bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of an Isoprene Synthase from Leaves of Quercus petraea (Mattuschka) Liebl.
Authors: Schnitzler J.‐P. , Arenz R. , Steinbrecher R. , Lehning Andrea 
Published: February 2014

Abstract:Biogenic emission of isoprene (2‐methyl‐1,3‐butadiene) by many plant species plays an important role in atmospheric chemistry. Its rapid breakdown in the atmosphere substantially affects the oxidation potential of the atmosphere. Leaves of Quercus petraea were found to contain an enzyme which catalyses the conversion of dimethylallyl pyrophosphate (DMAPP) to isoprene. A standard enzyme assay was established and the isoprene synthase activity was characterized in purified leaf extracts. Optimum enzyme activity was observed at pH 8.5. The enzyme had an apparent Km of 0.97 mM for its substrate DMAPP, but isopentenyl pyrophosphate (IPP), the isomeric form of DMAPP, was not converted to isoprene by the enzyme extract. The temperature optimum of the enzyme activity was 35 °C. Isoprene synthase activity was strictly dependent on the presence of bivalent cations, with magnesium being most effective. Molecular weight determination by FPLC revealed the presence of a single protein with a native molecular weight of approximately 90–100 kDa.
Taxonomic Studies in Foliicolous Species of the GenusPorinaI. ThePorina rufulaAggregate
Authors: Lücking R. 
Published: February 2014

Abstract:An analysis of character variation in species of thePorina rufulaaggregate, i.e.P. rufula(Kremp.) Vain.,P. limbulata(Kremp.) Vain.,P. rubentior(Stirt.) Müll. Arg., andP. pseudofulvellaSérus., showed that the hitherto applied concepts of species delimitation ‐ based on perithecial size and colour ‐ are not appropriate and should be replaced by a concept which primarily regards perithecial colour and shape as specific characters. Revision of type specimens proved the identity ofP. rufulaandP. pseudofulvella, whereasP. limbulatasensu Santesson had to be split intoP. limbulatas. str. andP. leptospermoidesMüll. Arg. Evolutionary tendencies are seen in reduction of thallus morphology and perithecial pigments as an adaptation to shady habitats, indicatingP. leptospermoidesas a more primitive andP. rufulaas a more advanced taxon. Judging from species distribution, the phylogenetic origin of theP. rufulaaggregate might be in the Neotropics.
Apoptosis in Plants
Authors: Havel L. , Durzan D.J. 
Published: February 2014

Abstract:Apoptosis is a feature of animal cells that explains some aspects of programmed cell death in plants. Differences between plant and animal cell development require that concepts be reexamined to signify how plant cells have evolved the need for cell elimination in the meristematic growth habit, life cycle, and alternation of generations. Central to this theme is the regulation of divisional cycles for mitosis, meiosis, apomeiosis, and their related sexual and asexual reproductive processes. Apoptosis depends on the coordinated expression of genes regulating divisional cycles and apoptotic pathways so that irreversible nuclear and cytoplasmic elimination occurs. Cellular degradation products are salvaged to sustain adaptation, viability, structural function, and ontogeny. The cell wall is usually retained and further differentiated or eliminated. A model of factors predisposing apoptosis and comprising checkpoints in cell divisional cycles is presented for comparisons among plant and animal cells.
The Role of Starch in the Gravitropic Response of the Lentil Root
Authors: Aarrouf J. , Perbal G. 
Published: February 2014

Abstract:It is well accepted that the amyloplasts of the cap are responsible for gravisensing in primary roots. However, roots with starch‐depleted plastids are able to respond to gravistimulus, but their curvature is slower than that of roots containing amyloplasts. The goal of our experiment was to analyse the effects of natural variations of statolith starch in the gravitropic response of lentil roots to a stimulation in the horizontal position. In lentil seedlings grown in the vertical position for 26 h, the volume of the amyloplasts in the statocytes differed between individual roots. The amount of starch in the cap was determined parallel to the rate of gravitropic curvature. There was no statistical correlation between the intensity of the gravitropic response and the starch content in the statocytes. Lentil roots were treated with gibberellic acid (GA3) at 32°C in order to reduce the volume of starch in the statoliths. There was 53% less starch in the cap of GA3treated roots as compared to the cap of control roots. But there was no relationship between starch content in the cap and the responsiveness of the root to a gravistimulus, except when the amount of starch was small.
The Arabidopsis thaliana AtSUC2 Gene is Specifically Expressed in Companion Cells
Authors: Stadler Ruth , Sauer N. 
Published: February 2014

