bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modulation of carbon and nitrogen allocation in Urtica dioica and Plantago major by elevated CO2: Impact of accumulation of nonstructural carbohydrates and ontogenetic drift
Authors: den Hertog J. , Stulen I. , Fonseca F. , Delea P. 
Published: May 2006

Doubling the atmospheric CO2 concentration from 350 to 700 μ1 1−1 increased the relative growth rate (RGR) of hydroponically grown Urtica dioica L. and Plantago major ssp. pleiosperma Pilger only for the first 10–14 days. Previous experiments with P. major led to the conclusion that RGR did not respond in proportion to the rate of photosynthesis. The present paper is focussed on the analysis of the impact of changes in leaf morphology, dry matter partitioning, dry matter chemical composition and ontogenetic drift on this discrepancy.Soon after the start of the treatment, carbohydrate concentrations were higher at elevated CO2: a reaction that was largely due to starch accumulation. An increase in the percentage of leaf dry matter and decreases in the specific leaf area (SLA) and the shoot nitrogen concentration were correlated with an increase in the total nonstructural carbohydrate concentration (TNC). A combination of accumulation of soluble sugars and starch and ontogenetic drift explains the decrease in SLA at the elevated CO2 level. A similar ontogenetic effect of elevated CO2 was observed on the specific root length (SRL). Other variables such as shoot nitrogen concentration and percentage leaf dry matter were not affected by correction of data for TNC levels. The net diurnal fluctuation of the carbohydrate pool in P. major was equal for both CO2 concentrations, indicating that the growth response to elevated CO2 may be ruled by variables other than photosynthesis, as for instance sink strength.Elevated CO2 did not greatly influence the partitioning of nitrogen between soluble and insoluble, reduced N and nitrate, nor the allocation of dry matter between leaf. stem and root. The finding that the root to shoot ratio (R/S) was not affected by elevated CO2 implies that, in order to maintain a balanced activity between roots and shoot, no shift in partitioning of dry matter upon doubling of the atmospheric CO2 concentration is required. Our data on R/S are in good agreement with the response of R/S to high CO2 predicted by models based on such a theorem.
Time dependent K+ currents through plasmalemma of laticifer protoplasts from Hevea brasiliensis
Authors: Bouteau François , Bousquet Ulrike , Pennarun Anne‐Marie , Convert Monique , Dellis Olivier , Cornel Daniel , Rona Jean‐Pierre 
Published: May 2006

The purpose of our work was to investigate the functioning of K+ channels in protoplasts of laticifers of Hevea brasiliensis Muell. Arg., anastomosed into a network devoid of large central vacuoles, after tapping stress. Physiological functions such as proton pump activity and uptake of sucrose (a rubber precursor) were maintained, when the voltage‐clamp method was used in vivo to record the whole‐cell K+ current during the stress response.A time‐dependent inward current was induced in 50 mM KCl and rapidly inactivated (about 100 ms). The activation potential of this inward K+ channel was not closely dependent on Ek. This would be coherent with the ‘valve model’ of Schroeder and Fang (1991, Proc. Natl. Acad. Sci. USA 88: 11583–11587) involving the activation of a H+‐pump accounting for the K+ uptake observed in laticiferous cells under stress. The activation half‐time of outward currents was clearly voltage dependent: from about 350 to 60 ms for 125 and 155 mV, respectively. Time‐dependent outward current sensitivity to 5 mM BaCl2 or CaCl2 or to 5 μM Erythrosin B showed that the K+ channels could be Ca2+‐dependent. Because of the positive values of the activation potential of the outward current, the possibility opens that an action potential exists, these cells being specialized for stress response.
Methods and applications to control the uptake rate of carbon
Authors: Ingestad Torsten , Hellgren Olof , Hesseldahl Hans , Ingestad Ann‐Britt Lund 
Published: May 2006

