bluuebunny/crossref_metadata_2025_split huggingface dataset:
Apparent transinhibition of peptide uptake in the scutellum of barley grain
Authors: Sopanen Tuomas , Sinervo Tuija , Mikola Juhani 
Published: April 2006

The uptake of glycylsarcosine (Gly‐Sar) into scutella separated from germinating grains of barley (Hordeum vulgare L. cv. Himalaya) is inhibited by other peptides; in most cases the inhibition is not purely competitive but of a mixed type (simultaneous increase in the apparent Km and decrease in Vmax) (Sopanen, T. 1979. FEBS Lett. 108: 447–450). The aim of the present experiments was to elucidate the mechanism of the mixed inhibition by studying how peptides already taken up into the cells affect the uptake of Gly‐Sar.When scutella were preincubated in the presence of various peptides, 11 of the 13 peptides tested inhibited the subsequent uptake of Gly‐Sar by 10 to 45%. The inhibition, studied in detail with leucylleucine and prolylproline, was due to a decrease in Vmax. The two peptides having no effect were glycylglycine and D‐alanyl‐L‐alanine which are the only peptides known to date acting as purely competitive inhibitors when present together with the substrate Gly‐Sar.Preincubation with leucine, proline and alanine was not inhibitory, although preincubation with the corresponding dipeptides was. This result, together with the demonstration of intact leucylleucine in the scutella after preincubation with leucylleucine, indicates that the inhibition was caused by the intact peptides.The results support the notion that in the mixed type inhibition the increase in the apparent Km is due to competition for the carrier at the outside of the membrane, while the decrease in Vmax is due to peptides taken up and binding to the carrier at the inside of the membrane.
Metabolism of Urtica dioica as dependent on the supply of mineral nutrients
Authors: Hofstra Rinie (J. J.) , Lanting Lineke , de Visser Ries 
Published: April 2006

Plants of Urtica dioica L., a very nitrophilous species, were grown in a nutrient solution containing either high (100%) or low (2%) nutrient supply. Part of these plants were subjected to a sudden switch from 100% to 2% or vice versa. Plant weight, sugar and organic nitrogen (both soluble and insoluble) and nitrate content were measured during growth. The activities of two nitrogen assimilating enzymes, nitrate reductase (NR) and glutamine synthetase (GS) were determined.Growth of Urtica dioica was retarded at low nutrient supply. Root growth was limited by another factor than nitrogen. This was shown by a higher protein content. In the first period after a switch from 100% to 2%, redistribution of nitrogen from shoot to root could be demonstrated, and leakage from the root into the nutrient solution. It is suggested that in these conditions GS in the root reacted to this downward flux. Comparison with earlier findings on the less nitrophilous Plantago lanceolata showed that at 100% nutrient supply a correlation occurs between nitrate reduction and glutamine synthetase activity in that plant part which exported reduced nitrogen: the root in P. lanceolata and the shoot in U. dioica. In the importing plant part, glutamine synthetase was influenced by nitrate reduction as well as by imported reduced nitrogen.
Ferredoxin‐sulfite reductase and ferredoxin‐nitrite reductase activities in leaves of Pisum sativum: Changes during ontogeny and in vitro regulation by sulfide
Authors: von Arb Christoph , Brunold Christian 
Published: April 2006

Since ferredoxin‐dependent sulfite reductase (EC 1.8.7.1) and nitrite reductase (EC 1.7.7.1) can both catalyze the reduction of SO2‐3 and NO−2, physiological and biochemical evidence is needed for properly classifying the two enzyme activities. They were therefore compared during ontogeny of pea leaves and in the effect of their products, sulfide and ammonium, on their catalytic activity. In the crude extract of the young second leaf of pea plants, Pisum sativum L. cv. Vatters Frühbusch, no ferredoxin‐nitrite reductase activity could be detected, but ferredoxin‐sulfite reductase and ATP‐sulfurylase (EC 2.7.7.4), measured for comparison, were at 24 and 14%, respectively, of their maximal activity per leaf. After 11 and 12 days, respectively, ATP‐sulfurylase and ferredoxin‐sulfite reductase were no longer detectable, whereas ferredoxin‐nitrite reductase was still at more than 30% of its maximal activity per leaf. Ferredoxin‐sulfite reductase was inhibited by 50% with 18 μM and 100% with 30 μM sulfide produced by this enzyme during its assay. Sulfide at 100 μM added to the assay mixture completely inhibited ferredoxin‐sulfite reductase activity in the crude extract, the 30000 g pellet and its supernatant. The same addition reduced ferredoxinnitrite reductase activity by 20% in the crude extract and by 100% in the 30000 g pellet. NH+4 at 100 μM did not affect ferredoxin‐sulfite reductase or ferredoxin‐nitrite reductase activity.The inhibition by sulfide and the changes in activity during ontogeny similar to ATP‐sulfurylase (which catalyzes the first step of assimilatory sulfate reduction) represent biochemical and physiological evidence for the correct classification of ferredoxin‐sulfite reductase. The complete inhibition of ferredoxin‐nitrite reductase activity in the 30000 g pellet by S2‐ indicates that this activity was due to a ferredoxin‐sulfite reductase.
Effect of CO2 and phosphate deprivation on the control of nitrate, nitrite and ammonium metabolism in Chlorella
Authors: Di Martino Rigano Vittoria , Martello Anna , Di Martino Catello , Rigano Carmelo 
Published: April 2006

