bluuebunny/crossref_metadata_2025_split huggingface dataset:
Creating contextually authentic science in a “low‐performing” urban elementary school
Authors: Buxton Cory A. 
Published: May 2006

AbstractThis article reports on a 2½‐year collaborate project to reform the teaching and learning of science in the context of Mae Jemison Elementary, the lowest performing elementary school in the state of Louisiana. I outline a taxonomy of authentic science inquiry experiences and then use the resulting framework to focus on how project participants interpreted and enacted ideas about collaboration and authenticity. The resulting contextually authentic science inquiry model links the strengths of a canonically authentic model of science inquiry (grounded in the Western scientific canon) with the strengths of a youth‐centered model of authenticity (grounded in student‐generated inquiry), thus bringing together relevant content standards and topics with critical social relevance. I address the question of how such enactments may or may not promote doing science together and consider the implications of this model for urban science education. © 2006 Wiley Periodicals, Inc. J Res Sci Teach 43: 695–721, 2006
Reproductive life history of South African cheetahs (Acynonyx jubatus jubatus) at the San Diego Zoo Wild Animal Park, 1970–2005
Authors: Augustus Paula , Casavant Kelly , Troxel Natalie , Rieches Randy , Bercovitch Fred 
Published: May 2006

AbstractWe analyzed 35 years of data from a captive breeding program of cheetahs to determine basic reproductive life history characteristics of females. Breeding females ranged in age from 2.7–10.5 years. Sixteen females and over 13 males produced 129 cubs in 36 litters, with an average litter size of 3.6. Older females produced significantly fewer cubs per litter than younger females, but cub survivorship was comparable across female ages. Sex ratio was balanced at birth and 71% of infants survived the weaning period. Given that the reproductive output of captive cheetahs in our study is similar to that in other zoologic institutions and to cheetahs in the wild, we suggest that reproductive deficits in captive cheetahs arise from the inability of some pairs to breed, due to a lack of mating preference, rather than from a species‐wide problem. Zoo Biol 0:1–8, 2006. © 2006 Wiley‐Liss, Inc.
Incorporation of 5‐aminolevulinic acid into chlorophyll in darkness in barley
Authors: Packer Nicolle , Adamson Heather 
Published: May 2006

The incorporation of radioactive aminolevulinic acid (ALA) into chlorophyll (Chl) a and b, as well as protochlorophyllide (Pchlide) in light‐grown barley seedlings (Hordeum vulgare L. cv. Clipper) transferred to darkness is demonstrated.In the experiments described, 6‐day‐old, glasshouse‐grown seedlings were transferred to darkness and incubated in [14C]‐ or [3H]‐ ALA for 18 h.Chl a and b were extracted and purified to constant specific radioactivity by HPLC and TLC of their magnesium‐free derivatives, pheophytin a and b. The presence of label in the tetrapyrrole ring of the Chls was established by removal of the phytol chain by alkaline hydrolysis and determination of the specific radioactivity of the chlorin e6 and rhodin g7 derivatives.Barley seedlings that had been grown in darkness for 5 days, transferred to light for 20 h, and then returned to darkness in the presence of radioactive ALA also incorporated label into Chl. However, this was only apparent in intact seedlings. Excised leaves from greened etiolated plants did not incorporate ALA into Chl in darkness. This was consistent with the finding of Apel et al. (K. Apel, M. Motzkus and K. Dehesh, 1984. Planta 161: 550–554) and may account for their failure to obtain evidence for a light‐independent protochlorophyllide reductase in greening barley.Although the incorporation of ALA into Chl compared to Pchlide was slight (5%), the presence of label in the tetrapyrrole nucleus of Chl a and b is unequivocal evidence of a light‐independent pathway of Chl biosynthesis in barley that has been exposed to light during development. Limited entry of exogenous labelled ALA into the precursor pools leading to the dark reduction of Pchlide is postulated.
Metabolism of [13C]‐labelled photosynthate in plant cytosol and bacteroids of root nodules of Glycine max
Authors: Kouchi Hiroshi , Yoneyama Tadakatsu 
Published: May 2006

