bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calorimetric Properties of Dehydrating Pollen (Analysis of a Desiccation-Tolerant and an Intolerant Species)
Authors: Buitink J. , Walters-Vertucci C. , Hoekstra F. A. , Leprince O. 
Published: October 2016

Abstract
The physical state of water in the desiccation-tolerant pollen of Typha latifolia L. and the desiccation-sensitive pollen of Zea mays L. was studied using differential scanning calorimetry in an attempt to further unravel the complex mechanisms of desiccation tolerance. Melting transitions of water were not observed at water content (wc) values less than 0.21 (T. latifolia) and 0.26 (Z. mays) g H2O/g dry weight. At moisture levels at which melting transitions were not observable, water properties could be characterized by changes in heat capacity. Three hydration regions could be distinguished with the defining wc values changing as a function of temperature. Shifts in baseline power resembling second-order transitions were observed in both species and were interpreted as glass-to-liquid transitions, the glass-transition temperatures being dependent on wc. Irrespective of the extent of desiccation tolerance, both pollens exhibited similar state diagrams. The viability of maize pollen at room temperature decreased gradually with the removal of the unfrozen water fraction. In maize, viability was completely lost before grains were sufficiently dried to enter into a glassy state. Apparently, the glassy state per se cannot provide desiccation tolerance. From the existing data, we conclude that, although no major differences in the physical behavior of water could be distinguished between desiccation-tolerant and -intolerant pollens, the physiological response to the loss of water varies between the two pollen types.
Characterization of Membrane Properties in Desiccation-Tolerant and -Intolerant Carrot Somatic Embryos
Authors: Tetteroo FAA. , de Bruijn A. Y. , Henselmans RNM. , Wolkers W. F. , van Aelst A. C. , Hoekstra F. A. 
Published: October 2016

Abstract
In previous studies, we have shown that carrot (Daucus carota L.) somatic embryos acquire complete desiccation tolerance when they are treated with abscisic acid during culture and subsequently dried slowly. With this manipulable system at hand, we have assessed damage associated with desiccation intolerance. Fast drying caused loss of viability, and all K+ and carbohydrates leached from the somatic embryos within 5 min of imbibition. The phospholipid content decreased by about 20%, and the free fatty acid content increased, which was not observed after slow drying. However, the extent of acyl chain unsaturation was unaltered, irrespective of the drying rate. These results indicate that, during rapid drying, irreversible changes occur in the membranes that are associated with extensive leakage and loss of germinability. The status of membranes after 2 h of imbibition was analyzed in a freeze-fracture study and by Fourier transform infrared spectroscopy. Rapidly dried somatic embryos had clusters of intramembraneous particles in their plasma membranes, and the transition temperature of isolated membranes was above room temperature. Membrane proteins were irreversibly aggregated in an extended β-sheet conformation and had a reduced proportion of α--helical structures. In contrast, the slowly dried somatic embryos had irregularly distributed, but non-clustered, intramembraneous particles, the transition temperature was below room temperature, and the membrane proteins were not aggregated in a β-sheet conformation. We suggest that desiccation sensitivity of rapidly dried carrot somatic embryos is indirectly caused by an irreversible phase separation in the membranes due to de-esterification of phospholipids and accumulation of free fatty acids.
Chloroplast Distribution in Arabidopsis thaliana (L.) Depends on Light Conditions during Growth
Authors: Trojan A. , Gabrys H. 
Published: October 2016

Abstract
Chloroplasts of Arabidopsis thaliana move in response to blue light. Sensitivity to light and the range of fluence rates to which the chloroplasts respond were found to be comparable to those of other higher plants studied. We investigated typical chloroplast distributions in Arabidopsis grown under three different light conditions:standard-light conditions, similar to natural light intensities; weak-light intensities, close to the compensation point of photosynthesis; and strong-light intensities, close to the saturation of the light-response curve of photosynthesis. We observed a striking difference in chloroplast arrangement in darkness between plants grown under weak- and strong-light conditions. There was a slight difference after weak-light pretreatment, and the arrangements of chloroplasts after strong-light pretreatment in both plant groups were very similar. These results support the ecological significance of chloroplast movements.
The N-1-Naphthylphthalamic Acid-Binding Protein Is an Integral Membrane Protein
Authors: Bernasconi P. , Patel B. C. , Reagan J. D. , Subramanian M. V. 
Published: October 2016