Chlorella vulgaris Beijerinck, strain 211/12, uses nitrate, nitrite and ammonium at pH 8.2 but not at pH 6.4 when kept under conditions of CO2‐deprivation, as observed in cell suspensions aerated with CO2‐free air during a 20–30. h period Most of the nitrate absorbed at pH 8.2, however, was not assimilated but was released into the external medium as nitrite and ammonium. Cells of Chlorella previously grown in phosphate‐limited continuous cultures were unable to absorb nitrate, nitrite or ammonium under conditions of phosphate starvation at either pH 6.4 or 8.2 in cell suspensions flushed with air containing 5% CO2, However, in cell suspensions flushed with CO2‐free air, the capacity of the alga to absorb and reduce nitrate and to excrete nitrite and ammonium at pH 8.2 was restored.It is hypothesized that in Chlorella the metabolism of nitrate, nitrite and ammonium is influenced by the availability of other nutrients and controlled by the cell's carbon status at the level of ion entry into the cell. With respect to nitrate this carbon‐dependent control is distinct and works independently of that triggered by the cell's nitrogen status.
Photokinetic and photophysical parameters of the blue light induced phototransformation of phytochrome in the presence of flavin
Authors: Appenroth Klaus‐J. , Hermann Gudrun , Augsten Helmut , Müller Eberhard 
Published: April 2006

Flavin mononucleotide (FMN) transfers its excitation energy to phytochrome Pr with a rate constant <8.7 × 1011 I mol‐1 s‐1. This reaction is not specific for Pr. the transfer to the phytochrome Pfr proceeds with ?5.8 × 1011 1 mol‐1 s‐1. These rate constants are lower limits because the complex‐formation constants are unknown. Assuming a horsier energy transfer a greater complex‐formation constant, as well as a greater orientation factor or a smaller distance in the complex FMN‐Pfr than in FMN‐Pr would be the possible reason for the difference between the rate constants.It is shown that the “flavin effect” can only be of physiological relevance if the local phytochrome concentration does not reach the millimolar range at the same place Under these conditions the reaction Pr Pfr proceeds more effectively, but the reaction Pr Pfr less effectively than in the absence of the donor FMN. which gives rise to a shift of the equilibrium in favour of Pfr.
Light period of Crassulacean Acid Metabolism: Control of carbon transfer from malic acid to carbohydrates by CO2 concentration
Authors: Fischer A. , Kluge M. 
Published: April 2006

In the CAM plants, Kalanchoë tubiflora (Harvey) Hasset, Sedum morganianum E. Walth and Sedum rubrotinctum R. T. Clausen, the effects of CO2 concentrations on the light‐dependent 14C transfer from the nocturnally synthetized [14C]‐malic acid to starch have been studied. CO2 concentrations up to 5 × 103 μ1 1–1 did not inhibit this carbon transfer. Higher CO2 concentrations, however, were increasingly inhibitory. At 104 μl 1–1 CO2, the carbon transfer was practically prevented.The malic acid consumption in the light showed the same response to CO2 concentrations as the [l4C]‐transfer. Photosynthesis itself was not inhibited by the CO2 concentrations applied. It is assumed that, during phase III of CAM, light controls the internal CO2 concentration via photosynthesis; and that the internal CO2 concentration then controls the rate of malate decarboxylation.
Quantitative relationships between osmotic potential amd epicotyl growth in Vigna radiata as affected by osmotic stress and cotyledon excision
Authors: Zhao Yu Ju , Kamisaka Seiichiro , Masuda Yoshio 
Published: April 2006