Well‐nodulated soybean (Glycine max L. Merr. cv. Akisengoku) plants were allowed to assimilate 13CO2. Plant cytosol and bacteroid fractions were isolated from nodules, and the kinetics of [13C]‐labelling of soluble carbohydrates, organic acids and amino acids were investigated.The concentrations of all metabolites, with the exception of trehalose and 3‐hydroxy‐butyrate, were 10‐ to 1000‐fold higher in plant cell cytosol than in bacteroids. The major portion of trehalose was found in bacteroids and 3‐hydroxybutyrate only in bacteroids. Sucrose was most highly labelled with 13C in nodules, and the levels and time‐course of labelling of sucrose were in good agreement with those of respired CO2 from the nodules. The levels and time‐courses of labelling of sucrose were closely similar in cytosol and bacteroids. Glucose was less labelled than sucrose and the level of labelling was consistently higher in cytosol than in bacteroids. The levels of [13C]‐labelling of organic acids and amino acids in nodules were lower than those of sucrose and of respired CO2. Tricarboxylic acid cycle intermediates, particularly succinate, were considerably less labelled in bacteroids than in the cytosol. All amino acids detected were also much more rapidly labelled in the cytosol. The results are discussed in relation to the utilization and possible compartmentation of carbon substrates in nodule tissues.
Patterns of adenine metabolism and caffeine biosynthesis in different parts of tea seedlings
Authors: Ashihara Hiroshi , Kubota Hiromi 
Published: May 2006

Contents of purine alkaloids in different parts of tea (Camellia sinensis L. cv. Yabukita) seedlings, seeds and tissue cultures were determined with high‐performance liquid chromatography. More than 99% of the caffeine detected was in the leaves of the 4‐month‐old seedlings. The amount expressed per g fresh weight was higher in older leaves. Theobromine, a precursor of caffeine biosynthesis, was found only in younger leaves. Zero or only trace amounts of theophylline, a degradation product of caffeine, were found in the seedlings. Almost all the caffeine in tea seeds was found in the seed coats. Theobromine and theophilline could not be detected in any part of the seeds.Tracer experiments using [8‐14C]‐adenine indicate that (i) caffeine biosynthesis from [8‐14C]‐adenine occurs only in younger leaves,(ii) “salvage” of [8‐14C]‐adenine for nucleic acid synthesis takes place in all parts of the seedlings, (iii) considerable degradation of [8‐14C]‐adenine by conventional purine degradation pathway via uric acid takes place in roots and lower parts of stem tissue.The results strongly suggest that caffeine is synthesized in younger leaves and accumulated within the leaves. Both caffeine contents and its synthetic activity from adenine were extremely low in tissue culture of tea.
Changes in the levels and composition of sterols in different tissues of Lolium temulentum plants during floral development
Authors: Garg Vipin K. , Paleg Leslie G. 
Published: May 2006

Free, esterified and glycosylated sterols were analysed separately from the shoot apices, leaves, leaf sheaths and stems of Lolium temulentum L. (strain Ceres) plants during floral development. Short‐day grown plants (50 days old) were induced to flower by exposure to a single long day. The four major sterols found by GC‐MS analysis were sitosterol, cholesterol, campesterol and stigmasterol. The sterol levels in the shoot apex were much higher than those in the leaf, leaf sheath and stem. A much greater proportion of cholesterol was found in the shoot apex than in other tissues and this may reflect a specific association of cholesterol with meristematic and/or reproductive tissues.During the inductive treatment, the sterol levels decreased in all four tissues. The major effect during early differentiation was the occurrence of transient increases in the free and esterified sterol levels in the leaf and the stem tissues. The steryl ester content peaked 24 h before the appearance of double ridges, followed by a peak in free sterol content at the double ridge stage. Similar changes could not be detected in the shoot apices. This is the first report of the sterol composition of developing shoot apices, and the results emphasize the dynamic nature of sterol metabolism during reproductive growth of L. temulentum.
Net CO2 output by CAM plants in the light: the role of leaf conductance
Authors: Frimert Volker , Kluge Manfred , Smith J. Andrew C. 
Published: May 2006