Abstract
N-1-Naphthylphthalmic acid (NPA)-binding protein is a plasmalemma (PM) protein involved in the control of cellular auxin efflux. We re-evaluated the spatial relationship of this protein with the PM of zucchini (Cucurbita pepo L.) hypocotyls. First, Triton X-114 partitioning indicated that the NPA-binding protein was more hydrophobic than most PM proteins. Second, the NPA-binding activity was found to be resistant to proteolytic digestion in membranes. Maximum concentrations of binding sites for NPA were virtually identical in untreated and proteinase K-treated PMs: 19.2 and 20.6 pmol [3H]NPA bound/mg protein, respectively. The insensitivity of the NPA-binding protein was not due to its presence inside tightly sealed vesicles or due to lack of protease activity in the conditions tested. This protein could be made sensitive to proteolytic degradation upon solubilization by 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate in the presence of sodium molybdate. Proteinase K treatment decreased the concentration of binding sites to 0.84 pmol [3H]NPA bound/mg protein from 9.2 for untreated, solubilized PM. Third, this activity could not be solubilized by chaotropic agents or sodium carbonate treatment of intact PM. This study indicates that the NPA-binding protein may be an integral membrane protein and contradicts previously reported findings that suggested that this protein was peripheral to the PM.
Alterations in Structural Polysaccharides during Liquefaction of Tomato Locule Tissue
Authors: Cheng G. W. , Huber D. J. 
Published: October 2016

Abstract
The locule tissue of tomato (Lycopersicon esculentum, Mill.) undergoes extensive liquefaction during ripening. In this study, the solubility, molecular mass, and glycosyl composition of locule pectic and alkali-soluble polysaccharides were examined with the aim of identifying features contributing to the unique properties of this tissue. Ethanol-insoluble solids were prepared from de-seeded locule tissue from tomato fruit at the immature green (IMG), mature green, and breaker stages of development. Ethanol-insoluble pectins were extracted sequentially in H2O, 50 mM trans-1,2-diaminocyclohexane-N,N,N[prime],N[prime]-tetraacetic acid, 50 mM Na2CO3, and 4 M KOH. At the IMG stage, nearly 85% of the locule pectins were solubilized by water, trans-1,2-diaminocyclohexane-N,N,N[prime],N[prime]-tetraacetic acid, and Na2CO3 solutions. Solubility increased only slightly with further locule development. The noncovalently associated polymers were of high molecular mass throughout liquefaction. Polymers extracted in mild alkali were of considerably lower molecular mass. Locule pectins in IMG fruit were heavily glycosylated with galactose, arabinose, and xylose. All pectin classes exhibited similar deglycosylation trends during liquefaction. Locule hemicelluloses were rich in glucose, xylose, and arabinose. These polymers collectively showed molecular mass downshifts with minimal compositional changes during liquefaction. The KOH-soluble material also included xylose-rich acidic polymers not matching the neutral sugar profile of the noncovalently associated pectic polymers.
Volatile Semiochemicals Released from Undamaged Cotton Leaves (A Systemic Response of Living Plants to Caterpillar Damage)
Authors: Rose USR. , Manukian A. , Heath R. R. , Tumlinson J. H. 
Published: October 2016

Abstract
Cotton plants (Gossypium hirsutum L.), attacked by herbivorous insects release volatile semiochemicals (chemical signals) that attract natural enemies of the herbivores to the damaged plants. We found chemical evidence that volatiles are released not only at the damaged site but from the entire cotton plant. The release of volatiles was detected from upper, undamaged leaves after 2 to 3 d of continuous larval damage on lower leaves of the same plant. Compounds released systemically were (Z)-3-hexenyl acetate, (E)-β-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-β-farnesene, (E,E)-α--farnesene, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. All systemically released compounds are known to be induced by caterpillar damage and are not released in significant amounts by undamaged plants. Other compounds, specifically indole, isomeric hexenyl butyrates, and 2-methylbutyrates, known to be released by cotton in response to caterpillar damage, were not released systemically. However, when upper, undamaged leaves of a caterpillar-damaged plant were damaged with a razor blade, they released isomeric hexenyl butyrates, 2-methylbutyrates, and large amounts of constitutive compounds in addition to the previously detected induced compounds. Control plants, damaged with a razor blade in the same way, did not release isomeric hexenyl butyrates or 2-methylbutyrates and released significantly smaller amounts of constitutive compounds. Indole was not released systemically, even after artificial damage.
Differential Expression of Lipoxygenase Isoenzymes in Embryos of Germinating Barley
Authors: Holtman W. L. , van Duijn G. , Sedee NJA. , Douma A. C. 
Published: October 2016