Abstract:Polyclonal antisera against a fusion protein of β‐galactosidase and the 20 C‐terminal amino acids of the Arabidopsis thaliana sucrose carrier AtSUC2 were used to determine the cellular localization of the AtSUC2 protein. Using fluorescence‐labelling on sections from different organs of Arabidopsis the AtSUC2 protein was immunolocalized exclusively in companion cells. The presented data indicate that phloem loading in Arabidopsis may be catalyzed by the AtSUC2 sucrose carrier which transports sucrose into the companion cells. No evidence for a participation of the second Arabidopsis sucrose transporter AtSUC1 has been obtained.
Population Size, Pollination and Breeding System of Silene stockenii Chater (Caryophyllaceae), an Annual Gynodioecious Species of Southern Spain
Authors: Talavera S. , Arista M. , Salgueiro F. J. 
Published: February 2014

Abstract:The distribution area, phenology, sex polymorphism, floral characteristics and breeding system of Silene stockenii (Caryophyllaceae), a narrowly endemic annual species of southern Spain, were studied. Only five populations were found in a total area of 2 ha. Silene stockenii is a gynodioecious species with fully female, fully hermaphrodite and intermediate plants bearing hermaphrodite, male‐sterile, and partially male‐sterile flowers. Male‐sterile flowers are typically smaller than hermaphrodites. Nectar production was significantly higher in hermaphrodite plants and during the female phase of hermaphrodite flowers. The red flowers appear during the spring (March‐May) and are pollinated by long‐tongued Bombyliidae. Hand pollinations revealed that the species is self‐compatible; however, natural self‐pollination is rare due to marked protandry. Hand pollination significantly increased the number of seeds per fruit and seed set, indicating limited pollination in the field. In controlled pollinations female plants of S. stockenii produced higher seed set than hermaphrodite plants, but in freely pollinated plants fruit set and seed production was similar in both morphs, indicating that pollinators do not discriminate in favour of hermaphrodite plants.
Evidence for Symplastic Phloem Unloading with Concomitant High Activity of Acid Cell Wall Invertase in Agrobacterium tumefaciens‐Induced Plant Tumors*
Authors: Pradel Katja S. , Rezmer Claudia , Krausgrill Silke , Rausch T. , Ullrich Cornelia I. 
Published: February 2014

Abstract:In stems of Ricinus communis and leaves of Kalanchoë daigremontiana, rapidly growing tumors were induced by the wild type strains of Agrobacterium tumefaciens C58 and A281 (p35 Sgusint). Transformed cells, monitored by histochemical β‐glucuronidase (GUS) staining, showed GUS activity in K. daigremontiana tumors in up to 100% of the tissue. In R. communis tumors, however, GUS activity was patchy, probably due to interference in gus expression from highly active phenolic compounds. Functionality of the sieve elements within the vascular bundles of the tumor and their connection with host stem bundles were shown by applying fluorescein to source leaves as a tracer of phloem‐mobile solutes. The transport pathway within the tumor and the mechanism of phloem unloading were investigated by iontophoretic injection of Lucifer yellow CH into sieve tubes. Apparent symplastic solute unloading into parenchyma cells was confirmed by localizing common primary pit fields by staining them with aniline blue. In spite of the evidence for symplastic unloading, the activity of acid cell wall invertase (CWI) was about tenfold higher in tumor than in the adjacent host stem tissue. These results indicate primary independence of phloem unloading of CWI in tumors.
Structural and Functional Evidence for Xylem‐Mediated Water Transport and High Transpiration in Agrobacterium tumefaciens‐Induced Tumors of Ricinus communis*
Authors: Schurr U. , Schuberth Bettina , Aloni R. , Pradel Katja S. , Schmundt D. , Jähne B. , Ullrich Cornelia I. 
Published: February 2014

