cv Pioneer 3906), hydroponically grown in the dark, were exposed to NaCl either gradually (salt acclimation) or in one step (salt shock). In the salt-acclimation treatment, root extension was indistinguishable from that of unsalinized controls for at least 6 d at concentrations up to 100 mM NaCl. By contrast, salt shock rapidly inhibited extension, followed by a gradual recovery, so that by 24 h extension rates were the same as for controls, even at 150 mM NaCl. Salt shock caused a rapid decrease in root water and solute potentials for the apical zones, and the estimated turgor potential showed only a small decline; similar but more gradual changes occurred with salt acclimation. The 5-bar decrease in root solute potential with salt shock (150 mM NaCl) during the initial 10 min of exposure could not be accounted for by dehydration, indicating that substantial osmotic adjustment occurred rapidly. Changes in concentration of inorganic solutes (Na+, K+, and Cl-) and organic solutes (proline, sucrose, fructose, and glucose) were measured during salt shock. The contribution of these solutes to changes in root solute potential with salinization was estimated.
Thermostability and Photostability of Photosystem II in Leaves of the Chlorina-f2 Barley Mutant Deficient in Light-Harvesting Chlorophyll a/b Protein Complexes
Authors: Havaux M. , Tardy F. 
Published: October 2016

Abstract
The chlorophyll-b-less chlorina-f2 barley mutant is deficient in the major as well as some minor light-harvesting chlorophyll-protein complexes of photosystem II (LHCII). Although the LHCII deficiency had relatively minor repercussions on the leaf photosynthetic performances, the responses of photosystem II (PSII) to elevated temperatures and to bright light were markedly modified. The chlorina-f2 mutation noticeably reduced the thermostability of PSII, with thermal denaturation of PSII starting at about 35[deg]C and 38.5[deg]C in chlorina-f2 and in the wild type, respectively. The increased susceptibility of PSII to heat stress in chlorina-f2 leaves was due to the weakness of its electron donor side, with moderate heat stress causing detachment of the 33-kD extrinsic PSII protein from the oxygen-evolving complex. Prolonged dark adaptation of chlorina-f2 leaves was also observed to inhibit the PSII donor side. However, weak illumination slowly reversed the dark-induced inhibition of PSII in chlorina-f2 and cancelled the difference in PSII thermostability observed between chlorina-f2 and wild-type leaves. The mutant was more sensitive to photoinhibition than the wild type, with strong light stress impairing the PSII donor side in chlorina-f2 but not in the wild type. This difference was not observed in anaerobiosis or in the presence of 3-(3,4-dichlorophenyl)- 1,1-dimethylurea, diuron. The acceptor side of PSII was only slightly affected by the mutation and/or the aforementioned stress conditions. Taken together, our results indicate that LHCII stabilize the PSII complexes and maintain the water-oxidizing system in a functional state under varying environmental conditions.
Leaf Respiration in Light and Darkness (A Comparison of Slow- and Fast-Growing Poa Species)
Authors: Atkin O. K. , Westbeek MHM. , Cambridge M. L. , Lambers H. , Pons T. L. 
Published: October 2016

Abstract
We investigated whether leaf dark respiration (nonphotorespiratory mitochondrial CO2 release) is inhibited by light in several Poa species, and whether differences in light inhibition between the species are related to differences in the rate of leaf net photosynthesis. Four lowland (Poa annua L., Poa compressa L., Poa pratensis L., and Poa trivialis L.), one subalpine (Poa alpina L.), and two alpine (Poa costiniana Vick. and Poa fawcettiae Vick.) Poa species differing in whole plant relative growth rates were grown under identical controlled conditions. Nonphotorespiratory mitochondrial CO2 release in the light (Rd) was estimated according to the Laisk method. Photosynthesis was measured at ambient CO2 partial pressure (35 Pa) and 500 [mu]mol photons m-2 s-1. The rate of photosynthesis per unit leaf mass was positively correlated with the relative growth rate, with the slow-growing alpine Poa species exhibiting the lowest photosynthetic rates. Rates of both Rd and respiration in darkness were also substantially lower in the alpine species. Nonphotorespiratory CO2 release in darkness was higher than Rd in all species. However, despite some variation between the species in the level of light inhibition of respiration, no relationship was observed between the level of inhibition and the rate of photosynthesis. Similarly, the level of inhibition was not correlated with the relative growth rate. Our results support the suggestion that rates of leaf respiration in the light are closely associated with rates in darkness.
Diurnal Fluctuations in Ethylene Formation in Chenopodium rubrum
Authors: Machackova I. , Chauvaux N. , Dewitte W. , van Onckelen H. 
Published: October 2016