The correlation between osmotic potential and epicotyl growth in intact and decotyiized mung bean seedlings (Vigna radiata (L.) Wilczek) grown under osmotic stress was studied. The following results were obtained: 1) Epicotyl elongation in intact seedlings grown in vermiculite containing 0.2 M mannitol was not substantially affected, but was strongly inhibited in decotylized ones. 2) Osmotic potential in the epicotyl was. decreased by osmotic stress due to 0.2 M mannitol, and was increased by cotyledon excision. 3) Epicotyl elongation was well correlated with net osmotic concentration, which is. the difference in osmotic concentration between the vacuolar sap of epicotyl cells and the 0.2 M mannitol added to the vermiculite. The net osmotic concentration was also correlated with cell elongation, but not with cell division in the epicotyl. 4) The concentrations of soluble sugars, free amino acids and potassium ions in the epicotyl increased in response to osmotic stress. Cotyledon excision decreased the concentrations of soluble sugars and free amino acids, while it had no effect on potassium ion concentration.Based on these results, a role of osmoregulation in regulating epicotyl growth of mung bean is discussed in relation to osmotic stress and cotyledon excision.
Light‐induced, dark‐reversible colour shifts in petals of Phlox
Authors: Bjön Gunvor S. , Braune Wolfram , Björn Lars Olof 
Published: April 2006

Flowers of some Phlox (Phlox x paniculata L.) varieties undergo daily colour shifts, being blue in the early morning, turning red during the day, and returning to blue in the evening. The colour shift, which occurs only in the upper (adaxial) petal surfaces, is due to the daily changes in ambient light. In the laboratory, colour shifts could be induced by 2.5 h of ultraviolet, visible or far‐red light and recorded by reflectance spectrophotometry.There are indications that irradiations with different kinds of light cause qualitatively different colour shifts, and that thus more than one photoreceptor pigment and more than one primary light reaction may be involved. The presence of phytochrome was demonstrated in petals of white Phlox flowers by in vivo transmission spectrophotometry. It is therefore possible that colour shifts in coloured Phlox flowers are mediated by phytochrome. Possibly the movement of ions (e.g. hydrogen ions) into or out of the vacuole (where the visible pigments are located) is affected by light absorption in a pigment in the tonoplast.
Sugar transport in leaf discs ofPhaseolus coccinius
Authors: Daie J. 
Published: April 2006

Kinetic profiles for sucrose, glucose and 3‐OMG glucose were determined in leaf discs ofPhaseolus cocciniusL. (cv. Scarlet). All three sugars exhibited identical uptake kinetics. At sugar concentrations below 25 mM, transport was due to an active, carrier‐mediated transport system. A linear component was the dominant mode of uptake at sugar concentrations above 25 mM. Sucrose and glucose carriers were specific for these sugars, since no uptake inhibition was observed from competing sugars. Sucrose was not hydrolyzed by leaf tissue because the label in asymetrically labeled sucrose was not randomized. Furthermore, no label was present in hexose fractions when tissue was incubated with [84C]‐sucrose. Therefore, [14C]‐sucrose uptake did not reflect hexose uptake.Both saturable and linear components of uptake contribute significantly to total uptake rates. The former, however, is more important when apoplastic sugar concentrations are low. The molecular nature of the linear component is not well understood but accounts for most of the uptake at high sugar concentrations.
Uptake of amino acids and peptides by developing barley embryos
Authors: Sopanen Tuomas , Sinervo Tuija , Ahokas Hannu 
Published: April 2006

Developing embryos of barley (Hordeum vulgare L. cv. Bomi) detached 21–27 days after anthesis took up 1 mM [14C]‐glutamine at pH 5 and 30°C at a rate of about 20 nmol embryo−l h−1 (5 μol g−1h−1). The uptake was inhibited by about 50% by di‐nitrophenol and by about 80% by 300 mM unlabelled glutamine or alanine. The bulk of the uptake appeared, therefore, to be due to carrier‐mediated active transport. The pH optimum of the uptake was 4.5. Leucine, proline, lysine, arginine and as‐paragine were taken up at approximately similar rates as glutamine, and they also inhibited the uptake of glutamine. This, suggests that the uptake of glutamine was at least partly due to an unspecific carrier(s) also shared by other amino acids. The embryos also took up the dipepti.de glycykarcosine; the rate was about 6 nmol embryo−1h−1 (1.5 μol g−1h−1) (2 mM glycylsarcosine, pH 4.5, 30°C). The uptake was inhibited by about 70% by dinitrophenol or by 300 mM glycylglycine. This indicates that the bulk of the uptake was due to carrier‐mediated active transport. The pH optimum of the uptake was about 4.5.The rates of glutamine and glycylsarcosine uptake increased during the early and middle stages of embryo development (until day 28 after anthesis), but decreased towards the end of the maturation of the grain. These changes, as well as the relatively high activities, suggest that carrier‐mediated active uptake of amino acids, and possibly also that of peptides, plays a role in the nutrition of the developing embryo.
Dose responses of auxins
Authors: Nissen Per 
Published: April 2006