Abstract
Expression of lipoxygenase was studied in barley (Hordeum distichum L.) embryos during germination. Total lipoxygenase activity was high in quiescent grains, dropped during the 1st d of germination, and subsequently increased to a level similar to that in quiescent grains. The contribution of two isoenzymes, lipoxygenases 1 (LOX-1) and 2 (LOX-2), was studied at the activity, protein, and mRNA levels. Activity ratios of the two isoforms were determined via the ratio of 9- and 13-hydroperoxides, which are formed from linoleic acid. Isoenzyme protein levels were determined using specific monoclonal antibodies. mRNA levels were studied using the specific cDNA probes LoxA and LoxC, which correspond to LOX-1 and LOX-2, respectively. The major difference in temporal expression of LOX-1 and LOX-2 was observed in quiescent grains. At this stage, LOX-1 contributed almost exclusively to total lipoxygenase activity. LOX-2 activity rapidly increased until d 2 of germination. From this time point onward, LOX-1 and LOX-2 showed similar patterns at both activity and protein levels. The tissue distribution of the two isoenzymes in the germinating embryo was closely similar, with the highest expression levels in leaves and roots. The levels of LOX-1 and LOX-2 may be regulated mainly pretranslationally, as suggested by the similarity of the protein and mRNA patterns corresponding to the two isoforms.
Growth Inhibition in Suspension-Cultured Rice Cells under Phosphate Deprivation Is Mediated through Putrescine Accumulation
Authors: Shih C. Y. , Kao C. H. 
Published: October 2016

Abstract
The effects of phosphate deprivation on the growth and polyamine levels of suspension-cultured rice (Oryza sativa) cells were investigated. When rice suspension cells were deprived of phosphate, cell growth was markedly inhibited. Phosphate deprivation resulted in a higher putrescine level and lower spermidine and spermine levels in rice suspension cells. The growth of rice cells cultured in the absence of phosphate did not recover as a result of spermidine and spermine addition. D-Arginine and α--methylornithine, inhibitors of putrescine biosynthesis, caused a reduced level of putrescine in rice suspension cells cultured under phosphate deprivation. The growth of rice cells cultured in the absence of phosphate was completely recovered after the addition of D-arginine but not α--methylornithine. Our results indicate that putrescine accumulation is a factor causing growth inhibition of suspension-cultured rice cells under phosphate deprivation.
Biosynthesis of Caffeine in Leaves of Coffee
Authors: Ashihara H. , Monteiro A. M. , Gillies F. M. , Crozier A. 
Published: October 2016

Abstract
The levels of endogenous caffeine and theobromine were much higher in buds and young leaves of Coffea arabica L. cv Kent than in fully developed leaves. Biosynthesis of caffeine from 14C-labeled adenine, guanine, xanthosine, and theobromine was observed, whereas other studies (H. Ashihara, A.M. Monteiro, T. Moritz, F.M. Gillies, A. Crozier [1996] Planta 198: 334–339) have indicated that there is no detectable incorporation of label into caffeine when theophylline and xanthine are used as substrates for in vivo feeds with leaves of C. arabica. The capacity for caffeine biosynthesis, especially from guanine and xanthosine, was reduced markedly in both fully developed mature and aged leaves. Data obtained in pulse-chase experiments with young leaves indicate the operation of an AMP -&gt; IMP -&gt; xanthosine 5[prime]-monophosphate (or GMP -&gt; guanosine) -&gt; xanthosine -&gt; 7-methylxanthosine -&gt; 7-methylxanthine -&gt; theobromine -&gt; caffeine pathway. The data obtained provide strong evidence against proposals by G.M. Nazario and C.J. Lovatt ([1993] Plant Physiol 103: 1203–1210) concerning the independence of caffeine and theobromine biosynthesis pathways and the role of xanthine as a key intermediate in caffeine biosynthesis.
Analysis of Cytokinin Metabolism in ipt Transgenic Tobacco by Liquid Chromatography-Tandem Mass Spectrometry
Authors: Redig P. , Schmulling T. , Van Onckelen H. 
Published: October 2016