The reasons for CO2 release by some CAM plants during the light period were investigated by comparative gas‐exchange studies with three leaf‐succulent species, Kalanchoë tubiflora Hamet, Sedum morganianum E. Walth. and Sempervivum tectorum L. Sempervivum showed net CO2 output during the day at constant day‐night temperatures of both 15 and 25°C, whereas Kalanchoë and Sedum showed no CO2 release at this time at either temperature. Net nocturnal CO2 uptake was markedly reduced at 25°C compared with 15°C in Kalanchoë and Sempervivum, while CO2 was released at night at higher temperature by Sedum if leaf/air vapour pressure difference was also increased.Values for intercellular partial pressure of CO2 (piCO2) were calculated from leaf conductance and were characteristically lowest in the dark and highest in the light period. Maximum values of piCO2 ranged from 264 Pa in Sedum to 87 Pa in Kalanchoë, but were somewhat lower than those reported from direct measurements of the gas phase in other CAM plants. Leaf conductance declined with increasing piCO2 in all three species. Minimum values of approximately 0.2 mmol m−2 s−1 were observed at piCO2= 33 Pa in Kalanchoë and Sedum, with no further decrease at higher piCO2, implying that this largely represented the conductance of the cuticle. In Sempervivum, however, leaf conductance declined more gradually, and was as much as 0.8 mmol m−2 s−1 at the highest observed values of piCO2. The cause of net CO2 output in the light by Sempervivum thus appeared to be lower stomatal sensitivity to CO2, resulting in relatively high leaf conductance even at times when piCO2 greatly exceeded that of ambient air.
Regulation of nitrate reductase in detached oat leaves by light and oxygen
Authors: Kenis J. D. , Trippi V. S. 
Published: May 2006

Regulation of nitrate reductase (NR, EC 1.6.6.1) by oxygen concentration and light was studied in segments of oat (Avena sativa L. cv. Suregrain) leaves, using the in vivo nitrate reductase assay. The activity of NR decreased after excision in either light or darkness; the addition of cycloheximide prevented this decrease. Treatments that increased tissue permeability (anoxia, Triton X‐100) also increased NR activity. There was in general less NR activity in the light than in the dark and also less under aerobic (21–100% O2) than under anaerobic (0.3% O2) conditions. Treatments with antioxidants improved the activity in the light, but only at high O2 levels (21–100% O2).The results suggest that NR may be regulated by inhibitory proteins synthesized in either light or darkness, by permeability changes and by light‐induced oxidations that occur when O2 is present. Oxygen may control the activity by stimulating the synthesis of inhibitory proteins in the light and in the dark and by promoting oxidation of SH‐groups in the light.
Differences between the flag leaf and the ear of a spring wheat cultivar (Triticum aestivum cv. Arkas) with respect to the CO2 response of assimilation, respiration and stomatal conductance
Authors: Knoppik D. , Selinger H. , Ziegler‐Jöns A. 
Published: May 2006

The CO2‐ and H2O‐exchanges in the flag leaf and the ear of a spring wheat cultivar (Triticum aestivum L. cv. Arkas) were measured at CO2 partial pressures, pi(CO2), between 8 and 400 Pa under high photosynthetic photon flux densities (2000 μmol m−2 s−1). The experiments were carried out on each organ separately while attached to the intact plant, from the time of ear emergence through senescence. To study the contribution of the kernels to the gas exchange of ears, experiments were also carried out on sterilized ears (treatment A), and on ears from which the kernels were removed (treatment B).Flag leaves and ears differed considerably with regard to CO2‐dependence of assimilation, response of stomata to varying pa(CO2), CO2 compensation point (and its temperature dependence), dark respiration, and dissimilation in the light (i.e. CO2 production which is not due to oxygenation of ribulose 1,5‐bisphosphate). The higher dark respiration of the ear originated mainly from the kernels and continued to some extent in the light. Thus, the CO2 compensation point was attained at higher CO2 partial pressures for the ear than for the flag leaf.The CO2 uptake of the ear was not saturated at intercellular CO2 partial pressures below 180 Pa CO2, while that of the flag leaf reached saturation at about 80 Pa CO2. CO2‐saturated rates of CO2 uptake were 2.5 and 1.5 times the rates at natural CO2 partial pressure for ear and flag leaf, respectively. The stomatal conductance decreased with rising CO2 partial pressure above 35 Pa, in a more pronounced manner for the flag leaf than for the ear.
Responses of Pinus clausa, Pinus serotina and Pinus taeda seedlings to anaerobic solution culture. II. Changes in tissue nutrient concentration and net acquisition
Authors: Topa Mary A. , McLeod Kenneth W. 
Published: May 2006

Fifteen or 30 days of anaerobic growth conditions significantly reduced shoot and root nitrogen, potassium, phosphorus, iron and manganese concentrations in seedlings of pond pine (Pinus serotina Michx.), sand pine [P. clausa (Engelm.) Sarg.] and drought‐hardy and wet‐site loblolly pine (P. taeda L.) grown in a culture system using non‐circulating, continuously flowing solution. Calcium and shoot magnesium levels were least affected by anaerobic growth conditions – largely reflecting the passive nature of their uptake. Shoot and root nutrient content (mg nutrient pot‐1) followed similar trends, with wet‐site loblolly and pond pine seedlings least affected by anaerobic solution culture. Shoot biomass of wet‐site loblolly and pond pine seedlings was not affected by anaerobiosis, suggesting an increase in shoot nutrient utilization efficiency. Root biomass was significantly reduced by 15 or 30 days of anaerobiosis, with sand pine exhibiting the largest reduction in root dry weight (57%).These results suggest that anaerobiosis interferes with net nutrient acquisition, even under the high nutrient conditions provided by solution culture. Sand pine suffered the largest reductions in shoot and root biomass and nutrient concentrations, showing earlier symptoms of waterlogging injury and nutrient stress than drought‐hardy loblolly pine seedlings. Whether net nutrient acquisition decreased because of the reduction in root surface area available for absorption and/or reduced uptake efficiency cannot be ascertained from these data.
Effects of a brassinosteroid on growth and on H+‐extrusion in isolated radish cotyledons: comparison with the effects of benzyladenine
Authors: De Michelis Maria Ida , Lado Piera 
Published: May 2006

We investigated the effect of 24‐epibrassinolide (BR) on the cytokinin‐bioassay based on growth of isolated radish (Raphanus sativus L. cv. Tondo Rosso Quarantino) cotyledons. BR stimulated growth of the cotyledons by about 50% when applied at saturating concentrations (3 μM). This effect was much lower than that of saturating concentrations of benzyladenine (BA) which was about 150% at 10 μM BA. The effects of saturating concentrations of BR and BA were additive. BR, but not BA, stimulated H+‐secretion by the cotyledons (measured as acidification of the incubation medium) slightly but reproducibly. These results indicate that the modes of action of the two phytoregulators are at least partially different.BR‐induced stimulation of H+‐secretion was of similar amplitude to that induced by a concentration of fusicoccin (30 nM) such as to stimulate growth to the same extent as BR. These results suggest that BR‐induced stimulation of radish cotyledon growth might depend, at least in part, on BR‐induced acidification of the wall space, similar to that observed on Azuki bean epicotyls and maize roots.
Changes in accumulation of seed nitrogen compounds in maize under conditions of sulphur deficiency
Authors: Baudet Jacques , Huet Jean‐Claude , Jolivet Eugène , Lesaint Christiane , Mossé Jacques , Pernollet Jean‐Claude 
Published: May 2006

Maize (Zea mays L., hybrid INRA 260) was grown in the greenhouse with mineral nutrition of different sulphate concentrations. Mature seeds from these plants were compared for their free amino acid and protein N forms. For the most S‐deficient sample, the Asx (asparagine + aspartic acid) content increased by 30% as compared with control, while methionine and cysteine decreased (by 25 and 30%, respectively), as well as glycine, lysine, histidine, arginine and tryptophan. In seeds lowest in S the non‐protein N to total N ratio was 77% higher than in the control. Free asparagine dominated in starved seeds (50 mol % of total free amino acids) and was ten‐fold more concentrated than in the control, where proline was the predominant free amino acid. Thus the Asx of non‐protein N reached 28% of the total mol Asx of the whole starved seed. Altered S nutrition had virtually no effect on the amino acid composition of the main protein fractions, but it significantly changed their ratios. Zeins, which are poor in S‐containing amino acids, showed 25% higher level than in seeds supplied with normal S. As a counterbalance, two glutelin subfractions rich in S‐containing amino acids, decreased by 36–71% under limiting S nutrition.It is concluded that the plant reacts against S deficiency by modifying its N metabolism. Significant accumulation occurred of free asparagine, which is the main form of N transportation. The biosynthesis of seed storage protein occurred through the accumulation of the highest possible protein quantity allowed by the available S‐containing amino acids, i.e. proteins low in S‐containing amino acids were preferentially synthesized.
Effect of benzyladenine on the polypeptide pattern of plastids in excised watermelon cotyledons
Authors: Longo Giovanna P. , Bracale Marcella , Rossi Gianfranca , Longo Claudio P. 
Published: May 2006

We have shown in a previous paper that plastids of watermelon (Citrullus vulgaris Schrad., cv. Fairfax) cotyledons differentiate into amyloplasts when the cotyledons are grown in water and into prochloroplasts when they are grown in benzyladenine (BA) solution. In the present work we have tested whether this large difference in development of the plastids is accompanied by equally conspicuous changes in their polypeptide pattern. Cotyledons were grown for 4 days in the dark either on distilled water or on 10−5M BA. Alternatively they were transfered to 10−5M BA after 4 days of growth in water.Plastids of control cotyledons had a rather simple polypeptide pattern. The only prominent protein bands were the two subunits of ribulose bisphosphate carboxylase (EC 4.1.1.39). Contamination with storage protein was present. Plastids from BA‐treated cotyledons had a much more complex polypeptide pattern. No storage protein contamination was observed. Polypeptide bands present only as traces in the control and having molecular weights of 32, 44, 48 and 49 kDa increased in intensity after an exposure of only 6 h to BA. The 32‐kDa band seemed to be most dependent on the presence of the hormone. Contrary to what was observed in plastids, BA seemed to have no influence on the polypeptide pattern of mitochondria.
Controls on calcium ion fluxes in injured or shocked corn root cells: Importance of proton pumping and cell membrane potential
Authors: Rincon Magaly , Hanson John B. 
Published: May 2006

Passive influx of 45Ca2+ into non‐growing corn root tissue (Zea mays L.) was increased as a result of actions (cutting, rubbing, chilling, heating, acidifying) or agents (cyanide, uncouplers) known to depolarize the cell membrane, and was decreased by actions (washing) or agents (fusicoccin) known to hyperpolarize it. These responses indicate the presence of Ca2+ channels which are voltage controlled. If the injuries were extensive, however, voltage control was lost and hyperpolarization with fusicoccin was expressed by increased 45Ca2+ influx. Control could be regained by tissue washing, and millimolar levels of external Ca2+ would protect against loss of control. Influx of Ca2+ was strongly inhibited by La3+, but only weakly by verapamil. Intact roots showed greater cold shock sensitivity in maturing cells than in growing cells. We conclude that corn roots normally restrict Ca2+ influx by a mechanism linked to hyper‐polarization of the plasmalemma.Calcium ions which enter cold‐shocked tissue are partially extruded during the early phase of recovery by a process stimulated by fusicoccin and subject to uncoupling.
Effects of Ca2+/Mg2+ chelators, SKF 525‐A and rotenone on phytochrome‐mediated betacyanin formation in Amaranthus seedlings
Authors: Obrenović Sneẑana 
Published: May 2006

The effects of EDTA, EGTA, SKF 525‐A (a selective inhibitor of cytochrome P‐450) and rotenone were studied in betacyanin induction by 6 h red and 5 min far‐red light, using etiolated, three‐day‐old Amaranthus caudatus L. half‐seedlings. With 0.1 mM EDTA, EGTA and rotenone, and with 10 μM SKF 525‐A, mainly the far‐red reversible betacyanin induction by red light was suppressed. Only in 0.1 mM rotenone was about 50% of that effect compensated by an increased far‐red irreversible betacyanin induction. An unspecific inhibition was obtained with 0.1 mM SKF 525‐A in both control and illuminated plants.These results are consistent with the view that red light, but not far‐red, causes Ca2+ efflux from both mitochondria and cytoplasm, whereas Ca2+ uptake is indicated mainly after illumination. The resulting switch in the coupling of the mitochondrial electron transport to a Ca2+ dependent one in cytochrome P‐450 system via respiratory complex 1, appears to be responsible for the far‐red reversibility. However, the bulk of the high irradiance reaction seems to be related to another secondary messenger, alternative to Ca2+.