Published data for the most widely used bioassays for auxins as. well as other auxin‐induced responses, have been analyzed to determine whether the response is ultrasensitive, hyperbolic or subsensitive, i.e. whether the change from 10 to 90% of maximal response requires less than, equal to or more than an 81‐fold increase in external auxin concentration. Auxin‐dependent callus growth is most often ultrasensitive. Other responses, including the curvature of Avena coleoptiles, may show simple Mi‐chaelis‐Menten kinetics. In the majority of cases, however, the response is sub‐sensitive, often very markedly so. The finding of subsensitive responses is consistent with the proposal by A. J. Trewavas that plant development is regulated by changes in the sensitivity to plant growth substances.Detailed data for subsensitive dose responses, particularly auxin‐induced inhibition of root growth, can often be precisely represented by bi‐ or multiphasic isotherms, with the phases separated by sharp transitions. The relationship to auxin uptake and the relationship, if any, between carriers and receptors for auxins remain to be elucidated.
Photosynthetic and respiratory electron transport in Cu2+‐deficient Dunaliella
Authors: Sandmann Gerhard 
Published: April 2006

Growth inhibition of the green alga Dunalietla parva Lerche has been observed during cultivation in low Cu2+ media. A minimum endogenous Cu concentration for unrestricted growth of 100 to 200 nmol ml−1 packed cell volume was estimated. At lower concentrations, Cu deficiency causes a decrease in photosynthesis and respiration. Assay of photosynthetic electron transport rates as well as the determination of several redox components showed that the target of Cu deprivation in the photosynthetic apparatus is the synthesis of Cu‐containing plastocyanin. Consequently, inhibited formation of plastocyanin resulted in low activities of photosynthetic electron transport. A secondary, indirect effect of Cu deficiency is the reduction of thylakoid formation resulting in an additional decrease of photosynthesis compared to cultures with sufficient Cu2+.The inhibitory influence of low Cu2+ on respiration was located at the site of cytochrome oxidase. In contrast to blue‐green algae, a strong coordination of the biosynthesis of the cytochrome oxidase complex was evident. During restricted Cu2+ supply the formation of cytochiome aa3, another component besides Cu, was stalled. The resulting low activities of cytochrome oxidase are responsible for decreased respiratory electron transfer activity from NADPH to oxygen. At Cu2+ concentrations which exert only moderate effects on Dunalietla, the cytochrome oxidase reaction was more strongly affected than the photosystem I reaction.
A comparison of regulatory effects of chloride on nitrate uptake, and of nitrate on chloride uptake into Pisum sativum seedlings
Authors: Deane‐Drummond Celia E. 
Published: April 2006

Net nitrate uptake, 36ClO−3/NO−3 influx and 36Cl− influx into Pisum sativum L. cv. Feltham First seedlings have been examined following growth in culture medium containing different combinations of chloride and nitrate. When young (6 days old) seedlings, that had been grown in the absence of N were used, nitrate accumulation stimulated net nitrate uptake and 36ClO−3/NO−3 influx (r2= 0.99) while chloride accumulation inhibited nitrate uptake and 36ClO−3/NO−3 influx (r2= 0.65). When nitrate was provided during growth there was no effect of chloride pretreatment on net nitrate uptake and there was little effect of total [NO−3+ Cl−]i on 36ClO−3/NO−3 influx (r2= 0.26). A direct effect of Cl− on 36ClO−3/NO−3 influx was only found when seedlings had been starved of N for more prolonged periods (14 days).When moderate chloride was supplied during growth, 36Cl− influx was insensitive to nitrate or chloride accumulated, but significantly correlated with loge [NO−3+ Cl−]i (r2= 0.75). When trace amounts of Cl− were supplied during growth 36Cl− influx was inhibited by (a) NO−3 in the external medium and (b) Cl− pretreatment, but was insensitive to NO−3 pretreatment. The sensitivity of 36Cl− influx to external nitrate was not found following Cl− pretreatment in the absence of nitrate. The possibility that there are two populations of chloride carriers which differ in their sensitivity to external nitrate is discussed. Tentative schematic models to account for the regulation of nitrate and chloride uptake are proposed in the context of current hypotheses for regulation of ion transport and control systems theory.
Effects of alkali ions on the circadian leaf movements of Oxalis regnellii
Authors: Rinnan T. , Johnsson A. 
Published: April 2006