Abstract:Tumors induced by the wild‐type strain C58 of Agrobacterium tumefaciens in hypocotyls of Ricinus communis L. were investigated structurally and functionally with respect to xylem differentiation, cuticle and stomata development, water pathway and transpiration. Clearing of tissue with lactic acid and staining with lacmoid revealed a continuation of stem xylem into differentiated bundles in the tumor. Under the influence of tumors the host xylem below the tumors increased considerably in size. Transport of negatively‐charged dyes, amido black, acid fuchsin and the fluorescent pyrenetrisulfonate demonstrated a continuous water flow through the vessels from the stem into the tumor, and up to its surface. Infrared thermography and quantitative measurements of transpiration revealed that transpiration was about 15 times and 7.5 times higher at the tumor surface in comparison to host leaves and to leaves of non‐infected plants, respectively. Leaf CO2 assimilation rate remained unaffected by tumorisation. Tumor growth caused disruption of the epidermis, which did not regenerate and hence no cuticle developed to protect against water loss. Stomata located at the tumor rim hypertrophied and lost their function. Tumors are thus characterised as being structurally and functionally strong pathological water sinks on their host plant.
Frequency Resonances of the Circadian Rhythm of CAM Under External Temperature Rhythms of Varied Period Lengths in Continuous Light*
Authors: Lüttge U. , Grams T. E. E. , Hechler Bettina , Blasius B. , Beck F. 
Published: February 2014

Abstract:Net CO2 exchange (Jco2) of leaves of the CAM plant Kalanchoë daigremontiana Hamet et Perrier de la Bǎthie was studied in continuous light under the influence of temperature jumps of different period lengths. Each period consisted of two equal time intervals at a lower and a higher temperature, i.e. ≅24 and ≅29 °C respectively. At a period length of the imposed external temperature rhythm of 8 h the free running endogenous rhythm of Jco2 with a period length of 21.7 h was expressed. Under external rhythms of 12–28 h period length there was entrainment of Jco2. Under external rhythms of 40 and 56 h the time course of Jco2 became arrhythmic. In power spectra of the Jco2 time series obtained by Fourier analysis, besides the dominant frequency, there were other frequency peaks with lower Fourier amplitudes of Jco2. It was noted that these are natural number multiples of the major frequencies. A comparison shows that these frequencies correspond to the harmonic overtones of the basic oscillation of the free running endogenous rhythm of Jco2 at 24°C, viz. 1/22.5 h−1. The overall power of the enforced oscillations shows a typical resonance behaviour around the natural, free running frequency. The intriguing observation that external temperature jump rhythms lead to resonance, not only of the basic oscillation but also of its harmonic overtones, is discussed in relation to earlier findings suggesting the occurrence of paths between order and deterministic chaos in the CAM rhythm.
Experimental Studies on the Competitive Balance Between two Central European Roadside Grasses With Different Growth Forms
Authors: Beyschlag W. , Ryel R.J. , Ullmann I. , Eckstein J. 
Published: February 2014

Summary:Monocultures and 1:1 mixtures of the highly competitive grass Elymus repens (L.) Gould and the low competitive grass Puccinellia distans (Jacq.) Parl. were grown under controlled conditions in a growth chamber at four different soil depths and under various water and nutrient conditions in order to evaluate whether shallow soil depth could be the determining factor in causing a stable coexistence of the two species, or dominance of P. distans, as recently observed in the shallow soil areas of Middle European road shoulders. As expected, above‐ and belowground biomass production of monocultures of both species was strongly reduced by shallow soils under all treatments. However, with decreasing soil depth, the aboveground biomass fraction of P. distans was found to markedly increase relative to that of E. repens in the mixtures, particularly if the plants were grown under water‐stress conditions. Although biomass production of both species increased with high nutrient supply, nutrient levels did not affect the competitive relationship on shallow soils. Apparently, P. distans which naturally develops a rather extensive fine root system in the top 10–15 cm of soil is better able to effectively use the limited resources of shallow soil than the normally deeper rooted E. repens. In consequence, E. repens cannot produce enough aboveground biomass to effectively shade and ultimately exclude P. distans. Hydroculture experiments with both species at four different salinity levels revealed that biomass production of E. repens was more affected by salt stress than that of the facultative halophyte P. distans. Experiments are also presented which show that allelopathic effects of E. repens, which have been equivocally discussed in the literature, do not seem to affect biomass production of P. distans. It is concluded that shallow soil conditions are sufficient to create the observed patterns of co‐occurrence at the roadside, but that common road treatments like winter salt application or frequent mowing of the road shoulders further enhance the competitive ability of P. distans in the shallow soil areas close to the pavement.
Photoinhibition of Photosynthesis in Plants Growing in Natural Tropical Forest Gaps. A Chlorophyll Fluorescence Study
Authors: Krause G.H. , Winter K. 
Published: February 2014