Abstract
The endogenous levels of the major, naturally occurring cytokinins in Pisum sativum ribulose-1,5-bisphosphate carboxylase small subunit promoter-isopentenyl transferase gene (Pssu-ipt)-transformed tobacco (Nicotiana tabacum L.) callus were quantified using electrospray-liquid chromatography-tandem mass spectrometry during a 6-week subcultivation period. An ipt gene was expressed under control of a tetracycline-inducible promoter for a more detailed study of cytokinin accumulation and metabolism. Activation of the ipt in both expression systems resulted in the production of mainly zeatin-type cytokinins. No accumulation of isopentenyladenine or isopentenyladenosine was observed. In Pssu-ipt-transformed calli, as well as in the tetracycline-inducible ipt leaves, metabolic inactivation occurred through O-glucoside conjugation. No significant elevation of cytokinin N-glucosides levels was observed. Side-chain reduction to dihydrozeatin-type cytokinins was observed in both systems. The levels of the endogenous cytokinins varied in time and were subject to homeostatic regulatory mechanisms. Feeding experiments of ipt transgenic callus with [3H]isopentenyladenine and [3H]isopentenyladenosine mainly led to labeled adenine-like compounds, which are degradation products from cytokininoxidase activity. Incorporation of radioactivity in zeatin riboside was observed, although to a much lesser extent.
Role of Jasmonates in the Elicitor- and Wound-Inducible Expression of Defense Genes in Parsley and Transgenic Tobacco
Authors: Ellard-Ivey M. , Douglas C. J. 
Published: October 2016

Abstract
Jasmonates have been proposed to be signaling intermediates in the wound and/or elicitor-activated expression of plant defense genes. We used parsley (Petroselinum crispum) cell cultures and transgenic tobacco (Nicotiana tabacum) plants expressing 4CL1-GUS gene fusions to investigate the potential role played by jasmonates in mediating the wound and/or elicitor activation of phenylpropanoid and other defense-related genes. Jasmonates and α--linolenic acid strongly induced the expression of 4CL in a dose-dependent manner in parsley cells; methyl jasmonate also activated the coordinate expression of other phenylpropanoid genes and the accumulation of furanocoumarin phytoalexins. However, the response of the cells to optimal methyl jasmonate concentrations was distinct quantitatively and qualitatively from the response of elicitor-treated cells. In transgenic tobacco wound-inducible tobacco 4CL genes and a 4CL1 promoter-GUS transgene were responsive to jasmonates and α--linolenic acid in a dose-dependent manner. Pre-treatment of parsley cells or tobacco leaves with a lipoxygenase inhibitor reduced their responsiveness to the elicitor and to wounding. These results show that the elicitor response in parsley cells can be partially mimicked by jasmonate treatment, which supports a role for jasmonates in mediating wound-induced expression of 4CL and other phenylpropanoid genes.
Correlation of Rapid Cell Death with Metabolic Changes in Fungus-Infected, Cultured Parsley Cells
Authors: Naton B. , Hahlbrock K. , Schmelzer E. 
Published: October 2016

Abstract
To study in detail the hypersensitive reaction, one of the major defense responses of plants against microbial infection, we used a model system of reduced complexity with cultured parsley (Petroselinum crispum) cells infected with the phytopathogenic fungus Phytophthora infestans. Experimental conditions were established to maintain maximal viability of the cultured cells during co-cultivation with fungal germlings, and a large proportion of the infected parsley cells responded to fungal infection with rapid cell death, thereby exhibiting major features of the hypersensitive reaction in whole-plant-pathogen interactions. Rapid cell death clearly correlated with termination of further growth and development of the fungal pathogen. Thus, the system fulfilled important prerequisites for investigating cell-death-related metabolic changes in individual infected cells. Using cytochemical methods, we monitored the increase of mitochondrial activity in single infected cells and the intracellular accumulation of reactive oxygen species prior to the occurrence of rapid cell death. We obtained strong correlative evidence for the involvement of these intracellularly accumulating reactive oxygen species in membrane damage and in the resulting abrupt collapse of the cell.
Tissue-Specific and Light-Mediated Expression of the C4 Photosynthetic NAD-Dependent Malic Enzyme of Amaranth Mitochondria
Authors: Long J. J. , Berry J. O. 
Published: October 2016