The influence of alkali ions on the circadian leaf movements of Oxalis regnellii Mig. was investigated. Ions were given to the oscillating system via the transpiration stream of cut stalks in nutrient medium. Chloride solutions of Rb+, Cs+, Na+ and K+ were tested and the results compared to previously published LiCl‐results.The period of the circadian leaf movements was unaffected by a continual addition of Na+ or K+ to the nutrient medium (at least up to 40 mM). Rb+, in the concentration of 2.5 or 5 mM, caused a shortening of the period when applied continuously. Rb+ concentrations up to 60 mM were tested. Cs+ ions caused only lengthenings of the circadian period. Cs+ concentrations up to 40 mM were tested. Cs+ resembled Li+ in producing period lengthenings, but was not as effective as Li+ when compared on a concentration basis. Toxicity of the effective ions was in the following order: Li+Cs+Rb+, Rb+ pulses (50 mM, 4 h) phase‐shifted the rhythm and caused advances. A phase response curve was determined and the maximum steady state advances were of the order of 1 h. The dual effect of the Rb+ ions is discussed and is assumed to be due to two counteracting processes, exemplified by Rb+‐sensitive ATPase‐controlled pumping processes and protein synthesis. For comparison, the effects of Rb+ and Li+ in human depressive disorders is also discussed in relation to their influence on circadian systems. It is emphasized that Rb+ and K+ behave differently and are not interchangeable in their action on circadian systems.
ATP synthesis and utilization in the early stage of seed germination in relation to seed dormancy and quality
Authors: Perl M. 
Published: April 2006

In addition to the possible activities of the well‐known biochemical cycles, the ATP‐synthesizing system in dry seeds consists of a pathway which oxidizes malate and provides phosphoenolpyruvate (PEP). This system seems to be regulated primarily by the malate dehydrogenase (EC 1.1.1.37) activity, which together with the PEP carboxylase (EC 4.1.1.38) provides PEP and NADH. This latter compound may play a role as the “sparker” for the whole cycle.Breaking seed dormancy does not seem to be related to the rate of ATP synthesis per se but to facilitate enzyme‐substrate interaction, probably caused by intracellular compartment‐fusion. The compartmentation process is probably a result of the seed ripening and maturation functions.The ATP accumulated at the early stage of seed germination is a result of ATP synthesis and ATP utilization. Thus, ATP accumulation may result from a high rate of synthesis (high quality seeds) or from a low utilization ability (low‐quality seeds). Also, since 95% of the synthesized ATP is utilized concomitantly with its synthesis, the accumulated amount is relatively insignificant and does not indicate seed quality. This conclusion is also supported by many experimental results in which no such correlation was found.
Control of Na+ and K+ transport in Spergularia marina. III. Relationship between ion uptake and growth at moderate salinity
Authors: Cheeseman John M. , Wickens Linda K. 
Published: April 2006

In this paper, we continue our analysis of Na+ and K+ uptake by mid‐vegetative Spergularia marina (L.) Griseb. plants growing on 0.2x sea water medium, with attention to the relationship of ion uptake and growth. In the first part of the paper, growth analysis techniques are used to compare relative growth rates (RGR) and relative accumulation rates (RAR) for Na+ and K+. Under constant growth conditions, a high correlation between RGR and RAR indicated that growth and accumulation of both ions were well balanced, resulting in Na+ and K+ concentrations within the plants which were stable after adjustement to the saline medium. The analysis confirmed the existence of a Na+ ‐related growth stimulation in S. marina and an associated increase in the efficiency of K+ utilization for growth. When plants were subjected to more rapid salinization and step changes in the light intensity of the growth chamber, RGR and RAR were again similar, even through the discontinuities in growth conditions, suggesting that growth and ion accumulation were co‐regulated rather than simply correlated.The growth analysis data were then transformed to give net uptake rates for Na+ and K+ and the results were compared to those of isotope studies under similar growth conditions. In roots, the rates estimated by the two techniques differed substantially; net uptake rates reflected primarily growth, while isotope studies indicated a substantial ion exchange rate between mature cells and the growth medium. The rates of transport of either Na+ or K+ to the shoot were very similar using the two estimation techniques. As the rates measured with isotopes were taken from studies lasting at most a few hours, this suggested a very rapid turnover of the upwardly mobile Na+ and K+ pools in the roots.