Methods to control carbon and nutrient uptake at different availability of carbon were tested on plants of birch (Betula pendula Roth.) and tomato (Lycopersicon esculentum Mill. cv. Solentos). The present paper accounts for the methods and the possibility to maintain steady‐state, i.e., a long‐term and stable physiological state of acclimated plants. Steady‐state comprises, by definition, equality between constant relative growth rates, and relative uptake rates of carbon and nutrients. Two methods were tested. The first, not previously applied, method (a), was based on a constant relative addition rate of carbon, RAC. In the second method (b), a constant concentration of CO2 in the air, ca, was used to attain non‐limiting conditions. The methods are analogous to those used by us to control plant nutrition, and the generality of fluxes to quantify supply as well as uptake and growth was verified. Thus, different RAC resulted in clear‐cut responses, from strong reduction to non‐limitation of uptake and growth, whereas different ca levels in the range 100 to 700 ppm had comparatively small effects, with an unclear causality. Non‐limiting conditions were achieved at ca≥ 200 ppm. Effects reported in the literature have been based upon the control of ca, similarly to method (b), whereas results comparable to those obtained with method (a) are lacking.Transpiration rate increased rapidly at ca < 200 ppm CO2, and at low RAC levels, ≤ 0.1 day−1, wilting tendencies were observed. Elevated ca, 500 or 700 ppm, did not increase the relative growth rate (RG) but reduced transpiration and increased both nitrogen productivity (growth rate per unit of nitrogen in the plant) and transpiration productivity (growth rate per unit of water transpired by the plant). Obviously, effects of ca may be due to changed transpiration rate rather than to changed quantitative availability of CO2.Relative uptake (RUC) and growth (RG) rates were closely equal to the RAC applied (RAC≅ RUC≅ RG); i.e., the purely mathematical conditions defining steady‐state were fulfilled. This unambiguous and straightforward test of reliability confirms that experimental artefacts did not produce uncontrolled or unintended effects, so that the new technique allows an accurate control of CO2 uptake and plant growth. The results add to previous databases and reference systems, where limiting conditions grade and classify plant performance as deviations from maximum growth. Evidently, methodology in experimentation and in evaluation of plant responses, can be based upon unifying concepts and general theories.
Responses to ultraviolet‐B radiation (280–315 nm) of pea (Pisum sativum) lines differing in leaf surface wax
Authors: Gonzalez R. , Paul N. D. , Percy K. , Ambrose M. , McLaughlin C. K. , Barnes J. D. , Areses M. , Wellburn A. R. 
Published: May 2006

To test the hypothesis that leaf surface wax influences plant responses to UV‐B, 6 lines of cultivated pea (Pisum sativum L.), selected as having more or less wax, were grown at 0 or 6.5 kJ m‐2 day‐1 plant‐weighted UV‐B against a background of 850–950 μmol m‐2 s‐1 photosynthetically active radiation. In the 4 lines with least leaf surface wax the amount of wax on adaxial and abaxial leaf surfaces was increased following exposure to 6.5 kJ m‐2 day‐1 UV‐B, but UV‐B decreased surface wax in Scout, which had the greatest wax deposits. On the adaxial leaf surface, UV‐B radiation caused a shift in wax composition from alcohols to esters and hydrocarbons and the ratio of short to long chain length alkyl ester homologues was increased. There was no evidence of a shortening in carbon chain length of hydrocarbons, primary alcohols or fatty acids due to UV‐B and no significant correlation between wax amount and UV reflectance from leaves.UV‐B induced significant increases in UV‐absorbing compounds in the expanded leaves and buds of most lines. UV‐B reduced the growth of all lines. Foliage area (leaves plus stipules) declined by 5–30%, plant dry weight by 12–30%, and plant height by 24–38%. Reductions in growth occurred in the absence of any changes in chlorophyll fluorescence or photosynthetic rate. UV‐B also had no major effect on carbon allocation patterns. The effects of UV‐B on growth appeared to be due to changes in tissue extension and expansion. Indeed, many of the responses to UV‐B observed in this study of pea appear more consistent with indirect effects being expressed in developing tissues rather than through the direct action of UV‐B on mature tissues.There was no evidence that wax amount or biochemistry was associated with the sensitivity of the lines to UV‐B radiation. Furthermore, induction of pigments was not correlated with changes in growth. However, lines with the greatest constitutive amounts of pigments in unexpanded bud tissues were most tolerant of elevated UV‐B.
Daminozide and prohexadione have similar modes of action as inhibitors of the late stages of gibberellin metabolism
Authors: Brown Robert G. S. , Kawaide Hiroshi , Yang Young‐Yell , Rademacher Wilhelm , Kamiya Yuji 
Published: May 2006