Abstract
In the C4 dicotyledonous grain plant amaranth (Amaranthus hypochondriacus), a mitochondrial NAD-dependent malic enzyme (NAD-ME; EC 1.1.1.39) serves a specialized and essential role in photosynthetic carbon fixation. In this study we have examined specialized photosynthetic gene expression patterns for the NAD-ME α- subunit. We show here that the α- subunit gene is preferentially expressed in leaves and cotyledons (the most photosynthetically active tissues), and this expression is specific to the bundle-sheath cells of these tissues from the earliest stages of development. Synthesis of the α- subunit polypeptide and accumulation of its corresponding mRNA are strongly light-dependent, but this regulation is also influenced by seedling development. In addition, light-dependent accumulation of the α- subunit mRNA is regulated at transcriptional as well as posttranscriptional levels. Our findings demonstrate that the NAD-ME of amaranth has acquired numerous complex tissue-specific and light-mediated regulation patterns that define its specialized function as a key enzyme in the C4 photosynthetic pathway.
The Effects of Exogenous Auxins on Endogenous Indole-3-Acetic Acid Metabolism (The Implications for Carrot Somatic Embryogenesis)
Authors: Ribnicky D. M. , Ilic N. , Cohen J. D. , Cooke T. J. 
Published: October 2016

Abstract
The effect of auxin application on auxin metabolism was investigated in excised hypocotyl cultures of carrot (Daucus carota). Concentrations of both free and conjugated indole-3-acetic acid (IAA), [2H4]IAA, 2,4-dichlorophenoxyacetic acid, and naphthaleneacetic acid (NAA) were measured by mass spectroscopy using stable-isotope-labeled internal standards. [13C1]NAA was synthesized for this purpose, thus extending the range of auxins that can be assayed by stable-isotope techniques. 2,4-Dichlorophenoxyacetic acid promoted callus proliferation of the excised hypocotyls, accumulated as the free form in large quantities, and had minor effects on endogenous IAA concentrations. NAA promoted callus proliferation and the resulting callus became organogenic, producing both roots and shoots. NAA was found mostly in the conjugated form and had minor effects on endogenous IAA concentrations. [2H4]IAA had no visible effect on the growth pattern of cultured hypocotyls, possibly because it was rapidly metabolized to form inactive conjugates or possibly because it mediated a decrease in endogenous IAA concentrations by an apparent feedback mechanism. The presence of exogenous auxins did not affect tryptophan labeling of either the endogenous tryptophan or IAA pools. This suggested that exogenous auxins did not alter the IAA biosynthetic pathway, but that synthetic auxins did appear to be necessary to induce callus proliferation, which was essential for excised hypocotyls to gain the competence to form somatic embryos.
Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem
Authors: Zanetti S. , Hartwig U. A. , Luscher A. , Hebeisen T. , Frehner M. , Fischer B. U. , Hendrey G. R. , Blum H. , Nosberger J. 
Published: October 2016

Abstract
Symbiotic N2 fixation is one of the main processes that introduces N into terrestrial ecosystems. As such, it may be crucial for the sequestration of the extra C available in a world of continuously increasing atmospheric CO2 partial pressure (pCO2). The effect of elevated pCO2 (60 Pa) on symbiotic N2 fixation (15N-isotope dilution method) was investigated using Free-Air-CO2-Enrichment technology over a period of 3 years. Trifolium repens was cultivated either alone or together with Lolium perenne (a nonfixing reference crop) in mixed swards. Two different N fertilization levels and defoliation frequencies were applied. The total N yield increased consistently and the percentage of plant N derived from symbiotic N2 fixation increased significantly in T. repens under elevated pCO2. All additionally assimilated N was derived from symbiotic N2 fixation, not from the soil. In the mixtures exposed to elevated pCO2, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m-2 a-1 in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N2 fixation is a competitive advantage for T. repens in mixed swards with pasture grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole.