bluuebunny/crossref_metadata_2025_split huggingface dataset:
Signal transmission during gravitropic curvature of primary roots of Zea mays
Authors: MOORE R. , MAIMON E. 
Published: April 2006

ABSTRACTPrimary roots of Zea mays cv. Ageotropic are nonresponsive to gravity and elongate approximately 0.80 mm h−1. Applying mucilage‐like material (K‐Y Jelly) to the terminal 1.5 cm of these roots induces graviresponsiveness and slow elongation 28% (i.e. from 0.80 to 0.58mm h−1). Applying mucilage‐like material to one side of the terminal 1.5 cm of the root induces curvature toward the mucilage, irrespective of the root's orientation to gravity. Applying a 2‐mm‐wideband of mucilage‐like material to a root's circumference 8 to 10 mm behind the root cap neither induces gravicurvature nor affects elongation significantly. Similarly, applying mucilage‐like material to only the root cap does not significantly affect elongation or graviresponsiveness. Gravicurvature of mutant roots occurs only when mucilage‐like material is applied to the root/root‐cap junction. Reversing the caps of wild‐type and mutant roots produces gravitropic responses characteristic of the root cap rather than the host root. These results are consistent with the suggestion that gravitropic effectors are growth inhibitors that move apoplastically through mucilage between the root cap and root.
Field investigations of ammonia exchange between barley plants and the atmosphere. II. Nitrogen realiocation, free ammonium content and activities of ammonium‐assimilating enzymes in different leaves
Authors: SCHJOERRING J. K. , KYLLINGSBAEK A. , MORTENSEN J. V. , BYSKOV‐NIELSEN S. 
Published: April 2006

ABSTRACTThe activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) in different leaves of field‐grown spring barley were measured during the reproductive growth phase in 2 consecutive years. Concurrently, the contents of soluble ammonium ions and free amides in the leaves were determined. The studies were carried out to investigate the relationship between variations in these parameters and emission of NH3 from the plant foliage. GS and GOGAT activities declined very rapidly with leafage. The decline in enzyme activities was followed by an increase in soluble ammonium ions and amides in the leaf tissues. During the same period, about 75% of leaf and stem nitrogen was reallocated to the developing ear. The amount of NH3 volatilized from the foliage during the reproductive growth phase amounted to about 1% of the reallocated nitrogen. The experimental years were characterized by very favourable conditions for grain dry matter formation and for re‐utilization of nitrogen mobilized from leaves and stems. Ammonia volatilization occurring under conditions with declining GS and GOGAT activities and increasing tissue concentrations of NH4+ may be useful in protecting the plant from accumulation of toxic NH3 and NH4+ concentrations in the tissues.
Effects of doubled atmospheric carbon dioxide concentration on the responses of assimilation and conductance to humidity
Authors: BUNCE J. A. 
Published: April 2006

ABSTRACTExperiments were performed to determine if growth at elevated partial pressure of CO2 altered the sensitivity of leaf water vapour conductance and rate of CO2 assimilation to the leaf‐to‐air difference in the partial pressure of water vapour (Δw). Comparisons were made between plants grown and measured at 350 and 700 μPa Pa−1 partial pressures of CO2 for amaranth, soybean and sunflower grown in controlled environment chambers, soybean grown outdoors in pots, and orchard grass grown in field plots. In amaranth, soybean and orchard grass, both the absolute and the relative sensitivity of conductance to Δw at the leaf surface were less in plants grown and measured at the elevated CO2. In sunflower, there was no change in the sensitivity of conductance to Δw for the two CO2 partial pressures. Tests in soybeans and amaranth showed that the change in sensitivity resulted from elevated CO2 during the measurement of the Δw response. Assimilation rate of CO2 was not altered by Δw in amaranth, which has C4 metabolism. In sunflower, the assimilation rate of plants grown and measured at elevated CO2 was insensitive to Δw, consistent with the response of assimilation rate to intercellular CO2 partial pressure in the prevailing range. In soybean, the sensitivity of assimilation rate to Δw was not different between CO2 treatments, in contrast to what would be expected from the response of assimilation rate to intercellular CO2 partial pressure.
Photoinhibition of radish (Raphanus sativus L) seed germination: control of growth potential by cell‐wall yielding in the embryo
Authors: SCHOPFER P. , PLACHY C. 
Published: April 2006

ABSTRACTThe biophysical mechanism underlying photoinhibition of radish (Raphanus sativus L.) seed germination was investigated using three cultivars differing in sensitivity to continuous irradiation with far‐red light (high‐irradiance reaction of phytochrome). Sensitivity of germination to the inhibitory action of light was assessed by probing germination under osmotic stress (incubation in media of low water potentials adjusted with polyethylene glycol 6000) and expressed in terms of ‘germination potential’ (positive value of the water potential at which germination is inhibited by 50%). Far‐red light decreases the germination potential to various degrees in the different cultivars, reflecting the light‐sensitivity of germination in water. Removal of the seed coat increases the germination potential by a constant amount in darkness and light. It is concluded that germination depends on the expansive force of the embryo which can be drastically diminished by far‐red light. Seed‐coat constraint and expansive force of the embryo interact additively on the level of the germination potential. Photoinhibition of germination was accompanied by an inhibition of water uptake into the seed. Analysis of seed water relations showed that osmotic pressure and turgor assumed higher levels in photoinhibited seeds, compared to seeds germinating in darkness, while the water potential was close to zero under both conditions. Far‐red light produced a shift (to less negative values) in the curve relating water‐uptake rate to external water potential, i.e. a reduction in the driving force for water uptake. It is concluded that photoinhibition of germination results from the maintenance of a high threshold of cell‐wall extensibility in the embryo.
Light induction of alternative pathway capacity in leaf slices of Belgium endive
Authors: ATKIN O. K. , CUMMINS W. R. , COLLIER D. E. 
Published: April 2006

ABSTRACTThe effect of light on the development of the capacity for alternative pathway respiration was investigated in leaf slices of Belgium endive (Cichorum intybus L. cv. deliva). Dark‐grown plants possessed little capacity for the cyanide‐insensitive alternative pathway. In contrast, plants grown in continuous light had significant alternative pathway capacity. Light‐grown plants also had substantially higher concentrations of ethanol‐soluble carbohydrates in their leaves than plants grown in complete darkness. Despite these differences in leaf carbohydrate status and alternative pathway capacity of light‐ and dark‐grown leaf tissue, no differences were found in the activity of the alternative pathway, which was negligible in both treatments. Dark‐grown plants were adenylate restricted, as indicated by the increase in cytochrome pathway activity following uncoupling. Adenylates did not limit respiration in light‐grown leaf tissue. Plants that had been grown for 8d in complete darkness were also transferred to continuous light. Respiration of dark controls steadily declined over 11d following the transfer of plants to the light, due primarily to a decrease in cytochrome pathway activity. No such decline was observed in the plants transferred to continuous light. Transfer to continuous light led to significant increases in alternative pathway capacity relative to the dark controls. Alternative pathway activity remained negligible in both the dark controls and in plants transferred to continuous light. The results of this study suggest then that light per se may be responsible for the induction of alternative pathway capacity in Belgium endive.
Nitrogen relations of the sorghum‐Sfriga hermonthica hostparasite association: growth and photosynthesis
Authors: CECHIN I. , PRESS M. C. 
Published: April 2006

ABSTRACTThe extent to which the parasitic angiosperm Striga hermonthica reduces the growth of its sorghum host is dependent on the concentration of nitrogen (as NH4NO3 in 40% Long Ashton Solution) supplied to the plants. The biomass of 0.5,1 and 2 mol m−3 N‐grown infected plants was 22,30 and 66%, respectively, of uninfected plants after 140d growth. The biomass of 3 and 4 mol m−3 N‐grown infected plants differed little from uninfected plants. No grain was set in 0.5 and 1 mol m−3 N‐grown infected plants, grain yield reached 42 and 73% of controls in 2 and 3 mol m−3 N‐grown plants, and was unaffected in 4 mol m−3 N‐grown plants. Striga hermonthica also altered the allometry and architecture of the host, at all but the highest N concentration. Higher N concentration (3 and 4 mol m −3 N) reduced the growth of S. hermonthica. Foliar N concentrations in sorghum ranged from 11 mg g−1 dwt. in 0.5 mol m−3 N‐grown plants, to 28 mg g−1 dwt. in 4 mol m−3 N‐grown plants, and were not affected by S. hermonthica. Higher N concentrations were measured in S. hermonthica, and ranged from 18 to 45 mg g−1 dwt. in 0.5 and 3 mol m−3 N‐grown plants, respectively. The relationship between photosynthesis (CO2 flux) and N concentration differed between uninfected and infected sorghum. This was most apparent in 0.5 mol m−3 N‐grown plants, with rates of 16 and 11 μmol m−2 s−1 in uninfected and infected plants, respectively (at 1500–1800 μmol m−2 s−1 photosynthetic photon flux density). At higher N concentrations, this difference was smaller, with both sets of plants reaching 26 μmol m−2 s−1 at 4 mol m−3 N. Varying the level of S. hermonthica infection showed that the effect of N on host photosynthesis cannot be explained by differences in the mass or number of parasites supported by the host. At low levels of infection in 1 mol m−3 N‐grown plants, the negative effect of the parasite was reversed, and photosynthesis in infected plants exceeded that in uninfected plants by 20%. Photosynthesis in S. hermonthica at 3 mol m−3 N (8 μmol m−2 s−1) was double that in 0.5 mol m−3 N‐grown plants. Stable carbon isotope and gas exchange measurements data demonstrated that this higher level of autotrophic carbon fixation was accompanied by a lower dependency on hetero trophic carbon. The latter ranged from 27 to 6% in 0 5 mol m−3 and 3 mol m−3 N‐grown plants, respectively.
The effects of temperature and pH on the apparent Michaelis constant of glutathione reductase from maize (Zea mays L.)
Authors: TURNER L. B. , POLLOCK C. J. 
Published: April 2006

ABSTRACTThe interacting effects of temperature and pH on the kinetics of glutathione reductase from maize have been studied in detail. The apparent Km for oxidized glutathione (GSSG) measured with desalted crude extracts increased in an exponential manner with rising temperature as a single variable. Increasing pH as a single variable also resulted in higher values of apparent Km for GSSG. When pH was allowed to vary with temperature, a curve which combined the pH and temperature responses was observed. Temperature had the stronger influence and this combined curve was displaced from the temperature curve due to the effect of pH. The pH to which the assay buffer was adjusted at 30°C had an influence on the pattern of the results in this type of experiment. The response of apparent Km for NADPH, and of apparent Km for GSSG using partially‐purified extracts, were also examined. The variation with temperature, at constant pH, was again exponential. The pattern of change of apparent Km with temperature is strongly dependent on experimental conditions. Affinity/temperature relationships deduced from such data would only reflect enzyme function in vivo if the physiological environment could be reproduced exactly in the assay mixture.
The effect of ammonium ions on membrane potential and anion flux in roots of barley and tomato
Authors: AYLING S. M. 
Published: April 2006

ABSTRACTThe effects of ammonium (0–5 mol m−3) on root hair membrane potential and on the influx of nitrate and phosphate were investigated in roots of intact barley and tomato plants. In both species, addition of ammonium to the medium bathing the roots caused an almost immediate depolarization of the membrane potential; the depolarization was greater at higher concentrations of ammonium. Influx of 13NC3− and 32Pi was inhibited over the same time scale and concentration range. In tomato roots, there was little further depolarization of the membrane potential or inhibition of anion influx at ammonium concentrations above 0.4 mol m−3. In barley roots, the inhibition of nitrate influx and the depolarization of the membrane potential did not saturate below 5 mol m−3 ammonium.
Prosopis chilensis is a plant highly tolerant to heat shock
Authors: MEDINA C. , CARDEMIL L. 
Published: April 2006

ABSTRACTAt temperatures between 25 and 35°C, 100% of Prosopis chilensis seeds germinated within 24 h. At higher temperatures, the germination rate was reduced; at 50°C, seeds did not germinate. After germination at 25°C, the optimal temperature for seedling growth was 35°C and the seedlings did not grow at a temperature of 50°C. However, when germination was at 35°C, the optimal temperature for seedling growth was 40°C and some seedlings grew at 50°C, suggesting that thermotolerance was induced during seed germination at 35°C. Further thermotolerance can be induced in seedlings germinated at 35°C, by exposing them to 40°C for 2h. Under these conditions, seedlings exhibited increased growth rate at 45 and 50°C. Fluorography of SDS‐polyacrylamide gel electrophoresis of the proteins synthesized and accumulated during 2 h at temperatures of 35, 40, 45 and 50°C in the presence of [35S]methionine revealed the expression of 11 proteins not detectable at 35°C. Most of the proteins present at 35°C also increased in expression. The temperature for maximal expression of these proteins was 45°C.
Purification of β1,4 glucanase from ethylene‐treated leaflet abscission zones of Sambucus nigra
Authors: WEBB S. T. J. , TAYLOR J. E. , COUPE S. A. , FERRARESE L. , ROBERTS J. A. 
Published: April 2006

ABSTRACTLeaflet abscission in Sambucus nigra is the result of cell wall breakdown at the site of separation. Associated with wall degradation is an increase in the activity of the enzyme β1,4 glucanase (E.C.3.1.2.4) in the cells that comprise the abscission zone. The enzyme has been extracted from abscission zone tissue and purified using a substrate affinity column. A qualitative enzyme assay procedure has been developed and this has facilitated the purification process. The β1,4 glucanase enzyme has a pH optimum of 7 and a molecular mass of 54kDa. Antibodies have been raised to the purified protein. The role of the enzyme in the abscission process is discussed.
Integration of hydraulic and chemical signalling in the control of stomatal conductance and water status of droughted plants
Authors: TARDIEU F. , DAVIES W. J. 
Published: April 2006

ABSTRACTWe describe here an integration of hydraulic and chemical signals which control stomatal conductance of plants in drying soil, and suggest that such a system is more likely than control based on chemical signals or water relations alone. The determination of xylem [ABA] and the stomatal response to xylem [ABA] are likely to involve the water flux through the plant. (1) If, as seems likely, the production of a chemical message depends on the root water status (Ψr), it will not depend solely on the soil water potential (Ψs) but also on the flux of water through the soil‐plant‐atmosphere continuum, to which are linked the difference between Ψr and Ψs. (2) The water flux will also dilute the concentration of the message in the xylem sap. (3) The stomatal sensitivity to the message is increased as leaf water potential falls. Stomatal conductance, which controls the water flux, therefore would be controlled by a water‐flux‐dependent message, with a water‐flux‐dependent sensitivity. In such a system, we have to consider a common regulation for stomatal conductance, leaf and root water potentials, water flux and concentration of ABA in the xylem. In order to test this possibility, we have combined equations which describe the generation and effects of chemical signals and classical equations of water flux. When the simulation was run for a variety of conditions, the solution suggested that such common regulation can operate. Simulations suggest that, as well as providing control of stomatal conductance, integration of chemical and hydraulic signalling may also provide a control of leaf water potential and of xylem [ABA], features which are apparent from our experimental data. We conclude that the root message would provide the plant with a means to sense the conditions of water extraction (soil water status and resisance to water flux) on a daily timescale, while the short‐term plant response to this message would depend on the evaporative demand.
15N natural abundance of plant and soil components of a Banksia woodland ecosystem in relation to nitrate utilization, life form, mycorrhizal status and N2‐fixing abilities of component species
Authors: PATE J. S. , STEWART G. R. , UNKOVICH M. 
Published: April 2006

ABSTRACTStudies of the variation in δ15N values for plants from a fire‐prone Banksia woodland in South West Australia showed that pioneer herbaceous, non‐mycorrhizal species which were active in nitrate reduction and storage, had the highest values (1.81%c). A detailed study of one such species Ptilotus polystachus demonstrated a close correspondence between the δ15N values of soil nitrate, xylem nitrate and leaf total nitrogen, suggesting an exclusive reliance on nitrate ions as nitrogen source. These pioneer species also showed a preponderance of the chloroplastic isoform of glutamine synthetase while woody species generally had higher activity associated with the cytosolic isoform. The group comprising monocotyledonous hemicryptophytes and geophytes contained species with slightly positive δ15N values and moderately active in nitrate reduction and storage. Nitrogen‐fixing species had the lowest δ15N values (–0.36‰), irrespective of their apparent utilisation of nitrate. However, woody resprouter species which had low levels of nitrate reduction and storage had δ15N values which fell within the range of values obtained for the miscellaneous assemblage of N2‐fixing species. Consequently, 15N abundance values failed to distinguish N2 fixing from non‐fixing woody species, and therefore, could not be used in the ecosystem to determine the dependence of putative nitrogen fixing species on N2 fixation. The study demonstrated complex patterns of nitrogen utilization in the ecosystem in which exploitation of different nitrogen resources related to plant life form and the physiological attributes of nitrogen assimilation by component species.
Effects of the ecto‐ and VA‐mycorrhizal fungi Hydnagium carneum and Glomus clarum on the δ15N and δ13C values of Eucalyptus globulus and Ricinus communis
Authors: HANDLEY L. L. , DAFT M. J. , WILSON J. , SCRIMGEOUR C. M. , INGLEBY K. , SATTAR M. A. 
Published: April 2006

ABSTRACTGlasshouse experiments with Ricinus communis showed that the presence/absence of a VA mycorrhizal fungus (Glomus clarum) changed the δ15N value of the host by as much as 2‰ when the plants were given urea (released as NH4+) as their only N‐source. This small change in Δ15N would create a large error in calculating sources of plant N. In particular, these results throw into doubt any models of N‐cycling which assume that soil N can be treated as a single source. The correct N‐source value for VAM‐infected NH4− ‐using plants may be the δ15N of soil NH4++ 2‰. Treatment effects were also found in the distribution of δ15N and % N among plant organs. Plants with VAM had a lower N:P atom ratio and were larger in total biomass. Carbon discrimination (δ13C) was greater in the VA‐infected plants. The measured effects of VAM infection suggest that for some plants the fungus may be the primary site of N assimilation. A parallel experiment with Eucalyptus globulus and the ectomycorrhizal fungus Hydnangium carneum resulted in no significant differences in any of the variables measured for this host‐fungus pair when the sole N‐sources were inorganic (NO3− and NH4+ released from urea). Ectomycorrhizal fungi are diverse in their physiological behaviour, and these data should not be taken as being representative of the whole group. More work is required with other types of mycorrhiza and more complex sources of N. Future work will include a water balance to partition the effects of water use and nutrient supply in determining δ13C. An on‐line combustion‐ANCA‐MS method is described for fully automated measurement of natural abundance levels of 15/14N and 13/12C for plant materials. This method achieves the required precision while dramatically increasing sample throughout.
Ear photosynthesis, carbon isotope discrimination and the contribution of respiratory CO2 to differences in grain mass in durum wheat
Authors: ARAUS J. L. , BROWN H. R. , FEBRERO A. , BORT J. , SERRET M. D. 
Published: April 2006

ABSTRACTThe role of ear photosynthesis in grain filling was studied in a number of durum wheat (Triticum turgidum var durum L.) landraces and varieties from the Middle East, North Africa, and from the collections of ‘Institut National de la Recherche Agronomique’ (INRA, France) and ‘Centro International de Mejora de Maiz y Trigo’ (CIMMYT, Mexico). Plants were grown in the field in a Mediterranean climate. Flag leaves (blade plus sheath) and ears were kept in the dark from 1 week after anthesis to maturity which reduced grain weight by 22.4% and 59.0%, respectively. In a further experiment, the carbon isotope discrimination ratio (Δ) of ear bracts, awns and flag leaves was measured on samples taken at anthesis and on mature kernels. The mean value of Δ for the water soluble fraction of bracts (17.0‰) and awns (17.7‰) were lower than those of leaves (19.5‰) and fairly similar to those of kernels (17.4‰) averaged across all genotypes. Data indicate that most of the photosynthates in the grain come from ear parts and not from flag leaves. In addition, a higher water use efficiency (WUE) of ear parts than of the flag leaf is suggested by their lower Δ values. Gas exchange in ears and flag leaves was measured during grain filling. Averaged over all genotypes, CO2 diffusive conductance was about five times higher in the flag leaf than in the spike (with distal portions of awns outside the photosynthetic chamber) 2 weeks after anthesis. In absolute terms, the dark respiration rate (Rd) was greater than the net photosynthesis rate (Pn) by a factor of 1.74 in the spike, whereas Rd was much smaller, only 22.1, 65.7 and 24.8% of Pn in blade, sheath and awns, respectively. Data indicate that photosynthesis, and hence the water use efficiency (photosynthesis/transpiration), is greatly underestimated in ears because of the high rates of respiration which diminish the measured rates of net CO2 exchange. Results of 13C discrimination and gas exchange show that genotypes from North Africa have higher WUE than those from the Middle East. The high Rd values of ears as well as their low diffusive conductance suggest that CO2 from respiration may be used as source of carbon for ear photosynthesis. In the same way, the anatomy of glumes, for example, supports the role of bracts using internal CO2 as source of photosynthesis. In the first experiment, the Δ in mature grains from culms with darkened ears compared with control culms provided further evidence in support of this hypothesis. Thus, the Δ from kernels of control plants was 0.40 higher than that from ear‐darkened plants, probably because of some degree of refixation (recycling) of respired CO2 in the grains.