One of the effects of daminozide is to retard shoot growth in certain plant species, but its mode of action is unclear. Prohexadione, an acylcyclohexanedione, also causes retardation of shoot growth, but it is active in all plant systems tested so far. This inhibition has been shown to be a result of competition with the natural co‐substrate, 2‐oxoglutarate, at the active site of hydroxylases involved in the later stages of the gibberellin (GA) biosynthesis pathway. In order to determine the mode of action of daminozide in relation to prohexadione, the potencies of the two retardants as inhibitors of 3β‐hydroxylation of GAs in cell‐free systems from pumpkin (Cucurbita maxima) endosperm and French bean (Phaseolus coccineus) cotyledons were studied. Several compounds, related to or representing structural links between daminozide and prohexadione, were also included in this investigation. Daminozide was found to inhibit only the bean 3β‐hydroxylase to a significant degree, whereas prohexadione inhibited both the bean and pumpkin enzymes.Further information was obtained from the GC‐MS analysis of GAs found in the newly formed parts of the shoots of peanut seedlings treated with the two compounds. Both growth retardants inhibited the formation of GA1, whereas its immediate precursor, GA20, accumulated. Furthermore, levels of GA8 (2β‐hydroxy GA1) were also reduced, but by a smaller relative amount.These results clearly indicate for the first time that daminozide has the same mode of action as prohexadione in distinct plant species, namely to inhibit the 3β‐hydroxylase and, to a lesser extent, the 2β‐hydroxylase. This is probably due to the structural similarity of the two inhibitors with 2‐oxoglutarate.
Ethylene in seed dormancy and germination
Authors: KeÇpczyński Jan , KeÇpczyńska Ewa 
Published: May 2006

The role of ethylene in the release of primary and secondary dormancy and the germination of non‐dormant seeds under normal and stressed conditions is considered. In many species, exogenous ethylene, or ethephon – an ethylene‐releasing compound ‐ stimulates seed germination that may be inhibited because of embryo or coat dormancy, adverse environmental conditions or inhibitors (e.g. abscisic acid, jasmonate). Ethylene can either act alone, or synergistically or additively with other factors. The immediate precursor of ethylene biosynthesis, 1‐aminocyclopropane‐1‐carboxylic acid (ACC), may also improve seed germination, but usually less effectively. Dormant or non‐dormant inhibited seeds have a lower ethylene production ability, and ACC and ACC oxidase activity than non‐dormant, uninhibited seeds. Aminoethoxyvinyl‐glycine (AVG) partially or markedly inhibits ethylene biosynthesis in dormant or non‐dormant seeds, but does not affect seed germination. Ethylene binding is required in seeds of many species for dormancy release or germination under optimal or adverse conditions. There are examples where induction of seed germination by some stimulators requires ethylene action. However, the mechanism of ethylene action is almost unknown.The evidence presented here shows that ethylene performs a relatively vital role in dormancy release and seed germination of most plant species studied.
Ultraviolet‐B radiation causes shade‐type ultrastructural changes in Brassica napus
Authors: Fagerberg Wayne R. , Bornman Janet F. 
Published: May 2006

Cell and chloroplast structural changes in palisade cells from mature leaves of Brassica napus L. cv. Paroll were quantified following exposure of plants to enhanced ultraviolet‐B (280–320 nm; 13 kJ m−2 day−1 biologically effective UV‐B) radiation at two different levels of photosynthetically active radiation (PAR, 400–700 nm; 200 and 700 μmol m−2 s−1). Short‐term changes in leaf ultrastructure after 30 min and longer term changes after one day and one week were analyzed using stereological techniques incorporating light and electron microscopy and mathematical reconstruction of a mean cell for each sample.Ultraviolet‐B together with either relatively high or low PAR resulted in cell structural changes resembling those typical of plants under shade conditions, with the most marked response occurring after 30 min of UV‐B radiation. The ultrastructural changes at the cellular level were generally similar in both the relatively high and low PAR plus UV‐B radiation treatments. The surface areas of all three thylakoid types, the appressed, non‐appressed and margin thylakoids increased in the palisade tissue under supplemental UV‐B irradiation.Although the appressed and non‐appressed thylakoids increased in surface area, they did not increase equally, leaving open the possibility that the two thylakoid types have independent regulatory systems or different sensitivity to UV‐B radiation. Increased thylakoid packing (mm2 thylakoid membrane per mm2 leaf surface) in UV‐B‐exposed plants may increase the statistical probability of photon interception. An increased level of UV‐absorbing pigments after one week of supplemental UV‐B radiation did not prevent or significantly ameliorate UV effects. Our data supported the assumption that UV‐B radiation may have a regulatory role besides damaging effects and that an increased UV‐B environment will likely increase this regulatory influence of UV‐B radiation.
Effects of increasing inorganic carbon supply to roots on net nitrate uptake and assimilation in tomato seedlings
Authors: Gao Z. F. , Lips S. H. 
Published: May 2006

We investigated the influence of an increased inorganic carbon supply in the root medium on NO−3 uptake and assimilation in seedlings of Lycopersicon esculentum (L.) Mill. cv. F144. The seedlings were pre‐grown for 4 to 7 days with 0 or 100 mM NaCl in hydroponic culture using 0.2 mM NO−3 (group A) or 0.2 mM NH+4 (group B) as nitrogen source. The nutrient solution for group A plants was aerated with air or with air containing 4 800 μumol mol−1 CO2. Nitrate uptake rate and root and leaf malate contents in these plants were determined. The plants of group B were subdivided into two sets. Plants of one set were transferred either to N‐free solution containing 0 or 5 mM NaHCO3, or to a medium containing 2 mM NO−3 and 5 mM NaHCO3. Both sets of group B plants were grown for 12 h in darkness prior to 2 h of illumination, and were assayed for malate content and NO−3 uptake rate (only for plants grown in N‐free solution). The second set of group B plants was labeled with 14C by a 1‐h pulse of H14CO−3 which was added to a 5 mM NaHCO3 solution containing 0 or 100 mM NaCl and 0 or 2 mM NO−3, and 14C‐assimilates were extracted and fractionated.The roots of group B plants growing in carbonated medium accumulated twice as much malate as did control plants. This malate was accumulated only when NO−3 was absent from the root medium. Both a high level of root malate and aeration with CO2‐enriched air stimulated NO−3 uptake. Analysis of 14C‐assimilates indicated that with no NO−3 in the medium, the 14C was present mainly in organic acids, whereas with NO−3, a large proportion of 14C was incorporated into amino acids. Transport of root‐incorporated 14C to the shoot was enhanced by NO−3, while the amino acid fraction was the major 14C‐assimilates in the shoot. It is concluded that inorganic carbon fixed through phosphoenolpyruvate carboxylase (EC 4.1.1.31) in roots of tomato plants may have two fates: (a) as a carbon skeleton for amino acid synthesis; and (b) to accumulate, mainly as malate, in the roots, in the absence of a demand for the carbon skeleton. Inorganic carbon fixation in the root provides carbon skeletons for the assimilation of the NH+4 resulting from NO3 reduction, and the subsequent removal of amino acids through the xylem. This ‘removal’ of NO−3 from the cytoplasm of the root cells may in turn increase NO−3 uptake.
Gibberellin mutants
Authors: Ross John J. , Murfet Ian C. , Reid James B. 
Published: May 2006

Research on gibberellin (GA) mutants is reviewed, focusing on reports, published since 1993. The mutants have usually been identified via a shoot elongation screen. This screen exposes mutations influencing GA synthesis, deactivation and reception, and also those acting further down the elongation pathway. Mutations blocking synthesis lead to a dwarf. GA‐responsive phenotype. Numerous such mutations are now known. For some steps homologous mutations are known across 4 to 6 model species. Examples include the early step, geranylgeranyl diphosphate to copalyl diphosphate, and the activation step, GA26to GA1. Several GA‐synthesis mutations have now been characterised at the molecular level and all are in structural genes. It is now clear some steps are controlled by gene families with distinct tissue specificity. Further, some enzymes control more than one step in the biosynthetic pathway. The only mutation known to block deactivation. sin in pea, leads to an elongated phenotype.The GA response mutants are less well understood and are a more diverse group. They include elongated mutants with a constitutive GA response (spy in arabidopsis. la cry‐s in pea and sln in barley) or an enhanced GA response (phyB in arabidopsis. lv in pea and Ih in cucumber). Short response mutants include at least three types. One group accumulates GAs and are mostly unresponsive to applied GA (gai in arabidopsis. D8 in maize. Rht3 in wheat). A recently identified group, exemplified by Igr in pea and gas in barley, have a short stature and reduced response but attain full responses with very high doses of exogenous GA. How close these mutations act to GA reception remains to be determined. Lastly, a number of mutants with short stature and reduced GA response differ in overall phenotype from GA‐deficient plants and cannot be made to mimic wild type even at high GA application rates. These mutations act beyond GA reception and some have already proved useful in elucidating other pathways that affect shoot elongation. For example, the lk and lkb mutations in pea appear to block brassinolide synthesis and this in turn prevents normal GA‐mediated elongation responses.
Infrared microspectroscopy: Sampling heterogeneity in plant cell wall composition and architecture
Authors: McCann M. C. , Chen L. , Roberts K. , Kemsley E. K. , Sene C. , Carpita N. C. , Stacey N. J. , Wilson R. H. 
Published: May 2006

The use of probes such as monoclonal and polyclonal antibodies to specific cell wall components, at both the light and electron microscope levels, has demonstrated the diversity in cell wall composition between species, between tissues, between different regions of the cell surface, and even within a single wall. Traditional methods of cell wall analysis have provided valuable information on wall composition and architecture, but, by having to rely on the use of bulk samples, have averaged out this intrinsic heterogeneity. Fourier Transform Infrared (FTIR) microspectroscopy addresses this problem by providing chemical information from an area as small as 10×10 μm of a single cell wall fragment or area of a tissue section that has been imaged with a microscope accessory.We have used FTIR microspectroscopy as a powerful and extremely rapid assay for wall components and putative cross‐links in muro. The spectra are sensitive to polymer conformation, and the use of polarisers in the microscope accessory allows the orientation of particular functional groups to be determined, with respect to the long axis of elongating cells. The spectra constitute species and tissue‐specific ‘fingerprints’, and the use of classical discriminant analysis may provide the opportunity for correlating spectral features with chemical, architectural or rheological wall properties. Spectral mapping of an area of a specimen allows the morphological features resulting from cell growth and differentiation to be characterised chemically at the single cell level.
Closeness in Young Adult Sibling Relationships: Affective and Physiological Processes
Authors: Shortt Joann Wu , Gottman John M. 
Published: May 2006

AbstractWhat aspects of the relationships of young adult siblings are related to closeness or distance? This study takes a process approach to answering this question, contrasting it with the status approach of family structure variables. Close and distant sibling pairs were compared on physiological variables and specific aspects of warmth, con‐flict, and power during two conversations ‐ one on enjoyable topics and one on topics of disagreement. While there was no evidence that sibling closeness was related to family structure variables, differences in closeness were found in affective patterns and physiological responses during sibling interaction. Interaction between close sib‐lings was characterized not only by higher positive affect but also by fewer power struggles and lower heart rate reactivity. Close siblings also had higher scores on emotional empathy and cognitive aspects of empathy such as perspective‐taking than distant siblings. The developmental importance of considering power struggles in young adult sibling relationships was also discussed.
Friendships and Violent Behavior During Adolescence
Authors: Dishion Thomas J. , Eddy J. Mark , Haas Eric , Li Fuzhong , Spracklen Kathleen 
Published: May 2006

AbstractThis study investigated the extent to which interpersonal processes within male friendships are associated with violent behavior patterns during adolescence. At ages 13‐14, 15‐16, and 17‐18, we observed the participants (206 boys) in our laboratory discussing problem solving situations with a close friend. Although the boys typically brought in different friends for each of the three assessments, we found considerable continuity in the boys' behaviors, most notably in the topics discussed. In particular, the tendency of a dyad to engage in deviant and violent talk was uniquely associated with violence in adolescence, controlling for childhood antisocial behavior and coercive discipline practices in the home. These findings suggest that adolescent violence is embedded within enduring social interactional patterns of friendships, where the faces change but the process remains the same.