Abstract:Photoinhibition of photosynthesis was monitored by means of chlorophyll a fluorescence in leaves of plants growing in 60–80 m2 light gaps in a moist tropical lowland forest located on Barro Colorado Island in central Panama. In these forest gaps, photon flux density was low (less than 100 μmol photons m−2 s−1) during most of the day, but increased on clear days to 1.7‐1.8 mmol photons m−2 s−1 for 1–2 h during midday. Nine species representing different taxa and life‐forms were examined. Leaves of all species exhibited substantial photoinhibition in situ during high light exposure, as manifested by a decrease in the ratio of variable to maximum fluorescence emission, FV/FM. Recovery (reversion of fluorescence quenching) took place in the shade following high light exposure. The major part of recovery occurred in a fast phase within about 1 h after the high light period. A slow phase of recovery proceeded for another 4–5 h until sunset. After 30–60 min of recovery in the shade, calculated rates of PSII electron transport remained significantly (5–15%) reduced in comparison to rates obtained prior to high light exposure; after about 2 h of recovery, inhibition was negligible. All species responded to the high light periods and following shade periods in a very similar manner. It is concluded that photoinhibition and recovery exhibited by these gap leaves reflect a dynamic regulatory mechanism of thermal energy dissipation that allows plants of different life‐forms to cope with periods of high light in tropical forest gaps.
Origin of the Woody Macaronesian Sempervivoideae and the Phylogenetic Position of the East African Species of Aeonium
Authors: Mes T. H. M. , van Brederode J. , Hart H. ‘t 
Published: February 2014

Abstract:Evolutionary relationships among the genera of Macaronesian Sempervivoideae, Aeonium, Aichryson, Greenovia, and Monanthes, were studied using sequence variation of the chloroplast DNA trnL (UAA) ‐ trnF (GAA) spacer and the nuclear ribosomal Internal Transcribed Spacer 2 (ITS2). Phylogenetic analysis indicates that the Moroccan Sedum sect. Monanthoidea is the sister taxon of the Macaronesian Sempervivoideae. In combination with the terminal position in the Macaronesian Sempervivoideae of the East African A. leucoblepharum, which has formerly been assumed to be the sister taxon of the other species of Macaronesian Sempervivoideae (i.e. Aichryson and Monanthes), a recent remigration to Africa is suggested. Statistical support for the terminal position of A. leucoblepharum using only spacer sequences is without homoplasy but not high since only single mutations in both the chloroplast and nuclear sequence characterize the clade containing A. leucoblepharum. A. leucoblepharum and the Canarian species with a similar growth‐form share 50% of the RAPDs. Within a clade comprising woody species with yellow flowers and a herbaceous rosette, the highest genetic divergence, as determined with RAPDs, is found between A. simsii and the woody Macaronesian and African species. The extremely close genetic ties among the woody and branched (sub)shrubs indicate that, when compared to the other species of the genus, the woody, African Aeonium species are not the sister group of the Macaronesian Sempervivoideae and substantiate the view that an ancestor of A. leucoblepharum recently migrated from the Canary Islands to East Africa and Arabia through long distance dispersal, rather than being a relict of an African Aeonium flora from the Tertiary.
Maternal Effect on Embryogenesis in Tobacco Overexpressing Rice Phytochrome A*
Authors: Emmler K. , Schäfer E. 
Published: February 2014