Abstract
Ethylene formation was studied in 5- to 6-d-old Chenopodium rubrum seedlings under the following light regimes: continuous light (CL), continuous darkness (CD), and alternating light/darkness (12 h of each). No significant regular oscillations in ethylene formation were found in either the CL or CD groups. In the light/dark regime, pronounced diurnal fluctuations in ethylene formation were observed. Activity of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase was transiently increased on transfer from light to dark and vice versa. In CL, ACC oxidase activity did not change significantly, whereas in CD, it decreased continuously after the initial increase. The in vivo levels of ACC and N-malonyl-ACC (MACC) were constant for the first few hours of darkness, then decreased dramatically, but increased again in the light. In constant darkness, the level of ACC displayed endogenous rhythm, with minimum values at h 12 and 44, and a maximum value at h 32 to 36. The level of MACC in both shoots and roots decreased in the CD group until h 12, and then remained constant until h 30 before decreasing continuously. We conclude that the photoperiodic regime affects both ACC and MACC levels, as well as the conversion of ACC to ethylene. Correlation of the described changes in ethylene formation to photoperiodic flower induction is discussed.
Reduction of Uroporphyrinogen Decarboxylase by Antisense RNA Expression Affects Activities of Other Enzymes Involved in Tetrapyrrole Biosynthesis and Leads to Light-Dependent Necrosis
Authors: Mock H. P. , Grimm B. 
Published: October 2016

Abstract
We introduced a full-length cDNA sequence encoding tobacco (Nicotiana tabacum) uroporphyrinogen III decarboxylase (UROD; EC 4.1.1.37) in reverse orientation under the control of a cauliflower mosaic virus 35S promoter derivative into the tobacco genome to study the effects of deregulated UROD expression on tetrapyrrole biosynthesis. Transformants with reduced UROD activity were characterized by stunted plant growth and necrotic leaf lesions. Antisense RNA expression caused reduced UROD protein levels and reduced activity to 45% of wild type, which was correlated with the accumulation of uroporphyrin(ogen) and with the intensity of necrotic damage. Chlorophyll levels were only slightly reduced (up to 15%), indicating that the plants sustained cellular damage from accumulating photosensitive porphyrins rather than from chlorophyll deficiency. A 16-h light/8-h dark regime at high-light intensity stimulates the formation of leaf necrosis compared with a low-light or a 6-h high-light treatment. Transgenic plants grown at high light also showed inactivation of 5-aminolevulinate dehydratase and porphobilinogen deaminase, whereas the activity of coproporphyrinogen oxidase and the 5-aminolevulinate synthesizing capacity were not altered. We conclude that photooxidation of accumulating uroporphyrin(ogen) leads to the generation of oxygen species, which destabilizes other enzymes in the porphyrin metabolic pathway. This porphyrin-induced necrosis resembles the induction of cell death observed during pathogenesis and air pollution.
P Metabolism in the Bean-Rhizobium tropici Symbiosis
Authors: Al-Niemi T. S. , Kahn M. L. , McDermott T. R. 
Published: October 2016

Abstract
Nodulated legumes require more P than legumes growing on mineral nitrogen, but little is known about the basis for the higher P requirement. Experiments were conducted to determine how Rhizobium tropici responds to P limitation and to understand how P is partitioned between the symbionts under conditions of adequate or limiting P. Free-living R. tropici responds to P stress by increasing P transport capacity and inducing both an acid and an alkaline phosphatase. This P-stress response occurs when the medium P concentration decreases below 1 [mu]M. Both P-stress-inducible phosphatases are found in bacteroids taken from plants growing with adequate P, suggesting that P levels in the symbiosome space is low enough to induce the expression of these enzymes. Bacteroid alkaline phosphatase-specific activity was highest during vegetative growth of the bean plant, but decreased approximately 75% during the host reproductive stages. In hydroponic experiments 32P-tracer studies showed that in vivo rates of P accumulation were significantly higher in bacteroids from P-limited plants compared with those from plants that had been supplied with adequate P. In contrast, label accumulation in leaves was greatest in plants grown with adequate P.
Relationship of Endo-β-D-Mannanase Activity and Cell Wall Hydrolysis in Tomato Endosperm to Germination Rates
Authors: Dahal P. , Nevins D. J. , Bradford K. J. 
Published: October 2016

Abstract
The endosperm tissue enclosing the radicle tip (endosperm cap) governs radicle emergence in tomato (Lycopersicon esculentum Mill.) seeds. Weakening of the endosperm cap has been attributed to hydrolysis of its mannan-rich cell walls by endo-β-D-mannanase. To test this hypothesis, we measured mannanase activity in tomato endosperm caps from seeds allowed to imbibe under conditions of varying germination rates. Over a range of suboptimal temperatures, mannanase activity prior to radicle emergence increased in accordance with accumulated thermal time. Reduced water potential delayed or prevented radicle emergence but enhanced mannanase activity in the endosperm caps. Abscisic acid did not prevent the initial increase in mannanase activity, although radicle emergence was markedly delayed. Sugar composition and percent mannose (Man) content of endosperm cap cell walls did not change prior to radicle emergence under any condition. Man, glucose, and other sugars were released into the incubation solution by endosperm caps isolated from intact seeds during imbibition. Pregerminative release of Man was suppressed and the release of glucose was enhanced when seeds were incubated in osmoticum or abscisic acid; the opposite occurred in the presence of gibberellin. Thus, whereas sugar release patterns were sensitive to environmental and hormonal factors affecting germination, neither assayable endo-β-D-mannanase activity nor changes in cell wall sugar composition of endosperm caps correlated well with tomato seed germination rates under all conditions.