Abstract:When analyzing tobacco lines overexpressing various types of rice phytochrome A, we observed seedlings with fused cotyledons. Phytochrome A is a member of the phytochrome family of plant red/far‐red absorbing photoreceptors. Reciprocal crossings with wild‐type tobacco indicated that this abnormal phenotype was maternally inherited. Mother plants that were expected to produce abnormal seedlings, were raised under different conditions and seeds collected separately from individual capsules. The frequency of abnormal seedlings increased in seeds from later flowers but decreased when mother plants were raised under continuous white light. The interaction of the overexpressed phytochrome A proteins with endogenous plant hormones might be responsible for cotyledon fusion. The abnormal phenotype could partially be recovered by application of gibberellic acid to intact flowers at the time of pollination. In contrast, the synthetic auxin NAA slightly enhanced the degree of cotyledon fusion. Even wild‐type tobacco seedlings exhibited partial fusion of cotyledons if flowers were treated with 2,4‐D and occasionally the shoot apex was replaced by a second root. Application of GA3 to the flowers, in contrast, impaired the development of the radicule. These observations are discussed with respect to maternal effects in plant embryogenesis.
Regulation of CAM and Respiratory Recycling by Water Supply in Higher Poikilohydric Plants — Haberlea rhodopensis Friv. and Ramonda serbica Panč, at Transition from Biosis to Anabiosis and Vice Versa
Authors: Markovska Y. , Tsonev T. , Kimenov G. 
Published: February 2014

Abstract:In this paper the expression of C3 and CAM in the resurrection plants Haberlea rhodopensis Friv. and Ramonda serbica Panč, during the transition from biosis to anabiosis and Wee versa is reported for the first time. The transition from predominantly C3 metabolism to net dark fixation of CO2 occurred in leaves of R.serbica during desiccation. Desiccated plants of H. rhodopensis react by reducing light assimilation of CO2. When watering was resumed night time fixation of CO2 by R. serbica was observed within 24 hours. The recovery of CO2 fixation by H. rhodopensis was not seen until the 8 th day. Desiccated and rehydrated plants of H. rhodopensis recapture a higher proportion of respiratory CO2 than well‐watered plants. Since both species have little capacity for water conservation in their tissues, the early onset of high recycling of CO2 following drought could be an important mechanism for potentially saving water.
Gas Exchange, Water Loss and Biomass Production in Rice and Wild Oryza Species in Well‐Watered and Water‐Limiting Growth Conditions
Authors: Yeo M. E. , Cuartero J. , Flowers T. J. , Yeo A. R. 
Published: February 2014

Abstract:A major reason for the drought susceptibility of cultivated rice is the inability to regulate water loss as effectively as other cereals. We report studies of growth and gas exchange under well‐watered and water‐limiting conditions on selected species of Oryza and seek to relate this physiological information to the ecology of the genus. The immediate ancestor of the Oryza sativa cultigen is native to swamps and marshes, and wet habitats are typical for the genus as a whole. However, the ecological range of some species does extend to habitats that dry out seasonally. In all species studied growth was reduced by water deficit. In all species studied leaves had small absolute water contents and began to roll at a relative water content above 90%. However, there were species differences in leaf rolling and the response of stomatal conductance to an increase in vapour pressure deficit. Following re‐watering, there were persistent reductions in stomatal conductance in most of the species tested, but the assimilation rate was not reduced in all of these cases. Where there was a persistant reduction in assimilation rate, there was also a reduction in carboxylation efficiency. It was a frequent observation that plants had a stomatal conductance greater than expected for their carbon assimilation rate; that is in the range where substantial changes in conductance have little effect upon photosynthesis. It is suggested that a reason for this may be the cooling of leaves which have a small thermal capacity in environments which often combine high temperature, humidity and irradiance. Large conductances combined with small water contents may be no disadvantage in the natural habitats of Oryza, but provide some reasons for the poor regulation of water loss in cultivated rice. Although there were significant differences in gas exchange amongst species the advantages that were observed over O. sativa were not of a magnitude likely to justify wide hybridisation. This implies that improvement in the drought resistance of rice is more likely to come from increasing water acquisition than from decreasing water loss.